1
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Epasto LM, Maimbourg T, Rosso A, Kurzbach D. Unified understanding of the breakdown of thermal mixing dynamic nuclear polarization: The role of temperature and radical concentration. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2024; 362:107670. [PMID: 38603922 DOI: 10.1016/j.jmr.2024.107670] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Revised: 04/03/2024] [Accepted: 04/03/2024] [Indexed: 04/13/2024]
Abstract
We reveal an interplay between temperature and radical concentration necessary to establish thermal mixing (TM) as an efficient dynamic nuclear polarization (DNP) mechanism. We conducted DNP experiments by hyperpolarizing widely used DNP samples, i.e., sodium pyruvate-1-13C in water/glycerol mixtures at varying nitroxide radical (TEMPOL) concentrations and microwave irradiation frequencies, measuring proton and carbon-13 spin temperatures. Using a cryogen consumption-free prototype-DNP apparatus, we could probe cryogenic temperatures between 1.5 and 6.5 K, i.e., below and above the boiling point of liquid helium. We identify two mechanisms for the breakdown of TM: (i) Anderson type of quantum localization for low radical concentration, or (ii) quantum Zeno localization occurring at high temperature. This observation allowed us to reconcile the recent diverging observations regarding the relevance of TM as a DNP mechanism by proposing a unifying picture and, consequently, to find a trade-off between radical concentration and electron relaxation times, which offers a pathway to improve experimental DNP performance based on TM.
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Affiliation(s)
- Ludovica M Epasto
- University of Vienna, Faculty of Chemistry, Institute of Biological Chemistry, Währinger Str. 38, 1090, Vienna, Austria; University of Vienna, Vienna Doctoral School in Chemistry (DoSChem), Währinger Str. 42, 1090, Vienna, Austria
| | - Thibaud Maimbourg
- Université Paris-Saclay, CNRS, CEA, Institut de physique théorique, 91191, Gif-sur-Yvette, France
| | - Alberto Rosso
- Université Paris-Saclay, CNRS, LPTMS, 91405, Orsay, France.
| | - Dennis Kurzbach
- University of Vienna, Faculty of Chemistry, Institute of Biological Chemistry, Währinger Str. 38, 1090, Vienna, Austria; University of Vienna, Vienna Doctoral School in Chemistry (DoSChem), Währinger Str. 42, 1090, Vienna, Austria.
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2
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Alaniva N, Saliba EP, Judge PT, Sesti EL, Harneit W, Corzilius B, Barnes AB. Electron-decoupled MAS DNP with N@C 60. Phys Chem Chem Phys 2023; 25:5343-5347. [PMID: 36734969 PMCID: PMC9930727 DOI: 10.1039/d2cp04516h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Frequency-chirped microwaves decouple electron- and 13C-spins in magic-angle spinning N@C60:C60 powder, improving DNP-enhanced 13C NMR signal intensity by 12% for 7 s polarization, and 5% for 30 s polarization. This electron decoupling demonstration is a step toward utilizing N@C60 as a controllable electron-spin source for magic-angle spinning magnetic resonance experiments.
