Antimicrobial, antioxidant and DNA-binding studies of palladium(II) complexes with different chelate ligands containing nitrogen donor atoms

Abstract

The antimicrobial and antioxidant activities, as well as the DNA-bin­ding of four square-planar Pd(II) complexes, [Pd(terpy)Cl]+ (C1), [Pd(en)Cl2] (C2), [Pd(DMEAImiPr)Cl2] (C3) and [Pd(dach)Cl2] (C4) (terpy = 2,2′:6′,2′′-terpyridine, en = ethylenediamine, dach = trans-1,2-diaminocyclohexane and DMEAImiPr = N²-((1,3-dihydro-1,3-diisopropyl-4,5-dimethyl)-2H-imidazol-2-ylidene)-N¹,N¹-dimethyl-1,2-ethanediamine are reported. The antimicrobial activities of the Pd(II) com­plexes with the appropriate ligands were tested using the microdilution method against 18 strains of microorganisms, whereby the minimal inhibitory concen­tration (MIC) and the minimal microbicidal concentration (MMC) were deter­mined. The antibiofilm activity of [Pd(terpy)Cl]+ and the corresponding ligand were determined on a formed biofilm. The intensity of antimicrobial activity varied depending on the type of microorganism and the tested compound. The C1 complex with the corresponding ligand demonstrated significantly greater overall antimicrobial activity than C2, C3 and C4. The antibacterial activity of the C1 complex was better than its antifungal activity that was overall greater than that of the positive control, fluconazole. The greatest sensitivity for C1 and L1 was with Penicillium italicum (MIC < 0.49 μg mL-1) among the fungi, and with Proteus mirabilis ATCC 12453 (MIC = 0.98 μg mL-1) among the tested bacteria. The tested compounds show low and moderate antibiofilm activity. The com­plexes showed weak antioxidant properties when tested using the DPPH (1,1-diphenyl-2-picrylhydrazyl) method. The interaction of the metal complexes C1–C4 with calf thymus DNA (CT-DNA) was further examined by absorption (UV–Vis) and emission spectral studies (EthBr displacement studies). Overall, the investigated complexes exhibited good DNA interaction ability.