THE 1 1 GLYCINE ZWITTERION-WATER COMPLEX - AN AB-INITIO ELECTRONIC-STRUCTURE STUDY/

More than a dozen stationary points on the potential energy surface fo r the 1:1 glycine zwitterion-water complex have been investigated at H artree-Fock or MP2 levels of theory with basis sets ranging from split valence (4-31G) to split valence plus polarization and diffuse functi on(6-31 ++ G*) quality. Only one true minimum (GLYZWM, C-1 symmetry) could be located on the potential energy surface. GLYZWM features a br idged water molecule acting as both a hydrogen bond acceptor and donor with the NH3+ and CO2- units of the glycine zwitterion. The total hyd rogen bond energy in GLYZWM is computed as 16 kcal/mol(MP2/6-31 ++ G* //6-31 ++ G*, including corrections for basis set superpositions erro rs). The computed vibrational frequencies and normal mode forms of the GLYZWM complex resemble in many cases experimental assignments made f or the glycine zwitterion in bulk water on the basis of Raman spectros copy. (C) 1996 by John Wiley & Sons, Inc.