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Affiliation(s)
- Nicholas Alaniva
- Laboratory of Physical Chemistry, ETH Zürich, Zürich 8093, Switzerland. .,Washington University in St. Louis, St. Louis 63130, MO, USA
| | - Edward P. Saliba
- Washington University in St. LouisSt. Louis 63130MOUSA,Massachusetts Institute of TechnologyCambridge 02139MAUSA
| | | | | | - Wolfgang Harneit
- Department of Physics, Universität OsnabrückOsnabrück 49076Germany
| | - Björn Corzilius
- Institute of Chemistry, Department Life, Light & Matter, Universität Rostock18059 RostockGermany
| | - Alexander B. Barnes
- Laboratory of Physical Chemistry, ETH ZürichZürich 8093Switzerland+41 44 633 43 81
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3
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Tan KO, Yang L, Mardini M, Cheong CB, Driesschaert B, Dincă M, Griffin RG. Observing Nearby Nuclei on Paramagnetic Trityls and MOFs via DNP and Electron Decoupling. Chemistry 2022; 28:e202202556. [PMID: 36089532 PMCID: PMC9795816 DOI: 10.1002/chem.202202556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Indexed: 12/30/2022]
Abstract
Dynamic nuclear polarization (DNP) is an NMR sensitivity enhancement technique that mediates polarization transfer from unpaired electrons to NMR-active nuclei. Despite its success in elucidating important structural information on biological and inorganic materials, the detailed polarization-transfer pathway from the electrons to the nearby and then the bulk solvent nuclei, and finally to the molecules of interest-remains unclear. In particular, the nuclei in the paramagnetic polarizing agent play significant roles in relaying the enhanced NMR polarizations to more remote nuclei. Despite their importance, the direct NMR observation of these nuclei is challenging because of poor sensitivity. Here, we show that a combined DNP and electron decoupling approach can facilitate direct NMR detection of these nuclei. We achieved an ∼80 % improvement in NMR intensity via electron decoupling at 0.35 T and 80 K on trityl radicals. Moreover, we recorded a DNP enhancement factor of ϵ ${\varepsilon{} }$ ∼90 and ∼11 % higher NMR intensity using electron decoupling on paramagnetic metal-organic framework, magnesium hexaoxytriphenylene (MgHOTP MOF).
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Affiliation(s)
- Kong Ooi Tan
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA),Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA),Laboratoire des Biomolécules, LBM, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris (France)
| | - Luming Yang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA),Research Group EPR Spectroscopy, Max Planck Institute for Multidisciplinary Sciences, Göttingen 37077 (Germany)
| | - Michael Mardini
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA),Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA)
| | - Choon Boon Cheong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA),Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA),Institute of Sustainability for ChemicalsEnergy and Environment, 1 Pesek Road, Jurong Island, Singapore 627833 (Singapore)
| | - Benoit Driesschaert
- Department of Pharmaceutical Sciences, School of Pharmacy, West Virginia University, Morgantown, WV-2650 (USA)
| | - Mircea Dincă
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA)
| | - Robert G. Griffin
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA),Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA-02139 (USA)
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4
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Jardón-Álvarez D, Malka T, van Tol J, Feldman Y, Carmieli R, Leskes M. Monitoring electron spin fluctuations with paramagnetic relaxation enhancement. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2022; 336:107143. [PMID: 35085928 DOI: 10.1016/j.jmr.2022.107143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Revised: 12/30/2021] [Accepted: 01/03/2022] [Indexed: 06/14/2023]
Abstract
The magnetic interactions between the spin of an unpaired electron and the surrounding nuclear spins can be exploited to gain structural information, to reduce nuclear relaxation times as well as to create nuclear hyperpolarization via dynamic nuclear polarization (DNP). A central aspect that determines how these interactions manifest from the point of view of NMR is the timescale of the fluctuations of the magnetic moment of the electron spins. These fluctuations, however, are elusive, particularly when electron relaxation times are short or interactions among electronic spins are strong. Here we map the fluctuations by analyzing the ratio between longitudinal and transverse nuclear relaxation times T1/T2, a quantity which depends uniquely on the rate of the electron fluctuations and the Larmor frequency of the involved nuclei. This analysis enables rationalizing the evolution of NMR lineshapes, signal quenching as well as DNP enhancements as a function of the concentration of the paramagnetic species and the temperature, demonstrated here for LiMg1-xMnxPO4 and Fe(III) doped Li4Ti5O12, respectively. For the latter, we observe a linear dependence of the DNP enhancement and the electron relaxation time within a temperature range between 100 and 300 K.
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Affiliation(s)
- Daniel Jardón-Álvarez
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Tahel Malka
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Johan van Tol
- National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Dr, Tallahassee, FL 32310, United States
| | - Yishay Feldman
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Raanan Carmieli
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Michal Leskes
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel.
