Dynamic Nuclear Polarization with a Rigid Biradical

Matsuki, Yoh; Maly, Thorsten; Ouari, Olivier; Karoui, Hakim; Moigne, F. Le; Rizzato, Egon; Lyubenova, Sevdalina; Herzfeld, Judith; Prisner, Thomas F.; Tordo, Paul; Griffin, Robert G.

doi:10.1002/anie.200805940

Cited by 257 publications

(306 citation statements)

References 25 publications

(52 reference statements)

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“…Thus, the OE exhibits a ∼ ω 0I dependence as opposed to the inverse dependences predicted for the SE 1, 9-11 and CE. [12][13][14][15][16][17][18] We further investigated the field dependence of the OE and SE in the BDPA/PS sample. Shown in Figure 5 is the comparison of the DNP field profiles of this sample at three different magnetic fields.…”

Section: Resultsmentioning

confidence: 99%

“…In particular, the development of gyrotron and other high frequency microwave sources permits DNP to be performed at magnetic fields used in contemporary NMR experiments (5-20 T). [1][2][3][4][5][6][7][8] To date these experiments, which have focused mostly on insulating solids formed from glassy, frozen solutions of proteins and other nonconducting materials, have relied primarily on narrow line monoradicals and the solid effect (SE) 1,[9][10][11] or nitroxide biradicals and the cross effect (CE) [12][13][14][15][16][17][18] to mediate the polarization process. These approaches have resulted in large signal enhancements and have enabled many experiments that would otherwise be impossible.…”

Section: Introductionmentioning

confidence: 99%

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Overhauser effects in insulating solids

Can

Caporini

Mentink-Vigier

et al. 2014

The Journal of Chemical Physics

172

226

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We report magic angle spinning, dynamic nuclear polarization (DNP) experiments at magnetic fields of 9.4 T, 14.1 T, and 18.8 T using the narrow line polarizing agents 1,3-bisdiphenylene-2-phenylallyl (BDPA) dispersed in polystyrene, and sulfonated-BDPA (SA-BDPA) and trityl OX063 in glassy glycerol/water matrices. The 1 H DNP enhancement field profiles of the BDPA radicals exhibit a significant DNP Overhauser effect (OE) as well as a solid effect (SE) despite the fact that these samples are insulating solids. In contrast, trityl exhibits only a SE enhancement. Data suggest that the appearance of the OE is due to rather strong electron-nuclear hyperfine couplings present in BDPA and SA-BDPA, which are absent in trityl and perdeuterated BDPA (d 21 -BDPA). In addition, and in contrast to other DNP mechanisms such as the solid effect or cross effect, the experimental data suggest that the OE in non-conducting solids scales favorably with magnetic field, increasing in magnitude in going from 5 T, to 9.4 T, to 14.1 T, and to 18.8 T. Simulations using a model two spin system consisting of an electron hyperfine coupled to a 1 H reproduce the essential features of the field profiles and indicate that the OE in these samples originates from the zero and double quantum cross relaxation induced by fluctuating hyperfine interactions between the intramolecular delocalized unpaired electrons and their neighboring nuclei, and that the size of these hyperfine couplings is crucial to the magnitude of the enhancements. Microwave power dependent studies show that the OE saturates at considerably lower power levels than the solid effect in the same samples. Our results provide new insights into the mechanism of the Overhauser effect, and also provide a new approach to perform DNP experiments in chemical, biophysical, and physical systems at high magnetic fields. INTRODUCTIONThe last decade has witnessed a renaissance in the use of high frequency dynamic nuclear polarization (DNP) to enhance sensitivity in nuclear magnetic resonance (NMR) experiments. In particular, the development of gyrotron and other high frequency microwave sources permits DNP to be performed at magnetic fields used in contemporary NMR experiments (5-20 T). 1-8 To date these experiments, which have focused mostly on insulating solids formed from glassy, frozen solutions of proteins and other nonconducting materials, have relied primarily on narrow line monoradicals and the solid effect (SE) 1, 9-11 or nitroxide biradicals and the cross effect (CE) [12][13][14][15][16][17][18] to mediate the polarization process. These approaches have resulted in large signal enhancements and have enabled many experiments that would otherwise be impossible. [19][20][21][22][23] by Overhauser 25 and confirmed by Carver and Slichter, 26 has not been identified or utilized during the course of this renaissance. Although the possibility of an OE in insulator was discussed by Abragam, 27 the conventional wisdom is that Overhauser DNP is important only in systems with mobile electrons ...

