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Chaklashiya RK, Equbal A, Shernyukov A, Li Y, Tsay K, Stern Q, Tormyshev V, Bagryanskaya E, Han S. Dynamic Nuclear Polarization Using Electron Spin Cluster. J Phys Chem Lett 2024; 15:5366-5375. [PMID: 38735065 DOI: 10.1021/acs.jpclett.4c00182] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/14/2024]
Abstract
Dynamic nuclear polarization (DNP) utilizing narrow-line electron spin clusters (ESCs) to achieve nuclear spin resonance matching (ESC-DNP) by microwave irradiation is a promising way to achieve NMR signal enhancements with a wide design scope requiring low microwave power at high magnetic field. Here we present the design for a trityl-based tetra-radical (TetraTrityl) to achieve DNP for 1H NMR at 7 T, supported by experimental data and quantum mechanical simulations. A slow-relaxing (T1e ≈ 1 ms) 4-ESC is found to require at least two electron spin pairs at <8 Å e-e spin distance to yield 1H ESC-DNP enhancement, while squeezing the rest of the e-e spin distances to <12 Å results in optimal 1H ESC-DNP enhancements. Fast-relaxing ESCs (T1e ≈ 10 μs) are found to require a weakly coupled narrow-line radical (sensitizer) to extract polarization from the ESC. These results provide design principles for achieving a power-efficient DNP at high field via ESC-DNP.
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Affiliation(s)
- Raj K Chaklashiya
- Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, United States
| | - Asif Equbal
- Division of Chemistry, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
- Center for Quantum and Topological Systems, NYUAD Research Institute, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates
| | - Andrey Shernyukov
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS, Novosibirsk 630090, Russia
| | - Yuanxin Li
- Department of Chemistry & Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, United States
| | - Karen Tsay
- Department of Chemistry & Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, United States
| | - Quentin Stern
- Department of Chemistry, Northwestern University, Wilmette, Illinois 60208, United States
| | - Victor Tormyshev
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS, Novosibirsk 630090, Russia
| | - Elena Bagryanskaya
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS, Novosibirsk 630090, Russia
| | - Songi Han
- Department of Chemistry, Northwestern University, Wilmette, Illinois 60208, United States
- Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, California 93106, United States
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2
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Equbal A, Ramanathan C, Han S. Dipolar Order Induced Electron Spin Hyperpolarization. J Phys Chem Lett 2024; 15:5397-5406. [PMID: 38739470 PMCID: PMC11129302 DOI: 10.1021/acs.jpclett.4c00294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 05/04/2024] [Accepted: 05/06/2024] [Indexed: 05/16/2024]
Abstract
The structure of coupled electron spin systems is of fundamental interest to many applications, including dynamic nuclear polarization (DNP), enhanced nuclear magnetic resonance (NMR), the generation of electron spin qubits for quantum information science (QIS), and quantitative studies of paramagnetic systems by electron paramagnetic resonance (EPR). However, the characterization of electron spin coupling networks is nontrivial, especially at high magnetic fields. This study focuses on a system containing high concentrations of trityl radicals that give rise to a DNP enhancement profile of 1H NMR characteristic of the presence of electron spin clusters. When this system is subject to selective microwave saturation through pump-probe ELectron DOuble Resonance (ELDOR) experiments, electron spin hyperpolarization is observed. We show that the generation of an out-of-equilibrium longitudinal dipolar order is responsible for the transient hyperpolarization of electron spins. Notably, the coupled electron spin system needs to form an AX-like system (where the difference in the Zeeman interactions of two spins is larger than their coupling interaction) such that selective microwave irradiation can generate signatures of electron spin hyperpolarization. We show that the extent of dipolar order, as manifested in the extent of electron spin hyperpolarization generated, can be altered by tuning the pump or probe pulse length, or the interpulse delay in ELDOR experiments that change the efficiency to generate or readout longitudinal dipolar order. Pump-probe ELDOR with selective saturation is an effective means for characterizing coupled electron spins forming AX-type spin systems that are foundational for DNP and quantum sensing.
