Vibrational studies of Thyroxine hormone: Comparative study with quantum chemical calculations

The FTIR and Raman techniques have been used to record spectra of Thyroxine. The stable geometrical parameters and vibrational wave numbers were calculated based on potential energy distribution (PED) using vibrational energy distribution analysis (VEDA) program. The vibrational energies are assigned to monomer, chain dimer and cyclic dimers of this molecule using the basis set B3LYP/LANL2DZ. The computational scaled frequencies are in good agreements with the experimental results. The study is extended to calculate the HOMO-LUMO energy gap, Molecular Electrostatic Potential (MEP) surface, hardness (eta), chemical potential (mu), Global electrophilicity index (omega) and different thermo dynamical properties of Thyroxine in different states. The calculated HOMO-LUMO energies show the charge transfer occurs within the molecule. The calculated Natural bond orbital (NBO) analysis confirms the presence of intra-molecular charge transfer as well as the hydrogen bonding interaction. (C) 2017 Elsevier B.V. All rights reserved.