Polarization of Nuclear Spins in Metals

Carver, Thomas R.; Slichter, Charles P.

doi:10.1103/physrev.92.212.2

Cited by 589 publications

(478 citation statements)

References 3 publications

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“…In these approaches, the sensitivity is enhanced by a factor of (γ I /γ S ) or about 4 for I= 1 H and S= 13 C and 10 when S= 15 N. Another, and in fact the original, example of a polarization transfer experiment was proposed by Overhauser [8] and involved transfer of conduction electron polarization to nuclear spins in metals. Carver and Slichter [9,10] verified Overhauser's hypothesis that such transfers and signal enhancements were possible with low field (3.03 mT) experiments performed on samples of Li metal and other materials with mobile electrons. During the 1970's, the analogous nuclear Overhauser effect (NOE) was used extensively to increase sensitivity in spectra of low-γ species, and it is currently employed to estimate internuclear distances for structure determination by solution state NMR.…”

Section: Introductionmentioning

confidence: 82%

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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Section: Introductionmentioning

confidence: 82%

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

View full text Add to dashboard Cite

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“…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 such as conductors (metals and low dimensional conductors) or in liquid solution.…”

Section: Introductionmentioning

confidence: 92%

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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“…DNP increases the sensitivity of NMR experiments (signal-to-noise ratio, S/N), [1][2][3] enabling the study of low concentrated systems which were not in the scope of NMR until now. NMR signal enhancement is achieved by transferring large electron polarization to surrounding nuclei via DNP.…”

Section: A Introductionmentioning

confidence: 99%

Dynamic nuclear polarization of spherical nanoparticles

Akbey

Altın

Linden

et al. 2013

Phys. Chem. Chem. Phys.

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Spherical silica nanoparticles of various particle sizes (B10 to 100 nm), produced by a modified Stoeber method employing amino acids as catalysts, are investigated using Dynamic Nuclear Polarization (DNP) enhanced Nuclear Magnetic Resonance (NMR) spectroscopy. This study includes ultra-sensitive detection of surface-bound amino acids and their supramolecular organization in trace amounts, exploiting the increase in NMR sensitivity of up to three orders of magnitude via DNP. Moreover, the nature of the silicon nuclei on the surface and the bulk silicon nuclei in the core (sub-surface) is characterized at atomic resolution. Thereby, we obtain unique insights into the surface chemistry of these nanoparticles, which might result in improving their rational design as required for promising applications, e.g. as catalysts or imaging contrast agents. The non-covalent binding of amino acids to surfaces was determined which shows that the amino acids not just function as catalysts but become incorporated into the nanoparticles during the formation process. As a result only three distinct Q-types of silica signals were observed from surface and core regions. We observed dramatic changes of DNP enhancements as a function of particle size, and very small particles (which suit in vivo applications better) were hyperpolarized with the best efficiency. Nearly one order of magnitude larger DNP enhancement was observed for nanoparticles with 13 nm size compared to particles with 100 nm size.We determined an approximate DNP penetration-depth (B4.2 or B5.7 nm) for the polarization transfer from electrons to the nuclei of the spherical nanoparticles. Faster DNP polarization buildup was observed for larger nanoparticles. Efficient hyperpolarization of such nanoparticles, as achieved in this work, can be utilized in applications such as magnetic resonance imaging (MRI). A IntroductionDNP increases the sensitivity of NMR experiments (signal-to-noise ratio, S/N), 1-3 enabling the study of low concentrated systems which were not in the scope of NMR until now. NMR signal enhancement is achieved by transferring large electron polarization to surrounding nuclei via DNP. In the last decade, there has been remarkable progress in solution and solid-state DNP-NMR as well as in imaging through the application of hyperpolarization methods. [4][5][6][7] As pointed out recently, this ''renaissance of DNP'' combined with high magnetic fields will further grow in the coming years, enabling demanding applications with better resolution. 8,9 Materials and biological systems such as membrane or microcrystalline proteins, 10-13 fibrils, 14 ligands bound to receptors, 15 polymers, [16][17][18] surface-bound species, 19-23 and other low concentrated samples were studied beneficially using DNP-NMR. 13,[24][25][26] Cryogenic temperatures are required to slow down nuclear and electron relaxation and to allow an efficient polarization transfer in solid-state DNP NMR experiments. In contrast to biological systems, 15,27-29 most technically relevant materials ...

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Polarization of Nuclear Spins in Metals

Cited by 589 publications

References 3 publications

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

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

Overhauser effects in insulating solids

Dynamic nuclear polarization of spherical nanoparticles

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