51
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Sugishita T, Matsuki Y, Fujiwara T. Absolute 1H polarization measurement with a spin-correlated component of magnetization by hyperpolarized MAS-DNP solid-state NMR. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2019; 99:20-26. [PMID: 30849736 DOI: 10.1016/j.ssnmr.2019.02.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2018] [Revised: 02/14/2019] [Accepted: 02/14/2019] [Indexed: 06/09/2023]
Abstract
Sensitivity of magic-angle spinning (MAS) NMR spectroscopy has been dramatically improved by the advent of high-field dynamic nuclear polarization (DNP) technique and its rapid advances over the past decades. In this course, discussions on ways to improve the DNP enhancement factor or the overall sensitivity gain have been numerous, and led to a number of methodological and instrumental breakthroughs. Beyond the sensitivity gain, however, discussions on accurate quantification of the 1H polarization amplitude achievable in a sample with DNP have been relatively rare. Here, we propose a new method for quantifying the local 1H hyperpolarization amplitude, which is applicable to un-oriented/powdered solid samples under MAS NMR conditions. The method is based on the ability to observe the high-order spin-correlated term (2IzSz) intrinsic to a hyperpolarized IS two-spin state, separately from the lowest-order Zeeman term (Sz) in quasi-equilibrium magnetization. The quantification procedure does not require evaluation of signal amplitudes for a "microwave-off" condition and for an un-doped reference sample, and thus enables quick and accurate quantification unaffected by the effects of the paramagnetic quenching and the MAS-induced depolarization. The method is also shown to elucidate spatial polarization distribution through the 2IzSz term prepared domain-selectively. As a potential application, we also demonstrate 2D DQ-SQ spectroscopy utilizing the 2IzSz term that is generated in a spatially selective manner without using IS dipolar or J coupling. These salient features may be evolved into a way for characterizing mesoscopic molecular assemblies of medical/biological importance.
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Affiliation(s)
| | - Yoh Matsuki
- Institute for Protein Research, Osaka University, Japan; Quantum Information and Quantum Biology Division, Institute for Open and Transdisciplinary Research Initiatives, Osaka University, Japan
| | - Toshimichi Fujiwara
- Institute for Protein Research, Osaka University, Japan; Quantum Information and Quantum Biology Division, Institute for Open and Transdisciplinary Research Initiatives, Osaka University, Japan.
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52
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Thureau P, Juramy M, Ziarelli F, Viel S, Mollica G. Brute-force solvent suppression for DNP studies of powders at natural isotopic abundance. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2019; 99:15-19. [PMID: 30836289 DOI: 10.1016/j.ssnmr.2019.02.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 02/15/2019] [Accepted: 02/15/2019] [Indexed: 06/09/2023]
Abstract
A method based on highly concentrated radical solutions is investigated for the suppression of the NMR signals arising from solvents that are usually used for dynamic nuclear polarization experiments. The presented method is suitable in the case of powders, which are impregnated with a radical-containing solution. It is also demonstrated that the intensity and the resolution of the signals due to the sample of interest is not affected by the high concentration of radicals. The method proposed here is therefore valuable when sensitivity is of the utmost importance, namely samples at natural isotopic abundance.
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Affiliation(s)
| | - Marie Juramy
- Aix Marseille Univ, CNRS, ICR, Marseille, France
| | - Fabio Ziarelli
- Aix Marseille Univ, CNRS, Centrale Marseille, FSCM, Marseille, France
| | - Stephane Viel
- Aix Marseille Univ, CNRS, ICR, Marseille, France; Institut Universitaire de France, Paris, France
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53
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Li Y, Equbal A, Tagami K, Han S. Electron spin density matching for cross-effect dynamic nuclear polarization. Chem Commun (Camb) 2019; 55:7591-7594. [PMID: 31165810 PMCID: PMC6597276 DOI: 10.1039/c9cc03499d] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A new design principle for a mixed broad (TEMPO) and narrow (Trityl) line radical to boost the dynamic nuclear polarization efficiency is electron spin density matching, suggesting a polarizing agent of one Trityl tethered to at least two TEMPO moieties.
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Affiliation(s)
- Yuanxin Li
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, USA.
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54
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Brownbill NJ, Lee D, De Paëpe G, Blanc F. Detection of the Surface of Crystalline Y 2O 3 Using Direct 89Y Dynamic Nuclear Polarization. J Phys Chem Lett 2019; 10:3501-3508. [PMID: 31150249 PMCID: PMC6589743 DOI: 10.1021/acs.jpclett.9b01185] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2019] [Accepted: 05/31/2019] [Indexed: 05/29/2023]
Abstract
Nuclei with low gyromagnetic ratio (γ) present a serious sensitivity challenge for nulear magnetic resonance (NMR) spectroscopy. Recently, dynamic nuclear polarization (DNP) has shown great promise in overcoming this hurdle by indirect hyperpolarization (via 1H) of these low-γ nuclei. Here we show that at a magnetic field of 9.4 T and cryogenic temperature of about 110 K direct DNP of 89Y in a frozen solution of Y(NO3)3 can offer signal enhancements greater than 80 times using exogeneous trityl OX063 monoradical by satisfying the cross effect magic angle spinning (MAS) DNP mechanism. The large signal enhancement achieved permits 89Y NMR spectra of Y2O3 and Gd2O3-added Y2O3 materials to be obtained quickly (∼30 min), revealing a range of surface yttrium hydroxyl groups in addition to the two octahedral yttrium signals of the core. The results open up promises for the observation of low gyromagnetic ratio nuclei and the detection of corresponding surface and (sub-)surface sites.
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Affiliation(s)
- Nick J. Brownbill
- Department
of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, United
Kingdom
| | - Daniel Lee
- Univ.
Grenoble Alpes, CEA, IRIG, MEM, F-38000 Grenoble, France
| | - Gaël De Paëpe
- Univ.
Grenoble Alpes, CEA, IRIG, MEM, F-38000 Grenoble, France
| | - Frédéric Blanc
- Department
of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, United
Kingdom
- Stephenson
Institute for Renewable Energy, University
of Liverpool, Crown Street, Liverpool L69 7ZF, United Kingdom
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55
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Brodrecht M, Herr K, Bothe S, de Oliveira M, Gutmann T, Buntkowsky G. Efficient Building Blocks for Solid-Phase Peptide Synthesis of Spin Labeled Peptides for Electron Paramagnetic Resonance and Dynamic Nuclear Polarization Applications. Chemphyschem 2019; 20:1475-1487. [PMID: 30950574 DOI: 10.1002/cphc.201900211] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 03/22/2019] [Indexed: 11/11/2022]
Abstract
Specific spin labeling allows the site-selective investigation of biomolecules by EPR and DNP enhanced NMR spectroscopy. A novel spin labeling strategy for commercially available Fmoc-amino acids is developed. In this approach, the PROXYL spin label is covalently attached to the hydroxyl side chain of three amino acids hydroxyproline (Hyp), serine (Ser) and tyrosine (Tyr) by a simple three-step synthesis route. The obtained PROXYL containing building-blocks are N-terminally protected by the Fmoc-protection group, which makes them applicable for the use in solid-phase peptide synthesis (SPPS). This approach allows the insertion of the spin label at any desired position during SPPS, which makes it more versatile than the widely used post synthetic spin labeling strategies. For the final building-blocks, the radical activity is proven by EPR. DNP enhanced solid-state NMR experiments employing these building-blocks in a TCE solution show enhancement factors of up to 26 for 1 H and 13 C (1 H→13 C cross-polarization). To proof the viability of the presented building-blocks for insertion of the spin label during SPPS the penta-peptide Acetyl-Gly-Ser(PROXYL)-Gly-Gly-Gly was synthesized employing the spin labeled Ser building-block. This peptide could successfully be isolated and the spin label activity proved by EPR and DNP NMR measurements, showing enhancement factors of 12.1±0.1 for 1 H and 13.9±0.5 for 13 C (direct polarization).
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Affiliation(s)
- Martin Brodrecht
- Institut für Physikalische Chemie, Technische Universität Darmstadt, 64287, Darmstadt, Germany
| | - Kevin Herr
- Institut für Physikalische Chemie, Technische Universität Darmstadt, 64287, Darmstadt, Germany
| | - Sarah Bothe
- Institut für Physikalische Chemie, Technische Universität Darmstadt, 64287, Darmstadt, Germany
| | - Marcos de Oliveira
- Institut für Physikalische Chemie, Technische Universität Darmstadt, 64287, Darmstadt, Germany
| | - Torsten Gutmann
- Institut für Physikalische Chemie, Technische Universität Darmstadt, 64287, Darmstadt, Germany.,University Kassel, Institute for Chemistry, Heinrich-Plett-Straße 40, D-34132, Kassel
| | - Gerd Buntkowsky
- Institut für Physikalische Chemie, Technische Universität Darmstadt, 64287, Darmstadt, Germany
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56
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Purea A, Reiter C, Dimitriadis AI, de Rijk E, Aussenac F, Sergeyev I, Rosay M, Engelke F. Improved waveguide coupling for 1.3 mm MAS DNP probes at 263 GHz. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 302:43-49. [PMID: 30953925 DOI: 10.1016/j.jmr.2019.03.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Revised: 03/26/2019] [Accepted: 03/27/2019] [Indexed: 06/09/2023]
Abstract
We consider the geometry of a radially irradiated microwave beam in MAS DNP NMR probes and its impact on DNP enhancement. Two related characteristic features are found to be relevant: (i) the focus of the microwave beam on the DNP MAS sample and (ii) the microwave magnetic field magnitude in the sample. We present a waveguide coupler setup that enables us to significantly improve beam focus and field magnitude in 1.3 mm MAS DNP probes at a microwave frequency of 263 GHz, which results in an increase of the DNP enhancement by a factor of 2 compared to previous standard hardware setups. We discuss the implications of improved coupling and its potential to enable cutting-edge applications, such as pulsed high-field DNP and the use of low-power solid-state microwave sources.
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57
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Pell AJ, Pintacuda G, Grey CP. Paramagnetic NMR in solution and the solid state. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2019; 111:1-271. [PMID: 31146806 DOI: 10.1016/j.pnmrs.2018.05.001] [Citation(s) in RCA: 208] [Impact Index Per Article: 41.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 05/11/2018] [Accepted: 05/12/2018] [Indexed: 05/22/2023]
Abstract
The field of paramagnetic NMR has expanded considerably in recent years. This review addresses both the theoretical description of paramagnetic NMR, and the way in which it is currently practised. We provide a review of the theory of the NMR parameters of systems in both solution and the solid state. Here we unify the different languages used by the NMR, EPR, quantum chemistry/DFT, and magnetism communities to provide a comprehensive and coherent theoretical description. We cover the theory of the paramagnetic shift and shift anisotropy in solution both in the traditional formalism in terms of the magnetic susceptibility tensor, and using a more modern formalism employing the relevant EPR parameters, such as are used in first-principles calculations. In addition we examine the theory first in the simple non-relativistic picture, and then in the presence of spin-orbit coupling. These ideas are then extended to a description of the paramagnetic shift in periodic solids, where it is necessary to include the bulk magnetic properties, such as magnetic ordering at low temperatures. The description of the paramagnetic shift is completed by describing the current understanding of such shifts due to lanthanide and actinide ions. We then examine the paramagnetic relaxation enhancement, using a simple model employing a phenomenological picture of the electronic relaxation, and again using a more complex state-of-the-art theory which incorporates electronic relaxation explicitly. An additional important consideration in the solid state is the impact of bulk magnetic susceptibility effects on the form of the spectrum, where we include some ideas from the field of classical electrodynamics. We then continue by describing in detail the solution and solid-state NMR methods that have been deployed in the study of paramagnetic systems in chemistry, biology, and the materials sciences. Finally we describe a number of case studies in paramagnetic NMR that have been specifically chosen to highlight how the theory in part one, and the methods in part two, can be used in practice. The systems chosen include small organometallic complexes in solution, solid battery electrode materials, metalloproteins in both solution and the solid state, systems containing lanthanide ions, and multi-component materials used in pharmaceutical controlled-release formulations that have been doped with paramagnetic species to measure the component domain sizes.