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Affiliation(s)
- Asif Equbal
- Department
of Chemistry, New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, United Arab Emirates
- Center
for Quantum and Topological Systems, New
York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, United Arab Emirates
| | - Chandrasekhar Ramanathan
- Department
of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755, 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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3
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Wenckebach WT. Spectral diffusion of electron spin polarization in glasses doped with radicals for DNP. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2024; 360:107651. [PMID: 38430621 DOI: 10.1016/j.jmr.2024.107651] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2024] [Revised: 02/24/2024] [Accepted: 02/24/2024] [Indexed: 03/05/2024]
Abstract
Spectral diffusion of electron spin polarization plays a key part in dynamic nuclear polarization (DNP). It determines the distribution of polarization across the electron spin resonance (ESR) line and consequently the polarization that is available for transfer to the nuclear spins. Various authors have studied it experimentally by means of electron-electron double resonance (ELDOR) and proposed and used macroscopic models to interpret these experiments. However, microscopic models predicting the rate of spectral diffusion are scarce. The present article is an attempt to fill this gap. It derives a spectral diffusion equation from first principles and uses Monte Carlo simulations to determine the parameters in this equation. The derivation given here builds on an observation made in a previous article on nuclear dipolar relaxation: spectral diffusion is also spatial diffusion and the random distribution of spins in space limits the former. This can be modelled assuming that rapid flip-flop transitions between a spin and its nearest neighbour do not contribute to diffusion of polarization across the ESR spectrum. The present article presents predictions of the spectral diffusion constant and shows that this limitation may lower the spectral diffusion constant by several orders of magnitude. As a check the constant is determined from first principles for a sample containing 40 mM TEMPOL. Including the limitation then results in a value that is close to that obtained from an analysis of previously reported ELDOR experiments.
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Affiliation(s)
- W Th Wenckebach
- National High Magnetic Field Laboratory, University of Florida, Gainesville, FL, USA; Paul Scherrer Institute, CH-5232, Villigen, Switzerland.
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4
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Bussandri S, Shimon D, Equbal A, Ren Y, Takahashi S, Ramanathan C, Han S. P1 Center Electron Spin Clusters Are Prevalent in Type Ib Diamonds. J Am Chem Soc 2024; 146:5088-5099. [PMID: 38112330 DOI: 10.1021/jacs.3c06705] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
Understanding the spatial distribution of the P1 centers is crucial for diamond-based sensors and quantum devices. P1 centers serve as polarization sources for dynamic nuclear polarization (DNP) quantum sensing and play a significant role in the relaxation of nitrogen vacancy (NV) centers. Additionally, the distribution of NV centers correlates with the distribution of P1 centers, as NV centers are formed through the conversion of P1 centers. We utilized DNP and pulsed electron paramagnetic resonance (EPR) techniques that revealed strong clustering of a significant population of P1 centers that exhibit exchange coupling and produce asymmetric line shapes. The 13C DNP frequency profile at a high magnetic field revealed a pattern that requires an asymmetric EPR line shape of the P1 clusters with electron-electron (e-e) coupling strengths exceeding the 13C nuclear Larmor frequency. EPR and DNP characterization at high magnetic fields was necessary to resolve energy contributions from different e-e couplings. We employed a two-frequency pump-probe pulsed electron double resonance technique to show cross-talk between the isolated and clustered P1 centers. This finding implies that the clustered P1 centers affect all of the P1 populations. Direct observation of clustered P1 centers and their asymmetric line shape offers a novel and crucial insight into understanding magnetic noise sources for quantum information applications of diamonds and for designing diamond-based polarizing agents with optimized DNP efficiency for 13C and other nuclear spins of analytes. We propose that room temperature 13C DNP at a high field, achievable through straightforward modifications to existing solution-state NMR systems, is a potent tool for evaluating and controlling diamond defects.
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Affiliation(s)
- Santiago Bussandri
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, United States
| | - Daphna Shimon
- Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra, Givat Ram, Jerusalem 9190401, Israel
| | - Asif Equbal
- Department of Chemistry, New York University, Abu Dhabi 129188, United Arab Emirates
- Center for Quantum and Topological Systems, New York University, Abu Dhabi 129188, United Arab Emirates
| | - Yuhang Ren
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | - Susumu Takahashi
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Chandrasekhar Ramanathan
- Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755, 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, California 93106, United States
- Department of Chemistry, Northwestern University, Evanston, Illinois 600208, United States
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5
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Tobar C, Albanese K, Chaklashiya R, Equbal A, Hawker C, Han S. Multi Electron Spin Cluster Enabled Dynamic Nuclear Polarization with Sulfonated BDPA. J Phys Chem Lett 2023; 14:11640-11650. [PMID: 38108283 DOI: 10.1021/acs.jpclett.3c02428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Dynamic nuclear polarization (DNP) can amplify the solid-state nuclear magnetic resonance (NMR) signal by several orders of magnitude. The mechanism of DNP utilizing α,γ-bisdiphenylene-β-phenylallyl (BDPA) variants as Polarizing Agents (PA) has been the subject of lively discussions on account of their remarkable DNP efficiency with low demand for microwave power. We propose that electron spin clustering of sulfonated BDPA is responsible for its DNP performance, as revealed by the temperature-dependent shape of the central DNP profile and strong electron-electron (e-e) crosstalk seen by Electron Double Resonance. We demonstrate that a multielectron spin cluster can be modeled with three coupled spins, where electron J (exchange) coupling between one of the e-e pairs matching the NMR Larmor frequency induces the experimentally observed absorptive central DNP profile, and the electron T1e modulated by temperature and magic-angle spinning alters the shape between an absorptive and dispersive feature. Understanding the microscopic origin is key to designing new PAs to harness the microwave-power-efficient DNP effect observed with BDPA variants.
