Computer experiments on aqueous solutions. III. Monte Carlo calculation on the hydration of tertiary butyl alcohol in an infinitely dilute aqueous solution with a new water–butanol pair potential

Abstract

Monte Carlo calculations have been carried out for an infinitely dilute aqueous solution of tertiary butylalcohol (TBA) at 298.15 K and ordinary density by the Metropolis scheme in an NVT ensemble. The total number of molecules is 216, one of which is TBA. For water–water interaction, the MCY (Matsuoka–Clementi–Yoshimine) potential is used, whereas a new pair potential is determined for water–TBA interaction from ab initio LCAO SCF MO calculations for more than 380 different dimeric configurations with an STO-3G basis set and subsequent multiparameter fitting of MO data thus obtained to an appropriate potential function with a nonlinear optimization method. In the Monte Carlo run, 3 600 000 configurations have been generated and final 2 000 000 configurations have been used to obtain energetic and structural information on the hydration structure of TBA. As in the case of the methanol solution studied previously, the potential energy and structure of water tend to be stabilized by the introduction of one TBA molecule, and two strong hydrogen bonds between TBA and the surrounding water molecules favor the formation of a bulky and stable hydration shell which includes cooperatively connected hydrophobic hydration structures. This is clearly shown in density diagrams for water around TBA which visualize remarkable structuration of water. The iceberglike structure around TBA is more pronounced than that of methanol.