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. These methods have included earlier studies (by the speaker and coworkers) of protein and lipid systems under crowded conditions, and the surprising observation that surface hydration water is not perturbed by protecting osmolytes. While ODNP has been applied to a variety of biological systems, as well as polymer systems, it still possesses many fundamental capabilities and a flexibility that remain largely untapped. ODNP should serve as an excellent tool for understanding water confinement and the role it plays in a vast range of applications, from the binding of proteins to syntheses inside reverse micelles. Rigorous studies, however, hinge on the development of techniques 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. By integrating ODNP with modern NMR relaxometry techniques, we facilitate its deployment in truly heterogeneous systems such as the reverse micelle. We pursue careful temperature-dependent studies that will reveal the activation energy of translational motion of water at different locations adjacent to the surfactant <i>vs.</i> centered in the reverse micelle. We will discuss how these studies translate to a broader understanding of systems involving confined water.

View of confinement from the perspective of water molecules, as observed by Overhauser dynamic nuclear polarization

2019 Fall National Meeting

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