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Affiliation(s)
- Celeste Tobar
- Department of Chemistry and Biochemistry, University of California, Santa Barbara 93106, California, United States
| | - Kaitlin Albanese
- Materials Department, University of California, Santa Barbara 93106, California, United States
| | - Raj Chaklashiya
- Materials Department, University of California, Santa Barbara 93106, California, United States
| | - Asif Equbal
- Department of Chemistry, NYU Abu Dhabi, Saadiyat Campus, PO Box 129188, Abu Dhabi 00000, United Arab Emirates
| | - Craig Hawker
- Materials Department, University of California, Santa Barbara 93106, California, United States
| | - Songi Han
- Department of Chemistry, Northwestern University, Evanston 60208, Illinois, United States
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6
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Shu C, Yang Z, Rajca A. From Stable Radicals to Thermally Robust High-Spin Diradicals and Triradicals. Chem Rev 2023; 123:11954-12003. [PMID: 37831948 DOI: 10.1021/acs.chemrev.3c00406] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2023]
Abstract
Stable radicals and thermally robust high-spin di- and triradicals have emerged as important organic materials due to their promising applications in diverse fields. New fundamental properties, such as SOMO/HOMO inversion of orbital energies, are explored for the design of new stable radicals, including highly luminescent ones with good photostability. A relation with the singlet-triplet energy gap in the corresponding diradicals is proposed. Thermally robust high-spin di- and triradicals, with energy gaps that are comparable to or greater than a thermal energy at room temperature, are more challenging to synthesize but more rewarding. We summarize a number of high-spin di- and triradicals, based on nitronyl nitroxides that provide a relation between the experimental pairwise exchange coupling constant J/k in the high-spin species vs experimental hyperfine coupling constants in the corresponding monoradicals. This relation allows us to identify outliers, which may correspond to radicals where J/k is not measured with sufficient accuracy. Double helical high-spin diradicals, in which spin density is delocalized over the chiral π-system, have been barely explored, with the sole example of such high-spin diradical possessing alternant π-system with Kekulé resonance form. Finally, we discuss a high-spin diradical with electrical conductivity and derivatives of triangulene diradicals.
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Affiliation(s)
- Chan Shu
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
| | - Zhimin Yang
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
| | - Andrzej Rajca
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
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7
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Palani RS, Mardini M, Delage-Laurin L, Banks D, Ouyang Y, Bryerton E, Kempf JG, Swager TM, Griffin RG. Amplified Overhauser DNP with Selective Deuteration: Attenuation of Double-Quantum Cross-Relaxation. J Phys Chem Lett 2023; 14:95-100. [PMID: 36573841 PMCID: PMC9903202 DOI: 10.1021/acs.jpclett.2c03087] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
We recently used selective 2H labeling of BDPA to investigate the Overhauser Effect (OE) dynamic nuclear polarization (DNP) mechanism in insulating solids doped with 1,3-bis(diphenylene)-2-phenylallyl (BDPA), and established that the α and γ 1H spins on the fluorene rings are responsible for generating a zero quantum (ZQ) mediated positive bulk polarization. Here, we establish that the phenyl 1H spins relax via double-quantum (DQ) processes and therefore contribute negative enhancements which attenuate the OE-DNP. With measurements at different magnetic field strengths, we show that phenyl-d5-BDPA offers >50% improvement in OE-DNP enhancement compared to h21-BDPA attaining a maximum of ∼90 at 14.1 T and 5 kHz MAS, the highest observed OE-DNP enhancement to date under these conditions. The approach may be utilized to optimize other polarizing agents exhibiting an OE, an important DNP mechanism with a favorable field and spinning frequency dependence.
