Quantum chemical, vibrational, microhardness, thermal and antibacterial studies on polymorphic drug crystal: Sulfanilamide (β-form)

Abstract

The widely known pharmaceutical drug compound, Sulfanilamide, crystallized in the β-form of its polymorphic phases by slow evaporation of the parent solution at room temperature. The single crystal X-ray diffraction study provided information about the cell parameters, confirming the β-phase of the compound. Optimization of the molecule by quantum chemical computations, viz., Hartree-Fock (HF) Theory and Density Functional Theory (DFT) using the B3LYP function with 6–311++G(d,p) basis set for both in restricted methods were carried out. The Frontier Molecular Orbital studies gave the HOMO and LUMO values, and Mulliken charge analysis showed the possible charge delocalization and donor-acceptor sites. Vibrational bands of the functional groups present in the β-Sulfanilamide compound were identified and investigated using FT-IR and FT-Raman spectroscopy in the range of 4000–400 cm−1. The grown crystal was transparent in the entire UV region with a lower cut off wavelength of 241 nm as investigated by the UV–Vis-NIR analysis. Thermogravimetric and differential thermal analyses of the compound were carried out and the results were plotted as TGA/DTA graph. Microhardness tests were used to determine the mechanical parameters of this pharmaceutical compound. Sulfanilamide, a well-known antibacterial agent and used to treat a variety of bacterial infections, was tested using the zone inhibition method and the antibacterial activity was confirmed.