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

•The polymorphic phase (β-form) of the drug molecule, sulfanilamide, was successfully synthesized and the single crystal diffraction studies were carried out to confirm the crystalline phase.•Quantum chemical methods were adopted to optimize the molecule and structural bond geometries were compared between the methods.•Further, vibrational spectra were computed and experimental counterparts were recorded and compared. The shifting of bands due to the intermolecular interactions were also narrated.•HOMO-LUMO analysis was also attempted and the nature of the molecule was identified.•Mechanical and thermal analyses were carried out and suitability of the compound for pharmacological applications were discussed with antibacterial study. 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.