CONFORMATIONAL BEHAVIOR OF ALPHA-ALANINE - MATRIX-ISOLATION INFRARED AND THEORETICAL DFT AND AB-INITIO STUDY

Two conformers of the nonionized alpha-alanine and its isotopomer N,N, O-d(3)-alanine have been observed in low-temperature Ar matrixes. Thei r infrared spectra have been analyzed and assigned using DFT/B3LYP/aug -cc-pVDZ and MP2/aug-cc-pVDZ geometry and frequency theoretical calcul ations. Two different intramolecular H-bonds, bifurcated NH2... O=C an d N ... H-O, were found in the observed alpha-alanine conformers, I an d IIa, We found that the DFT/B3LYP/aug-cc-pVDZ method yields vibration al frequencies of the alpha-alanine conformers in excellent agreement with the experimental data.