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Affiliation(s)
- Andrew J Pell
- Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Svante Arrhenius väg 16 C, SE-106 91 Stockholm, Sweden.
| | - Guido Pintacuda
- Institut des Sciences Analytiques (CNRS UMR 5280, ENS de Lyon, UCB Lyon 1), Université de Lyon, 5 rue de la Doua, 69100 Villeurbanne, France
| | - Clare P Grey
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
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58
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Walder B, Berk C, Liao WC, Rossini AJ, Schwarzwälder M, Pradere U, Hall J, Lesage A, Copéret C, Emsley L. One- and Two-Dimensional High-Resolution NMR from Flat Surfaces. ACS CENTRAL SCIENCE 2019; 5:515-523. [PMID: 30937379 PMCID: PMC6439530 DOI: 10.1021/acscentsci.8b00916] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Indexed: 05/02/2023]
Abstract
Determining atomic-level characteristics of molecules on two-dimensional surfaces is one of the fundamental challenges in chemistry. High-resolution nuclear magnetic resonance (NMR) could deliver rich structural information, but its application to two-dimensional materials has been prevented by intrinsically low sensitivity. Here we obtain high-resolution one- and two-dimensional 31P NMR spectra from as little as 160 picomoles of oligonucleotide functionalities deposited onto silicate glass and sapphire wafers. This is enabled by a factor >105 improvement in sensitivity compared to typical NMR approaches from combining dynamic nuclear polarization methods, multiple-echo acquisition, and optimized sample formulation. We demonstrate that, with this ultrahigh NMR sensitivity, 31P NMR can be used to observe DNA bound to miRNA, to sense conformational changes due to ion binding, and to follow photochemical degradation reactions.
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Affiliation(s)
- Brennan
J. Walder
- Institut
des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Christian Berk
- Department
of Chemistry and Applied Biosciences, ETH
Zürich, Vladimir Prelog Weg 1-5, CH−8093 Zürich, Switzerland
| | - Wei-Chih Liao
- Department
of Chemistry and Applied Biosciences, ETH
Zürich, Vladimir Prelog Weg 1-5, CH−8093 Zürich, Switzerland
| | - Aaron J. Rossini
- Institut
des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Department
of Chemistry, Iowa State University, Ames, Iowa 50011-3020, United States
| | - Martin Schwarzwälder
- Department
of Chemistry and Applied Biosciences, ETH
Zürich, Vladimir Prelog Weg 1-5, CH−8093 Zürich, Switzerland
| | - Ugo Pradere
- Department
of Chemistry and Applied Biosciences, ETH
Zürich, Vladimir Prelog Weg 1-5, CH−8093 Zürich, Switzerland
| | - Jonathan Hall
- Department
of Chemistry and Applied Biosciences, ETH
Zürich, Vladimir Prelog Weg 1-5, CH−8093 Zürich, Switzerland
| | - Anne Lesage
- Institut
de Sciences Analytiques, Centre de RMN à Très Hauts
Champs, Université de Lyon (CNRS/ENS
Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Christophe Copéret
- Department
of Chemistry and Applied Biosciences, ETH
Zürich, Vladimir Prelog Weg 1-5, CH−8093 Zürich, Switzerland
| | - Lyndon Emsley
- Institut
des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- E-mail:
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59
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Equbal A, Leavesley A, Jain SK, Han S. Cross-Effect Dynamic Nuclear Polarization Explained: Polarization, Depolarization, and Oversaturation. J Phys Chem Lett 2019; 10:548-558. [PMID: 30645130 DOI: 10.1021/acs.jpclett.8b02834] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The scope of this Perspective is to analytically describe NMR hyperpolarization by the three-spin cross effect (CE) dynamic nuclear polarization (DNP) using an effective Hamiltonian concept. We apply, for the first time, the bimodal operator-based Floquet theory in the Zeeman-interaction frame for two and three coupled spins to derive the known interaction Hamiltonian for CE-DNP. With a unified understanding of CE-DNP, and supported by empirical observation of the state of electron spin polarization under the given experimental conditions, we explain diverse manifestations of CE from oversaturation, enhanced hyperpolarization by broad-band saturation, to nuclear spin depolarization under magic-angle spinning.
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Affiliation(s)
- Asif Equbal
- Department of Chemistry and Biochemistry , University of California, Santa Barbara , Santa Barbara , California 93106 , United States
| | - Alisa Leavesley
- Department of Chemistry and Biochemistry , University of California, Santa Barbara , Santa Barbara , California 93106 , United States
| | - Sheetal Kumar Jain
- Department of Chemistry and Biochemistry , University of California, Santa Barbara , Santa Barbara , California 93106 , United States
| | - Songi Han
- Department of Chemistry and Biochemistry , University of California, Santa Barbara , Santa Barbara , California 93106 , United States
- Department of Chemical Engineering , University of California, Santa Barbara , Santa Barbara , California 93106 , United States
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60
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Dol C, Gerbaud G, Guigliarelli B, Bloch E, Gastaldi S, Besson E. Modulating lifetimes and relaxation times of phenoxyl radicals through their incorporation into different hybrid nanostructures. Phys Chem Chem Phys 2019; 21:16337-16344. [DOI: 10.1039/c9cp03052b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Playing with the structural features of various hybrid materials enables to adjust physical properties of phenoxyl radicals.
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Affiliation(s)
| | | | | | - Emily Bloch
- Aix Marseille Univ
- CNRS
- MADIREL
- Marseille
- France
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61
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Xiao D, Xu S, Brownbill NJ, Paul S, Chen LH, Pawsey S, Aussenac F, Su BL, Han X, Bao X, Liu Z, Blanc F. Fast detection and structural identification of carbocations on zeolites by dynamic nuclear polarization enhanced solid-state NMR. Chem Sci 2018; 9:8184-8193. [PMID: 30568769 PMCID: PMC6254210 DOI: 10.1039/c8sc03848a] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Accepted: 10/02/2018] [Indexed: 12/20/2022] Open
Abstract
Acidic zeolites are porous aluminosilicates used in a wide range of industrial processes such as adsorption and catalysis. The formation of carbocation intermediates plays a key role in reactivity, selectivity and deactivation in heterogeneous catalytic processes. However, the observation and determination of carbocations remain a significant challenge in heterogeneous catalysis due to the lack of selective techniques of sufficient sensitivity to detect their low concentrations. Here, we combine 13C isotopic enrichment and efficient dynamic nuclear polarization magic angle spinning nuclear magnetic resonance spectroscopy to detect carbocations in zeolites. We use two dimensional 13C-13C through-bond correlations to establish their structures and 29Si-13C through-space experiments to quantitatively probe the interaction between multiple surface sites of the zeolites and the confined hydrocarbon pool species. We show that a range of various membered ring carbocations are intermediates in the methanol to hydrocarbons reaction catalysed by different microstructural β-zeolites and highlight that different reaction routes for the formation of both targeted hydrocarbon products and coke exist. These species have strong van der Waals interaction with the zeolite framework demonstrating that their accumulation in the channels of the zeolites leads to deactivation. These results enable understanding of deactivation pathways and open up opportunities for the design of catalysts with improved performances.
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Affiliation(s)
- Dong Xiao
- State Key Laboratory of Catalysis , Dalian Institute of Chemical Physics , Chinese Academy of Sciences , 457 Zhongshan Road , Dalian 116023 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
- Department of Chemistry , University of Liverpool , Crown Street , Liverpool , L69 7ZD , UK .
| | - Shutao Xu
- National Engineering Laboratory for Methanol to Olefins , Dalian National Laboratory for Clean Energy , Dalian Institute of Chemical Physics , Chinese Academy of Sciences , Dalian 116023 , China
| | - Nick J Brownbill
- Department of Chemistry , University of Liverpool , Crown Street , Liverpool , L69 7ZD , UK .
| | - Subhradip Paul
- DNP MAS NMR Facility , Sir Peter Mansfield Imaging Centre , University of Nottingham , Nottingham NG7 2RD , UK
| | - Li-Hua Chen
- State Key Laboratory of Advanced Technology for Materials Synthesis and Processing , Wuhan University of Technology , 122 Luoshi Road , 430070 , Wuhan , China
| | - Shane Pawsey
- Bruker BioSpin Corporation , 15 Fortune Drive , Billerica , Massachusetts 01821 , USA
| | - Fabien Aussenac
- Bruker BioSpin , 34 rue de I'Industrie BP 10002 , 67166 Wissembourg Cedex , France
| | - Bao-Lian Su
- State Key Laboratory of Advanced Technology for Materials Synthesis and Processing , Wuhan University of Technology , 122 Luoshi Road , 430070 , Wuhan , China
- CMI (Laboratory of Inorganic Materials Chemistry) , University of Namur , 61 rue de Bruxelles , B-5000 Namur , Belgium
| | - Xiuwen Han
- State Key Laboratory of Catalysis , Dalian Institute of Chemical Physics , Chinese Academy of Sciences , 457 Zhongshan Road , Dalian 116023 , China
| | - Xinhe Bao
- State Key Laboratory of Catalysis , Dalian Institute of Chemical Physics , Chinese Academy of Sciences , 457 Zhongshan Road , Dalian 116023 , China
| | - Zhongmin Liu
- State Key Laboratory of Catalysis , Dalian Institute of Chemical Physics , Chinese Academy of Sciences , 457 Zhongshan Road , Dalian 116023 , China
- National Engineering Laboratory for Methanol to Olefins , Dalian National Laboratory for Clean Energy , Dalian Institute of Chemical Physics , Chinese Academy of Sciences , Dalian 116023 , China
| | - Frédéric Blanc
- Department of Chemistry , University of Liverpool , Crown Street , Liverpool , L69 7ZD , UK .
- Stephenson Institute for Renewable Energy , University of Liverpool , Crown Street , Liverpool L69 7ZD , UK
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62
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Perras FA, Pruski M. Large-scale ab initio simulations of MAS DNP enhancements using a Monte Carlo optimization strategy. J Chem Phys 2018; 149:154202. [PMID: 30342444 DOI: 10.1063/1.5042651] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Magic-angle-spinning (MAS) dynamic nuclear polarization (DNP) has recently emerged as a powerful technology enabling otherwise unrealistic solid-state NMR experiments. The simulation of DNP processes which might, for example, aid in refining the experimental conditions or the design of better performing polarizing agents, is, however, plagued with significant challenges, often limiting the system size to only 3 spins. Here, we present the first approach to fully ab initio large-scale simulations of MAS DNP enhancements. The Landau-Zener equation is used to treat all interactions concerning electron spins, and the low-order correlations in the Liouville space method is used to accurately treat the spin diffusion, as well as its MAS speed dependence. As the propagator cannot be stored, a Monte Carlo optimization method is used to determine the steady-state enhancement factors. This new software is employed to investigate the MAS speed dependence of the enhancement factors in large spin systems where spin diffusion is of importance, as well as to investigate the impacts of solvent and polarizing agent deuteration on the performance of MAS DNP.
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63
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Lund A, Equbal A, Han S. Tuning nuclear depolarization under MAS by electron T 1e. Phys Chem Chem Phys 2018; 20:23976-23987. [PMID: 30211922 DOI: 10.1039/c8cp04167a] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The Cross-Effect (CE) Dynamic Nuclear Polarization (DNP) mechanism under Magic Angle Spinning (MAS) induces depletion or "depolarization" of the NMR signal, in the absence of microwave irradiation. In this study, the role of T1e on nuclear depolarization under MAS was tested experimentally by systematically varying the local and global electron spin concentration using mono-, bi- and tri-radicals. These spin systems show different depolarization effects that systematically tracked with their different T1e rates, consistent with theoretical predictions. In order to test whether the effect of T1e is directly or indirectly convoluted with other spin parameters, the tri-radical system was doped with different concentrations of GdCl3, only tuning the T1e rates, while keeping other parameters unchanged. Gratifyingly, the changes in the depolarization factor tracked the changes in the T1e rates. The experimental results are corroborated by quantum mechanics based numerical simulations which recapitulated the critical role of T1e. Simulations showed that the relative orientation of the two g-tensors and e-e dipolar interaction tensors of the CE fulfilling spin pair also plays a major role in determining the extent of depolarization, besides the enhancement. This is expected as orientations influence the efficiency of the various level anti-crossings or the "rotor events" under MAS. However, experimental evaluation of the empirical spectral diffusion parameter at static condition showed that the local vs. global e-e dipolar interaction network is not a significant variable in the commonly used nitroxide radical system studied here, leaving T1e rates as the major modulator of depolarization.
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Affiliation(s)
- Alicia Lund
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106-9510, USA.
