INTERPHASE SOLUBILITY AND CHROMATOGRAPHIC RETENTION

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The proposed work aims to establish a foundation for predicting partitioning and selectivities of solute molecules within chain molecule "interphases", including the bonded stationary phases of reversed-phase liquid chromatography, and amphiphilic aggregates, such as monolayers, bilayers, vesicles, liposomes, and micelles. This work represents a continuing collaboration of a group at the University of Florida with a group at UCSF, combining theory and experiment. We have developed statistical mechanical theory for solute uptake which is supported by neutron scattering experiments of solute distribution in bilayers, retention vs. co- solvent composition in RPLC, and spectroscopic results on micelles. Our experiments in bilayers confirm the predicted expulsion of solute with surface denisty, due to configurational entropy. We have developed new methods for synthesizing bonded phases of varying surface density, and have shown partitioning to be a function of surface density. Preliminary theory further suggests molecular selectivity will increase with surface density. We have studied effects of interphase structure on retention. Here we aim to study effects of solute structure on retention. Solutes will include chains, rods, and disks; we expect that the high selectivities among molecules result from packing in the interphase. We also plan to study long chain solutes, homopolymers and heteropolymers, vs. chain length, composition, and temperature. We aim to develop a molecular framework to understand how molecules partition into semi-ordered phases of chain molecules, including: (i) the molecular mechanisms of retention and selectivity in RPC, (ii) the fundamental physical chemistry of membranes and micelles. This should have broad implications for optimization in chromatography of small molecules and proteins; insertion of drugs, metabolites and proteins into membranes; adsorption of proteins at polymeric surfaces, and thus bear on fundamental issues of separations and biomedical sciences.