Mono-cyclopentyl substituted [1,3,4]thiadiazole thione tautomer: study of the spectroscopic, geometric, thermal, and biological properties

Regarding the importance of thiol-thione tautomer structure and the existence of hydrogen bonding in thione tautomer structure and its effect on geometric, physicochemical, and biological properties, mono-cyclopentyl-substituted bismuthiol was synthesized via a telescopic process in a green medium. The pure product was characterized by physical and spectroscopic techniques. The suitable crystals for single crystal study were obtained after trying different solvents and mixed solvents, and long clear needle-like crystals could be isolated from a mixture of n-hexane and ethyl acetate (volume ratio of 8:2). The FTIR spectra of bismuthiol, 2,5-bis-cyclopentylsulfanyl-[1,3,4]thiadiazole, and 5-cyclopentylsulfanyl-3H-[1,3,4]thiadiazole-2-thione were studied to define the characteristic wavenumbers of thiol and thione structures. A possible hyper-conjugative interaction between the S–H and π bond of C=N, the existence of C=S and C–N–H. and stability of thione structure was demonstrated for the new product, which supports our prediction of thione or thiol structure using the study of IR spectra. Furthermore, the influence of change in 1,3,4-thiadiazol ring and the presence N–H functional group of thione structure on the transition phases and thermal stability of bismuthiol, bis-cyclopentyl-substituted, and mono-cyclopentyl-substituted bismuthiol were investigated using TGA/DTA and DSC profile analysis. The SwissADME tool was employed to predict the biocheminformatic information of bismuthiol, bis- and mono-cyclopentyl-substituted bismuthiols, which displayed high potential of all 1,3,4-thiadizole derivatives in pharmaceutical and medicine areas. Finally, an in vitro antibacterial activity of the mono- and bis-cyclopentyl substituted bismuthiol against the gram-negative (Escherichia coli ATCC 25922) and gram-positive (Staphylococcus aureus ATCC 25923) bacterial species was conducted by the disk diffusion method with cefazolin as a blank antibiotic. The results showed superior antibacterial efficiency of both derivatives.