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Robert G Griffin - One of the best experts on this subject based on the ideXlab platform.
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time optimized pulsed dynamic Nuclear Polarization
Science Advances, 2019Co-Authors: Kong Ooi Tan, R. T. Weber, Chen Yang, Guinevere Mathies, Robert G GriffinAbstract:Pulsed dynamic Nuclear Polarization (DNP) techniques can accomplish electron-Nuclear Polarization transfer efficiently with an enhancement factor that is independent of the Zeeman field. However, they often require large Rabi frequencies and, therefore, high-power microwave irradiation. Here, we propose a new low-power DNP sequence for static samples that is composed of a train of microwave pulses of length τp spaced with delays d. A particularly robust DNP condition using a period τm = τp + d set to ~1.25 times the Larmor period τLarmor is investigated which is a time-optimized pulsed DNP sequence (TOP-DNP). At 0.35 T, we obtained an enhancement of ~200 using TOP-DNP compared to ~172 with Nuclear spin orientation via electron spin locking (NOVEL), a commonly used pulsed DNP sequence, while using only ~7% microwave power required for NOVEL. Experimental data and simulations at higher fields suggest a field-independent enhancement factor, as predicted by the effective Hamiltonian.
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pulsed dynamic Nuclear Polarization with trityl radicals
Journal of Physical Chemistry Letters, 2016Co-Authors: Guinevere Mathies, Sheetal Jain, Marcel Reese, Robert G GriffinAbstract:Continuous-wave (CW) dynamic Nuclear Polarization (DNP) is now established as a method of choice to enhance the sensitivity in a variety of NMR experiments. Nevertheless, there remains a need for the development of more efficient methods to transfer Polarization from electrons to nuclei. Of particular interest are pulsed DNP methods because they enable a rapid and efficient Polarization transfer that, in contrast with CW DNP methods, is not attenuated at high magnetic fields. Here we report Nuclear spin orientation via electron spin-locking (NOVEL) experiments using the polarizing agent trityl OX063 in glycerol/water at a temperature of 80 K and a magnetic field of 0.34 T. 1H NMR signal enhancements up to 430 are observed, and the buildup of the local Polarization occurs in a few hundred nanoseconds. Thus, NOVEL can efficiently dynamically polarize 1H atoms in a system that is of general interest to the solid-state DNP NMR community. This is a first, important step toward the general application of pulsed...
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mechanisms of dynamic Nuclear Polarization in insulating solids
PMC, 2015Co-Authors: Thach V Can, Robert G GriffinAbstract:Dynamic Nuclear Polarization (DNP) is a technique used to enhance signal intensities in NMR experiments by transferring the high Polarization of electrons to their surrounding nuclei. The past decade has witnessed a renaissance in the development of DNP, especially at high magnetic fields, and its application in several areas including biophysics, chemistry, structural biology and materials science. Recent technical and theoretical advances have expanded our understanding of established experiments: for example, the cross effect DNP in samples spinning at the magic angle. Furthermore, new experiments suggest that our understanding of the Overhauser effect and its applicability to insulating solids needs to be re-examined. In this article, we summarize important results of the past few years and provide quantum mechanical explanations underlying these results. We also discuss future directions of DNP and current limitations, including the problem of resolution in protein spectra recorded at 80-100 K.
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high field dynamic Nuclear Polarization nmr with surfactant sheltered biradicals
Journal of Physical Chemistry B, 2014Co-Authors: Matthew K. Kiesewetter, Robert G Griffin, Vladimir K Michaelis, Joseph J Walish, Timothy M. SwagerAbstract:We illustrate the ability to place a water-insoluble biradical, bTbk, into a glycerol/water matrix with the assistance of a surfactant, sodium octyl sulfate (SOS). This surfactant approach enables a previously water insoluble biradical, bTbk, with favorable electron–electron dipolar coupling to be used for dynamic Nuclear Polarization (DNP) Nuclear magnetic resonance (NMR) experiments in frozen, glassy, aqueous media. Nuclear Overhauser enhancement (NOE) and paramagnetic relaxation enhancement (PRE) experiments are conducted to determine the distribution of urea and several biradicals within the SOS macromolecular assembly. We also demonstrate that SOS assemblies are an effective approach by which mixed biradicals are created through an assembly process.
