Explicit Solvation Shell Model and Continuum Solvation Models for Solvation Energy and pKa Determination of Amino Acids

The study of the Explicit Solvation Shell Model (ESS) presented recently [da Silva, E. F.; Svendsen, H. F.; Merz, K. M. J. Phys. Chem. A 2009, 113, 6404.] for calculation of solvation free energy of ions is extended for the study for amino acids. Solvation free energies and p K a of a data set of 10 amino acids is calculated using ESS. The data set of amino acids is selected based on their potential to be regarded as solvents for postcombustion CO 2 capture processes. Calculated results are compared against experimental p K a and p K a calculated from PCM, SM8T, and DivCon continuum solvation models. Error estimates of p K a from different models vs experimental p K a data are also given to evaluate the results calculated by different solvation models. This study also involves a comprehensive study of gas phase basicity, proton affinity,Δ G acid 0, Δ H acid 0, protonation entropy with density functional methods (B3LYP/6-311++G(d,p)) and composite methods (G3MP2B3, G3MP2, CBS-QB3, G4MP2) and their comparison with experimental results for amino acids.