Fabrication and Characterization of S-Benzyldithiocarbazate Schiff Base Microcrystals by a Reprecipitation Method for Enhanced Antibacterial Activity

Abstract

In this study, the microcrystallization of the 2-thiophenecarboxaldehyde Schiff base of S-benzyldithiocarbazate (i.e. benzyl (2E)-2-[(thiophen-2-yl)methylidene]hydrazine-1-carbodithioate [TASBnDTC]) was fabricated by a reprecipitation method in an organic solvent-water system using different crystallization parameters, including temperature and the concentration of the target compound. The size, anisotropy, crystalline phase, and surface morphology of the TASBnDTC microcrystals were characterized by dynamic light scattering and scanning electron microscopy. The stability of the Schiff base microcrystals was also evaluated. Different sizes of surfactant-dispersed TASBnDTC microcrystals (1505, 2194, and 2447 nm) were fabricated from three different concentrations of the Schiff base (0.001 M, 0.002 M, and 0.003 M, respectively) in an acetone-water system. The TASBnDTC microcrystals were also evaluated by X-ray powder diffraction and were found to differ slightly in molecular form but were otherwise similar, irrespective of the different TASBnDTC concentrations. The synthesized Schiff bases and their microcrystals were also screened for their antibacterial activities against four different grampositive and gram-negative bacterial strains (Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Staphylococcus aureus) using the agar well diffusion method. The growth inhibition was enhanced by 8.0 to 10.75 mm against the four bacteria by TASBnDTC microcrystals compared to the bulk molecular form, which showed no inhibitory activity at all. However, the inhibition was less that that achieved with the standard streptomycin antibiotic, which gave zones of inhibition of 18.0 to 23.0 mm against the four bacterial strains. Overall, the Schiff base microcrystals show potential for use in various biological applications. They also have potential physical and optical applications due to their high surface-to-volume ratio and the molecular alignment on the surface of the microcrystals.