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observation of strongly forbidden solid effect dynamic Nuclear Polarization transitions via electron electron double resonance detected nmr
Journal of Chemical Physics, 2013Co-Authors: Albert A Smith, Björn Corzilius, Timothy M. Swager, Olesya Haze, Robert G GriffinAbstract:We present electron paramagnetic resonance experiments for which solid effect dynamic Nuclear Polarization transitions were observed indirectly via Polarization loss on the electron. This use of indirect observation allows characterization of the dynamic Nuclear Polarization (DNP) process close to the electron. Frequency profiles of the electron-detected solid effect obtained using trityl radical showed intense saturation of the electron at the usual solid effect condition, which involves a single electron and nucleus. However, higher order solid effect transitions involving two, three, or four nuclei were also observed with surprising intensity, although these transitions did not lead to bulk Nuclear Polarization—suggesting that higher order transitions are important primarily in the transfer of Polarization to nuclei nearby the electron. Similar results were obtained for the SA-BDPA radical where strong electron-Nuclear couplings produced splittings in the spectrum of the indirectly observed solid effect conditions. Observation of high order solid effect transitions supports recent studies of the solid effect, and suggests that a multi-spin solid effect mechanism may play a major role in Polarization transfer via DNP.
Albert A Smith - One of the best experts on this subject based on the ideXlab platform.
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observation of strongly forbidden solid effect dynamic Nuclear Polarization transitions via electron electron double resonance detected nmr
Journal of Chemical Physics, 2013Co-Authors: Albert A Smith, Björn Corzilius, Timothy M. Swager, Olesya Haze, Robert G GriffinAbstract:We present electron paramagnetic resonance experiments for which solid effect dynamic Nuclear Polarization transitions were observed indirectly via Polarization loss on the electron. This use of indirect observation allows characterization of the dynamic Nuclear Polarization (DNP) process close to the electron. Frequency profiles of the electron-detected solid effect obtained using trityl radical showed intense saturation of the electron at the usual solid effect condition, which involves a single electron and nucleus. However, higher order solid effect transitions involving two, three, or four nuclei were also observed with surprising intensity, although these transitions did not lead to bulk Nuclear Polarization—suggesting that higher order transitions are important primarily in the transfer of Polarization to nuclei nearby the electron. Similar results were obtained for the SA-BDPA radical where strong electron-Nuclear couplings produced splittings in the spectrum of the indirectly observed solid effect conditions. Observation of high order solid effect transitions supports recent studies of the solid effect, and suggests that a multi-spin solid effect mechanism may play a major role in Polarization transfer via DNP.
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solvent free dynamic Nuclear Polarization of amorphous and crystalline ortho terphenyl
Journal of Physical Chemistry B, 2013Co-Authors: Tachung Ong, Albert A Smith, Timothy M. Swager, Vladimir K Michaelis, Joseph J Walish, Bjorn Corzilius, Melody L Makjurkauskas, Andrew M Clausen, Janet C Cheetham, Robert G GriffinAbstract:Dynamic Nuclear Polarization (DNP) of amorphous and crystalline ortho-terphenyl (OTP) in the absence of glass forming agents is presented in order to gauge the feasibility of applying DNP to pharmaceutical solid-state Nuclear magnetic resonance experiments and to study the effect of intermolecular structure, or lack thereof, on the DNP enhancement. By way of 1H–13C cross-Polarization, we obtained a DNP enhancement (e) of 58 for 95% deuterated OTP in the amorphous state using the biradical bis-TEMPO terephthalate (bTtereph) and e of 36 in the crystalline state. Measurements of the 1H T1 and electron paramagnetic resonance experiments showed the crystallization process led to phase separation of the Polarization agent, creating an inhomogeneous distribution of radicals within the sample. Consequently, the effective radical concentration was decreased in the bulk OTP phase, and long-range 1H–1H spin diffusion was the main Polarization propagation mechanism. Preliminary DNP experiments with the glass-forming ...
