We seek to understand the fundamental properties of water molecules under confinement, initially utilizing reverse micelles as a model system. In particular, the development of specialized but robust spectroscopic techniques will highlight the change in translational and rotational dynamics of the water at different levels of confinement. Overhauser Dynamic Nuclear Polarization (ODNP) isolates the translational motion of water near a selectively placed spin label, and reads out the result through variable enhancement of NMR (Nuclear Magnetic Resonance) signal. ODNP does not rely on higher-order spectroscopic effects, requires only a simple, versatile, and non-perturbative labeling strategy, and functions seamlessly in opaque, viscous, and other “dirty” systems. Despite previous applications to biological and polymer systems, ODNP still possesses many fundamental capabilities and a flexibility that remain largely untapped. In particular, it offers a window into understanding water confinement and the role it plays in a vast range of applications, from the binding of proteins, to syntheses inside reverse micelles. However, these studies require the development of extensions to ODNP that can properly map out the behavior of surface and confined water across different compartments and phases in highly heterogeneous and/or porous materials. Emphasizing reverse micelles as model systems, we describe our progress towards measurements in highly phase-heterogeneous and confined systems and we include comparisons to molecular modeling simulations. We present holistic improvements to the ODNP methodology that enable its application to these systems. Finally, we demonstrate that ODNP can work synergistically with <sup>2</sup>H NMR relaxometry and <sup>1</sup>H NMR diffusometry develop a complete picture of translational motion of the water, rotational motion of the water, and translational motion of the reverse micelle assemblies, respectively.

Magnetic single- and dual-resonant relaxometry to probe the dynamics of water molecules under confinement

ACS Spring Meeting 2021

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