The structure of betaxolol studied by infrared spectroscopy and natural bond orbital theory

Betaxolol is a selective β1 receptor blocker used in the treatment of hypertension and glaucoma. A study of the betaxolol structure based on infrared spectroscopy and natural bond orbital (NBO) theory is the main aim of the present research.FTIR spectra of the solid betaxolol were recorded in the region from 4000 to 400 cm−1, in the temperature range between 25 and −170 °C. For spectral interpretation, spectrum of the deuterated betaxolol and the theoretical vibrational spectra of the conformer present in the solid obtained at the B3LYP/6-31G* level of theory, were used. Further insight into the structure was provided by natural bond orbital theory. NBO analysis of the conformer, before and after optimization, was carried out at the same level of theory referred above.Vibrational modes involved in hydrogen bond in the stretching and bending region were used in the estimation of the enthalpy using empirical correlations between enthalpy and the frequency shift that occurs as a result of the establishment of intermolecular hydrogen bonds.A detailed study of the structure of betaxolol and of its intermolecular interactions was obtained from the combination spectroscopy and NBO theory.