Molecular Motions and Interactions as Studied by Dynamic Nuclear Polarization (DNP) in Free Radical Solutions

Müller‐Warmuth, W.; Meise-Gresch, K.

doi:10.1016/b978-0-12-025511-5.50007-4

Cited by 162 publications

(166 citation statements)

References 11 publications

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“…4). This plot generally gives a straight line whose intercept at infinite power is equal to the inverse of the maximal enhancement at EPR saturation [8]. The main deviations from a linear relation can be caused by heating with the MW power [14].…”

Section: First Dnp Experimental Results On a Water-tempol Samplementioning

confidence: 99%

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First DNP Results from a Liquid Water-TEMPOL Sample at 400 MHz and 260 GHz

et al. 2008

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Abstract. Using a newly designed liquid-state dynamic nuclear polarization (DNP) spectrometer operating at a magnetic field of 9.2 T, a DNP enhancement of #4.0(1) was achieved for protons in a liquid water-TEMPOL sample. The DNP mechanism was observed to be the Overhauser effect, where the polarization was transfered via electronproton dipolar relaxation. At full microwave power, the sample was heated by 17 K above room temperature, causing a significant increase in the DNP enhancement. These first results from the Frankfurt liquid-state DNP spectrometer represent a significant step towards the application of DNP to large biomolecules in the liquid state.

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Section: First Dnp Experimental Results On a Water-tempol Samplementioning

confidence: 99%

“…6). The past situation of liquidstate DNP at low magnetic fields was summarized in two review articles [7,8].…”

Section: Introductionmentioning

confidence: 99%

First DNP Results from a Liquid Water-TEMPOL Sample at 400 MHz and 260 GHz

et al. 2008

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“…In particular, the theoretical enhancement for electron-nuclear polarization transfers is approximately ~(γ e /γ I ), where now the ratio is ~660, because of the large magnetic moment of the electron relative to the 1 H, making the gains in sensitivity large. Accordingly, during the 1960's and 1970's, there were extensive efforts to perform electron-nuclear polarization transfer in liquids [24,25] and solids [26,27]. All of these experiments, collectively known as dynamic nuclear polarization (DNP), require that the electron paramagnetic resonance (EPR) spectrum be irradiated with microwaves that drive the exchange of polarization between the electrons and the nuclear spins.…”

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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“…Furthermore, the Overhauser effect loses efficiency with increasing magnetic field. Several studies have been reported about DNP on solvent molecules at low magnetic fields (B 7 1 T) using organic radicals as polarizers [2]. Considerable enhancements of different nuclei, such as 31 P, 15 N and 13 C (but not 1 H), were reported at 5 T in nonaqueous solutions [8].…”

Section: Introductionmentioning

confidence: 99%

“…Dynamic nuclear polarization (DNP) of nuclei in liquid solutions containing paramagnetic centers has been studied since the early years of magnetic resonance to achieve information about molecular motion and electronnuclear spin relaxation [1,2]. In the past few years, this technique has attracted a lot of attention again since it could provide a means to overcome the sensitivity limits in solution and solid-state nuclear magnetic resonance (NMR) towards studying macromolecular complexes.…”

Section: Introductionmentioning

confidence: 99%

Studies of Dynamic Nuclear Polarization with Nitroxides in Aqueous Solution

et al. 2008

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Abstract. The dynamic nuclear polarization effect between the nitroxide radical TEMPO and the 1 H protons of water solution was investigated at an electron pumping frequency of 9.7 GHz for different experimental conditions. In particular, we compared 14 N-4-hydroxy-TEMPO (TEMPOL) with 4-oxo-TEMPO and evaluated the effect of 2 H and 15 N isotope labelling. Furthermore, we tested the effect of concomitant irradiation on both electron paramagnetic resonance (EPR) lines with the 15 N-labelled compound. Our results show that the reduction in the EPR line width given by the 2 H and 15 N labelling and the collapse in the number of hyperfine lines due to 15 N substitution leads to the highest enhancement of e " #140 ever reported in the literature. Concomitant pumping on two hyperfine lines does not give higher enhancements at our experimental conditions.

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Molecular Motions and Interactions as Studied by Dynamic Nuclear Polarization (DNP) in Free Radical Solutions

Cited by 162 publications

References 11 publications

First DNP Results from a Liquid Water-TEMPOL Sample at 400 MHz and 260 GHz

First DNP Results from a Liquid Water-TEMPOL Sample at 400 MHz and 260 GHz

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

Studies of Dynamic Nuclear Polarization with Nitroxides in Aqueous Solution

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