Dynamic nuclear polarization (DNP) is a powerful method to enhance NMR sensitivity. Much progress has been achieved recently to optimize DNP performance at high magnetic fields in solid-state samples, mostly by utilizing the solid or the cross effect. In liquids, only the Overhauser mechanism is active, which exhibits a DNP field profile matching the EPR line shape of the radical, distinguishable from other DNP mechanisms. Here, we observe DNP enhancements with a field profile indicative of the solid effect and thermal mixing at ∼320 K and a magnetic field of 9.4 T in the fluid phase of 1,2-dimyristoyl-sn-glycero-3phosphocholine (DMPC) lipid bilayers doped with the radical BDPA (1,3-bis(diphenylene)-2-phenylallyl). This interesting observation might open up new perspectives for DNP applications in macromolecular systems at ambient temperatures.

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.

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TEMPOL nitroxide radicals are frequently used as a polarizing agent for liquid-state Overhauser dynamic nuclear polarization. To achieve large signal enhancements at high magnetic fields (9.4 T), fast picosecond to sub-picosecond dynamics between nitroxide and the target solvent molecule are required. Such dynamics have been predicted by molecular dynamic studies and attributed to fast inner-sphere motions of a transient radical–solvent complex. Here, we systematically study a series of nitroxide radicals with different substituents around the electron spin-bearing NO moiety and different overall sizes to quantify the contribution of the rotational dynamics of the radical to these inner-sphere dynamics. The experiments are performed at a 9.4 T magnetic field, which exhibits high sensitivity to rotational motion contributions in a low picosecond time range. We can show that the observed enhancements can be quantitatively predicted taking the rotational motion of the radical into account.

Vinylarenes represent an important class of core skeleton embedded in natural products, organic materials, and pharmaceutical molecules. Therefore, numerous efforts have been devoted to developing efficient methods for their preparation....