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high field 13c dynamic Nuclear Polarization with a radical mixture
Journal of the American Chemical Society, 2013Co-Authors: Vladimir K Michaelis, Björn Corzilius, Albert A Smith, Timothy M. Swager, Olesya Haze, Robert G GriffinAbstract:We report direct 13C dynamic Nuclear Polarization at 5 T under magic-angle spinning (MAS) at 82 K using a mixture of monoradicals with narrow EPR linewidths. We show the importance of optimizing both EPR linewidth and electron relaxation times by studying direct DNP of 13C using SA-BDPA and trityl radical, and achieve 13C enhancements above 600. This new approach may be best suited for dissolution DNP and for studies of 1H depleted biological and other nonprotonated solids.
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water soluble narrow line radicals for dynamic Nuclear Polarization
Journal of the American Chemical Society, 2012Co-Authors: Olesya Haze, Björn Corzilius, Albert A Smith, Robert G Griffin, Timothy M. SwagerAbstract:The synthesis of air-stable, highly water-soluble organic radicals containing a 1,3-bis(diphenylene)-2-phenylallyl (BDPA) core is reported. A sulfonated derivative, SA-BDPA, retains the narrow electron paramagnetic resonance linewidth (<30 MHz at 5 T) of the parent BDPA in highly concentrated glycerol/water solutions (40 mM), which enables its use as polarizing agent for solid effect dynamic Nuclear Polarization (SE DNP). A sensitivity enhancement of 110 was obtained in high-field magic-angle-spinning (MAS) NMR experiments. The ease of synthesis and high maximum enhancements obtained with the BDPA-based radicals constitute a major advance over the trityl-type narrow-line Polarization agents.
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Dynamic Nuclear Polarization with a Water-Soluble Rigid Biradical
Journal of the American Chemical Society, 2012Co-Authors: Matthew K. Kiesewetter, Björn Corzilius, Albert A Smith, Robert G Griffin, Timothy M. SwagerAbstract:A new biradical polarizing agent, bTbtk-py, for dynamic Nuclear Polarization (DNP) experiments in aqueous media is reported. The synthesis is discussed in light of the requirements of the optimum, theoretical, biradical system. To date, the DNP NMR signal enhancement resulting from bTbtk-py is the largest of any biradical in the ideal glycerol/water solvent matrix, e = 230. EPR and X-ray crystallography are used to characterize the molecule and suggest approaches for further optimizing the biradical distance and relative orientation.
Shimon Vega - One of the best experts on this subject based on the ideXlab platform.
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Nuclear dePolarization and absolute sensitivity in magic angle spinning cross effect dynamic Nuclear Polarization
Physical Chemistry Chemical Physics, 2015Co-Authors: Frederic Mentinkvigier, Sabine Hediger, Subhradip Paul, Akiva Feintuch, Shimon Vega, Gaël De PaëpeAbstract: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 eon/off. While TOTAPOL delivers an enhancement eon/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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fast passage dynamic Nuclear Polarization on rotating solids
Journal of Magnetic Resonance, 2012Co-Authors: Frederic Mentinkvigier, Hartmut Oschkinat, Shimon Vega, Yonatan Hovav, Umit Akbey, Akiva FeintuchAbstract:Abstract Magic Angle Spinning (MAS) Dynamic Nuclear Polarization (DNP) has proven to be a very powerful way to improve the signal to noise ratio of NMR experiments on solids. The experiments have in general been interpreted considering the Solid-Effect (SE) and Cross-Effect (CE) DNP mechanisms while ignoring the influence of sample spinning. In this paper, we show experimental data of MAS-DNP enhancements of 1 H and 13 C in proline and SH3 protein in glass forming water/glycerol solvent containing TOTAPOL. We also introduce a theoretical model that aims at explaining how the Nuclear Polarization is built in MAS-DNP experiments. By using Liouville space based simulations to include relaxation on two simple spin models, {electron–nucleus} and {electron–electron–nucleus}, we explain how the basic MAS-SE-DNP and MAS-CE-DNP processes work. The importance of fast energy passages and short level anti-crossing is emphasized and the differences between static DNP and MAS-DNP is explained. During a single rotor cycle the enhancement in the {electron–electron–nucleus} system arises from MAS-CE-DNP involving at least three kinds of two-level fast passages: an electron–electron dipolar anti-crossing, a single quantum electron MW encounter and an anti-crossing at the CE condition inducing Nuclear Polarization in- or decrements. Numerical, powder-averaged, simulations were performed in order to check the influence of the experimental parameters on the enhancement efficiencies. In particular we show that the spinning frequency dependence of the theoretical MAS-CE-DNP enhancement compares favorably with the experimental 1 H and 13 C MAS-DNP enhancements of proline and SH3.
