Raman and IR Spectral and DFT Based Vibrational and Electronic Characterization of Isolated and Zwitterionic Forms of L-Tyrosine

Abstract

Comparative structural and vibrational investigations in two different forms of the L-Tyrosine (L-TYR) have been carried out using Raman and IR spectral and DFT methods. For the optimized structures of the most stable conformers the vibrational assignments of the experimental IR and Raman bands have been proposed using the results of the DFT-B3LYP computations and the PEDs computed using GAR2PED software. The optimized geometrical structures of the molecule belong to the C1 point group in the zwitterionic and isolated forms of the molecule. Possibility of the charge transfer phenomena in the molecule has been investigated in light of the HOMO–LUMO analysis. The electron density mappings of the iso-surfaces with the molecular electrostatic potential (MEP) have been carried out to obtain the different information associated with the size, shape, charge density distribution and site of chemical reactivity of the molecule. On the basis of the NBO analysis presence of intramolecular H bonding and intramolecular charge transfer (ICT) have been proposed.