THEORETICAL STUDY OF THE CARNOSINE N1H TAUTOMER IN THE ZWITTERIONIC FORM

Abstract

. In the present work, the spatial and electronic structures of the lowest energy conformation of the carnosine N1H tautomer in the zwitterionic form, which has a wide range of applications, have been studied. The calculations were performed by the DFT quantum-chemical method based on the B3LYP hybrid functional and the 6-31+G(d,p) basis set in gas, water, and DMSO using the Gaussian 09 and GaussView 6.0.16 programs. The geometry parameters, values of electronic energy, dipole moments, values of partial charges on atoms, HOMO and LUMO energies, descriptors of reactivity of a molecule were calculated and NBO analysis is carried out. The molecular electrostatic potential (MEP) maps and frontier orbitals were visualized. The structural and electronic rearrangements in the molecule and changes in various parameters depending on the dielectric constant of the medium were analyzed. It was found that the influence of the solvent does not play a significant role for this structure, very similar results were obtained for the aqueous medium and DMSO. However, the optimization of the geometry of this carnosine zwitterion tautomer in the gas phase, led to the elimination of the hydrogen atom from the terminal NH3+ group and its addition to the COO- group, actually converting the zwitterionic form into a neutral one.