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64
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Verde-Sesto E, Goujon N, Sardon H, Ruiz P, Huynh TV, Elizalde F, Mecerreyes D, Forsyth M, O’Dell LA. DNP NMR Studies of Crystalline Polymer Domains by Copolymerization with Nitroxide Radical Monomers. Macromolecules 2018. [DOI: 10.1021/acs.macromol.8b01665] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Ester Verde-Sesto
- POLYMAT, University of the Basque Country UPV/EHU, Joxe Mari Korta Center, Avda. Tolosa 7, 20018 Donostia-San Sebastian, Spain
| | - Nicolas Goujon
- Institute for Frontier Materials, Deakin University, Geelong, Victoria 3220, Australia
| | - Haritz Sardon
- POLYMAT, University of the Basque Country UPV/EHU, Joxe Mari Korta Center, Avda. Tolosa 7, 20018 Donostia-San Sebastian, Spain
| | - Pauline Ruiz
- Institute for Frontier Materials, Deakin University, Geelong, Victoria 3220, Australia
| | - Tan Vu Huynh
- Institute for Frontier Materials, Deakin University, Geelong, Victoria 3220, Australia
| | - Fermin Elizalde
- POLYMAT, University of the Basque Country UPV/EHU, Joxe Mari Korta Center, Avda. Tolosa 7, 20018 Donostia-San Sebastian, Spain
| | - David Mecerreyes
- POLYMAT, University of the Basque Country UPV/EHU, Joxe Mari Korta Center, Avda. Tolosa 7, 20018 Donostia-San Sebastian, Spain
- Ikerbasque, Basque
Foundation for Science, E-48011 Bilbao, Spain
| | - Maria Forsyth
- Institute for Frontier Materials, Deakin University, Geelong, Victoria 3220, Australia
- Ikerbasque, Basque
Foundation for Science, E-48011 Bilbao, Spain
| | - Luke A. O’Dell
- Institute for Frontier Materials, Deakin University, Geelong, Victoria 3220, Australia
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65
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Sesti EL, Saliba EP, Alaniva N, Barnes AB. Electron decoupling with cross polarization and dynamic nuclear polarization below 6 K. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 295:1-5. [PMID: 30077145 PMCID: PMC7015119 DOI: 10.1016/j.jmr.2018.07.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Revised: 07/17/2018] [Accepted: 07/21/2018] [Indexed: 05/05/2023]
Abstract
Dynamic nuclear polarization (DNP) can improve nuclear magnetic resonance (NMR) sensitivity by orders of magnitude. Polarizing agents containing unpaired electrons required for DNP can broaden nuclear resonances in the presence of appreciable hyperfine couplings. Here we present the first cross polarization experiments implemented with electron decoupling, which attenuates detrimental hyperfine couplings. We also demonstrate magic angle spinning (MAS) DNP experiments below 6 K, producing unprecedented nuclear spin polarization in rotating solids. 13C correlation spectra were collected with MAS DNP below 6 K for the first time. Polarization build-up times with MAS DNP (T1DNP, 1H) of urea in a frozen glassy matrix below 6 K were measured for both the solid effect and the cross effect. Trityl radicals exhibit a T1DNP (1H) of 18.7 s and the T1DNP (1H) of samples doped with 20 mM AMUPol is only 1.3 s. MAS below 6 K with DNP and electron decoupling is an effective strategy to increase NMR signal-to-noise ratios per transient while retaining short polarization periods.
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Affiliation(s)
- Erika L Sesti
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
| | - Edward P Saliba
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
| | - Nicholas Alaniva
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
| | - Alexander B Barnes
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA.
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66
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Wisser D, Karthikeyan G, Lund A, Casano G, Karoui H, Yulikov M, Menzildjian G, Pinon AC, Purea A, Engelke F, Chaudhari SR, Kubicki D, Rossini AJ, Moroz IB, Gajan D, Copéret C, Jeschke G, Lelli M, Emsley L, Lesage A, Ouari O. BDPA-Nitroxide Biradicals Tailored for Efficient Dynamic Nuclear Polarization Enhanced Solid-State NMR at Magnetic Fields up to 21.1 T. J Am Chem Soc 2018; 140:13340-13349. [DOI: 10.1021/jacs.8b08081] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Dorothea Wisser
- Institut de Sciences Analytiques, Centre de RMN à Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | | | - Alicia Lund
- Institut de Sciences Analytiques, Centre de RMN à Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Gilles Casano
- AixMarseille Univ, CNRS, ICR, 13013 Marseille, France
| | - Hakim Karoui
- AixMarseille Univ, CNRS, ICR, 13013 Marseille, France
| | - Maxim Yulikov
- Department of Chemistry and Applied Biosciences, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland
| | - Georges Menzildjian
- Institut de Sciences Analytiques, Centre de RMN à Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Arthur C. Pinon
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | | | | | - Sachin R. Chaudhari
- Institut de Sciences Analytiques, Centre de RMN à Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Dominik Kubicki
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Aaron J. Rossini
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Ilia B. Moroz
- Department of Chemistry and Applied Biosciences, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland
| | - David Gajan
- Institut de Sciences Analytiques, Centre de RMN à Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Christophe Copéret
- Department of Chemistry and Applied Biosciences, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland
| | - Gunnar Jeschke
- Department of Chemistry and Applied Biosciences, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland
| | - Moreno Lelli
- Department of Chemistry “Ugo Schiff”, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Florence, Italy
- Magnetic Resonance Center (CERM), University of Florence, Via L. Sacconi 6, 50019 Sesto Fiorentino, Florence, Italy
| | - Lyndon Emsley
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Anne Lesage
- Institut de Sciences Analytiques, Centre de RMN à Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Olivier Ouari
- AixMarseille Univ, CNRS, ICR, 13013 Marseille, France
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67
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Mentink-Vigier F, Marin-Montesinos I, Jagtap AP, Halbritter T, van Tol J, Hediger S, Lee D, Sigurdsson ST, De Paëpe G. Computationally Assisted Design of Polarizing Agents for Dynamic Nuclear Polarization Enhanced NMR: The AsymPol Family. J Am Chem Soc 2018; 140:11013-11019. [PMID: 30095255 PMCID: PMC6145599 DOI: 10.1021/jacs.8b04911] [Citation(s) in RCA: 77] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Indexed: 12/11/2022]
Abstract
We introduce a new family of highly efficient polarizing agents for dynamic nuclear polarization (DNP)-enhanced nuclear magnetic resonance (NMR) applications, composed of asymmetric bis-nitroxides, in which a piperidine-based radical and a pyrrolinoxyl or a proxyl radical are linked together. The design of the AsymPol family was guided by the use of advanced simulations that allow computation of the impact of the radical structure on DNP efficiency. These simulations suggested the use of a relatively short linker with the intention to generate a sizable intramolecular electron dipolar coupling/ J-exchange interaction, while avoiding parallel nitroxide orientations. The characteristics of AsymPol were further tuned, for instance with the addition of a conjugated carbon-carbon double bond in the 5-membered ring to improve the rigidity and provide a favorable relative orientation, the replacement of methyls by spirocyclohexanolyl groups to slow the electron spin relaxation, and the introduction of phosphate groups to yield highly water-soluble dopants. An in-depth experimental and theoretical study for two members of the family, AsymPol and AsymPolPOK, is presented here. We report substantial sensitivity gains at both 9.4 and 18.8 T. The robust efficiency of this new family is further demonstrated through high-resolution surface characterization of an important industrial catalyst using fast sample spinning at 18.8 T. This work highlights a new direction for polarizing agent design and the critical importance of computations in this process.
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Affiliation(s)
- Frédéric Mentink-Vigier
- Univ.
Grenoble Alpes, CEA, CNRS, INAC-MEM, F-38000 Grenoble, France
- CIMAR/NMR
National High Magnetic Field Laboratory, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, United States
| | | | - Anil P. Jagtap
- Department
of Chemistry, University of Iceland, Science
Institute, Dunhaga 3, 107 Reykjavik, Iceland
| | - Thomas Halbritter
- Department
of Chemistry, University of Iceland, Science
Institute, Dunhaga 3, 107 Reykjavik, Iceland
| | - Johan van Tol
- EMR
National High Magnetic Field Laboratory, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, United States
| | - Sabine Hediger
- Univ.
Grenoble Alpes, CEA, CNRS, INAC-MEM, F-38000 Grenoble, France
| | - Daniel Lee
- Univ.
Grenoble Alpes, CEA, CNRS, INAC-MEM, F-38000 Grenoble, France
| | - Snorri Th. Sigurdsson
- Department
of Chemistry, University of Iceland, Science
Institute, Dunhaga 3, 107 Reykjavik, Iceland
| | - Gaël De Paëpe
- Univ.
Grenoble Alpes, CEA, CNRS, INAC-MEM, F-38000 Grenoble, France
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68
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Zhao L, Pinon AC, Emsley L, Rossini AJ. DNP-enhanced solid-state NMR spectroscopy of active pharmaceutical ingredients. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2018; 56:583-609. [PMID: 29193278 DOI: 10.1002/mrc.4688] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2017] [Revised: 11/15/2017] [Accepted: 11/19/2017] [Indexed: 06/07/2023]
Abstract
Solid-state NMR spectroscopy has become a valuable tool for the characterization of both pure and formulated active pharmaceutical ingredients (APIs). However, NMR generally suffers from poor sensitivity that often restricts NMR experiments to nuclei with favorable properties, concentrated samples, and acquisition of one-dimensional (1D) NMR spectra. Here, we review how dynamic nuclear polarization (DNP) can be applied to routinely enhance the sensitivity of solid-state NMR experiments by one to two orders of magnitude for both pure and formulated APIs. Sample preparation protocols for relayed DNP experiments and experiments on directly doped APIs are detailed. Numerical spin diffusion models illustrate the dependence of relayed DNP enhancements on the relaxation properties and particle size of the solids and can be used for particle size determination when the other factors are known. We then describe the advanced solid-state NMR experiments that have been enabled by DNP and how they provide unique insight into the molecular and macroscopic structure of APIs. For example, with large sensitivity gains provided by DNP, natural isotopic abundance, 13 C-13 C double-quantum single-quantum homonuclear correlation NMR spectra of pure APIs can be routinely acquired. DNP also enables solid-state NMR experiments with unreceptive quadrupolar nuclei such as 2 H, 14 N, and 35 Cl that are commonly found in APIs. Applications of DNP-enhanced solid-state NMR spectroscopy for the molecular level characterization of low API load formulations such as commercial tablets and amorphous solid dispersions are described. Future perspectives for DNP-enhanced solid-state NMR experiments on APIs are briefly discussed.
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Affiliation(s)
- Li Zhao
- Department of Chemistry, Iowa State University, Ames, IA, USA
- US DOE Ames Laboratory, Ames, IA, USA
| | - Arthur C Pinon
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
| | - Lyndon Emsley
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
| | - Aaron J Rossini
- Department of Chemistry, Iowa State University, Ames, IA, USA
- US DOE Ames Laboratory, Ames, IA, USA
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69
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Thurber KR, Le TN, Changcoco V, Brook DJR. Verdazyl-ribose: A new radical for solid-state dynamic nuclear polarization at high magnetic field. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 289:122-131. [PMID: 29501956 PMCID: PMC5856651 DOI: 10.1016/j.jmr.2018.02.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Revised: 02/20/2018] [Accepted: 02/21/2018] [Indexed: 06/08/2023]
Abstract
Solid-state dynamic nuclear polarization (DNP) using the cross-effect relies on radical pairs whose electron spin resonance (ESR) frequencies differ by the nuclear magnetic resonance (NMR) frequency. We measure the DNP provided by a new water-soluble verdazyl radical, verdazyl-ribose, under both magic-angle spinning (MAS) and static sample conditions at 9.4 T, and compare it to a nitroxide radical, 4-hydroxy-TEMPO. We find that verdazyl-ribose is an effective radical for cross-effect DNP, with the best relative results for a non-spinning sample. Under non-spinning conditions, verdazyl-ribose provides roughly 2× larger 13C cross-polarized (CP) NMR signal than the nitroxide, with similar polarization buildup times, at both 29 K and 76 K. With MAS at 7 kHz and 1.5 W microwave power, the verdazyl-ribose does not provide as much DNP as the nitroxide, with the verdazyl providing less NMR signal and a longer polarization buildup time. When the microwave power is decreased to 30 mW with 5 kHz MAS, the two types of radical are comparable, with the verdazyl-doped sample having a larger NMR signal which compensates for its longer polarization buildup time. We also present electron spin relaxation measurements at Q-band (1.2 T) and ESR lineshapes at 1.2 and 9.4 T. Most notably, the verdazyl radical has a longer T1e than the nitroxide (9.9 ms and 1.3 ms, respectively, at 50 K and 1.2 T). The verdazyl electron spin lineshape is significantly affected by the hyperfine coupling to four 14N nuclei, even at 9.4 T. We also describe 3000-spin calculations to illustrate the DNP potential of possible radical pairs: verdazyl-verdazyl, verdazyl-nitroxide, or nitroxide-nitroxide pairs. These calculations suggest that the verdazyl radical at 9.4 T has a narrower linewidth than optimal for cross-effect DNP using verdazyl-verdazyl pairs. Because of the hyperfine coupling contribution to the electron spin linewidth, this implies that DNP using the verdazyl radical would improve at lower magnetic field. Another conclusion from the calculations is that a verdazyl-nitroxide bi-radical would be expected to be slightly better for cross-effect DNP than the nitroxide-nitroxide bi-radicals commonly used now, assuming the same spin-spin coupling constants.