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dynamic Nuclear Polarization assisted spin diffusion for the solid effect case
Journal of Chemical Physics, 2011Co-Authors: Yonatan Hovav, Akiva Feintuch, Shimon VegaAbstract:The dynamic Nuclear Polarization (DNP) process in solids depends on the magnitudes of hyperfine interactions between unpaired electrons and their neighboring (core) nuclei, and on the dipole–dipole interactions between all nuclei in the sample. The Polarization enhancement of the bulk nuclei has been typically described in terms of a hyperfine-assisted Polarization of a core nucleus by microwave irradiation followed by a dipolar-assisted spin diffusion process in the core–bulk Nuclear system. This work presents a theoretical approach for the study of this combined process using a density matrix formalism. In particular, solid effect DNP on a single electron coupled to a Nuclear spin system is considered, taking into account the interactions between the spins as well as the main relaxation mechanisms introduced via the electron, Nuclear, and cross-relaxation rates. The basic principles of the DNP-assisted spin diffusion mechanism, polarizing the bulk nuclei, are presented, and it is shown that the polariza...
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dynamic Nuclear Polarization assisted spin diffusion for the solid effect case
Journal of Chemical Physics, 2011Co-Authors: Yonatan Hovav, Akiva Feintuch, Shimon VegaAbstract:The dynamic Nuclear Polarization (DNP) process in solids depends on the magnitudes of hyperfine interactions between unpaired electrons and their neighboring (core) nuclei, and on the dipole-dipole interactions between all nuclei in the sample. The Polarization enhancement of the bulk nuclei has been typically described in terms of a hyperfine-assisted Polarization of a core nucleus by microwave irradiation followed by a dipolar-assisted spin diffusion process in the core-bulk Nuclear system. This work presents a theoretical approach for the study of this combined process using a density matrix formalism. In particular, solid effect DNP on a single electron coupled to a Nuclear spin system is considered, taking into account the interactions between the spins as well as the main relaxation mechanisms introduced via the electron, Nuclear, and cross-relaxation rates. The basic principles of the DNP-assisted spin diffusion mechanism, polarizing the bulk nuclei, are presented, and it is shown that the Polarization of the core nuclei and the spin diffusion process should not be treated separately. To emphasize this observation the coherent mechanism driving the pure spin diffusion process is also discussed. In order to demonstrate the effects of the interactions and relaxation mechanisms on the enhancement of the Nuclear Polarization, model systems of up to ten spins are considered and Polarization buildup curves are simulated. A linear chain of spins consisting of a single electron coupled to a core nucleus, which in turn is dipolar coupled to a chain of bulk nuclei, is considered. The interaction and relaxation parameters of this model system were chosen in a way to enable a critical analysis of the Polarization enhancement of all nuclei, and are not far from the values of (13)C nuclei in frozen (glassy) organic solutions containing radicals, typically used in DNP at high fields. Results from the simulations are shown, demonstrating the complex dependences of the DNP-assisted spin diffusion process on variations of the relevant parameters. In particular, the effect of the spin lattice relaxation times on the Polarization buildup times and the resulting end Polarization are discussed, and the quenching of the Polarizations by the hyperfine interaction is demonstrated.