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Overhauser effects in insulating solids

Can

Caporini

Mentink-Vigier

et al. 2014

The Journal of Chemical Physics

172

226

View full text Add to dashboard Cite

show abstract

“…9 Replacing methyl groups adjacent to the nitroxide group with cyclohexyl or phenyl groups increases electronic relaxation times, facilitating more complete saturation of the EPR. 10 Today, the nitroxide biradicals AMUPol (Figure 1).…”

Section: Dnpmentioning

confidence: 99%

Materials Characterization by Dynamic Nuclear Polarization-Enhanced Solid-State NMR Spectroscopy

Rossini

2018

J. Phys. Chem. Lett.

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High-resolution solid-state NMR spectroscopy is a powerful tool for the study of organic and inorganic materials because it can directly probe the symmetry and structure at nuclear sites, the connectivity/bonding of atoms and precisely measure inter-atomic distances. However, NMR spectroscopy is hampered by intrinsically poor sensitivity, consequently, the application of NMR spectroscopy to many solid materials is often infeasible. High-field dynamic nuclear polarization (DNP) has emerged as a technique to routinely enhance the sensitivity of solid-state NMR experiments by one to three orders of magnitude. This perspective gives a general overview of how DNP enables advanced solid-state NMR experiments on a variety of materials. DNP-enhanced solid-state NMR experiments provide unique insights into the molecular structure, which makes it possible to form structure-activity relationships that ultimately assist in the rational design and improvement of materials. Disciplines Materials Chemistry | Physical Chemistry CommentsThis document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in The Journal of Physical Chemistry Letters, copyright © American Chemical Society after peer review. To access the final edited and published work see doi: 10.1021/acs.jpclett.8b01891. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Abstract High-resolution solid-state NMR spectroscopy is a powerful tool for the study of organic and

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“…[24][25][26][27][28][29][30] The CE utilizes biradicals, where two electrons are tethered together in the correct relative orientation, [28][29][30] as polarizing agents, and to date it has proven to be the most efficient DNP mechanism for high field experiments, yielding 1 H enhancements of up to 250. 31,32 The third mechanism, thermal mixing (TM), is important when the EPR spectrum is homogeneously broadened -when , δ ≥ ω 0I . [33][34][35] However, at high fields (≥5 T) the g-anisotropies of many polarizing agents are typically larger than the homogeneous contributions to the linewidth, and therefore, TM has not been an important mechanism in most contemporary magic angle spinning DNP experiments.…”

Section: Introductionmentioning

confidence: 99%

Solid effect dynamic nuclear polarization and polarization pathways

Smith¹,

Corzilius²,

Barnes³

et al. 2012

The Journal of Chemical Physics

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113

143

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Using dynamic nuclear polarization (DNP)/nuclear magnetic resonance instrumentation that utilizes a microwave cavity and a balanced rf circuit, we observe a solid effect DNP enhancement of 94 at 5 T and 80 K using trityl radical as the polarizing agent. Because the buildup rate of the solid effect increases with microwave field strength, we obtain a sensitivity gain of 128. The data suggest that higher microwave field strengths would lead to further improvements in sensitivity. In addition, the observation of microwave field dependent enhancements permits us to draw conclusions about the path that polarization takes during the DNP process. By measuring the time constant for the polarization buildup and enhancement as a function of the microwave field strength, we are able to compare models of polarization transfer, and show that the major contribution to the bulk polarization arises via direct transfer from electrons, rather than transferring first to nearby nuclei and then transferring to bulk nuclei in a slow diffusion step. In addition, the model predicts that nuclei near the electron receive polarization that can relax, decrease the electron polarization, and attenuate the DNP enhancement. The magnitude of this effect depends on the number of near nuclei participating in the polarization transfer, hence the size of the diffusion barrier, their T 1 , and the transfer rate. Approaches to optimizing the DNP enhancement are discussed.

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Dynamic Nuclear Polarization with a Rigid Biradical

Cited by 257 publications

References 25 publications

Overhauser effects in insulating solids

Overhauser effects in insulating solids

Materials Characterization by Dynamic Nuclear Polarization-Enhanced Solid-State NMR Spectroscopy

Solid effect dynamic nuclear polarization and polarization pathways

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