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Affiliation(s)
- Kent R Thurber
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, United States.
| | - Thanh-Ngoc Le
- Department of Chemistry, San José State University, One Washington Square, San José, CA 95192, United States
| | - Victor Changcoco
- Department of Chemistry, San José State University, One Washington Square, San José, CA 95192, United States
| | - David J R Brook
- Department of Chemistry, San José State University, One Washington Square, San José, CA 95192, United States
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70
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Plainchont B, Berruyer P, Dumez JN, Jannin S, Giraudeau P. Dynamic Nuclear Polarization Opens New Perspectives for NMR Spectroscopy in Analytical Chemistry. Anal Chem 2018; 90:3639-3650. [PMID: 29481058 DOI: 10.1021/acs.analchem.7b05236] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Dynamic nuclear polarization (DNP) can boost sensitivity in nuclear magnetic resonance (NMR) experiments by several orders of magnitude. This Feature illustrates how the coupling of DNP with both liquid- and solid-state NMR spectroscopy has the potential to considerably extend the range of applications of NMR in analytical chemistry.
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Affiliation(s)
- Bertrand Plainchont
- Université de Nantes , CNRS, CEISAM UMR 6230 , 44322 Nantes Cedex 03 , France
| | - Pierrick Berruyer
- Université Claude Bernard Lyon 1, CNRS, ENS de Lyon , Institut des Sciences Analytiques, UMR 5280 , 5 Rue de la Doua , 69100 Villeurbanne , France
| | - Jean-Nicolas Dumez
- Institut de Chimie des Substances Naturelles, CNRS UPR 2301 , Univ. Paris Sud, Université Paris-Saclay , 91190 Gif-sur Yvette , France
| | - Sami Jannin
- Université Claude Bernard Lyon 1, CNRS, ENS de Lyon , Institut des Sciences Analytiques, UMR 5280 , 5 Rue de la Doua , 69100 Villeurbanne , France
| | - Patrick Giraudeau
- Université de Nantes , CNRS, CEISAM UMR 6230 , 44322 Nantes Cedex 03 , France.,Institut Universitaire de France , 75005 Paris , France
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71
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Mentink-Vigier F, Vega S, De Paëpe G. Fast and accurate MAS-DNP simulations of large spin ensembles. Phys Chem Chem Phys 2018; 19:3506-3522. [PMID: 28093594 DOI: 10.1039/c6cp07881h] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A deeper understanding of parameters affecting Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP), an emerging nuclear magnetic resonance hyperpolarization method, is crucial for the development of new polarizing agents and the successful implementation of the technique at higher magnetic fields (>10 T). Such progress is currently impeded by computational limitation which prevents the simulation of large spin ensembles (electron as well as nuclear spins) and to accurately describe the interplay between all the multiple key parameters at play. In this work, we present an alternative approach to existing cross-effect and solid-effect MAS-DNP codes that yields fast and accurate simulations. More specifically we describe the model, the associated Liouville-based formalism (Bloch-type derivation and/or Landau-Zener approximations) and the linear time algorithm that allows computing MAS-DNP mechanisms with unprecedented time savings. As a result, one can easily scan through multiple parameters and disentangle their mutual influences. In addition, the simulation code is able to handle multiple electrons and protons, which allows probing the effect of (hyper)polarizing agents concentration, as well as fully revealing the interplay between the polarizing agent structure and the hyperfine couplings, nuclear dipolar couplings, nuclear relaxation times, both in terms of depolarization effect, but also of polarization gain and buildup times.
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Affiliation(s)
- Frédéric Mentink-Vigier
- Univ. Grenoble Alpes, INAC, MEM, F-38000 Grenoble, France and CEA, INAC, MEM, F-38000 Grenoble, France.
| | - Shimon Vega
- Weizmann institute of Science, Rehovot, Israel
| | - Gaël De Paëpe
- Univ. Grenoble Alpes, INAC, MEM, F-38000 Grenoble, France and CEA, INAC, MEM, F-38000 Grenoble, France.
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72
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Jagtap AP, Geiger MA, Stöppler D, Orwick-Rydmark M, Oschkinat H, Sigurdsson ST. bcTol : a highly water-soluble biradical for efficient dynamic nuclear polarization of biomolecules. Chem Commun (Camb) 2018; 52:7020-3. [PMID: 27161650 DOI: 10.1039/c6cc01813k] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Dynamic nuclear polarization (DNP) is an efficient method to overcome the inherent low sensitivity of magic-angle spinning (MAS) solid-state NMR. We report a new polarizing agent (), designed for biological applications, that yielded an enhancement value of 244 in a microcrystalline SH3 domain sample at 110 K.
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Affiliation(s)
- Anil P Jagtap
- University of Iceland, Department of Chemistry, Science Institute, Dunhaga 3, 107 Reykjavik, Iceland.
| | - Michel-Andreas Geiger
- NMR supported structural biology, Leibniz-Institut for Molecular Biology (FMP), Robert-Roessle-Str. 10, 13125 Berlin, Germany.
| | - Daniel Stöppler
- NMR supported structural biology, Leibniz-Institut for Molecular Biology (FMP), Robert-Roessle-Str. 10, 13125 Berlin, Germany.
| | - Marcella Orwick-Rydmark
- NMR supported structural biology, Leibniz-Institut for Molecular Biology (FMP), Robert-Roessle-Str. 10, 13125 Berlin, Germany.
| | - Hartmut Oschkinat
- NMR supported structural biology, Leibniz-Institut for Molecular Biology (FMP), Robert-Roessle-Str. 10, 13125 Berlin, Germany.
| | - Snorri Th Sigurdsson
- University of Iceland, Department of Chemistry, Science Institute, Dunhaga 3, 107 Reykjavik, Iceland.
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73
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Liao WC, Ghaffari B, Gordon CP, Xu J, Copéret C. Dynamic Nuclear Polarization Surface Enhanced NMR spectroscopy (DNP SENS): Principles, protocols, and practice. Curr Opin Colloid Interface Sci 2018. [DOI: 10.1016/j.cocis.2018.02.006] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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74
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Rogawski R, Sergeyev IV, Zhang Y, Tran TH, Li Y, Tong L, McDermott AE. NMR Signal Quenching from Bound Biradical Affinity Reagents in DNP Samples. J Phys Chem B 2017; 121:10770-10781. [PMID: 29116793 PMCID: PMC5842680 DOI: 10.1021/acs.jpcb.7b08274] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
We characterize the effect of specifically bound biradicals on the NMR spectra of dihydrofolate reductase from E. coli. Dynamic nuclear polarization methods enhance the signal-to-noise of solid state NMR experiments by transferring polarization from unpaired electrons of biradicals to nuclei. There has been recent interest in colocalizing the paramagnetic polarizing agents with the analyte of interest through covalent or noncovalent specific interactions. This experimental approach broadens the scope of dynamic nuclear polarization methods by offering the possibility of selective signal enhancements and the potential to work in a broad range of environments. Paramagnetic compounds can have other effects on the NMR spectroscopy of nearby nuclei, including broadening of nuclear resonances due to the proximity of the paramagnetic agent. Understanding the distance dependence of these interactions is important for the success of the technique. Here we explore paramagnetic signal quenching due to a bound biradical, specifically a biradical-derivatized trimethoprim ligand of E. coli dihydrofolate reductase. Biradical-derivatized trimethoprim has nanomolar affinity for its target, and affords strong and selective signal enhancements in dynamic nuclear polarization experiments. In this work, we show that, although the trimethoprim fragment is well ordered, the biradical (TOTAPOL) moiety is disordered when bound to the protein. The distance dependence in bleaching of NMR signal intensity allows us to detect numerous NMR signals in the protein. We present the possibility that static disorder and electron spin diffusion play roles in this observation, among other contributions. The fact that the majority of signals are observed strengthens the case for the use of high affinity or covalent radicals in dynamic nuclear polarization solid state NMR enhancement.
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Affiliation(s)
- Rivkah Rogawski
- Department of Chemistry, Columbia University , New York, New York 10027, United States
| | - Ivan V Sergeyev
- Department of Chemistry, Columbia University , New York, New York 10027, United States
| | - Yinglu Zhang
- Department of Biological Sciences, Columbia University , New York, New York 10027, United States
| | - Timothy H Tran
- Department of Biological Sciences, Columbia University , New York, New York 10027, United States
| | - Yongjun Li
- Department of Chemistry, Columbia University , New York, New York 10027, United States
| | - Liang Tong
- Department of Biological Sciences, Columbia University , New York, New York 10027, United States
| | - Ann E McDermott
- Department of Chemistry, Columbia University , New York, New York 10027, United States
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75
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Mentink-Vigier F, Mathies G, Liu Y, Barra AL, Caporini MA, Lee D, Hediger S, G Griffin R, De Paëpe G. Efficient cross-effect dynamic nuclear polarization without depolarization in high-resolution MAS NMR. Chem Sci 2017; 8:8150-8163. [PMID: 29619170 PMCID: PMC5861987 DOI: 10.1039/c7sc02199b] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Accepted: 10/01/2017] [Indexed: 11/21/2022] Open
Abstract
Dynamic nuclear polarization (DNP) has the potential to enhance the sensitivity of magic-angle spinning (MAS) NMR by many orders of magnitude and therefore to revolutionize atomic resolution structural analysis. Currently, the most widely used approach to DNP for studies of chemical, material, and biological systems involves the cross-effect (CE) mechanism, which relies on biradicals as polarizing agents. However, at high magnetic fields (≥5 T), the best biradicals used for CE MAS-DNP are still far from optimal, primarily because of the nuclear depolarization effects they induce. In the presence of bisnitroxide biradicals, magic-angle rotation results in a reverse CE that can deplete the initial proton Boltzmann polarization by more than a factor of 2. In this paper we show that these depolarization losses can be avoided by using a polarizing agent composed of a narrow-line trityl radical tethered to a broad-line TEMPO. Consequently, we show that a biocompatible trityl-nitroxide biradical, TEMTriPol-1, provides the highest MAS NMR sensitivity at ≥10 T, and its relative efficiency increases with the magnetic field strength. We use numerical simulations to explain the absence of depolarization for TEMTriPol-1 and its high efficiency, paving the way for the next generation of polarizing agents for DNP. We demonstrate the superior sensitivity enhancement using TEMTriPol-1 by recording the first solid-state 2D 13C-13C correlation spectrum at natural isotopic abundance at a magnetic field of 18.8 T.
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Affiliation(s)
| | - Guinevere Mathies
- Francis Bitter Magnet Laboratory , Department of Chemistry , Massachusetts Institute of Technology , Cambridge , MA 02139 , USA
| | - Yangping Liu
- Tianjin Key Laboratory on Technologies Enabling Development of Clinical Therapeutics and Diagnostics , School of Pharmacy , Tianjin Medical University , Tianjin 300070 , China
| | - Anne-Laure Barra
- Laboratoire National des Champs Magnétiques Intenses - CNRS , Univ. Grenoble Alpes , F-38042 Grenoble , France
| | - Marc A Caporini
- Bruker BioSpin Corporation , 15 Fortune Drive , Billerica , MA 01821 , USA
| | - Daniel Lee
- Univ. Grenoble Alpes , CEA , CNRS , INAC-MEM , F-38000 Grenoble , France .
| | - Sabine Hediger
- Univ. Grenoble Alpes , CEA , CNRS , INAC-MEM , F-38000 Grenoble , France .
| | - Robert G Griffin
- Francis Bitter Magnet Laboratory , Department of Chemistry , Massachusetts Institute of Technology , Cambridge , MA 02139 , USA
| | - Gaël De Paëpe
- Univ. Grenoble Alpes , CEA , CNRS , INAC-MEM , F-38000 Grenoble , France .