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5
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Biedenbänder T, Aladin V, Saeidpour S, Corzilius B. Dynamic Nuclear Polarization for Sensitivity Enhancement in Biomolecular Solid-State NMR. Chem Rev 2022; 122:9738-9794. [PMID: 35099939 DOI: 10.1021/acs.chemrev.1c00776] [Citation(s) in RCA: 42] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Solid-state NMR with magic-angle spinning (MAS) is an important method in structural biology. While NMR can provide invaluable information about local geometry on an atomic scale even for large biomolecular assemblies lacking long-range order, it is often limited by low sensitivity due to small nuclear spin polarization in thermal equilibrium. Dynamic nuclear polarization (DNP) has evolved during the last decades to become a powerful method capable of increasing this sensitivity by two to three orders of magnitude, thereby reducing the valuable experimental time from weeks or months to just hours or days; in many cases, this allows experiments that would be otherwise completely unfeasible. In this review, we give an overview of the developments that have opened the field for DNP-enhanced biomolecular solid-state NMR including state-of-the-art applications at fast MAS and high magnetic field. We present DNP mechanisms, polarizing agents, and sample constitution methods suitable for biomolecules. A wide field of biomolecular NMR applications is covered including membrane proteins, amyloid fibrils, large biomolecular assemblies, and biomaterials. Finally, we present perspectives and recent developments that may shape the field of biomolecular DNP in the future.
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Affiliation(s)
- Thomas Biedenbänder
- Institute of Chemistry, University of Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany.,Department Life, Light & Matter, University of Rostock, Albert-Einstein-Straße 25, 18059 Rostock, Germany
| | - Victoria Aladin
- Institute of Chemistry, University of Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany.,Department Life, Light & Matter, University of Rostock, Albert-Einstein-Straße 25, 18059 Rostock, Germany
| | - Siavash Saeidpour
- Institute of Chemistry, University of Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany.,Department Life, Light & Matter, University of Rostock, Albert-Einstein-Straße 25, 18059 Rostock, Germany
| | - Björn Corzilius
- Institute of Chemistry, University of Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany.,Department Life, Light & Matter, University of Rostock, Albert-Einstein-Straße 25, 18059 Rostock, Germany
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6
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Equbal A, Jain SK, Li Y, Tagami K, Wang X, Han S. Role of electron spin dynamics and coupling network in designing dynamic nuclear polarization. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2021; 126-127:1-16. [PMID: 34852921 DOI: 10.1016/j.pnmrs.2021.05.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2021] [Accepted: 05/22/2021] [Indexed: 06/13/2023]
Abstract
Dynamic nuclear polarization (DNP) has emerged as a powerful sensitivity booster of nuclear magnetic resonance (NMR) spectroscopy for the characterization of biological solids, catalysts and other functional materials, but is yet to reach its full potential. DNP transfers the high polarization of electron spins to nuclear spins using microwave irradiation as a perturbation. A major focus in DNP research is to improve its efficiency at conditions germane to solid-state NMR, at high magnetic fields and fast magic-angle spinning. In this review, we highlight three key strategies towards designing DNP experiments: time-domain "smart" microwave manipulation to optimize and/or modulate electron spin polarization, EPR detection under operational DNP conditions to decipher the underlying electron spin dynamics, and quantum mechanical simulations of coupled electron spins to gain microscopic insights into the DNP mechanism. These strategies are aimed at understanding and modeling the properties of the electron spin dynamics and coupling network. The outcome of these strategies is expected to be key to developing next-generation polarizing agents and DNP methods.
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Affiliation(s)
- Asif Equbal
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA 93106, United States
| | - Sheetal Kumar Jain
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA 93106, United States
| | - Yuanxin Li
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA 93106, United States
| | - Kan Tagami
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA 93106, United States
| | - Xiaoling Wang
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA 93106, United States; Department of Physics, 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; Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106, United States.
