PREPARATION, CHARACTERIZATION AND ANTIBACTERIAL STUDIES OF HYDRAZONE SUBSTITUTED MOLYBDENUM CARBONYLS

Abstract

The hydrazones; (E)-N'-(3-methoxybenzylidene)nicotinohydrazide (ANH) and (E)-N'-(2-hydroxybenzylidene)isonicotinohydrazide (SIH) were prepared by condensation reaction between either m-anisaldehyde or salicylaldehyde with nicotinic hydrazide and isoniazid respectively. Substituting CO in Mo hexacarbonyl with the hydrazones in the presence of trimethylamine N-oxide as decarbonylating agent at ambient temperature under inert atmosphere produced tricarbonyl constituents. The complexes were characterized via spectroscopic techniques, elemental analysis and evaluated for antibacterial mode and action. FTIR/Raman, 1H and 13C MMR spectra obtained revealed that three CO were substituted for hydrazones in the hexacarbonyl, consistent with CHN elemental analysis. The ancillary ligands coordinate through the pyrimidine nitrogen to the Mo centre in a meridional geometry; Mo(CO)3(ANH)3 and Mo(CO)3(SIH)3. The coordination mode afforded a fairly stable complex which released CO in DMSO with release rate of 1.9 × 10-3 and 1.07 × 10-2 kCO) s-1. Examination of compounds ability to release CO to myoglobin under physiological pH revealed that carbonmonoxyhemoglobin was spontaneously formed at 3 to 4 seconds of introduction of the complexes. Antibacterial action against both Gram-negative and -positive bacteria revealed that Mo(CO)3(ANH)3 shows both bacteriostatic and bactericidal action against E coli, S. aureus and P. aeruginosa with activity comparable to the ampicillin control. The Mo(CO)3(SIH)3 analogue was however not effective in inhibiting the growth of the organisms at concentrations below 1000 µM . The methoxy and hydroxyl group on the ligand is suspected to account for the differences in action. The hydrophilic hydroxyl group in Mo(CO)3(SIH)3 can hinder it cell wall penetrating ability compared to the lipophilic group present in Mo(CO)3(ANH)3.