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Acidity and Basicity of alpha-Amino Acids by the COSMO, COSMO-RS and Modified Cluster-Continuum Methods. Part 1. Glycine, Alanine and Proline

The problem of calculation of the basicity (pKA1) and acidity (pKA2) constants of glycine (Gly), alanine (Ala) and proline (Pro) is addressed by the COSMO, COSMO.RS and newly developed modified cluster continuum model (MCCM). The latter is based on the clusters of zwitterions and ions of Gly, Ala and Pro formed by a number of H2O molecules via hydrogen bridges. The number of hydrogen bridges should be preserved in isodesmic reactions describing protonation and deprotonation processes as well as solvation of the proton. Selection of the number of water molecules forming the first microsolvation shell is briefly discussed. Agreement with the measured experimental data is pretty good for all three approaches.

amino acid; acidity; basicity; solvent effect; isodesmic reaction

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