Ordering selected Zn(II), Cu(II), Pd(II) and Co(III) complex compounds: their separately and combinedly antibacterial therapy and DNA-binding studies.

In this study, four Co(III)-, Cu(II)-, Zn(II)- and Pd(II)-based potent antibacterial complexes of formula K ₃ [Co(ox) ₃ ]·3H ₂ O ( I ), [Cu(phen) ₂ Cl]Cl·6.5H ₂ O ( II ), [Zn(phen) ₃ ]Cl ₂ ( III ) and [Pd(phen) ₂ ](NO ₃ ) ₂ ( IV ) (where ox is oxalato and phen is 1,10-phenanthroline) were synthesized. They were characterized by elemental analysis, molar conductivity measurements, UV-vis, Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ( ¹ H-NMR) techniques. These metal complexes were ordered in three combination series of I + II , I + II + III and I + II + III + IV . Antibacterial screening for each metal complex and their combinations against Gram-positive and Gram-negative bacteria revealed that all compounds were more potent antibacterial agents against the Gram-negative than those of the Gram-positive bacteria. The four metal complexes showed antibacterial activity in the order I > II > III > IV , and the activity of their combinations followed the order of I + II + III + IV > I + II + III > I + II . The DNA-binding properties of complex ( I ) and its three combinations were studied using electronic absorption and fluorescence (ethidium bromide displacement assay) spectroscopy. The results obtained indicated that all series interact effectively with calf thymus DNA (CT-DNA). The binding constant ( K _b ), the number of binding sites ( n ) and the Stern-Volmer constant ( K _sv ) were obtained based on the results of fluorescence measurements. The calculated thermodynamic parameters supported that hydrogen bonding and van der Waals forces play a major role in the association of each series of metal complexes with CT-DNA and follow the above-binding affinity order for the series. Communicated by Ramaswamy H. Sarma.