Solvation free energy of the proton in acetonitrile

Abstract

Solvation free energy of the proton in solution is used to describe proton transfer processes in that solution. In addition, the solvation free energy of the proton is involved in several chemical and biological processes. Although several methodological approaches have been used to estimate the solvation free energy of the proton in solutions (mainly in water), there is no consensus estimate of the solvation free energy of the proton. In this work, we have reported the solvation free energy of the proton in acetonitrile using the cluster continuum solvation model. To compute the solvation free energy of the proton within this model, one needs the structures of neutral and protonated acetonitrile clusters. Thus, we thoroughly explored the potential energy surfaces (PESs) of the clusters in the solvent phase using several incremental levels of theory. We generated initial structures using classical molecular dynamics. Then the generated structures have been successively optimized at the MN15/6-31++G(d,p) and MP2/aug-cc-pVDZ levels of theory. Finally, single point extrapolations to the complete basis set (CBS) limit have been performed at the MP2 level of theory. As results, the solvation free energy (respectively enthalpy) of the proton in acetonitrile is estimated to be −1022.0 kJmol−1 (respectively −1056.5 kJmol−1) at the MP2/CBS level of theory. The calculated solvation free energy of the proton in acetonitrile is found to be in excellent agreement with the experimental estimate based on the tetraphenylarsonium-tetraphenylborate (TATB) approach.