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Affiliation(s)
| | | | | | - Daniel Banks
- Bruker Biospin Corporation, Billerica, Massachusetts 01821, United States
| | | | - Eric Bryerton
- Virginia Diodes Corporation, Charlottesville, Virginia 22902, United States
| | - James G Kempf
- Bruker Biospin Corporation, Billerica, Massachusetts 01821, United States
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8
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Perras FA, Flesariu DF, Southern SA, Nicolaides C, Bazak JD, Washton NM, Trypiniotis T, Constantinides CP, Koutentis PA. Methyl-Driven Overhauser Dynamic Nuclear Polarization. J Phys Chem Lett 2022; 13:4000-4006. [PMID: 35482607 DOI: 10.1021/acs.jpclett.2c00748] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The Overhauser effect is unique among DNP mechanisms in that it requires the modulation of the electron-nuclear hyperfine interactions. While it dominates DNP in liquids and metals, where unpaired electrons are highly mobile, Overhauser DNP is possible in insulating solids if rapid structural modulations are linked to a modulation in hyperfine coupling. Herein, we report that Overhauser DNP can be triggered by the strategic addition of a methyl group, demonstrated here in a Blatter's radical. The rotation of the methyl group leads to a modulation of the hyperfine coupling to its protons, which in turn facilitates electron-nuclear cross-relaxation. Removal of the methyl protons, through deuteration, quenches the process, as does the reduction of the hyperfine coupling strength. This result suggests the possibility for the design of tailor-made Overhauser DNP polarizing agents for high-field MAS-DNP.
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Affiliation(s)
| | - Dragos F Flesariu
- Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
| | | | | | - J David Bazak
- Physical & Computational Science Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Nancy M Washton
- Physical & Computational Science Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | | | - Christos P Constantinides
- Department of Natural Sciences, University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, Michigan 48128-1491, United States
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9
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Tan KO, Griffin RG. Observation of a Four-Spin Solid Effect. J Chem Phys 2022; 156:174201. [PMID: 35525661 PMCID: PMC9068241 DOI: 10.1063/5.0091663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The two-spin solid effect (2SSE) is one of the established continuous wave dynamic nuclear polarization mechanisms that enables enhancement of nuclear magnetic resonance signals. It functions via a state-mixing mechanism that mediates the excitation of forbidden transitions in an electron–nuclear spin system. Specifically, microwave irradiation at frequencies ωμw ∼ ω0S ± ω0I, where ω0S and ω0I are electron and nuclear Larmor frequencies, respectively, yields enhanced nuclear spin polarization. Following the recent rediscovery of the three-spin solid effect (3SSE) [Tan et al., Sci. Adv. 5, eaax2743 (2019)], where the matching condition is given by ωμw = ω0S ± 2ω0I, we report here the first direct observation of the four-spin solid effect (4SSE) at ωμw = ω0S ± 3ω0I. The forbidden double- and quadruple-quantum transitions were observed in samples containing trityl radicals dispersed in a glycerol–water mixture at 0.35 T/15 MHz/9.8 GHz and 80 K. We present a derivation of the 4SSE effective Hamiltonian, matching conditions, and transition probabilities. Finally, we show that the experimental observations agree with the results from numerical simulations and analytical theory.
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Affiliation(s)
| | - Robert G. Griffin
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, United States of America
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10
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Kuzhelev AA, Dai D, Denysenkov V, Prisner TF. Solid-like Dynamic Nuclear Polarization Observed in the Fluid Phase of Lipid Bilayers at 9.4 T. J Am Chem Soc 2022; 144:1164-1168. [PMID: 35029974 DOI: 10.1021/jacs.1c12837] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Dynamic nuclear polarization (DNP) is a powerful method to enhance NMR sensitivity. Much progress has been achieved recently to optimize DNP performance at high magnetic fields in solid-state samples, mostly by utilizing the solid or the cross effect. In liquids, only the Overhauser mechanism is active, which exhibits a DNP field profile matching the EPR line shape of the radical, distinguishable from other DNP mechanisms. Here, we observe DNP enhancements with a field profile indicative of the solid effect and thermal mixing at ∼320 K and a magnetic field of 9.4 T in the fluid phase of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid bilayers doped with the radical BDPA (1,3-bis(diphenylene)-2-phenylallyl). This interesting observation might open up new perspectives for DNP applications in macromolecular systems at ambient temperatures.
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Affiliation(s)
- Andrei A Kuzhelev
- Goethe University Frankfurt am Main, Institute of Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, Max von Laue Str. 7, 60438 Frankfurt am Main, Germany
| | - Danhua Dai
- Goethe University Frankfurt am Main, Institute of Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, Max von Laue Str. 7, 60438 Frankfurt am Main, Germany
| | - Vasyl Denysenkov
- Goethe University Frankfurt am Main, Institute of Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, Max von Laue Str. 7, 60438 Frankfurt am Main, Germany
| | - Thomas F Prisner
- Goethe University Frankfurt am Main, Institute of Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, Max von Laue Str. 7, 60438 Frankfurt am Main, Germany
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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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