Comparing vibrational spectra of free bumetanide and its solutions

Bumetanide, which is known as a potent diuretic, is currently under investigation for its potential anti-epileptic effects in neonatal seizures. The purpose of this study was to examine the molecular structure of bumetanide both in the free form and its solutions via vibrational spectra (FT-IR, FT-Raman spectroscopies) and quantum chemical calculations. FT-IR and FT-Raman spectra of the title compound were recorded for the solid phase and the solutions of DMSO and ethanol. Optimized molecular geometry and vibrational wavenumbers of bumetanide were calculated by DFT/B3LYP functional with 6-31G(d,p), 6-31G++(d,p) and 6-311++G(d,p) basis sets. The assignment of the vibrational modes were performed based on total energy distribution (TED). The same calculations were performed for the molecule in DMSO and ethanol solutions using the polarizable conductor continuum model (CPCM) method. Lastly, probable donor-acceptor interactions of the molecule were examined with NBO analysis in different media. In all forms of bumetanide (the free molecule and the other solvents), some significant changes were observed in the dihedral angles and the vibrational frequencies.