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theoretical aspects of dynamic Nuclear Polarization in the solid state the cross effect
Journal of Magnetic Resonance, 2010Co-Authors: Yonatan Hovav, Akiva Feintuch, Shimon VegaAbstract:Abstract Dynamic Nuclear Polarization has gained high popularity in recent years, due to advances in the experimental aspects of this methodology for increasing the NMR and MRI signals of relevant chemical and biological compounds. The DNP mechanism relies on the microwave (MW) irradiation induced Polarization transfer from unpaired electrons to the nuclei in a sample. In this publication we present Nuclear Polarization enhancements of model systems in the solid state at high magnetic fields. These results were obtained by numerical calculations based on the spin density operator formalism. Here we restrict ourselves to samples with low electron concentrations, where the dipolar electron–electron interactions can be ignored. Thus the DNP enhancement of the Polarizations of the nuclei close to the electrons is described by the Solid Effect mechanism. Our numerical results demonstrate the dependence of the Polarization enhancement on the MW irradiation power and frequency, the hyperfine and Nuclear dipole–dipole spin interactions, and the relaxation parameters of the system. The largest spin system considered in this study contains one electron and eight nuclei. In particular, we discuss the influence of the Nuclear concentration and relaxation on the Polarization of the core nuclei, which are coupled to an electron, and are responsible for the transfer of Polarization to the bulk nuclei in the sample via spin diffusion.
Björn Corzilius - One of the best experts on this subject based on the ideXlab platform.
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observation of strongly forbidden solid effect dynamic Nuclear Polarization transitions via electron electron double resonance detected nmr
Journal of Chemical Physics, 2013Co-Authors: Albert A Smith, Björn Corzilius, Timothy M. Swager, Olesya Haze, Robert G GriffinAbstract:We present electron paramagnetic resonance experiments for which solid effect dynamic Nuclear Polarization transitions were observed indirectly via Polarization loss on the electron. This use of indirect observation allows characterization of the dynamic Nuclear Polarization (DNP) process close to the electron. Frequency profiles of the electron-detected solid effect obtained using trityl radical showed intense saturation of the electron at the usual solid effect condition, which involves a single electron and nucleus. However, higher order solid effect transitions involving two, three, or four nuclei were also observed with surprising intensity, although these transitions did not lead to bulk Nuclear Polarization—suggesting that higher order transitions are important primarily in the transfer of Polarization to nuclei nearby the electron. Similar results were obtained for the SA-BDPA radical where strong electron-Nuclear couplings produced splittings in the spectrum of the indirectly observed solid effect conditions. Observation of high order solid effect transitions supports recent studies of the solid effect, and suggests that a multi-spin solid effect mechanism may play a major role in Polarization transfer via DNP.
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high field 13c dynamic Nuclear Polarization with a radical mixture
Journal of the American Chemical Society, 2013Co-Authors: Vladimir K Michaelis, Björn Corzilius, Albert A Smith, Timothy M. Swager, Olesya Haze, Robert G GriffinAbstract:We report direct 13C dynamic Nuclear Polarization at 5 T under magic-angle spinning (MAS) at 82 K using a mixture of monoradicals with narrow EPR linewidths. We show the importance of optimizing both EPR linewidth and electron relaxation times by studying direct DNP of 13C using SA-BDPA and trityl radical, and achieve 13C enhancements above 600. This new approach may be best suited for dissolution DNP and for studies of 1H depleted biological and other nonprotonated solids.
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water soluble narrow line radicals for dynamic Nuclear Polarization
Journal of the American Chemical Society, 2012Co-Authors: Olesya Haze, Björn Corzilius, Albert A Smith, Robert G Griffin, Timothy M. SwagerAbstract:The synthesis of air-stable, highly water-soluble organic radicals containing a 1,3-bis(diphenylene)-2-phenylallyl (BDPA) core is reported. A sulfonated derivative, SA-BDPA, retains the narrow electron paramagnetic resonance linewidth (<30 MHz at 5 T) of the parent BDPA in highly concentrated glycerol/water solutions (40 mM), which enables its use as polarizing agent for solid effect dynamic Nuclear Polarization (SE DNP). A sensitivity enhancement of 110 was obtained in high-field magic-angle-spinning (MAS) NMR experiments. The ease of synthesis and high maximum enhancements obtained with the BDPA-based radicals constitute a major advance over the trityl-type narrow-line Polarization agents.