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76
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Lilly Thankamony AS, Wittmann JJ, Kaushik M, Corzilius B. Dynamic nuclear polarization for sensitivity enhancement in modern solid-state NMR. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2017; 102-103:120-195. [PMID: 29157490 DOI: 10.1016/j.pnmrs.2017.06.002] [Citation(s) in RCA: 268] [Impact Index Per Article: 38.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 06/03/2017] [Accepted: 06/08/2017] [Indexed: 05/03/2023]
Abstract
The field of dynamic nuclear polarization has undergone tremendous developments and diversification since its inception more than 6 decades ago. In this review we provide an in-depth overview of the relevant topics involved in DNP-enhanced MAS NMR spectroscopy. This includes the theoretical description of DNP mechanisms as well as of the polarization transfer pathways that can lead to a uniform or selective spreading of polarization between nuclear spins. Furthermore, we cover historical and state-of-the art aspects of dedicated instrumentation, polarizing agents, and optimization techniques for efficient MAS DNP. Finally, we present an extensive overview on applications in the fields of structural biology and materials science, which underlines that MAS DNP has moved far beyond the proof-of-concept stage and has become an important tool for research in these fields.
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Affiliation(s)
- Aany Sofia Lilly Thankamony
- Institute of Physical and Theoretical Chemistry, Institute of Biophysical Chemistry, and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany
| | - Johannes J Wittmann
- Institute of Physical and Theoretical Chemistry, Institute of Biophysical Chemistry, and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany
| | - Monu Kaushik
- Institute of Physical and Theoretical Chemistry, Institute of Biophysical Chemistry, and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany
| | - Björn Corzilius
- Institute of Physical and Theoretical Chemistry, Institute of Biophysical Chemistry, and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany.
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77
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Rogawski R, McDermott AE. New NMR tools for protein structure and function: Spin tags for dynamic nuclear polarization solid state NMR. Arch Biochem Biophys 2017; 628:102-113. [PMID: 28623034 PMCID: PMC5815514 DOI: 10.1016/j.abb.2017.06.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Revised: 06/05/2017] [Accepted: 06/12/2017] [Indexed: 12/13/2022]
Abstract
Magic angle spinning solid state NMR studies of biological macromolecules [1-3] have enabled exciting studies of membrane proteins [4,5], amyloid fibrils [6], viruses, and large macromolecular assemblies [7]. Dynamic nuclear polarization (DNP) provides a means to enhance detection sensitivity for NMR, particularly for solid state NMR, with many recent biological applications and considerable contemporary efforts towards elaboration and optimization of the DNP experiment. This review explores precedents and innovations in biological DNP experiments, especially highlighting novel chemical biology approaches to introduce the radicals that serve as a source of polarization in DNP experiments.
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Affiliation(s)
- Rivkah Rogawski
- Department of Chemistry, Columbia University, NY, NY 10027, United States
| | - Ann E McDermott
- Department of Chemistry, Columbia University, NY, NY 10027, United States.
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78
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Chaudhari S, Wisser D, Pinon AC, Berruyer P, Gajan D, Tordo P, Ouari O, Reiter C, Engelke F, Copéret C, Lelli M, Lesage A, Emsley L. Dynamic Nuclear Polarization Efficiency Increased by Very Fast Magic Angle Spinning. J Am Chem Soc 2017; 139:10609-10612. [PMID: 28692804 PMCID: PMC5719465 DOI: 10.1021/jacs.7b05194] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Indexed: 12/03/2022]
Abstract
Dynamic nuclear polarization (DNP) has recently emerged as a tool to enhance the sensitivity of solid-state NMR experiments. However, so far high enhancements (>100) are limited to relatively low magnetic fields, and DNP at fields higher than 9.4 T significantly drops in efficiency. Here we report solid-state Overhauser effect DNP enhancements of over 100 at 18.8 T. This is achieved through the unexpected discovery that enhancements increase rapidly with increasing magic angle spinning (MAS) rates. The measurements are made using 1,3-bisdiphenylene-2-phenylallyl dissolved in o-terphenyl at 40 kHz MAS. We introduce a source-sink diffusion model for polarization transfer which is capable of explaining the experimental observations. The advantage of this approach is demonstrated on mesoporous alumina with the acquisition of well-resolved DNP surface-enhanced 27Al cross-polarization spectra.
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Affiliation(s)
- Sachin
R. Chaudhari
- Institut
de Sciences Analytiques, Centre de RMN à Très Hauts
Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Dorothea Wisser
- Institut
de Sciences Analytiques, Centre de RMN à Très Hauts
Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Arthur C. Pinon
- Institut
des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - Pierrick Berruyer
- Institut
de Sciences Analytiques, Centre de RMN à Très Hauts
Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - David Gajan
- Institut
de Sciences Analytiques, Centre de RMN à Très Hauts
Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Paul Tordo
- Aix-Marseille
Université, CNRS, ICR UMR 7273, 13397 Marseille, France
| | - Olivier Ouari
- Aix-Marseille
Université, CNRS, ICR UMR 7273, 13397 Marseille, France
| | | | | | - Christophe Copéret
- Department
of Chemistry and Applied Biosciences, ETH
Zürich, CH-8093 Zürich, Switzerland
| | - Moreno Lelli
- Center for
Magnetic Resonance, Department of Chemistry, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy
| | - Anne Lesage
- Institut
de Sciences Analytiques, Centre de RMN à Très Hauts
Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France
| | - Lyndon Emsley
- Institut
des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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79
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Perras FA, Sadow A, Pruski M. In Silico Design of DNP Polarizing Agents: Can Current Dinitroxides Be Improved? Chemphyschem 2017; 18:2279-2287. [DOI: 10.1002/cphc.201700299] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Revised: 06/07/2017] [Indexed: 12/18/2022]
Affiliation(s)
| | - Aaron Sadow
- US DOE Ames Laboratory Ames IA 50011 USA
- Department of Chemistry Iowa State University Ames IA 50011 USA
| | - Marek Pruski
- US DOE Ames Laboratory Ames IA 50011 USA
- Department of Chemistry Iowa State University Ames IA 50011 USA
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80
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Saliba EP, Sesti EL, Scott FJ, Albert BJ, Choi EJ, Alaniva N, Gao C, Barnes AB. Electron Decoupling with Dynamic Nuclear Polarization in Rotating Solids. J Am Chem Soc 2017; 139:6310-6313. [DOI: 10.1021/jacs.7b02714] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Edward P. Saliba
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Erika L. Sesti
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Faith J. Scott
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Brice J. Albert
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Eric J. Choi
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Nicholas Alaniva
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Chukun Gao
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Alexander B. Barnes
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
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81
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Rogawski R, Sergeyev IV, Li Y, Ottaviani MF, Cornish V, McDermott AE. Dynamic Nuclear Polarization Signal Enhancement with High-Affinity Biradical Tags. J Phys Chem B 2017; 121:1169-1175. [PMID: 28099013 DOI: 10.1021/acs.jpcb.6b09021] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Dynamic nuclear polarization is an emerging technique for sensitizing solid-state NMR experiments by transferring polarization from electrons to nuclei. Stable biradicals, the polarization source for the cross effect mechanism, are typically codissolved at millimolar concentrations with proteins of interest. Here we describe the high-affinity biradical tag TMP-T, created by covalently linking trimethoprim, a nanomolar affinity ligand of dihydrofolate reductase (DHFR), to the biradical polarizing agent TOTAPOL. With TMP-T bound to DHFR, large enhancements of the protein spectrum are observed, comparable to when TOTAPOL is codissolved with the protein. In contrast to TOTAPOL, the tight binding TMP-T can be added stoichiometrically at radical concentrations orders of magnitude lower than in previously described preparations. Benefits of the reduced radical concentration include reduced spectral bleaching, reduced chemical perturbation of the sample, and the ability to selectively enhance signals for the protein of interest.
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Affiliation(s)
- Rivkah Rogawski
- Department of Chemistry, Columbia University , New York, New York 10027, United States
| | - Ivan V Sergeyev
- Department of Chemistry, Columbia University , New York, New York 10027, United States
| | - Yongjun Li
- Department of Chemistry, Columbia University , New York, New York 10027, United States
| | - M Francesca Ottaviani
- Department of Pure and Applied Sciences, University of Urbino , Loc. Crocicchia, 61029 Urbino, Italy
| | - Virginia Cornish
- Department of Chemistry, Columbia University , New York, New York 10027, United States
| | - Ann E McDermott
- Department of Chemistry, Columbia University , New York, New York 10027, United States
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82
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Gast P, Mance D, Zurlo E, Ivanov KL, Baldus M, Huber M. A tailored multi-frequency EPR approach to accurately determine the magnetic resonance parameters of dynamic nuclear polarization agents: application to AMUPol. Phys Chem Chem Phys 2017; 19:3777-3781. [DOI: 10.1039/c6cp05864g] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Multi- and very high-field electron paramagnetic resonance provides essential parameters to characterize dynamic nuclear polarization agents.
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Affiliation(s)
- P. Gast
- Department of Physics
- Huygens-Kamerlingh Onnes Laboratory
- Leiden University
- 2300 RA Leiden
- The Netherlands
| | - D. Mance
- NMR Spectroscopy
- Bijvoet Center for Biomolecular Research
- Utrecht University
- Utrecht
- The Netherlands
| | - E. Zurlo
- Department of Physics
- Huygens-Kamerlingh Onnes Laboratory
- Leiden University
- 2300 RA Leiden
- The Netherlands
| | - K. L. Ivanov
- International Tomography Center
- Siberian Branch of the Russian Academy of Science
- Novosibirsk 630090
- Russia
- Novosibirsk State University
| | - M. Baldus
- NMR Spectroscopy
- Bijvoet Center for Biomolecular Research
- Utrecht University
- Utrecht
- The Netherlands
| | - M. Huber
- Department of Physics
- Huygens-Kamerlingh Onnes Laboratory
- Leiden University
- 2300 RA Leiden
- The Netherlands
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83
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Stöppler D, Song C, van Rossum BJ, Geiger MA, Lang C, Mroginski MA, Jagtap AP, Sigurdsson ST, Matysik J, Hughes J, Oschkinat H. Dynamic Nuclear Polarization Provides New Insights into Chromophore Structure in Phytochrome Photoreceptors. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201608119] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Daniel Stöppler
- Leibniz-Institut für Molekulare Pharmakologie (FMP); NMR-supported Structural Biology; Robert-Rössle-Str. 10 13125 Berlin Germany
- Freie Universität Berlin; Fachbereich BCP; Takustr. 3 14195 Berlin Germany
| | - Chen Song
- Universität Leipzig; Institut für Analytische Chemie; Linnéstr. 3 04103 Leipzig Germany
| | - Barth-Jan van Rossum
- Leibniz-Institut für Molekulare Pharmakologie (FMP); NMR-supported Structural Biology; Robert-Rössle-Str. 10 13125 Berlin Germany
| | - Michel-Andreas Geiger
- Leibniz-Institut für Molekulare Pharmakologie (FMP); NMR-supported Structural Biology; Robert-Rössle-Str. 10 13125 Berlin Germany
- Freie Universität Berlin; Fachbereich BCP; Takustr. 3 14195 Berlin Germany
| | - Christina Lang
- Justus-Liebig-Universität Gießen; Institut für Pflanzenphysiologie; Senckenbergstr. 3 35390 Gießen Germany
| | - Maria-Andrea Mroginski
- Technische Universität Berlin; Institut für Chemie; Straße des 17. Juni 135 10623 Berlin Germany
| | | | | | - Jörg Matysik
- Universität Leipzig; Institut für Analytische Chemie; Linnéstr. 3 04103 Leipzig Germany
| | - Jon Hughes
- Justus-Liebig-Universität Gießen; Institut für Pflanzenphysiologie; Senckenbergstr. 3 35390 Gießen Germany
| | - Hartmut Oschkinat
- Leibniz-Institut für Molekulare Pharmakologie (FMP); NMR-supported Structural Biology; Robert-Rössle-Str. 10 13125 Berlin Germany
- Freie Universität Berlin; Fachbereich BCP; Takustr. 3 14195 Berlin Germany
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84
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Stöppler D, Song C, van Rossum BJ, Geiger MA, Lang C, Mroginski MA, Jagtap AP, Sigurdsson ST, Matysik J, Hughes J, Oschkinat H. Dynamic Nuclear Polarization Provides New Insights into Chromophore Structure in Phytochrome Photoreceptors. Angew Chem Int Ed Engl 2016; 55:16017-16020. [DOI: 10.1002/anie.201608119] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 09/30/2016] [Indexed: 11/12/2022]
Affiliation(s)
- Daniel Stöppler
- Leibniz-Institut für Molekulare Pharmakologie (FMP); NMR-supported Structural Biology; Robert-Rössle-Str. 10 13125 Berlin Germany
- Freie Universität Berlin; Fachbereich BCP; Takustr. 3 14195 Berlin Germany
| | - Chen Song
- Universität Leipzig; Institut für Analytische Chemie; Linnéstr. 3 04103 Leipzig Germany
| | - Barth-Jan van Rossum
- Leibniz-Institut für Molekulare Pharmakologie (FMP); NMR-supported Structural Biology; Robert-Rössle-Str. 10 13125 Berlin Germany
| | - Michel-Andreas Geiger
- Leibniz-Institut für Molekulare Pharmakologie (FMP); NMR-supported Structural Biology; Robert-Rössle-Str. 10 13125 Berlin Germany
- Freie Universität Berlin; Fachbereich BCP; Takustr. 3 14195 Berlin Germany
| | - Christina Lang
- Justus-Liebig-Universität Gießen; Institut für Pflanzenphysiologie; Senckenbergstr. 3 35390 Gießen Germany
| | - Maria-Andrea Mroginski
- Technische Universität Berlin; Institut für Chemie; Straße des 17. Juni 135 10623 Berlin Germany
| | | | | | - Jörg Matysik
- Universität Leipzig; Institut für Analytische Chemie; Linnéstr. 3 04103 Leipzig Germany
| | - Jon Hughes
- Justus-Liebig-Universität Gießen; Institut für Pflanzenphysiologie; Senckenbergstr. 3 35390 Gießen Germany
| | - Hartmut Oschkinat
- Leibniz-Institut für Molekulare Pharmakologie (FMP); NMR-supported Structural Biology; Robert-Rössle-Str. 10 13125 Berlin Germany
- Freie Universität Berlin; Fachbereich BCP; Takustr. 3 14195 Berlin Germany
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85
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Chaudhari SR, Berruyer P, Gajan D, Reiter C, Engelke F, Silverio DL, Copéret C, Lelli M, Lesage A, Emsley L. Dynamic nuclear polarization at 40 kHz magic angle spinning. Phys Chem Chem Phys 2016; 18:10616-22. [PMID: 27035630 PMCID: PMC5048395 DOI: 10.1039/c6cp00839a] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 03/11/2016] [Indexed: 01/07/2023]
Abstract
DNP-enhanced solid-state NMR spectroscopy under magic angle spinning (MAS) is rapidly developing into a powerful analytical tool to investigate the structure of a wide range of solid materials, because it provides unsurpassed sensitivity gains. Most developments and applications of DNP MAS NMR were so far reported at moderate spinning frequencies (up to 14 kHz using 3.2 mm rotors). Here, using a 1.3 mm MAS DNP probe operating at 18.8 T and ∼100 K, we show that signal amplification factors can be increased by up to a factor two when using smaller volume rotors as compared to 3.2 mm rotors, and report enhancements of around 60 over a range of sample spinning rates from 10 to 40 kHz. Spinning at 40 kHz is also shown to increase (29)Si coherence lifetimes by a factor three as compared to 10 kHz, substantially increasing sensitivity in CPMG type experiments. The contribution of quenching effects to the overall sensitivity gain at very fast MAS is evaluated, and applications are reported on a functionalised mesostructured organic-inorganic material.
