High frequency (140 GHz) dynamic nuclear polarization: Polarization transfer to a solute in frozen aqueous solution

Gerfen, Gary J.; Becerra, Lino; Hall, Dennis A.; Griffin, Robert G.; Temkin, R.J.; Singel, David J.

doi:10.1063/1.468818

Cited by 180 publications

(174 citation statements)

References 12 publications

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“…The enhancements obtained at 9T from the glycine sample (Fig. 2) are almost identical in magnitude to previous results obtained at 5T [16], indicating that the inverse dependence of the thermal mixing enhancement on the static magnetic field has been overcome under the conditions of these experiments.…”

Section: Dnp Cp Of Static Samplessupporting

confidence: 87%

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Dynamic nuclear polarization at 9 T using a novel 250 GHz gyrotron microwave source

Bajaj

Farrar

Hornstein

et al. 2011

Journal of Magnetic Resonance

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In this communication, we report enhancements of nuclear spin polarization by dynamic nuclear polarization (DNP) in static and spinning solids at a magnetic field strength of 9T (250 GHz for g = 2 electrons, 380 MHz for 1 H). In these experiments, 1 H enhancements of up to 170 ± 50 have been observed in 1-13 C-glycine dispersed in a 60:40 glycerol/water matrix at temperatures of 20 K; in addition, we have observed significant enhancements in 15 N spectra of unoriented pf1-bacteriophage. Finally, enhancements of ~17 have been obtained in two-dimensional 13 C-13 C chemical shift correlation spectra of the amino acid U-13 C, 15 N-proline during magic angle spinning (MAS), demonstrating the stability of the DNP experiment for sustained acquisition and for quantitative experiments incorporating dipolar recoupling. In all cases, we have exploited the thermal mixing DNP mechanism with the nitroxide radical 4-amino-TEMPO as the paramagnetic dopant. These are the highest frequency DNP experiments performed to date and indicate that significant signal enhancements can be realized using the thermal mixing mechanism even at elevated magnetic fields. In large measure, this is due to the high microwave power output of the 250 GHz gyrotron oscillator used in these experiments.

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Section: Dnp Cp Of Static Samplessupporting

confidence: 87%

“…As a means to increase the sensitivity of these experiments, we have previously employed dynamic nuclear polarization (DNP) to enhance NMR signals in both static and rotating solids at 5T [16][17][18][19]. DNP involves the irradiation of a coupled electron-nuclear spin system in the neighborhood of the electron Larmor frequency.…”

Section: Introductionmentioning

confidence: 99%

Dynamic nuclear polarization at 9 T using a novel 250 GHz gyrotron microwave source

Bajaj

Farrar

Hornstein

et al. 2011

Journal of Magnetic Resonance

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“…Typical pulse sequences for DNP enhanced MAS experiments are described in several papers [29,43,49,50] and the sequence used to acquire the multidimensional spectra presented here is illustrated in Figure 3.…”

Section: Dnp Experiments On the Membrane Protein Bacteriorhodopsinmentioning

confidence: 99%

“…To satisfy these requirements, we turned to gyrotrons, a type of cyclotron resonance maser, as microwave sources for DNP experiments [28][29][30]. This choice was motivated by the fact that gyrotrons are fast wave devices [31], with interaction structures whose dimensions are large compared to the operating wavelength, and as such are capable of generating high powers (10-100 watts CW) for the extended periods typical of multidimensional NMR experiments.…”

Section: Introductionmentioning

confidence: 99%

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

Bajaj

Hornstein

Kreischer

et al. 2007

Journal of Magnetic Resonance

162

130

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In this paper, we describe a 250 GHz gyrotron oscillator, a critical component of an integrated system for magic angle spinning (MAS) dynamic nuclear polarization (DNP) experiments at 9T, corresponding to 380 MHz 1 H frequency. The 250 GHz gyrotron is the first gyro-device designed with the goal of seamless integration with an NMR spectrometer for routine DNP-enhanced NMR spectroscopy and has operated under computer control for periods of up to 21 days with a 100% duty cycle. Following a brief historical review of the field, we present studies of the membrane protein bacteriorhodopsin (bR) using DNP-enhanced multidimensional NMR. These results include assignment of active site resonances in [U-13 C, 15 N]-bR and demonstrate the utility of DNP for studies of membrane proteins. Next, we review the theory of gyro-devices from quantum mechanical and classical viewpoints and discuss the unique considerations that apply to gyrotron oscillators designed for DNP experiments. We then characterize the operation of the 250 GHz gyrotron in detail, including its long-term stability and controllability. We have measured the spectral purity of the gyrotron emission using both homodyne and heterodyne techniques. Radiation intensity patterns from the corrugated waveguide that delivers power to the NMR probe were measured using two new techniques to confirm pure mode content: a thermometric approach based on the temperaturedependent color of liquid crystalline media applied to a substrate and imaging with a pyroelectric camera. We next present a detailed study of the mode excitation characteristics of the gyrotron. Exploration of the operating characteristics of several fundamental modes reveals broadband continuous frequency tuning of up to 1.8 GHz as a function of the magnetic field alone, a feature that may be exploited in future tunable gyrotron designs. Oscillation of the 250 GHz gyrotron at the second harmonic of cyclotron resonance begins at extremely low beam currents (as low 12 mA) at frequencies between 320-365 GHz, suggesting an efficient route for the generation of even higher frequency radiation. The low starting currents were attributed to an elevated cavity Q, which is confirmed by cavity thermal load measurements. We conclude with an appendix containing a detailed description of the control system that safely automates all aspects of the gyrotron operation.

