Background: Thiamine hydrochloride is a vital nutrient for development, growth and variety of other body functions. It is also used as a co-factor for several enzymatic reactions. An early study showed that thiamine can form ionic salt with metals such as [Th]2+[MX4]2-, [Th]2+([MX3]-)2, or [Th+]2[MX4]2- (M = Zn2+ Co2+, Ni2+ when X = Cl-, Br- and Th = thiamine).
Methods: In this study, thiamine hydrochloride reacts with iron (II), zinc (II) and cobalt (II) to form [Fe6L2(NH3)12(H2O)12](SO4)6.10H2O, [Zn3L(H2O)6Cl3]Cl3 and [Co3L(H2O)6Cl3]Cl3 complexes, respectively. Antimicrobial activity was carried out by agar well diffusion method.
Results: Structures of these complexes were characterized by different methods like IR, EIMS and CHN analysis. The ligand and their complexes were screened for antimicrobial activities. The maximum antibacterial activity against Gram positive bacterial strains (C. xerosis 23 mm, S. aureus, and S. saprophyticus, 22 mm) was observed by Th-Zn complex. The highest antibacterial activity against Gram negative bacterial strains was observed as follows: Th-Zn complex (25 mm, S. dysenteriae), Th-Co complex (20 mm, S. paratyphi B and vibrio) and Th-Fe complex (20 mm, E. aerogene). All complexes were found to be inactive against A. flavus, A. niger. C. tropicalis, Penicillium spp., Rhizopus spp., and S. cerevisiae fungal strains, while Th-Fe and Th-Co complexes showed very weak activity against C. albican (4mm).
Conclusion: In synthetic compounds, Th-Zn complex is responsible for good antibacterial activity against Gram positive bacterial strains. However, Th-Zn, Th-Co, and Th-Fe complexes are suitable for Gram negative strains. All compounds showed no activity against tested fungal strains. Consequently, these complexes might have good potential for further studies as antiobiotics.