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Affiliation(s)
- Sachin R. Chaudhari
- Institut de Sciences Analytiques , Centre de RMN à Très Hauts Champs , Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1) , France .
| | - Pierrick Berruyer
- Institut de Sciences Analytiques , Centre de RMN à Très Hauts Champs , Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1) , France .
| | - David Gajan
- Institut de Sciences Analytiques , Centre de RMN à Très Hauts Champs , Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1) , France .
| | | | | | - Daniel L. Silverio
- ETH Zürich , Department of Chemistry , Vladimir Prelog Weg 1-5 , CH-8093 Zürich , Switzerland
| | - Christophe Copéret
- ETH Zürich , Department of Chemistry , Vladimir Prelog Weg 1-5 , CH-8093 Zürich , Switzerland
| | - Moreno Lelli
- University of Florence , Chemistry Department , Magnetic Resonance Center , 50019 Sesto Fiorentino (FI) , Italy
| | - Anne Lesage
- Institut de Sciences Analytiques , Centre de RMN à Très Hauts Champs , Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1) , France .
| | - Lyndon Emsley
- Institut des Sciences et Ingénierie Chimiques , Ecole Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne , Switzerland .
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86
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Sauvée C, Casano G, Abel S, Rockenbauer A, Akhmetzyanov D, Karoui H, Siri D, Aussenac F, Maas W, Weber RT, Prisner T, Rosay M, Tordo P, Ouari O. Tailoring of Polarizing Agents in the bTurea Series for Cross-Effect Dynamic Nuclear Polarization in Aqueous Media. Chemistry 2016; 22:5598-606. [PMID: 26992052 DOI: 10.1002/chem.201504693] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2015] [Indexed: 11/10/2022]
Abstract
A series of 18 nitroxide biradicals derived from bTurea has been prepared, and their enhancement factors ɛ ((1)H) in cross-effect dynamic nuclear polarization (CE DNP) NMR experiments at 9.4 and 14.1 T and 100 K in a DNP-optimized glycerol/water matrix ("DNP juice") have been studied. We observe that ɛ ((1)H) is strongly correlated with the substituents on the polarizing agents, and its trend is discussed in terms of different molecular parameters: solubility, average e-e distance, relative orientation of the nitroxide moieties, and electron spin relaxation times. We show that too short an e-e distance or too long a T1e can dramatically limit ɛ ((1)H). Our study also shows that the molecular structure of AMUPol is not optimal and its ɛ ((1)H) could be further improved through stronger interaction with the glassy matrix and a better orientation of the TEMPO moieties. A new AMUPol derivative introduced here provides a better ɛ ((1)H) than AMUPol itself (by a factor of ca. 1.2).
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Affiliation(s)
- Claire Sauvée
- Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France
| | - Gilles Casano
- Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France
| | - Sébastien Abel
- Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France
| | - Antal Rockenbauer
- Institute of Materials and Environmental Chemistry, Hungarian Academy of Sciences, Department of Physics, Budapest University of Technology and Economics and MTA-BME Condensed Matter Research Group, Budafoki ut 8, 1111, Budapest, Hungary
| | - Dimitry Akhmetzyanov
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue Str. 7, 60438, Frankfurt-am-Main, Germany
| | - Hakim Karoui
- Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France
| | - Didier Siri
- Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France
| | - Fabien Aussenac
- Bruker BioSpin S.A.S., 34 rue de l'industrie, 67166, Wissembourg, France
| | - Werner Maas
- Bruker BioSpin Corporation, 15 Fortune Drive, Billerica, Massachusetts, 01821, USA
| | - Ralph T Weber
- Bruker BioSpin Corporation, 15 Fortune Drive, Billerica, Massachusetts, 01821, USA
| | - Thomas Prisner
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue Str. 7, 60438, Frankfurt-am-Main, Germany
| | - Mélanie Rosay
- Bruker BioSpin Corporation, 15 Fortune Drive, Billerica, Massachusetts, 01821, USA
| | - Paul Tordo
- Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France.
| | - Olivier Ouari
- Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France.
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87
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Liao SY, Lee M, Wang T, Sergeyev IV, Hong M. Efficient DNP NMR of membrane proteins: sample preparation protocols, sensitivity, and radical location. JOURNAL OF BIOMOLECULAR NMR 2016; 64:223-37. [PMID: 26873390 PMCID: PMC4826309 DOI: 10.1007/s10858-016-0023-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2015] [Accepted: 02/07/2016] [Indexed: 05/04/2023]
Abstract
Although dynamic nuclear polarization (DNP) has dramatically enhanced solid-state NMR spectral sensitivities of many synthetic materials and some biological macromolecules, recent studies of membrane-protein DNP using exogenously doped paramagnetic radicals as polarizing agents have reported varied and sometimes surprisingly limited enhancement factors. This motivated us to carry out a systematic evaluation of sample preparation protocols for optimizing the sensitivity of DNP NMR spectra of membrane-bound peptides and proteins at cryogenic temperatures of ~110 K. We show that mixing the radical with the membrane by direct titration instead of centrifugation gives a significant boost to DNP enhancement. We quantify the relative sensitivity enhancement between AMUPol and TOTAPOL, two commonly used radicals, and between deuterated and protonated lipid membranes. AMUPol shows ~fourfold higher sensitivity enhancement than TOTAPOL, while deuterated lipid membrane does not give net higher sensitivity for the membrane peptides than protonated membrane. Overall, a ~100 fold enhancement between the microwave-on and microwave-off spectra can be achieved on lipid-rich membranes containing conformationally disordered peptides, and absolute sensitivity gains of 105-160 can be obtained between low-temperature DNP spectra and high-temperature non-DNP spectra. We also measured the paramagnetic relaxation enhancement of lipid signals by TOTAPOL and AMUPol, to determine the depths of these two radicals in the lipid bilayer. Our data indicate a bimodal distribution of both radicals, a surface-bound fraction and a membrane-bound fraction where the nitroxides lie at ~10 Å from the membrane surface. TOTAPOL appears to have a higher membrane-embedded fraction than AMUPol. These results should be useful for membrane-protein solid-state NMR studies under DNP conditions and provide insights into how biradicals interact with phospholipid membranes.
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Affiliation(s)
- Shu Y Liao
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Myungwoon Lee
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Tuo Wang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | | | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
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88
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Siaw TA, Leavesley A, Lund A, Kaminker I, Han S. A versatile and modular quasi optics-based 200GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 264:131-153. [PMID: 26920839 PMCID: PMC4770585 DOI: 10.1016/j.jmr.2015.12.012] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2015] [Revised: 12/19/2015] [Accepted: 12/21/2015] [Indexed: 05/12/2023]
Abstract
Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3T) and cryogenic temperatures (∼ 2-90K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the "DNP power curve", i.e. the microwave (MW) power dependence of DNP enhancement, the "DNP spectrum", i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum, and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 and 201 GHz and outputs up to 140 mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the QO MW bridge will provide an efficient means to collect DNP data that is crucial for understanding the relationship between experimental and sample conditions, and the DNP performance. The modularity of this instrumental platform is suitable for future upgrades and extensions to include new experimental capabilities to meet contemporary DNP needs, including the simultaneous operation of two or more MW sources, time domain DNP, electron double resonance measurements, pulsed EPR operation, or simply the implementation of higher power MW amplifiers.
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Affiliation(s)
- Ting Ann Siaw
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, United States
| | - Alisa Leavesley
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, United States
| | - Alicia Lund
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, United States
| | - Ilia Kaminker
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, United States
| | - Songi Han
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, United States.
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89
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Lee D, Bouleau E, Saint-Bonnet P, Hediger S, De Paëpe G. Ultra-low temperature MAS-DNP. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 264:116-124. [PMID: 26920837 DOI: 10.1016/j.jmr.2015.12.010] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2015] [Revised: 12/15/2015] [Accepted: 12/16/2015] [Indexed: 05/05/2023]
Abstract
Since the infancy of NMR spectroscopy, sensitivity and resolution have been the limiting factors of the technique. Regular essential developments on this front have led to the widely applicable, versatile, and powerful spectroscopy that we know today. However, the Holy Grail of ultimate sensitivity and resolution is not yet reached, and technical improvements are still ongoing. Hence, high-field dynamic nuclear polarization (DNP) making use of high-frequency, high-power microwave irradiation of electron spins has become very promising in combination with magic angle sample spinning (MAS) solid-state NMR experiments. This is because it leads to a transfer of the much larger polarization of these electron spins under suitable irradiation to surrounding nuclei, greatly increasing NMR sensitivity. Currently, this boom in MAS-DNP is mainly performed at minimum sample temperatures of about 100K, using cold nitrogen gas to pneumatically spin and cool the sample. This Perspective deals with the desire to improve further the sensitivity and resolution by providing "ultra"-low temperatures for MAS-DNP, using cryogenic helium gas. Different designs on how this technological challenge has been overcome are described. It is shown that stable and fast spinning can be attained for sample temperatures down to 30K using a large cryostat developed in our laboratory. Using this cryostat to cool a closed-loop of helium gas brings the additional advantage of sample spinning frequencies that can greatly surpass those achievable with nitrogen gas, due to the differing fluidic properties of these two gases. It is shown that using ultra-low temperatures for MAS-DNP results in substantial experimental sensitivity enhancements and according time-savings. Access to this temperature range is demonstrated to be both viable and highly pertinent.
