Mechanisms of Noncatalytic Organic Chemical Reactions in Super- and Subcritical Water

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The energy representation of the molecular configuration in a dilute solution is introduced to express the solvent distribution around the solute over a one-dimensional coordinate specifying the solute-solvent interaction energy. In this representation, the correspondence is shown to be one-to-one between the set of solute-solvent interaction potentials and the set of distribution functions On the basis of the one-to-one correspondence, an approximate functional for the chemical potential of a solute in solution is constructed by adopting the Percus-Yevick-like approximation in the repulsive region of the solute-solvent interaction and the hypernetted-chain-like approximation in the attractive region. The chemical potential is then given exactly to second order with respect to the solvent density and to the solute-solvent interaction. It is demonstrated that the chemical potentials of nonpolar, polar, and ionic solutes in water are evaluated accurately and efficiently from the single functional over a wide range of thermodynamic conditions. Furthermore, the conformation of a nanoscale molecule such as protein varies strongly in response to solute-solvent interactions. An approach to the solvation free energy of a solute molecule with conformational flexibility thus needs to be established toward treating a solution system of functional importance. The method of energy representaion is extended to treat the solvation free energy of a flexible solute molecule, In this work, we examined solute systems in water with stretching and/or torsioal degrees of freedom for intramolecular motion, and demonstrated the performance of the method over a wide range of thermodynamic conditions including both ambient and supercritical. The aggregation behaviors of hydrophobic and hydrophilic solutes in water are also treated within the same framework.