New Bis-1,3,4-Thiadiazoles Based on Fumaric Acid: Preparation, Structure Elucidation, Antibacterial Activities, and Quantum-Chemical Studies

Abstract

New bis-1,3,4-thiadiazoles (1-7) were obtained by the reaction of fumaric acid and N-(alkyl/aryl/cyclic)thiosemicarbazides in the presence of  phosphorous oxychloride. The structures of all compounds were elucidated by FT-IR, ¹H NMR, and ¹³C NMR and elemental methods. Antibacterial activity of the compounds was studied for eight selected bacteria. Compounds (2-7) exhibited effect on K.pneumoniae. However, none of the compounds effect on P.aeruginosa, S. epidermidis, S. Kentucky, S. macrescens. Self-consistent reaction force (SCRF) calculations were performed in DMSO medium to examine solvent energies using CPCM and SMD models. 6-31G(d) and 6-311++G(2d,2p) basis sets were used for DFT calculations. Besides electronic parameters such as electronegativity, electrophilicity and spectroscopic examinations of the compounds, QTAIM, local electron affinities, and Fukui analyzes were also performed. Theoretical approaches supporting the experimental observations revealing that compounds containing aromatic and cyclic groups exhibit stronger antibacterial behavior than compounds containing aliphatic groups are detailed.