Surface-Only Spectroscopy for Diffusion-Limited Systems Using Ultra-Low Temperature DNP MAS NMR at 16.4 T

22 May 2020, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Conventional dynamic-nuclear-polarization (DNP) technique at T ~100 K can enhance sensitivity of magic-angle spinning (MAS) NMR over 100-fold for standard samples containing urea/proline at high-field conditions, B0= 9.4–16.4 T. In the scene of real applications, however, the achievable enhancement is often much lower than for urea/proline due to faster 1H relaxation (T1H) promoted by molecular-segmental fluctuations and methyl-group rotations active even at low temperatures, hindering an efficient polarization diffusion within the system. Here, we show at 16.4 T that ultra-low temperature (T≪100 K) provides a general way to improve the DNP efficiency for such diffusion-limited systems as we demonstrate on microcrystalline sample of a tripeptide N-f-MLF-OH. In a further step, the hyperpolarization localized at the crystal surface enabled “surface-only” spectroscopy eliminating background signals from the crystal core. The surface-only data, rather than the currently popular surface-enhanced data, should prove to be useful in many applications in biological and material sciences.

Keywords

Dynamic Nuclear Polarization Enhanced MAS NMR Spectroscopy
closed-cycle helium MAS
surface-only spectroscopy

Supplementary materials

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supplementalData MLF DNPv6
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