The behavior and interactions between water molecules and their environment vary greatly depending on whether they are presented in bulk or nanoscopic quantities. In our research we observe the behavior of water in small isolated environments using reverse micelles (RMs) as model systems. The behavior of water was observed for varying sizes of RMs formed using the cationic surfactant, cetyltrimethylammonium bromide (CTAB), with alcohol co-surfactants. We were able to distinguish between core and interfacial water as well as determine the relative ratio of core to interfacial water using 1H NMR. The core to interfacial ratio appears to be dependent on the co-surfactant used, while maintaining the expected increasing trend as w0, a measure of the radius of the RM, increases. After establishing baseline data with previously studied straight chain alcohol co-surfactants, we applied NMR experiments to determine whether or not RMs containing cholesterol in the interfacial layer could be formed. Our goal was to create more complex lipid boundaries as models that more closely mimic cellular membranes. We found that cholesterol could not be used as the sole co-surfactant in CTAB RMs. Cholesterol required a second co-surfactant with a limited range of ratios of CTAB to cholesterol to the other co-surfactant. Once we established that CTAB mixed micelles could be formed, acidic properties of the nanopools of water were analyzed. Aqueous acidity, in terms of pH, is generally conceptualized in ways that require a sizeable fraction of Avogadro’s number of water molecules. However, in RMs with only nanopools of water there are only a few hundred to a few hundred thousand water molecules. Interesting questions arise when one proton might effectively shift the pH by more than a pH unit. We explored shifts in these environments via fluorescence and 51V NMR spectroscopy. This poster will summarize our 1H NMR, 51V NMR and fluorescence data in support of our conclusions about the behavior of water in these RM environments.

Behavior of nanoscopic quantities of water in reverse micelles using NMR and fluorescence spectroscopies

251st National Meeting (2016)

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