This proposal asks for support to Investigate the behavior of assemblies of amphiphilic molecules, using computer simulation techniques. Amphiphiles are molecules with polar headgroups and hydrocarbon tails. They are constituents of soaps and detergents (fatty acids), and cellular and model biomembranes (phospholipids). Over the past decade, computer simulation has emerged as an important complement to real experiments in the study of such complex systems. It is proposed to use realistic intermolecular potential models and molecular dynamics calculations to study the structure and dynamics of assemblies of amphiphiles. Particular emphasis will be placed on the intramolecular structure of the alkyl chains (gauche/trans isomerization) and the nature of intermolecular chain-chain positional and orientational correlations in these systems. While the long-term objective is to study phospholipids which have two alkyl chains, the initial work will focus on assemblies of fatty acids with one chain per head-group. The specific systems to studied by molecular dynamics include the following: a) monolayers and bilayers of amphiphilic molecules (fatty acids) supported on hydrophobic or hydrophilic substrates (model biomembranes). b) monolayers of amphiphilic molecules at the air/water interface (Langmuir films). Of particular interest, is the characterization of the effects of density and temperature on phases that occur before the complete solidification of the monolayer. c) quasi-spherical aggregates of amphiphilic molecules in aqueous solution (micelles) with emphasis on the nature of the head-group solvation, chain conformations, and solubilization phenomena. d) bilayer and lamellar aggregates of amphiphilic molecules in aqueous solution. The eventual goal is to obtain structural and dynamical information on the behavior of amphiphilic assemblies that complements experiments currently underway at the University of Pennsylvania (Professors J. K. Blasie and S. J. Opella), and elsewhere, on the structure and function of (model) biomembranes and related systems.
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