Solvation cavity formation

The preceding calculations can also be performed for finite cavity sizes. For this case, there are some additional sources of small amounts of energy associated with cavity formation arising from surface tension, pressure-volume work, and electrostriction. Because of the Franck-Condon principle these do not affect the transition energy, but they have some influence on the heat of solvation. Jortner s (1964) results are summarized as follows ... 

A hybrid approach of the extended scaled particle theory (SPT) and the Poisson-Boltzmann (PB) equation for the solvation free energy of non-polar and polar solutes has been proposed by us. This new method is applied for the hydration free energy of the protein, avian pancreatic polypeptide (36 residues). The contributions form the cavity formation and the attractive interaction between the solute and the solvent to the solvation free energy compensate each other. The electrostatic conffibution is much larger than other terms in this hyelration free energy, because hydrophilic residues are ionized in water. This work is the first step toward further applications of our new method to free energy difference calculation appeared in the stability analysis of protein. 

Diels-Alder reactions. This tenn describes how much energy is needed for evaporation of the solvent per unit of volume and represents a measure of the internal water-water interactions. In contrast to the internal pressure, the ced of water is extremely high due to the large number of hydrogen bonds per unit volume. Since solvation and cavity formation lead to the rupture of solvent-solvent interactions, the ced essentially quantifies solvophobicity and hydrophobicity, and has been used successfully for describing solvent effects on Diels-Alder reactions. These studies stress the importance of hydrophobic interactions. The significance of these and the relative unimportance of internal pressure is further supported by the observation that Diels-Alder reactions in water are less accelerated by pressure than those in organic solvents, which is in line with the notion that pressure diminishes hydrophobic interactions. 

The difference in the energy levels of a solvated electron in solution and of an electron in vacuum may be considered as solution-to-vacuum equilibrium electronic work function. The quantity — A may be considered as free energy of electron solvation (i.e. with the formation of solvated electrons) it relates to an equilibrium process. That is, in the initial state the electron is in the equilibrium solvate cavity while in the final state it is in vacuum, close to the solution surface, and the solvent is in its equilibrium disordered state (i.e. there is no solvate cavity in it). 

A quite reliable estimate of the solvent effect results from theories that combine micro- and macro-scopic parameters of solute and solvent. For example, in the solvophobic theory, the energy of a solute molecule in solvent, Ejoin, is given as the sum of isolated molecule energy, Ej, and the solvation term, Ejo,v. The latter term encompasses the energy of cavity formation in the solvent to accommodate the solute, E, v, and the energy of subsequent solvent-solute interactions, Ej ,. The interaction part is composed of the energy of dispersion, Edi.p> and electrostatic, interactions. The final expression for E i can be written as... 

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