Physical/Analytical Seminar
"Building Ultra-sensitive Magnetic Resonance Techniques to Interrogate Water Under Confinement"
Abstract: Interfacial and confined water stores very large chemical energies that can aid (or hinder) macromolecular binding, collapse, and assembly events. But, it remains a relatively elusive target for modern spectroscopic techniques, because individual water molecules move in and out of interfacial layers and confined pockets on the sub-nanosecond timescale. Surprisingly, we can capture these fast water motions with magnetic resonance (using an emerging technique called Overhauser Dynamic Nuclear Polarization (ODNP)). After explaining the basic physics behind how this feat is achieved, we explore two brief stories. First, with Reverse Micelles as a model system, we explore the translational dynamics of water confined on the nanoscale. We show that the translational dynamics of water shut down when confined to pools on the order of a couple nanometers, even though such pools consist of hundreds of water molecules. These same measurements suggest that tens of thousands of water molecules would be required to recover bulk-like dynamics. These measurements emphasize how the cooperative nature of the water hydrogen-bond network causes geometry and lengthscale to play a dominant role in determining the properties of confined and interfacial water, even overwhelming the effects of surface chemistry. Second, we introduce a framework for capturing and analyzing all the coherence pathways in an NMR experiment. We demonstrate the versatility of this technique by recovering high sensitivity during low-field magnetic resonance measurements. This strategy proves essential to measuring ODNP on samples with low water content, and we also discuss the broader applicability of this technique, both within and beyond magnetic resonance.