Structural Properties of Ricobendazole and Cefradine using Vibrational Spectroscopy and Quantum Chemical Methods

Abstract

This research aims to analyse the structural, electronic and the vibrational features of ricobendazole (RBZ) and cefradine based on spectroscopic and quantum chemical approach. The basic structural properties of RBZ and cefradine have been examined based on optimized geometry, spectroscopic activity, intermolecular interaction, chemical reactivity, intramolecular hydrogen bonding and molecular docking analysis. The infra-red (IR) spectra of the RBZ and the cefradine have been recorded in the solid form of sample in which the pellet was prepared by mixing the KBr and white crystalline powder of the sample (RBZ and cefradine). The Fourier transform infrared (FT-IR) spectra has been listed in the order of (400 to 4000) cm −1 with a resolution of 4 cm , whereas the Raman spectra of the RBZ and the cefradine sample have been listed in the order (100 to 3500) cm −1 . The 96 normal modes of vibration of the RBZ and 123 normal modes of vibration of the cefradine were calculated by using the Gar2Ped program from Pulay’s recommendations along with their potential energy distribution (PED) by using the density functional theory (DFT) from the B3LYP/6-311++G(d,p) level of calculation. The comparison of simulated spectra with the observed spectra was carried out, which identifies the inter molecular hydrogen bonding in compact (solid) form in terms of red and blue shift. The minimum energy conformers of these molecules were identified by performing one-dimensional potential energy surface (PES) scan along the flexible bonds at B3LYP/6-311++G(d,p) level of calculation. The vibrational features of the molecules along with the potential energy distribution across the various modes of vibrations have been calculated. The chemical reactivity and stability of all the favorable conformers of RBZ and cefradine were predicted on the basis of energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) (i.e., HOMO-LUMO energy gap) and the natural bond orbital (NBO) procedure. The distribution of charges on the particular atoms of the molecule were calculated by molecular electrostatic potential (MEP) surface map which identifies the nucleophilic and the electrophilic regions. The quantitative investigation of the electrophilicity and the nucleophilicity indices was done by Hirshfeld charge analysis. The non-linear optical (NLO) activity of these molecules has been analyzed which motivates about the potential use of the molecules as NLO material. The variation of the thermodynamic parameters like: entropy, enthalpy and specific heat capacity with temperature have been explored. The Quantum theory of atoms in molecule (QTAIM) study is used to analyze the quality and the strength of the hydrogen bonding interactions. Furthermore, the molecular docking analysis were performed to investigate the active binding v −1 sites of the drug molecules with the predicted protein targets. Similarly, the structural stability and the fundamental chemical reactive sites of the frovatriptan molecule has been examined from the structural evaluation and the quantum chemical calculation technique. The conformational analysis was performed across the flexible bonds to indicate the most stable conformers from the DFT at B3LYP/6311++G(d,p) level of calculation. The chemical reactivity has been demonstrated in terms of the frontier molecular orbitals (HOMO-LUMO) energy gap, the MEP surface and the global reactivity. The local reactivity descriptors give an explanation about the donor, the acceptor and the free radical reactive sites present in the frovatriptan molecule. Furthermore, the NBO analysis was performed to study the interactions between the bonding and the anti-bonding orbitals. The expected use of the frovatriptan as NLO substance and the variation of the thermodynamic parameters like: entropy, enthalpy and specific heat capacity with temperature have been calculated. The druglikeness properties of frovatriptan have also been studied. Furthermore, the molecular docking with the expected targets has been performed to analyse the protein-ligand interaction as well as to predict the active sites of the drug molecule.