New di- and triorganotin(IV) carboxylates derived from a Schiff base: synthesis, characterization and in vitro antimicrobial activities

A new carboxylic acid, 2-{[5-(2-nitrophenyl)furan-2-yl]methyleneamino}benzoic acid (HOBZ), has been produced by reacting 5-(2-nitrophenyl)furfural with 2-aminobenzoic acid. Reactions of NaOBZ with organotin chlorides led to formation of [Me3Sn(OBZ)] (1), [Bu3Sn(OBZ)] (2), [Me2Sn(OBZ)(2)] (3) and [Bu2Sn(OBZ)(2)] (4). Complexes 1, 2, 3, 4 have been characterized using elemental analyses and infrared, H-1 NMR, C-13 NMR, Sn-119 NMR and Sn-119 Mossbauer spectroscopies. In the solid state, the OBZ ligands might coordinate to tin in an anisobidentate fashion via the carboxylate group. The in vitroantimicrobial activity of all compounds has been screened against the following fungi: Aspergillus niger, A. flavus, A. parasiticus, Penicillium citrinum, Candida dubliniensis, C. lusitaniae, C. albicans, C. tropicalis, C. parapsilosis and C. glabrata; and against the following bacteria: Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, Streptococcus sanguinis, Escherichia coli, Citrobacter frendii, Salmonella typhimurium and Pseudomonas aeruginosa. Complexes 2 and 4 exhibited higher biocide activity in comparison to 1 and 3 and to the control drugs nystatin and miconazole nitrate for the yeasts, and chloramphenicol and ampicillin for the bacteria. The biological activity of 2 was superior to that of 4. In addition, the toxicity of HOBZ, NaOBz and 1, 2, 3, 4 were determined using Chlorella vulgaris, revealing low toxicity of the complexes at MIC50 concentrations. We also performed cell viability studies, using XTT assay, displaying no change in the mitochondrial function after 2-4h of exposure of the microorganism to the complexes at MIC50 concentrations. The butyl-containing complexes 2 and 4 display greater lipophilicities than do the methyl analogues 1 and 3, thereby endowing 2 and 4 with superior abilities to cross the microbe cell membrane, the possible mechanism of action. Copyright (c) 2015 John Wiley & Sons, Ltd.