Gas-phase acidity of proline from density functional computations

Density functional computations using the B3LYP hybrid potential coupled wi th the extended 6-311++G** basis set were performed to evaluate gas-phase a cidity of proline at-amino acid. The computed value of gas-phase acidity is 1403.8 kJ/mol in good agreement with the experimental counterpart (1395.0 +/- 13.8 kJ/mol) and is referred to the deprotonated species deriving from the first relative minimum of neutral proline characterized by the exo ring conformation with the carboxyl group in cis position. The most stable neut ral proline isomer gives rise to a species for which the gas-phase acidify value (1384.5 kJ/mol) is also close to the experimental data. (C) 2001 John Wiley & Sons, Inc.