Investigation of intermolecular interactions in aqueous solutions using the effective fragment potential

Michael David Hands, Purdue University

Abstract

Intermolecular interactions in aqueous solutions are extremely important for many chemical phenomena, but are not completely understood. This thesis describes computer simulations of aqueous solutions with different small molecule solutes using the effective fragment potential (EFP) method, classical simulations, and ab initio calculations. Structure and bonding patterns in tert-butanol (TBA) – water mixtures are investigated by using molecular dynamics simulations with EFP. EFP is a model potential in which all parameters are obtained from a set of ab initio calculations on isolated fragment molecules. Mixed-basis EFP potentials (called "EFPm") for water and TBA molecules were prepared and tested in this work. The accuracy of these EFP potentials is justified by comparison of structures and binding energies in water, TBA, and water-TBA dimers with MP2/6-311++G(d,p) data. EFPm potentials for monovalent ions (F-, Cl-, Br-, I-, Li+, Na+, K+, and NH4+) were prepared and tested by comparison of structures and interaction energies of ion-(H2O)n, n = 1 - 6, clusters to experimental and ab initio results. The ion EFPm potentials were sufficiently accurate to allow us to model affinity of F- and I- to TBA in aqueous solution, by using EFPm MD simulations. The nature of π-hydrogen bonding of benzene in bulk water was explored with classical simulations. It was found that while enthalpy favors water hydrogen bonds, entropic factors stabilize more flexible water-benzene π-hydrogen bonds. This implies that formation of π-hydrogen bonding between water and aromatic residues may play an important role in biological binding, recognition, and signaling processes.

Degree

M.S.

Advisors

Slipchenko, Purdue University.

Subject Area

Chemistry|Physical chemistry

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