Comparative structural and vibrational study of the two low energy conformers of neurotransmitter molecule: Norepinephrine [(R)-4-(2-amino-1-hydroxyethyl) benzene-1, 2-diol]

Abstract

A computational investigation of the two lowest energy conformers of norepinephrine has been carried out at the level B3LYP using the basis set 6-311++G**. Out of the 11 possible lowest energy conformers, the two lowest energy conformers have been investigated thoroughly for the optimized geometries, fundamental frequencies, PEDs, APT charges, natural bond orbital (NBO) analysis, MEP, contour map, total density array, HOMO-LUMO energies. The second conformer is energetically at higher temperature by 293 K with respect to the first conformer. The bond angles and lengths do not show much variation while the dihedral angles vary significantly in going from conformer first to the conformer second. Some of the vibrational modes of the benzene moiety are conformation dependent to some extent whereas most of the normal modes of vibration of ethanolamine side chain vary significantly in going from one conformer to the other one. The MEP for the two lowest energy conformers suggests that the sites of the maximum positive and negative ESP change on changing the conformation. The atomic charges have also changed significantly from conformer C-I to the conformer C-II.