여러 수용액에서의 자유에너지와 물의 구조에 관한 몬테카를로 연구

Abstract

학위논문(박사) - 한국과학기술원 : 화학과, 1992.8, [ vii, 58 p. ]Part A ; Statistical thermodynamic computer simulations of pure liquid water and of the hydration of model compounds ($CH_4$, $CH_3OH$, $CH_3NH_2$, $CH_3COOH$, $CH_3NH_3^+$, and $CH_3COO^-$) that are prototypes of the side-chain groups of proteins were carried out at 25$^\circ$C under canonical ensemble conditions. The simulations employed a Monte Carlo method, with empirical pairwise potintial functions derived from ab initio quantum mechanical calculations, to compute the free volume of a molecule. Thermodynamic properties and solute-solvent radial distribution functions are reported. These include, in particular, the molar excess entropies of the various solute and solvent water molecules in dilute aqueous solution, computed from the free volumes. The excess free energies of these molecules were calculated from the computed entropies. According to these calculations, the nonpolar solute molecule $CH_4$ induces somewhat stronger interactions among the solvent water molecules (structure-forming hydrophobic hydration) than does an $H_2O$ molecule in pure liquid water, whereas the other polar solute molecules induce weaker(structure-breaking) interactions. The excellent agreement between the experimental and computed molar excess entropy in pure liquid water demonstrates that the modified free-volume theory can be applied in calculations of the excess free energy of dense and rotationally hindered systems. In all of the dilute aqueous solutions considered here, the average molar excess free energies of the solvent water molecules are higher than that in pure liquid water. However, in considring the total excess free energies of these systims, a methane solution is less stable (i.e., has higher free energy) than pure liquid water, whereas the other solutions are more stable. Part B ; Monte Carlo method was used to examine the distributions of nonshort-circuited rings of hydrogen-bonded molecules in TIP4P water and methane solution at five temperatures tanging fro...한국과학기술원 : 화학과