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Affiliation(s)
- Daniel Lee
- Univ. Grenoble Alpes, INAC, F-38000 Grenoble, France; CEA, INAC, F-38000 Grenoble, France
| | - Eric Bouleau
- Univ. Grenoble Alpes, INAC, F-38000 Grenoble, France; CEA, INAC, F-38000 Grenoble, France
| | - Pierre Saint-Bonnet
- Univ. Grenoble Alpes, INAC, F-38000 Grenoble, France; CEA, INAC, F-38000 Grenoble, France
| | - Sabine Hediger
- Univ. Grenoble Alpes, INAC, F-38000 Grenoble, France; CEA, INAC, F-38000 Grenoble, France; CNRS, SCIB, F-38000 Grenoble, France
| | - Gaël De Paëpe
- Univ. Grenoble Alpes, INAC, F-38000 Grenoble, France; CEA, INAC, F-38000 Grenoble, France
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90
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Matsuki Y, Idehara T, Fukazawa J, Fujiwara T. Advanced instrumentation for DNP-enhanced MAS NMR for higher magnetic fields and lower temperatures. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 264:107-115. [PMID: 26920836 DOI: 10.1016/j.jmr.2016.01.022] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 01/14/2016] [Accepted: 01/19/2016] [Indexed: 05/03/2023]
Abstract
Sensitivity enhancement of MAS NMR using dynamic nuclear polarization (DNP) is gaining importance at moderate fields (B0<9T) and temperatures (T>90K) with potential applications in chemistry and material sciences. However, considering the ever-increasing size and complexity of the systems to be studied, it is crucial to establish DNP under higher field conditions, where the spectral resolution and the basic NMR sensitivity tend to improve. In this perspective, we overview our recent efforts on hardware developments, specifically targeted on improving DNP MAS NMR at high fields. It includes the development of gyrotrons that enable continuous frequency tuning and rapid frequency modulation for our 395 GHz-600 MHz and 460 GHz-700 MHz DNP NMR spectrometers. The latter 700 MHz system involves two gyrotrons and a quasi-optical transmission system that combines two independent sub-millimeter waves into a single dichromic wave. We also describe two cryogenic MAS NMR probe systems operating, respectively, at T ∼ 100K and ∼ 30K. The latter system utilizes a novel closed-loop helium recirculation mechanism, achieving cryogenic MAS without consuming any cryogen. These instruments altogether should promote high-field DNP toward more efficient, reliable and affordable technology. Some experimental DNP results obtained with these instruments are presented.
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Affiliation(s)
- Yoh Matsuki
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Toshitaka Idehara
- Research Center for Development of Far-Infrared Region, University of Fukui, Bunkyo 3-9-1, Fukui 910-8507, Japan
| | - Jun Fukazawa
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Toshimichi Fujiwara
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
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91
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Rosay M, Blank M, Engelke F. Instrumentation for solid-state dynamic nuclear polarization with magic angle spinning NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 264:88-98. [PMID: 26920834 DOI: 10.1016/j.jmr.2015.12.026] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Revised: 12/17/2015] [Accepted: 12/18/2015] [Indexed: 05/08/2023]
Abstract
Advances in dynamic nuclear polarization (DNP) instrumentation and methodology have been key factors in the recent growth of solid-state DNP NMR applications. We review the current state of the art of solid-state DNP NMR instrumentation primarily based on available commercial platforms. We start with a general system overview, including options for microwave sources and DNP NMR probes, and then focus on specific developments for DNP at 100K with magic angle spinning (MAS). Gyrotron microwave sources, passive components to transmit microwaves, the DNP MAS probe, a cooling device for low-temperature MAS, and sample preparation procedures including radicals for DNP are considered.
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Affiliation(s)
- Melanie Rosay
- Bruker-Biospin, 15 Fortune Drive, Billerica, MA 01730, USA.
| | - Monica Blank
- Communications and Power Industries, 811 Hansen Way, Palo Alto, CA 94304, USA.
| | - Frank Engelke
- Bruker-Biospin, Silberstreifen 4, 76287 Rheinstetten, Germany.
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92
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Thurber K, Tycko R. Low-temperature dynamic nuclear polarization with helium-cooled samples and nitrogen-driven magic-angle spinning. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 264:99-106. [PMID: 26920835 PMCID: PMC4769783 DOI: 10.1016/j.jmr.2016.01.011] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Revised: 01/18/2016] [Accepted: 01/19/2016] [Indexed: 05/05/2023]
Abstract
We describe novel instrumentation for low-temperature solid state nuclear magnetic resonance (NMR) with dynamic nuclear polarization (DNP) and magic-angle spinning (MAS), focusing on aspects of this instrumentation that have not been described in detail in previous publications. We characterize the performance of an extended interaction oscillator (EIO) microwave source, operating near 264 GHz with 1.5 W output power, which we use in conjunction with a quasi-optical microwave polarizing system and a MAS NMR probe that employs liquid helium for sample cooling and nitrogen gas for sample spinning. Enhancement factors for cross-polarized (13)C NMR signals in the 100-200 range are demonstrated with DNP at 25K. The dependences of signal amplitudes on sample temperature, as well as microwave power, polarization, and frequency, are presented. We show that sample temperatures below 30K can be achieved with helium consumption rates below 1.3 l/h. To illustrate potential applications of this instrumentation in structural studies of biochemical systems, we compare results from low-temperature DNP experiments on a calmodulin-binding peptide in its free and bound states.
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Affiliation(s)
- Kent Thurber
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, United States
| | - Robert Tycko
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, United States.
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93
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Bouleau E, Saint-Bonnet P, Mentink-Vigier F, Takahashi H, Jacquot JF, Bardet M, Aussenac F, Purea A, Engelke F, Hediger S, Lee D, De Paëpe G. Pushing NMR sensitivity limits using dynamic nuclear polarization with closed-loop cryogenic helium sample spinning. Chem Sci 2015; 6:6806-6812. [PMID: 28757972 PMCID: PMC5508678 DOI: 10.1039/c5sc02819a] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 08/26/2015] [Indexed: 02/01/2023] Open
Abstract
We report a strategy to push the limits of solid-state NMR sensitivity far beyond its current state-of-the-art. The approach relies on the use of dynamic nuclear polarization and demonstrates unprecedented DNP enhancement factors for experiments performed at sample temperatures much lower than 100 K, and can translate into 6 orders of magnitude of experimental time-savings. This leap-forward was made possible thanks to the employment of cryogenic helium as the gas to power magic angle sample spinning (MAS) for dynamic nuclear polarization (DNP) enhanced NMR experiments. These experimental conditions far exceed what is currently possible and allows currently reaching sample temperatures down to 30 K while conducting experiments with improved resolution (thanks to faster spinning frequencies, up to 25 kHz) and highly polarized nuclear spins. The impressive associated gains were used to hyperpolarize the surface of an industrial catalyst as well as to hyperpolarize organic nano-assemblies (self-assembling peptides in our case), for whom structures cannot be solved using diffraction techniques. Sustainable cryogenic helium sample spinning significantly enlarges the realm and possibilities of the MAS-DNP technique and is the route to transform NMR into a versatile but also sensitive atomic-level characterization tool.
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Affiliation(s)
- E Bouleau
- Univ. Grenoble Alpes , INAC , F-38000 Grenoble , France .
- CEA , INAC , F-38000 Grenoble , France
| | - P Saint-Bonnet
- Univ. Grenoble Alpes , INAC , F-38000 Grenoble , France .
- CEA , INAC , F-38000 Grenoble , France
| | - F Mentink-Vigier
- Univ. Grenoble Alpes , INAC , F-38000 Grenoble , France .
- CEA , INAC , F-38000 Grenoble , France
| | - H Takahashi
- Univ. Grenoble Alpes , INAC , F-38000 Grenoble , France .
- CEA , INAC , F-38000 Grenoble , France
| | - J-F Jacquot
- Univ. Grenoble Alpes , INAC , F-38000 Grenoble , France .
- CEA , INAC , F-38000 Grenoble , France
| | - M Bardet
- Univ. Grenoble Alpes , INAC , F-38000 Grenoble , France .
- CEA , INAC , F-38000 Grenoble , France
| | - F Aussenac
- Bruker BioSpin SAS , Wissembourg , France
| | - A Purea
- Bruker BioSpin GmbH , Rheinstetten , Germany
| | - F Engelke
- Bruker BioSpin GmbH , Rheinstetten , Germany
| | - S Hediger
- Univ. Grenoble Alpes , INAC , F-38000 Grenoble , France .
- CEA , INAC , F-38000 Grenoble , France
- CNRS , SCIB , F-38000 Grenoble , France
| | - D Lee
- Univ. Grenoble Alpes , INAC , F-38000 Grenoble , France .
- CEA , INAC , F-38000 Grenoble , France
| | - G De Paëpe
- Univ. Grenoble Alpes , INAC , F-38000 Grenoble , France .
- CEA , INAC , F-38000 Grenoble , France
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94
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Salnikov ES, Sarrouj H, Reiter C, Aisenbrey C, Purea A, Aussenac F, Ouari O, Tordo P, Fedotenko I, Engelke F, Bechinger B. Solid-State NMR/Dynamic Nuclear Polarization of Polypeptides in Planar Supported Lipid Bilayers. J Phys Chem B 2015; 119:14574-83. [PMID: 26487390 DOI: 10.1021/acs.jpcb.5b07341] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Dynamic nuclear polarization has been developed to overcome the limitations of the inherently low signal intensity of NMR spectroscopy. This technique promises to be particularly useful for solid-state NMR spectroscopy where the signals are broadened over a larger frequency range and most investigations rely on recording low gamma nuclei. To extend the range of possible investigations, a triple-resonance flat-coil solid-state NMR probe is presented with microwave irradiation capacities allowing the investigation of static samples at temperatures of 100 K, including supported lipid bilayers. The probe performance allows for two-dimensional separated local field experiments with high-power Lee-Goldberg decoupling and cross-polarization under simultaneous irradiation from a gyrotron microwave generator. Efficient cooling of the sample turned out to be essential for best enhancements and line shape and necessitated the development of a dedicated cooling chamber. Furthermore, a new membrane-anchored biradical is presented, and the geometry of supported membranes was optimized not only for good membrane alignment, handling, stability, and filling factor of the coil but also for heat and microwave dissipation. Enhancement factors of 17-fold were obtained, and a two-dimensional PISEMA spectrum of a transmembrane helical peptide was obtained in less than 2 h.
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Affiliation(s)
- Evgeniy S Salnikov
- Institute of Chemistry, University of Strasbourg/CNRS, UMR7177 , 67070 Strasbourg, France
| | - Hiba Sarrouj
- Institute of Chemistry, University of Strasbourg/CNRS, UMR7177 , 67070 Strasbourg, France.,Bruker BioSpin, Silberstreifen, 76287 Rheinstetten, Germany
| | | | - Christopher Aisenbrey
- Institute of Chemistry, University of Strasbourg/CNRS, UMR7177 , 67070 Strasbourg, France
| | - Armin Purea
- Bruker BioSpin, Silberstreifen, 76287 Rheinstetten, Germany
| | - Fabien Aussenac
- Bruker BioSpin, 34, rue de l'Industrie, 67166 Wissembourg, France
| | - Olivier Ouari
- Aix Marseille Université, CNRS , Institut de Chimie Radicalaire, UMR 7273, 13013 Marseille, France
| | - Paul Tordo
- Aix Marseille Université, CNRS , Institut de Chimie Radicalaire, UMR 7273, 13013 Marseille, France
| | - Illya Fedotenko
- Aix Marseille Université, CNRS , Institut de Chimie Radicalaire, UMR 7273, 13013 Marseille, France
| | - Frank Engelke
- Bruker BioSpin, Silberstreifen, 76287 Rheinstetten, Germany
| | - Burkhard Bechinger
- Institute of Chemistry, University of Strasbourg/CNRS, UMR7177 , 67070 Strasbourg, France
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95
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Hoff DEM, Albert BJ, Saliba EP, Scott FJ, Choi EJ, Mardini M, Barnes AB. Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2015; 72:79-89. [PMID: 26482131 PMCID: PMC4762658 DOI: 10.1016/j.ssnmr.2015.10.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2015] [Revised: 09/30/2015] [Accepted: 10/01/2015] [Indexed: 05/05/2023]
Abstract
Hyperfine decoupling and pulsed dynamic nuclear polarization (DNP) are promising techniques to improve high field DNP NMR. We explore experimental and theoretical considerations to implement them with magic angle spinning (MAS). Microwave field simulations using the high frequency structural simulator (HFSS) software suite are performed to characterize the inhomogeneous phase independent microwave field throughout a 198GHz MAS DNP probe. Our calculations show that a microwave power input of 17W is required to generate an average EPR nutation frequency of 0.84MHz. We also present a detailed calculation of microwave heating from the HFSS parameters and find that 7.1% of the incident microwave power contributes to dielectric sample heating. Voltage tunable gyrotron oscillators are proposed as a class of frequency agile microwave sources to generate microwave frequency sweeps required for the frequency modulated cross effect, electron spin inversions, and hyperfine decoupling. Electron spin inversions of stable organic radicals are simulated with SPINEVOLUTION using the inhomogeneous microwave fields calculated by HFSS. We calculate an electron spin inversion efficiency of 56% at a spinning frequency of 5kHz. Finally, we demonstrate gyrotron acceleration potentials required to generate swept microwave frequency profiles for the frequency modulated cross effect and electron spin inversions.
