Carbon-13 nuclear magnetic resonance of polymers spinning at the magic angle

“…Some of the most successful approaches involve polarization transfer techniques, including cross polarization (CP) in solids [3,4] and INEPT transfers [5] in solution, in which the polarization of a spin with a large magnetic moment is transferred to one with a smaller moment. Today, CP is an integral part of high resolution magic angle spinning (MAS) experiments in solids [6] and multiple INEPT transfers are present in essentially every biological solution NMR experiment [7]. 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.…”

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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“…The original liquid-state 2QF COSY experiment is not compatible with solid-state applications as the cross-peaks, which indicate the through-bond connectivity, have an anti-phase relationship in which the doublet components (split in frequency by the scalar coupling) have opposite signs. In solids, where scalar couplings are seldom resolved even under magic-angle-spinning conditions 5 and high power proton decoupling, 6 considerable cancellation of the cross-peak is typical, and the through-bond correlation is difficult to ascertain. To provide a robust 2QF COSY experiment for solids it is necessary to transform the cross-peaks from anti-phase to in-phase, in which the doublet components have a uniform sign.…”

mentioning

confidence: 99%

Establishing Through-Bond Connectivity in Solids with NMR: Structure and Dynamics in HC₆₀⁺

et al. 2002

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Establishing through-bond and through-space connectivity is essential to the role of nuclear magnetic resonance (NMR) in answering questions of molecular structure and dynamics. In NMR, it is the scalar or J-coupling interaction that signifies covalent through-bond contact, while the dipolar coupling provides throughspace distance constraints. A variety of liquid-state NMR experiments have been developed that make use of scalar and dipolar couplings to transfer magnetization between pairs of nuclear spins and establish their through-bond and through-space connectivity, respectively, via cross-peaks in 2D NMR experiments. 1 While an array of experiments for determining through-space connectivity in disordered solids has also been developed, 2 relatively few correlation experiments in solids make use of scalar couplings. 3 Scalar coupling-driven correlation in solids is essential for two reasons. First, as in liquid-state NMR, delineating through-bond and through-space connectivity is a critical step for establishing structure. Second, unlike dipolar interactions, which can average to zero under molecular motion even in the solid state, scalar couplings are relatively insensitive to global molecular dynamics and can provide for correlation and spectral assignment in situations where dipolar-driven experiments fail. This is the case for HC 60 + , where significant (anisotropic) molecular motion renders dipolardriven transfer ineffective for 13 C chemical shift correlation. To characterize the covalent bonding network in HC 60 + we introduce a novel solid-state correlation method, which is a variant of the popular double-quantum-filtered correlation spectroscopy (2QF COSY) experiment in liquids. 4 This experiment maintains the many advantages of the 2QF COSY experiment but is also robust for solids (both dynamic and rigid) and is applicable under fast (>30 kHz) magic-angle-spinning (MAS) conditions. In HC 60 + this through-bond correlation answers a significant structural question by accurately identifying the direct bond between the protonated sp 3 hybridized carbon site and the sp 2 hybridized cationic site.The 2QF COSY provides through-bond connectivity via scalar coupling-driven coherence transfer and is often the first step in establishing the spectral assignment in any liquid-state NMR investigation. An important characteristic of the 2QF COSY experiment is the purely absorptive diagonal and cross-peaks, which provide considerably better resolution than earlier versions of the COSY experiment. The original liquid-state 2QF COSY experiment is not compatible with solid-state applications as the cross-peaks, which indicate the through-bond connectivity, have an anti-phase relationship in which the doublet components (split in frequency by the scalar coupling) have opposite signs. In solids, where scalar couplings are seldom resolved even under magic-angle-spinning

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Carbon-13 nuclear magnetic resonance of polymers spinning at the magic angle

Cited by 1,179 publications

References 1 publication

Atmospheric plasma deposition of diamond-like carbon coatings

Atmospheric plasma deposition of diamond-like carbon coatings

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

Establishing Through-Bond Connectivity in Solids with NMR: Structure and Dynamics in HC₆₀⁺

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Carbon-13 nuclear magnetic resonance of polymers spinning at the magic angle

Cited by 1,179 publications

References 1 publication

Atmospheric plasma deposition of diamond-like carbon coatings

Atmospheric plasma deposition of diamond-like carbon coatings

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

Establishing Through-Bond Connectivity in Solids with NMR: Structure and Dynamics in HC60+

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Product

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Establishing Through-Bond Connectivity in Solids with NMR: Structure and Dynamics in HC₆₀⁺