Our broad research umbrella is focused on the impact of small osmolytes on water in confinement environments. For this study we used a reverse micelle sysytem in which sodium diotylsufosuccinate (AOT) serves as the surfactant, isooctane as the solvent, and water or urea dissovled in water comprises the polar component. Reverse micelles are categorized by w0 = [polar component]/[surfactant]. In our experiment, we focus on five different values of w0 (w0 = 1, 5, 10, 20, 40) and four concentrations of urea (0M, 0.5M, 1M, 2M). With water as the polar component, our Dynamic Light Scattering (DLS) data illustrates the expected linear relationship between w0 (the ratio) and size. Interestingly within experimental error, DLS data indicate no impact of the presence of urea on size for w0 = 1, 5, and 10. With larger reverse micelles, specifically w0 = 20 and 40, there is a significant size contraction when urea is added. We attribute this to reduction of hydrogen bonding in the water due to the presence of urea. In contrast, using Coumarin 343 as a probe molecule Red-Edge Emission Spectroscopy (REES) shows a bigger impact on emission as excitation is shifted for smaller reverse micelles compared to the larger w0 samples. For the smaller reverse micelles, w0 = 1 and 5, the emission is blue-shifted whereas for w0 = 10, 20 and 40 there is very little change in the emission as excitation changes from 400 nm to 450 nm. Coumarin 343 is chosen because it is likely to be found in the polar phase. The shift in emission for small w0 suggests confinement is responsible and impacts all urea concentations. We have just begun 1D proton and EXY NMR experiments to further illucidate changes in the hydrogen bonding interactions to help explain what we see in both DLS and REES. Furthermore, we hope a deeper analysis of our time-resolved emission data will yield further insight ino the dynamics of the water-osmolyte polar phase.

Urea’s apparent impact on small AOT in isooctane reverse micelles: Constraints on the hydrogen bonding network

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