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Affiliation(s)
- Daniel E M Hoff
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
| | - Brice J Albert
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
| | - Edward P Saliba
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
| | - Faith J Scott
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
| | - Eric J Choi
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
| | - Michael Mardini
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
| | - Alexander B Barnes
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA.
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96
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Kubicki DJ, Casano G, Schwarzwälder M, Abel S, Sauvée C, Ganesan K, Yulikov M, Rossini AJ, Jeschke G, Copéret C, Lesage A, Tordo P, Ouari O, Emsley L. Rational design of dinitroxide biradicals for efficient cross-effect dynamic nuclear polarization. Chem Sci 2015; 7:550-558. [PMID: 29896347 PMCID: PMC5952883 DOI: 10.1039/c5sc02921j] [Citation(s) in RCA: 114] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Accepted: 10/12/2015] [Indexed: 12/27/2022] Open
Abstract
A series of 37 dinitroxide biradicals have been prepared and their performance studied as polarizing agents in cross-effect DNP NMR experiments at 9.4 T and 100 K in 1,1,2,2-tetrachloroethane (TCE). We observe that in this regime the DNP performance is strongly correlated with the substituents on the polarizing agents, and electron and nuclear spin relaxation times, with longer relaxation times leading to better enhancements. We also observe that deuteration of the radicals generally leads to better DNP enhancement but with longer build-up time. One of the new radicals introduced here provides the best performance obtained so far under these conditions.
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Affiliation(s)
- Dominik J Kubicki
- Institut des Sciences et Ingénierie Chimiques , Ecole Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne , Switzerland .
| | - Gilles Casano
- Aix-Marseille Université , CNRS , ICR UMR 7273 , 13397 Marseille , France . ;
| | - Martin Schwarzwälder
- ETH Zurich , Department of Chemistry, Laboratory of Inorganic Chemistry , 8093 Zurich , Switzerland
| | - Sébastien Abel
- Aix-Marseille Université , CNRS , ICR UMR 7273 , 13397 Marseille , France . ;
| | - Claire Sauvée
- Aix-Marseille Université , CNRS , ICR UMR 7273 , 13397 Marseille , France . ;
| | - Karthikeyan Ganesan
- Aix-Marseille Université , CNRS , ICR UMR 7273 , 13397 Marseille , France . ;
| | - Maxim Yulikov
- ETH Zurich , Department of Chemistry, Laboratory of Inorganic Chemistry , 8093 Zurich , Switzerland
| | - Aaron J Rossini
- Institut des Sciences et Ingénierie Chimiques , Ecole Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne , Switzerland .
| | - Gunnar Jeschke
- ETH Zurich , Department of Chemistry, Laboratory of Inorganic Chemistry , 8093 Zurich , Switzerland
| | - Christophe Copéret
- ETH Zurich , Department of Chemistry, Laboratory of Inorganic Chemistry , 8093 Zurich , Switzerland
| | - Anne Lesage
- Université de Lyon , Institut de Sciences Analytiques (CNRS / ENS de Lyon / UCB-Lyon 1) , Centre de RMN à Très Hauts Champs , 69100 Villeurbanne , France
| | - Paul Tordo
- Aix-Marseille Université , CNRS , ICR UMR 7273 , 13397 Marseille , France . ;
| | - Olivier Ouari
- Aix-Marseille Université , CNRS , ICR UMR 7273 , 13397 Marseille , France . ;
| | - Lyndon Emsley
- Institut des Sciences et Ingénierie Chimiques , Ecole Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne , Switzerland .
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97
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Mathies G, Caporini MA, Michaelis VK, Liu Y, Hu KN, Mance D, Zweier JL, Rosay M, Baldus M, Griffin RG. Efficient Dynamic Nuclear Polarization at 800 MHz/527 GHz with Trityl-Nitroxide Biradicals. Angew Chem Int Ed Engl 2015; 54:11770-4. [PMID: 26268156 PMCID: PMC5407364 DOI: 10.1002/anie.201504292] [Citation(s) in RCA: 141] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2015] [Revised: 06/16/2015] [Indexed: 11/08/2022]
Abstract
Cross-effect (CE) dynamic nuclear polarization (DNP) is a rapidly developing technique that enhances the signal intensities in magic-angle spinning (MAS) NMR spectra. We report CE DNP experiments at 211, 600, and 800 MHz using a new series of biradical polarizing agents referred to as TEMTriPols, in which a nitroxide (TEMPO) and a trityl radical are chemically tethered. The TEMTriPol molecule with the optimal performance yields a record (1) H NMR signal enhancement of 65 at 800 MHz at a concentration of 10 mM in a glycerol/water solvent matrix. The CE DNP enhancement for the TEMTriPol biradicals does not decrease as the magnetic field is increased in the manner usually observed for bis-nitroxides. Instead, the relatively strong exchange interaction between the trityl and nitroxide moieties determines the magnetic field at which the optimum enhancement is observed.
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Affiliation(s)
- Guinevere Mathies
- Francis Bitter Magnet Laboratory, Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139 (USA).
| | - Marc A Caporini
- Bruker BioSpin Corporation, 15 Fortune Drive, Billerica, MA 01821 (USA)
- Current address: Amgen Inc., 360 Binney Street, Cambridge, MA 02142 (USA)
| | - Vladimir K Michaelis
- Francis Bitter Magnet Laboratory, Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139 (USA)
| | - Yangping Liu
- Tianjin Key Laboratory on Technologies Enabling, Development of Clinical Therapeutics and Diagnostics, School of Pharmacy, Tianjin Medical University, Tianjin 300070 (China).
- Center for Biomedical EPR Spectroscopy and Imaging, Davis Heart and Lung Research Institute and Division of Cardiovascular Medicine, Department of Internal Medicine, The Ohio State University, Columbus, OH 43210 (USA).
| | - Kan-Nian Hu
- Francis Bitter Magnet Laboratory, Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139 (USA)
- Current address: Vertex Pharmaceuticals Incorporated, 50 Northern Avenue, Boston, MA 02210 (USA)
| | - Deni Mance
- NMR Spectroscopy, Department of Chemistry, Faculty of Science, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht (The Netherlands)
| | - Jay L Zweier
- Center for Biomedical EPR Spectroscopy and Imaging, Davis Heart and Lung Research Institute and Division of Cardiovascular Medicine, Department of Internal Medicine, The Ohio State University, Columbus, OH 43210 (USA)
| | - Melanie Rosay
- Bruker BioSpin Corporation, 15 Fortune Drive, Billerica, MA 01821 (USA)
| | - Marc Baldus
- NMR Spectroscopy, Department of Chemistry, Faculty of Science, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht (The Netherlands)
| | - Robert G Griffin
- Francis Bitter Magnet Laboratory, Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139 (USA).
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98
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Mathies G, Caporini MA, Michaelis VK, Liu Y, Hu KN, Mance D, Zweier JL, Rosay M, Baldus M, Griffin RG. Efficient Dynamic Nuclear Polarization at 800 MHz/527 GHz with Trityl-Nitroxide Biradicals. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201504292] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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99
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Mentink-Vigier F, Akbey Ü, Oschkinat H, Vega S, Feintuch A. Theoretical aspects of Magic Angle Spinning - Dynamic Nuclear Polarization. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 258:102-20. [PMID: 26232770 DOI: 10.1016/j.jmr.2015.07.001] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2015] [Revised: 07/01/2015] [Accepted: 07/04/2015] [Indexed: 05/06/2023]
Abstract
Magic Angle Spinning (MAS) combined with Dynamic Nuclear Polarization (DNP) has been proven in recent years to be a very powerful method for increasing solid-state NMR signals. Since the advent of biradicals such as TOTAPOL to increase the nuclear polarization new classes of radicals, with larger molecular weight and/or different spin properties have been developed. These have led to unprecedented signal gain, with varying results for different experimental parameters, in particular the microwave irradiation strength, the static field, and the spinning frequency. Recently it has been demonstrated that sample spinning imposes DNP enhancement processes that differ from the active DNP mechanism in static samples as upon sample spinning the DNP enhancements are the results of energy level anticrossings occurring periodically during each rotor cycle. In this work we present experimental results with regards to the MAS frequency dependence of the DNP enhancement profiles of four nitroxide-based radicals at two different sets of temperature, 110 and 160K. In fact, different magnitudes of reduction in enhancement are observed with increasing spinning frequency. Our simulation code for calculating MAS-DNP powder enhancements of small model spin systems has been improved to extend our studies of the influence of the interaction and relaxation parameters on powder enhancements. To achieve a better understanding we simulated the spin dynamics of a single three-spin system {ea-eb-n} during its steady state rotor periods and used the Landau-Zener formula to characterize the influence of the different anti-crossings on the polarizations of the system and their necessary action for reaching steady state conditions together with spin relaxation processes. Based on these model calculations we demonstrate that the maximum steady state nuclear polarization cannot become larger than the maximum polarization difference between the two electrons during the steady state rotor cycle. This study also shows the complexity of the MAS-DNP process and therefore the necessity to rely on numerical simulations for understanding parametric dependencies of the enhancements. Finally an extension of the spin system up to five spins allowed us to probe the first steps of the transfer of polarization from the nuclei coupled to the electrons to further away nuclei, demonstrating a decrease in the spin-diffusion barrier under MAS conditions.
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Affiliation(s)
| | - Ümit Akbey
- Leibniz-Institut für Molekulare Pharmakologie (FMP), NMR Supported Structural Biology, Robert Roessle Str. 10, 13125 Berlin, Germany; Aarhus Institute of Advanced Studies (AIAS), Aarhus University, Høegh-Guldbergs Gade 6B, Building: 1630, Room: 106, 8000 Aarhus C, Denmark; Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark
| | - Hartmut Oschkinat
- Leibniz-Institut für Molekulare Pharmakologie (FMP), NMR Supported Structural Biology, Robert Roessle Str. 10, 13125 Berlin, Germany
| | - Shimon Vega
- Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Akiva Feintuch
- Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot, Israel
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Mentink-Vigier F, Paul S, Lee D, Feintuch A, Hediger S, Vega S, De Paëpe G. Nuclear depolarization and absolute sensitivity in magic-angle spinning cross effect dynamic nuclear polarization. Phys Chem Chem Phys 2015; 17:21824-36. [PMID: 26235749 DOI: 10.1039/c5cp03457d] [Citation(s) in RCA: 120] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Over the last two decades solid state Nuclear Magnetic Resonance has witnessed a breakthrough in increasing the nuclear polarization, and thus experimental sensitivity, with the advent of Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP). To enhance the nuclear polarization of protons, exogenous nitroxide biradicals such as TOTAPOL or AMUPOL are routinely used. Their efficiency is usually assessed as the ratio between the NMR signal intensity in the presence and the absence of microwave irradiation εon/off. While TOTAPOL delivers an enhancement εon/off of about 60 on a model sample, the more recent AMUPOL is more efficient: >200 at 100 K. Such a comparison is valid as long as the signal measured in the absence of microwaves is merely the Boltzmann polarization and is not affected by the spinning of the sample. However, recent MAS-DNP studies at 25 K by Thurber and Tycko (2014) have demonstrated that the presence of nitroxide biradicals combined with sample spinning can lead to a depolarized nuclear state, below the Boltzmann polarization. In this work we demonstrate that TOTAPOL and AMUPOL both lead to observable depolarization at ≈110 K, and that the magnitude of this depolarization is radical dependent. Compared to the static sample, TOTAPOL and AMUPOL lead, respectively, to nuclear polarization losses of up to 20% and 60% at a 10 kHz MAS frequency, while Trityl OX63 does not depolarize at all. This experimental work is analyzed using a theoretical model that explains how the depolarization process works under MAS and gives new insights into the DNP mechanism and into the spin parameters, which are relevant for the efficiency of a biradical. In light of these results, the outstanding performance of AMUPOL must be revised and we propose a new method to assess the polarization gain for future radicals.
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