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7
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Cai X, Lucini Paioni A, Adler A, Yao R, Zhang W, Beriashvili D, Safeer A, Gurinov A, Rockenbauer A, Song Y, Baldus M, Liu Y. Highly Efficient Trityl-Nitroxide Biradicals for Biomolecular High-Field Dynamic Nuclear Polarization. Chemistry 2021; 27:12758-12762. [PMID: 34181286 DOI: 10.1002/chem.202102253] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Indexed: 12/22/2022]
Abstract
Dynamic nuclear polarization (DNP) is a powerful method to enhance the sensitivity of solid-state magnetic nuclear resonance (ssNMR) spectroscopy. However, its biomolecular applications at high magnetic fields (preferably>14 T) have so far been limited by the intrinsically low efficiency of polarizing agents and sample preparation aspects. Herein, we report a new class of trityl-nitroxide biradicals, dubbed SNAPols that combine high DNP efficiency with greatly enhanced hydrophilicity. SNAPol-1, the best compound in the series, shows DNP enhancement factors at 18.8 T of more than 100 in small molecules and globular proteins and also exhibits strong DNP enhancements in membrane proteins and cellular preparations. By integrating optimal sensitivity and high resolution, we expect widespread applications of this new polarizing agent in high-field DNP/ssNMR spectroscopy, especially for complex biomolecules.
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Affiliation(s)
- Xinyi Cai
- The province and ministry co-sponsored collaborative innovation center for medical epigenetics Tianjin Key Laboratory on Technologies Enabling Development of Clinical Therapeutics and Diagnostics School of Pharmacy, Tianjin Medical University, Tianjin, 300070, P. R. China
| | - Alessandra Lucini Paioni
- NMR Spectroscopy group Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Agnes Adler
- NMR Spectroscopy group Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Ru Yao
- The province and ministry co-sponsored collaborative innovation center for medical epigenetics Tianjin Key Laboratory on Technologies Enabling Development of Clinical Therapeutics and Diagnostics School of Pharmacy, Tianjin Medical University, Tianjin, 300070, P. R. China
| | - Wenxiao Zhang
- The province and ministry co-sponsored collaborative innovation center for medical epigenetics Tianjin Key Laboratory on Technologies Enabling Development of Clinical Therapeutics and Diagnostics School of Pharmacy, Tianjin Medical University, Tianjin, 300070, P. R. China
| | - David Beriashvili
- NMR Spectroscopy group Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Adil Safeer
- NMR Spectroscopy group Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Andrei Gurinov
- NMR Spectroscopy group Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Antal Rockenbauer
- Institute of Materials and Environmental Chemistry Hungarian Academy of Sciences and Department of Physics, Budapest University of Technology and Economics Budafoki ut 8, 1111, Budapest, Hungary
| | - Yuguang Song
- The province and ministry co-sponsored collaborative innovation center for medical epigenetics Tianjin Key Laboratory on Technologies Enabling Development of Clinical Therapeutics and Diagnostics School of Pharmacy, Tianjin Medical University, Tianjin, 300070, P. R. China
| | - Marc Baldus
- NMR Spectroscopy group Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Yangping Liu
- The province and ministry co-sponsored collaborative innovation center for medical epigenetics Tianjin Key Laboratory on Technologies Enabling Development of Clinical Therapeutics and Diagnostics School of Pharmacy, Tianjin Medical University, Tianjin, 300070, P. R. China
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8
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Heiliger J, Matzel T, Çetiner EC, Schwalbe H, Kuenze G, Corzilius B. Site-specific dynamic nuclear polarization in a Gd(III)-labeled protein. Phys Chem Chem Phys 2020; 22:25455-25466. [PMID: 33103678 DOI: 10.1039/d0cp05021k] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Dynamic nuclear polarization (DNP) of a biomolecule tagged with a polarizing agent has the potential to not only increase NMR sensitivity but also to provide specificity towards the tagging site. Although the general concept has been often discussed, the observation of true site-specific DNP and its dependence on the electron-nuclear distance has been elusive. Here, we demonstrate site-specific DNP in a uniformly isotope-labeled ubiquitin. By recombinant expression of three different ubiquitin point mutants (F4C, A28C, and G75C) post-translationally modified with a Gd3+-chelator tag, localized metal-ion DNP of 13C and 15N is investigated. Effects counteracting the site-specificity of DNP such as nuclear spin-lattice relaxation and proton-driven spin diffusion have been attenuated by perdeuteration of the protein. Particularly for 15N, large DNP enhancement factors on the order of 100 and above as well as localized effects within side-chain resonances differently distributed over the protein are observed. By analyzing the experimental DNP built-up dynamics combined with structural modeling of Gd3+-tags in ubiquitin supported by paramagnetic relaxation enhancement (PRE) in solution, we provide, for the first time, quantitative information on the distance dependence of the initial DNP transfer. We show that the direct 15N DNP transfer rate indeed linearly depends on the square of the hyperfine interaction between the electron and the nucleus following Fermi's golden rule, however, below a certain distance cutoff paramagnetic signal bleaching may dramatically skew the correlation.
