Search for new antimicrobials: spectroscopic, spectrometric, and in vitro antimicrobial activity investigation of Ga(III) and Fe(III) complexes with aroylhydrazones.

The in vitro antimicrobial activity of Fe(III) and Ga(III) complexes with N'-(2,3-dihydroxy-phenylmethylidene)-3-pyridinecarbohydrazide (H2L1), N'-(2,4-dihydroxy-phenyl-methylidene)-3-pyridinecarbohydrazide (H2L2), N'-(2,5-dihydroxy-phenylmethylidene)-3-pyridinecarbohydrazide (H2L3), N'-(2-hydroxy-3-methoxyphenyl-methylidene)-3-pyridine-carbohydrazide (H2L4), N'-(2-hydroxy-4-methoxyphenylmethyl-idene)-3-pyridine-carbohydrazide (H2L5), and N'-(2-hydroxy-5-methoxyphenylmethylidene)-3-pyridinecarbo-hydrazide (H2L6) toward several Gram-positive strains of Staphylococcus aureus, a Gram-negative strain of Escherichia coli, and a yeast Candida albicans were investigated. Fe(III)-complexes do not possess antimicrobial activity against all tested strains at concentrations up to 10 mg mL-1. Ga(III) complexes with dihydroxy derivatives showed selective activity, while the broadest range of antibacterial and antifungal activities was observed for complex with 2-hydroxy-3-methoxy-derivative, ligand H2L5. In addition, the coordination properties of ligands H2L1-H2L3 in solution were investigated by UV-Vis spectroscopy. The stability constants (logK) for Ga(III)-H2L 1:1 complexes in MeOH/H2O 1/1 at pH 2.52 were determined, and amounted to 5.8, 5.68, and 4.7, respectively. Detailed characterization of complexes was performed by high-resolution mass spectrometry. The fragmentation pathways for dimer [Fe2(L1)2]2+, [Fe(HL)2]+, [Ga(HL2)2]+ and adduct ions are given. The comparison with analogue Ga(III) and Fe(III) complexes with compounds H2L4-H2L6 was made as well.