AMINO-ACID ZWITTERIONS IN SOLUTION - GEOMETRIC, ENERGETIC, AND VIBRATIONAL ANALYSIS USING DENSITY-FUNCTIONAL THEORY CONTINUUM MODEL-CALCULATIONS

Glycine and alanine aminoacids chemistry in solution is explored using a hybrid three parameters density functional (B3PW91) together with a continuum model. Geometries, energies, and vibrational spectra of gly cine and alanine zwitterions are studied at the B3PW91/6-31 + G* leve l and the results compared with those obtained at the HF and MP2/6-31 + G* levels. Solvents effects are incorporated by means of an ellipso idal cavity model with a multipolar expansion (up to sixth order) of t he solute's electrostatic potential. Our results confirm the validity of the B3PW91 functional for studying aminoacid chemistry in solution. Taking into account the mon favorable scaling behavior of density fun ctional techniques with respect to correlated nb initio methods these studies could be extended to larger systems. (C) 1998 American Institu te of Physics.