Theoretical studies of condensed phase chemistry

Jiali Gao, Purdue University

Abstract

Monte Carlo simulations for dilute aqueous solutions including hydrocarbons, carboxylate and ammonium ions have been carried out in the NPT ensemble at 25$\sp\circ$C and 1 atm. The computed results are in accord with experimental heats of solution, and provide detailed insights into the hydrophobic effects, conformational equilibria, and the hydration of the ions. The intermolecular potential functions for the charged residues in proteins were also obtained through these computations. Further, the same procedure was applied to systems involving hexanol-water interfaces. In these studies, water penetration into the hydrophobic phases of the bilayer systems was found to be limited. Ab initio quantum mechanical calculations were performed to study the structures and binding energies of anion-water complexes in the gas phase. The theoretical binding energies predicted two years ago were found in excellent agreement with the recent experimental results. This combination of theory and experiment has been most valuable in developing the ion-molecule potential functions needed for condensed-phase simulations of these ions and biomolecular systems. Finally, statistical perturbation theory has been used to elucidate the conformational equilibrium of the peptide bond in N-methylacetamide in the gas phase and aqueous solution. The theoretical results indicate that there is essentially no conformation change on going from the gas phase into aqueous solution. Consequently, this suggests that the predominant trans peptide bonds in proteins are not due to the hydration effects.

Degree

Ph.D.

Advisors

Jorgensen, Purdue University.

Subject Area

Organic chemistry

COinS