This project focuses on the fundamental interactions of water with osmolytes in confined environments because structure and dynamics are impacted by both confinement and interaction with osymolytes. We use reverse micelles (RMs) to create nanoscopic polar pools. In this study, our osmolyte of focus is urea. As a first step we investigated the loading limits, that is, how much urea can be added to RMs containing water while retaining the RM structure. We began by assessing samples visually for cloudiness and /or phase separation. For samples where clear homogeneous solutions formed we measured particle size using dynamic light scattering (DLS). We determined that as urea concentration increases size also increases for the same w0 counter to work by Wiegabenga-Sanford, et al. with glucose as the osmolyte. This poster presents our size data and discusses interpretations of interactions that support this size trend. We used the samples with phase separation as evidence of the maximum loading limit and how that limit varied with size, for example, in larger RMs for instance w0=20 our results suggest that the loading limit is 1 M urea and in comparatively smaller RMs for instance w0=10 our results suggest that the loading limit is 6M. Additionally, we performed DLS measurements on the organic phase and were able to determine RMs still formed in the organic phase, however, there was wide size variability. We show, to a certain extent, the variability can be predicted based on the relative size of the aqueous layer.

Urea in confinement: Investigation of size and loading limit study

ACS Spring 2022

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