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“…We study specific examples of low-temperature (100 K) DNP samples, characterized by a high degree of spatial heterogeneity on a sub-mm scale. We report on our work in progress investi-gating the local microwave propagation modified through transverse confinement in DNP samples with possible consequences for the DNP spin transfer mechanism.DNP NMR [1] on solids samples, in particular, under magic-angle spinning (MAS) has become an extremely useful technique in solid-state NMR to enhance the weak NMR signal by one or two orders of magnitude [2][3][4]. Application examples range from the study of biomacromolecules [5-6] to material samples like zeolites or mesoporous silica with small molecules or catalytic compounds adsorbed at the inner surfaces of the mesoporous material [7][8][9].…”

mentioning

confidence: 99%

Sub-THz technology for dynamic nuclear polarization in nuclear magnetic resonance (DNP NMR): transverse confinement of microwave propagation through heterogeneous solid DNP samples

et al. 2017

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Passive microwave components for DNP NMR, the resulting spatial microwave field distribution at the sample site, the sample structure, the molecular structure, and DNP spin physics are closely linked to each other. We study specific examples of low-temperature (100 K) DNP samples, characterized by a high degree of spatial heterogeneity on a sub-mm scale. We report on our work in progress investi-gating the local microwave propagation modified through transverse confinement in DNP samples with possible consequences for the DNP spin transfer mechanism.DNP NMR [1] on solids samples, in particular, under magic-angle spinning (MAS) has become an extremely useful technique in solid-state NMR to enhance the weak NMR signal by one or two orders of magnitude [2][3][4]. Application examples range from the study of biomacromolecules [5-6] to material samples like zeolites or mesoporous silica with small molecules or catalytic compounds adsorbed at the inner surfaces of the mesoporous material [7][8][9].The mechanism by which DNP allows to enhance the nuclear spin polarization signals is based on a coherent spin polarization transfer in a strong static external magnetic field from unpaired electron spins in paramagnetic centers (e.g., radicals) to nuclear spins under irradiation of electron spin-resonant microwaves. A particular DNP mechanism working at high magnetic fields (e.g., 9 18 T) requires biradicals in the sample, now with two unpaired electron spins coupled by dipole-dipole interaction. Together with a nearby situated nuclear spin they form a three-spin system that gives rise to the DNP cross effect [10][11] being specifically efficient in DNP MAS NMR.Probes for MAS NMR capable of performing DNP experiments [12] inherit various traits from the subsystems composing them, which may lead to conflicting or challenging probe hardware boundary conditions. The sample is packed into a zirconia or sapphire MAS rotor spinning at a speed of ca. 10 kHz, driven by an airbearing microturbine. Tightly wound around the MAS rotor there is an NMR rf solenoidal coil with interturn spacings such that the radially (to the rotor axis) incident HE 11 or TEM 00 Gaussian microwave beam can irradiate the sample inside the rotor. A schematic view is shown in Fig. 1. The MAS system and the sample are kept at temperatures around 100...200 K in order to keep the spin relaxation time T 1e of the unpaired electron spins in the biradicals at large enough values (micro to milliseconds) to maintain the electron spin polarization or coherences during the DNP experiment.For a variety of DNP samples an additional complication appears whenever the sample is heterogeneous on a sub-mm scale. Examples are powders of mesoporous or nanoporous samples, layered samples of oriented biomembranes, or, e.g., simply powders with a grain size distribution on the order of 100 to 400 μm, impregnated by a solvent (e.g., tetra-chloroethane, TCE) and dissolved in it some biradical (AMUPol, TEKPol, and others) frozen at low temperature. It has been shown experimentally,...

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High frequency (140 GHz) dynamic nuclear polarization: Polarization transfer to a solute in frozen aqueous solution

Cited by 180 publications

References 12 publications

Dynamic nuclear polarization at 9 T using a novel 250 GHz gyrotron microwave source

Dynamic nuclear polarization at 9 T using a novel 250 GHz gyrotron microwave source

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

Sub-THz technology for dynamic nuclear polarization in nuclear magnetic resonance (DNP NMR): transverse confinement of microwave propagation through heterogeneous solid DNP samples

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