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Affiliation(s)
- Jörg Heiliger
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt am Main, Germany
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9
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Judge PT, Sesti EL, Price LE, Albert BJ, Alaniva N, Saliba EP, Halbritter T, Sigurdsson ST, Kyei GB, Barnes AB. Dynamic Nuclear Polarization with Electron Decoupling in Intact Human Cells and Cell Lysates. J Phys Chem B 2020; 124:2323-2330. [DOI: 10.1021/acs.jpcb.9b10494] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Patrick T. Judge
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
- Department of Biochemistry, Biophysics & Structural Biology, Washington University in St. Louis, St. Louis, Missouri 63110, United States
| | - Erika L. Sesti
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Lauren E. Price
- 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
| | - Nicholas Alaniva
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Edward P. Saliba
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Thomas Halbritter
- Department of Chemistry, Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland
| | - Snorri Th. Sigurdsson
- Department of Chemistry, Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland
| | - George B. Kyei
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63130, United States
- Noguchi Memorial Institute for Medical Research, College of Health Sciences, University of Ghana,
Legon, Accra 02233, Ghana
| | - Alexander B. Barnes
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, United States
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10
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Abstract
Dynamic nuclear polarization (DNP) is one of the most prominent methods of sensitivity enhancement in nuclear magnetic resonance (NMR). Even though solid-state DNP under magic-angle spinning (MAS) has left the proof-of-concept phase and has become an important tool for structural investigations of biomolecules as well as materials, it is still far from mainstream applicability because of the potentially overwhelming combination of unique instrumentation, complex sample preparation, and a multitude of different mechanisms and methods available. In this review, I introduce the diverse field and history of DNP, combining aspects of NMR and electron paramagnetic resonance. I then explain the general concepts and detailed mechanisms relevant at high magnetic field, including solution-state methods based on Overhauser DNP but with a greater focus on the more established MAS DNP methods. Finally, I review practical considerations and fields of application and discuss future developments.
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Affiliation(s)
- Björn Corzilius
- Institute of Chemistry and Department of Life, Light and Matter, University of Rostock, 18059 Rostock, Germany;
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11
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Saliba EP, Barnes AB. Fast electron paramagnetic resonance magic angle spinning simulations using analytical powder averaging techniques. J Chem Phys 2019; 151:114107. [PMID: 31542017 PMCID: PMC7043854 DOI: 10.1063/1.5113598] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Accepted: 08/27/2019] [Indexed: 11/14/2022] Open
Abstract
Simulations describing the spin physics underpinning nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy play an important role in the design of new experiments. When experiments are performed in the solid state, samples are commonly composed of powders or glasses, with molecules oriented at a large number of angles with respect to the laboratory frame. These powder angles must be represented in simulations to account for anisotropic interactions. Numerical techniques are typically used to accurately compute such powder averages. A large number of Euler angles are usually required, leading to lengthy simulation times. This is particularly true in broad spectra, such as those observed in EPR. The combination of the traditionally separate techniques of EPR and magic angle spinning (MAS) NMR could play an important role in future electron detected experiments, combined with dynamic nuclear polarization, which will allow for exceptional detection sensitivity of NMR spin coherences. Here, we present a method of reducing the required number of Euler angles in magnetic resonance simulations by analytically performing the powder average over one of the Euler angles in the static and MAS cases for the TEMPO nitroxide radical in a 7 T field. In the static case, this leads to a 97.5% reduction in simulation time over the fully numerical case and reproduces the expected spinning sideband manifold when simulated with a MAS frequency of 150 kHz. This technique is applicable to more traditional NMR experiments as well, such as those involving quadrupolar nuclei or multiple dimensions.
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Affiliation(s)
- Edward P Saliba
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, USA
| | - Alexander B Barnes
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, USA
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