Vibrational frequencies of cysteine and serine zwitterions-an ab initio assignment

The vibrational frequencies of cysteine and serine zwitterions are evaluated using ab initio methods at the 4-31G* level. The calculated frequencies along with the corresponding potential energy distributions are used to assign the IR and Raman spectra of the zwitterions of l-cysteine and d,l-serine. The calculated Raman activities, IR intensities along with the experimental Raman optical activities of these amino acids are used as aids in the assignments. The similarities and differences between the spectra of these amino acids are highlighted.