PHYSICS OF OIL PHASE IN OIL WATER TRANSFER EXPERIMENTS

University Of California San Francisco, San Francisco CA

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Abstract

Many biophysical modeling techniques use a low-resolution surface-area model to predict hydrophobicities. Such models contain a hydrophobicity free energy constant in units of kcal/angstrom squared often derived from oil-water transfer experiments on model compounds. However, the precise way to derive the constant is still under scrutiny, since different experiments can produce different values for the constant. Our work focuses on the physics of the oil phase which may cause this experiment-dependence. We are using Monte Carlo simulations of a lattice model of hydrocarbon-like fluids to study shape effects on chemical potentials. We are studying the molecular packing and the thermodynamics that arise from internal degrees of freedom in fluids of small molecules with non-isotropic shapes. Our goal is to understand these forces well enough to recommend analytic treatments of oil-water transfer data which eliminate the experiment-dependence of hydrophobic free energy constants.