Vibrational studies of amino acids experimentally and theoretically have been performed. The Semi-empirical methods optimization by PM6 and RM1 on the l- and d-amino acids (alanine, phenylalanine, aspartic and glutamic acid), showed no difference in energy between l-and d-isomers. The vibrational frequencies were calculated by semi-emprical methods (PM6 and RM1) and Ab Initio methods (B3LYP/6-31+G(d) and were scaled down by factors of 0.925 (RM1), 1.09 (PM6) and 0.89 (B3LYP/6-31+G(d)). The calculated and experimental vibrational frequencies have shown good general agreement.
International Letters of Chemistry, Physics and Astronomy (Volume 15)
M. E. Mohamed and A. M.A. Mohammed, "Experimental and Computational Vibration Study of Amino Acids", International Letters of Chemistry, Physics and Astronomy, Vol. 15, pp. 1-17, 2013