Antibacterial activity of transition metal complexes containing a tridentate NNO phenoxymethylpenicillin-based Schiff base. An anti-MRSA iron (II) complex

Transition metal complexes containing a phenoxymethylpenicillin-derived Schiff base (HL) 3 obtained from the condensation of phenoxymethylpenicillin (PMP) 1, with 1,2-diaminobenzene 2, were prepared. Spectroscopic and physicochemical techniques, namely, UV–Vis, FT-IR, ¹ H-NMR, EPR, mass spectrometry, magnetic susceptibility, molar conductance, DFT studies, together with elemental and thermal analyses were used to characterize the synthesized complexes. Based on the characterization studies, the general formulae [ML (OAc)(H ₂ O) ₂ ] where M = Fe 4, Co 5, Ni 6, Cu 7, and Zn 8, were proposed for the complexes. The Schiff base ligand 3 behaved as a monoanionic tridentate NNO chelating agent. On the basis of magnetic and spectral data an octahedral geometry for all the complexes was suggested. Schiff base ligand 3, and the metal complexes 4–8 were tested against G(+) or bactericidal activity by agar disc diffusion method and minimal inhibitory concentration (MIC). The results were compared with the activity of the standard drug PMP 1. In vitro bacterial viability revealed that 3 had similar activity than 1 and exhibited modification in its bactericidal activity when formed metal complexes. It was found that the complexes 4, 6 and 7 exhibited much better bactericidal activity than 1 against methicillin-resistant Staphilococcus Aureus (MRSA) being complex 4 the most promising compound showing a MIC value of 0.042 μmol/ml.