Quantum Chemistry Calculations On The Molecular Hydration

Solvation effect is related with solute–solvent interactions, for example dispersion,induction,repulsion and electrostatic interactions. In polar solvent, the energy of molecule solvation is mainly caused by solute–solvent electrostatic interactions. Solute's geometry impact the solute-solvent interaction, and causes their solvation effect appearing in different style. Molecular solvent is related to the prediction of drugs solubility, therefore, it is important to study the solvation effect on the molecule geometry level.1. The integral equation formalism version of polarizable continuum model (IEFPCM) was employed to compute thermodynamic properties of organic compounds in the aqueous solution. Three classes of homologous compounds are chosen: C1~C8 alkanes, C2~C8 dihydric alcohols, andα,ω-alkanedioic acids, HOOC-(CH2)n-COOH (n = 0~6). The molecular geometries, both in the gas phase and in the aqueous solution, were optimized using the B3LYP/6-31+G* method. The study focuses on the effects of increasing alkane chains as well as the effect of polar terminal groups on molecule hydration. The effects of solvation on a range of molecular properties, including the molecular dipole moment, total electronic energy, and Gibbs free energy, increase in the sequence of alkanes, dihydric alcohols, andα,ω-alkanedioic acids. With the increase in methylene groups, the dipole moment shows odd–even alternation. The alternation amplitude increases in the sequence of alkanes, dihydric alcohols, andα,ω-alkanedioic acids. The double polar terminal groups appear to be responsible for the odd-even alternation. The Gibbs free energies of solvation forα,ω-alkanedioic acids are consistently negative, ?Gsol < 0, along with the pronounced odd–even alternation. In contrast, for alkanes ?Gsol > 0 and it increases monotonically with the number of methylene groups (no odd-even alternation). The ?Gsol < 0 for dihydric alcohols but no odd-even alternation is observed.2. In order to study the effect of solute -solvent electrostatic interaction on the molecular hydration, and the temperature effect on the calculated results, the density functional theory (DFT) on the B3LYP/6-31G level and the Onsager model were used to...