Ab initio and DFT theoretical studies of pyridoxal-5′-phosphate methylamine Schiff base isomers

Optimized geometries and harmonic frequencies of 15 different isomeric configurations for three tautomeric (enol-, keto-, and zwitterionic) forms of pyridoxal-5′-phosphate methylamine Schiff base were obtained at the HF and B3LYP levels of theory with the 6-31G* basis set. Additionally, the B3LYP/6-31G* calculations of Raman activities and the B3LYP/6-31+G* calculations of optimized geometries and harmonic force fields were done for the most preferable isomers for investigated three forms of titled molecule. Theoretical vibrational frequencies were compared to FT Raman and infrared spectra of the solid pyridoxal-5′-phosphate methylamine Schiff base.