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Dynamic Nuclear Polarization with a Water-Soluble Rigid Biradical
Journal of the American Chemical Society, 2012Co-Authors: Matthew K. Kiesewetter, Björn Corzilius, Albert A Smith, Robert G Griffin, Timothy M. SwagerAbstract:A new biradical polarizing agent, bTbtk-py, for dynamic Nuclear Polarization (DNP) experiments in aqueous media is reported. The synthesis is discussed in light of the requirements of the optimum, theoretical, biradical system. To date, the DNP NMR signal enhancement resulting from bTbtk-py is the largest of any biradical in the ideal glycerol/water solvent matrix, e = 230. EPR and X-ray crystallography are used to characterize the molecule and suggest approaches for further optimizing the biradical distance and relative orientation.
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Rigid Orthogonal Bis-TEMPO Biradicals with Improved Solubility for Dynamic Nuclear Polarization
Journal of Organic Chemistry, 2012Co-Authors: Eric L. Dane, Björn Corzilius, Albert A Smith, Robert G Griffin, Olivier Ouari, Paul Tordo, Thorsten Maly, Egon Rizzato, Pierre Stocker, Timothy M. SwagertAbstract:The synthesis and characterization of oxidized bis-thioketal-trispiro dinitroxide biradicals that orient the nitroxides in a rigid, approximately orthogonal geometry are reported. The biradicals show better performance as polarizing agents in dynamic Nuclear Polarization (DNP) NMR experiments as compared to biradicals lacking the constrained geometry. In addition, the biradicals display improved solubility in aqueous media due to the presence of polar sulfoxides. The results suggest that the orientation of the radicals is not dramatically affected by the oxidation state of the sulfur atoms in the biradical, and we conclude that a biradical polarizing agent containing a mixture of oxidation states can be used for improved solubility without a loss in performance.
Songi Han - One of the best experts on this subject based on the ideXlab platform.
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cross effect dynamic Nuclear Polarization explained Polarization dePolarization and oversaturation
Journal of Physical Chemistry Letters, 2019Co-Authors: Asif Equbal, Alisa Leavesley, Sheetal K Jain, Songi HanAbstract: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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truncated cross effect dynamic Nuclear Polarization an overhauser effect doppelganger
Journal of Physical Chemistry Letters, 2018Co-Authors: Asif Equbal, Alisa Leavesley, Shengdian Huang, Suchada Rajca, Andrzej Rajca, Songi HanAbstract:The discovery of a truncated cross-effect (CE) in dynamic Nuclear Polarization (DNP) NMR that has the features of an Overhauser-effect DNP (OE-DNP) is reported here. The apparent OE-DNP, where minimal μw power achieved optimum enhancement, was observed when doping Trityl-OX063 with a pyrroline nitroxide radical that possesses electron-withdrawing tetracarboxylate substituents (tetracarboxylate-ester-pyrroline or TCP) in vitrified water/glycerol at 6.9 T and at 3.3 to 85 K, in apparent contradiction to expectations. While the observations are fully consistent with OE-DNP, we discover that a truncated cross-effect ( tCE) is the underlying mechanism, owing to TCP's shortened T1e. We take this observation as a guideline and demonstrate that a crossover from CE to tCE can be replicated by simulating the CE of a narrow-line (Trityl-OX063) and a broad-line (TCP) radical pair, with a significantly shortened T1e of the broad-line radical.
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overhauser dynamic Nuclear Polarization to study local water dynamics
Journal of the American Chemical Society, 2009Co-Authors: Brandon D Armstrong, Songi HanAbstract:Surface and internal water dynamics of molecules and soft matter are of great relevance to their structure and function, yet the experimental determination under ambient and steady-state conditions is challenging. One of the most powerful approaches to measure local water dynamics within 5 A distances is to utilize the modulation of the Nuclear spin relaxation rate of water protons through their time-dependent dipolar coupling to paramagnetic probes, here nitroxide spin labels. We recently introduced a method to obtain local water dynamics through Overhauser dynamic Nuclear Polarization (DNP). This has a unique advantage over other related techniques available in that a highly amplified proton Nuclear magnetic resonance signal carries the information, allowing the use of minute microliter sample volumes and 100 μM sample concentrations. The outcome of our approach is the quantitative determination of the key DNP parameter known as the coupling factor, which provides local translational diffusion dynamics ...
