Synthesis, characterisation, DNA and antibacterial activities of cu(I) complexes of bidentate quinolinyl Schiff base having triphenylphosphine ancillary ligand

Abstract

This work synthesized new biologically active Cu(I) complexes C1-C3, obtained from the reaction of Cu(I) nitrate with different bidentate quinolinyl Schiff base ligands (E)-N-(4-bromophenyl)-1-(quinolin-2-yl)methanimine, L1 ; (E)-N-(4-chlorophenyl)-1-(quinolin-2-yl)methanimine, L2 and (E)-1-(quinolin-2-yl)-N-(p-tolyl)methanimine, L3 with PPh3 ancillary ligand. The metal complexes with general formula [Cu L(PPh3)]NO3, were characterised by UV-Vis, FT-IR, NMR and MS, TGA/DTA and X-ray crystallography. The affinities of complexes to calf thymus-deoxyribuonucleic acid (CT-DNA) were investigated using and UV-Vis spectrometer and in vitro antibacterial activities against Staphylococcus aureus (SA), Escherichia coli (EC), Klebsiella pneumonia (KP) and Pseudomonas aeruginosa (PA) were investigated using agar well diffusion method with ofloxacin as reference. UV-Visible spectra revealed that ligands imino π → π* transition shifted to longer wavelengths consequent upon coordination to the copper centre. FT-IR result showed bathochromic shift in the imino (C=N) frequencies in the complexes further confirming coordination to the metal centre. The TGA results showed high stability, consistent with the mass spectra of the various m/z of all the complexes and PPh₃ fragments. Novel single crystals obtained in complexes C2 and C3 revealed monoclinic crystal systems depicting distorted tetrahedral geometries. Coordination to the metal center was bidentate for all the ligands through the pyridinyl N and imine N in conjunction with triphenylphosphine. In vitro antibacterial studies revealed that all the complexes exhibited stronger antibacterial activity relative to their parent ligands and PPh₃. The study found out that the metal complexes have better DNA binding and antibacterial performances hence could be used as potential chemotherapeutic agents.