Computational Studies of Vibration Spectra and Thermodynamic Properties of Metformin Using HF, DFT Methods

Abstract

The molecular vibrations of metformin, one of the important anti-diabetic drugs to treat Non Insulin Dependent Diabetes Mellitus (NIDDM) have been investigated at room temperature by Fourier transform infrared (FTIR) and Fourier transform Raman (FTR) spectroscopies. The solid phase FTIR and FT-Raman spectra of the title compound have been recorded in the regions 4000-400 and 3500-250 cm-1. A satisfactory band assignment has been made on the fundamental modes of vibration. Employing the ab - initio Hatree –Fock (HF) and Density Function Theory (DFT) methods, the theoretical vibrational frequencies and geometry parameters like bond lengths, bond angles etc have been calculated and compared with the experimental values. HF and DFT calculations were performed using the standard B3LYP/6-31G** method and basis set combination. Optimized geometries were obtained using the global optimization procedure. Theoretical investigations of harmonic vibrational frequencies and thermodynamic properties viz. the zero point vibrational energy (ZPVE), entropy, heat capacity have been carried out. It has been found that both methods gave consistent data for geometric parameters, but DFT yielded vibrational frequencies much closer to the experimental values.