Experimental studies of interfacial water are complicated by the inescapable presence of bulk water. Over the past decade, Overhauser Dynamic Nuclear Polarization (ODNP) has demonstrated remarkable aptitude for overcoming this problem. ODNP relies on chemistry to place a spin probe in a known location and on spin physics to read out the dynamics of water within 5-15 Å of that location, thereby extracting the interfacial water signal from the bulk. As a simple but important model system, we have selected AOT (Aerosol-OT, dioctyl sulfosuccinate sodium salt) reverse micelles (RMs) employing ODNP with the amphiphilic spin label CAT-16 (4-(N,N’-dimethyl-N-(hexadecyl)) ammonium- 2,2’,6,6’-tetramethylpiperidine-1-oxyl salt) to extract the interfacial water signal and TEMPO-sulfate to extract the RM core water signal. These results will offer a unique perspective on nanoscale water dynamics and provide benchmark measurements important to ODNP analysis of confined water in other, more complex material systems with less defined morphology. Here we present the development of a home-built NMR spectrometer and probe designed for ODNP measurements, as well as the design of a Python library that permits facile implementation of complex pulse sequences. We demonstrate the utility of modern NMR relaxometry techniques, in particular 2-Dimensional Inverse Laplace Transform (2D-ILT) <sup>1</sup>H and <sup>2</sup>H NMR relaxometry. In order to observe translational dynamics, ODNP requires an NMR resonance frequency near 15 MHz, an unusually low frequency that gives rise to obvious challenges for NMR sensitivity and for chemical shift resolution. Therefore, we demonstrate the ability of the 2D-ILT to separate water signal from that of other chemical species, and culminate with the first sensitive and selective measurements of ODNP inside the reverse micelle environment.

Closer look at confined water: Use of Overhauster Dynamic Nuclear Polarization to study nanoscale water dynamics in aerosol-OT reverse micelle model systems

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.