Exploring the impacts of nanoconfinement using nuclear magnetic resonance (NMR) spectroscopy
Date
2022
Authors
Miller, Samantha L., author
Levinger, Nancy, advisor
Krummel, Amber, committee member
Crans, Debbie, committee member
Graham, James, committee member
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Abstract
The chemical reactivity of molecules is typically studied under bulk aqueous conditions in the research laboratory. Although this standard may be appropriate for processes destined to be scaled up for industrial purposes, it ignores the fact that a great deal of the chemistry underlying physiological reactions occur in confined environments, like cellular organelles, protein pockets, or porous interfaces. The dissertation begins by describing the methodology for synthesizing size tunable reverse micelles, or surfactant enveloped nanodroplets. After physical perturbation, the ternary mixture of polar (usually aqueous), nonpolar, and amphiphilic surfactant self-assemble. Two small molecules, glucose and urea, were studied in these nano environments using a combination of analytical techniques including dynamic light scattering, differential scanning calorimetry, and molecular dynamics simulations that complemented the myriad nuclear magnetic resonance (NMR) spectroscopy studies. Quantification of single hydrogen exchange between glucose and water using exchange spectroscopy NMR in conjunction with custom MatLab code revealed that confinement of glucose and water within 8-10 nanometer reverse micelles slows the process of exchange by introducing a quantifiable energy barrier of ~75 kJ/mol. Deuterium NMR spectroscopy provided evidence for hydrogen tunneling below 283 K, a surprisingly high temperature for this phenomenon. The same robust methods of kinetic and structural analysis were used to characterize urea in water reverse micelles. Results showed that in addition to its well-known ability to denature proteins, urea can disrupt amphiphilic membranes and cause a ten-fold increase in the membrane surface area at low temperatures ~273 K as a result of this destabilization. Finally, the use of fluorine NMR spectroscopy demonstrated that the reverse micelle nanodroplet environments could achieve higher ionic strengths (~9.0 M) with simple divalent salts than possible in standard bulk solutions (~5.0 M). Together, these results presented compelling evidence that utilization of reverse micelle nanodroplets could provide alternative environments to facilitate previously inaccessible, novel conditions.
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Subject
nanoconfinement
reverse micelles
NMR
kinetic modeling