Room-temperature dynamic nuclear polarization enhanced NMR spectroscopy of small biological molecules in water

Danhua Dai,Xiao He,Xiao-Liang Yang,Jiafei Mao,Xianwei Wang,Vasyl Denysenkov,Clemens Glaubitz,Thomas Prisner,Yiwei Liu

doi:10.1038/s41467-021-27067-0

Abstract

Nuclear magnetic resonance (NMR) spectroscopy is a powerful and popular technique for probing the molecular structures, dynamics and chemical properties. However the conventional NMR spectroscopy is bottlenecked by its low sensitivity. Dynamic nuclear polarization (DNP) boosts NMR sensitivity by orders of magnitude and resolves this limitation. In liquid-state this revolutionizing technique has been restricted to a few specific non-biological model molecules in organic solvents. Here we show that the carbon polarization in small biological molecules, including carbohydrates and amino acids, can be enhanced sizably by in situ Overhauser DNP (ODNP) in water at room temperature and at high magnetic field. An observed connection between ODNP 13C enhancement factor and paramagnetic 13C NMR shift has led to the exploration of biologically relevant heterocyclic compound indole. The QM/MM MD simulation underscores the dynamics of intermolecular hydrogen bonds as the driving force for the scalar ODNP in a long-living radical-substrate complex. Our work reconciles results obtained by DNP spectroscopy, paramagnetic NMR and computational chemistry and provides new mechanistic insights into the high-field scalar ODNP.

Highlights

Nuclear magnetic resonance (NMR) spectroscopy is a powerful and popular technique for probing the molecular structures, dynamics and chemical properties
In this work, we have discovered a full scheme of new molecular targets for scalar Overhauser DNP (ODNP) 13C NMR spectroscopy ranging from structurally and chemically diverse small biological molecules to biologically relevant heterocyclic compounds
The H-bonding capacity of CH, OH, and NH groups with TEMPO-type radicals[55], suggests that a broad range of organic molecules could be explored by scalar ODNP 13C NMR spectroscopy

Summary

Introduction

Nuclear magnetic resonance (NMR) spectroscopy is a powerful and popular technique for probing the molecular structures, dynamics and chemical properties. Nuclear magnetic resonance (NMR) spectroscopy is an indispensable powerful technique for probing the molecular structure, dynamics, and chemical properties at or even beyond the atomic resolution It has strong impacts on a broad range of applications in chemistry, biology, material science, environmental science as well as chemical and pharmaceutical industries. DNP experiments are carried out mostly at cryogenic temperatures (usually below 120 K), at which the electron spin relaxation times are long enough for the efficient microwave saturation in solids Such low operation temperatures quench most molecular dynamics, prohibit chemical processes, and in many cases compromise the spectral resolution. In aqueous solutions of nitroxide radicals, translational and rotational motions, which drive the stochastic e-N dipolar crosstalk upon the radical-water encounter events, occur within this time scale These motions lead to a remarkable negative ODNP-enhancement of the water 1H NMR signal at 9.4 T34. The efficiency of ODNP driven by dipolar interactions drops significantly on more complex molecules[35]

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Conclusion