Experimental, quantum chemical and NBO/NLMO investigations of pantoprazole

•FT-IR and FT-Raman spectra of PPZ in solid phase were recorded and analyzed.•The vibrational wavenumbers were computed using B3LYP with 6-31G (d, p) basis set.•The vibrational assignment and spectroscopic analysis have been carried out.•The HOMO, LUMO energy gap were theoretically predicted.

The complete vibrational assignment and analysis of the fundamental modes of pantoprazole (PPZ) was carried out using the experimental FT-IR, FT-Raman and UV–Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT–B3LYP gradient calculations employing 6-31G (d, p) basis set. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO–LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of PPZ have been computed using B3LYP quantum chemical calculation. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.

Graphical abstractA complete vibrational analysis of PPZ is performed by combining the experimental and theoretical information using Pulay’s density functional theory (DFT) based on scaled quantum chemical approach. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.Figure optionsDownload full-size imageDownload as PowerPoint slide