Local Hydration Dynamics in Soft Matter by Dynamic Nuclear Polarization of 1H-Water

摘要

We present a unique approach for measuring the local diffusion coefficient of water inside or at the surface ofsoft matter systems, including lipid bilayer membranes, proteins, or protein assemblies. This is made possible by the useof dynamic nuclear polarization (DNP) of ~1H NMR signal of water via nitroxide based spin labels which are localizedonto specific membrane or protein sites through covalent linkage. The DNP-induced ~1H NMR signal enhancementcritically depends on the diffusion coefficient of the solvent within approximately 10 A distance of the spin labeled site.We discuss the usefulness of ~1H NMR in studying local water dynamics and accessibility in combination with electronspin spectroscopy and compare the results to the complementary technique of field cycling relaxometry (FC). Mostimportantly, the DNP approach allows us to work with sample volumes as small as 3-4 μL at spin label concentrationsnearing 100 μM giving ~2 orders of magnitude higher sensitivity compared with field cycling approaches, making thetechnique well suited for biological samples.