Neutral and zwitterionic glycine.H_2O complexes:A theoretical and matrix-isolation Fourier transform infrared study

摘要

The H-bond interaction between glycine and H_2O has been studied by a combined theoretical(DFT(B3LYP)/6-31 + +G**)and experimental(matrix-isolation FT-IR)methodology.The 1:1 and 1:2 complexes of the most stable conformation(I)of glycine appear to be neutral complexes which have been vibrationally characterized in detail.The higher stoichiometry complexes(glycine).(H_2O)_n with n larger than 3 are demonstrated to be zwitterionic H-bonded complexes.A set of characteristic IR absorption bands for this zwitterionic structure has been observed in low-temperature Ar matrices.This would be the first experimental IR evidence for proton transfer occurring between the NH_2 and COOH groups of amino acids by a H-bonded water molecular channel in isolated conditions.