Quantum-Chemical Study of the Biogenic Amino Acids

Ten amino acids have been subjected to the quantum chemical calculations using the ab initio MO-LCAO-SCF calculations and semiempirical PM3 method. When the geometry optimization started form the X-ray structure confirming the zwitterionic form, the ab initio calculations in vacuo result in the amino acid (canonical) form with the hydrogen atom attached not to the amine but to the carboxylate group. At the optimum geometry a number of properties were evaluated: dipole moment, dipole polarizability, molecular surface, molecular volume, HOMO, LUMO, ionization energy and electron affinity using the ΔSCF approach and their values corrected for electron correlation by the 2 nd –order perturbation theory (MP2). In addition, the molecular electrostatic potential and the charge density have been drawn. These properties have been mutually correlated by employing the statistical multivariate methods: the cluster analysis, the probabilistic neural network classifier, the principal component analysis and the Pearson pair correlation.