DNA-binding, spectroscopic and antimicrobial studies of palladium(II) complexes containing 2,2′-bipyridine and 1-phenylpiperazine

With the purpose of evaluating the ability of Pd(II) complex to interact with DNA molecule as the main biological target, two new complexes [Pd(bpy)(OH2)2] (1) and [Pd(Phenpip)(OH2)2] (2), where (bpy = 2,2′-bipyridine; Phenpip = 1-phenylpiperazine), have been synthesized and the binding properties of these complexes with CT-DNA were investigated. The intrinsic binding constants (Kb) calculated from UV–Vis absorption studies were 3.78 × 103 M−1 and 4.14 × 103 M−1 for complexes 1 and 2 respectively. Thermal denaturation has been systematically studied by spectrophotometric method and the calculated ΔTm was nearly 5 °C for each complex. All the results suggest an electrostatic and/or groove binding mode for the interaction between the complexes and CT-DNA. The redox behavior of the two complexes in the absence and in the presence of calf thymus DNA has been investigated by cyclic voltammetry. The cyclic voltammogram exhibits one quasi-reversible redox wave. The change in E1/2, ΔEp and Ipc/Ipa supports that the two complexes exhibit strong binding to calf thymus DNA. Further insight into the binding of complexes with CT-DNA has been made by gel electrophoresis, where the binding of complexes is confirmed through decreasing the intensity of DNA bands. The two complexes have been screened for their antimicrobial activities using the disc diffusion method against some selected Gram-positive and Gram-negative bacteria. The activity data showed that both complexes were more active against Gram-negative than Gram-positive bacteria. It may be concluded that the antimicrobial activity of the compounds is related to cell wall structure of bacteria.

Graphical abstract[Pd(bpy)(OH2] (1) and [Pd(Phenpip)(OH2) (2) where, (bpy = 2,2′-bipyridine; Phenpip = 1-phenylpiperazine) have been synthesized and characterized on the basis of elemental analysis. The interaction of these complexes with calf thymus DNA was extensively investigated by a variety of techniques, viz. spectroscopic, electrochemical, ethanol precipitation and gel electrophoresis. All studies showed that both complexes presumably intercalate in DNA by electrostatic and/or groove binding mode. The calculated binding strength (Kb) of the two complexes to CT-DNA was estimated to be of lower magnitude than that of the classical intercalator EB (Ethidium bromide) (Kb = 1.23(±0.07) × 105 M−1) supporting the electrostatic and/or groove binding mode. The antimicrobial tests showed that both complexes exhibited antimicrobial properties, and they were found to be more active against Gram-negative than Gram-positive bacteria.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Two new complexes [Pd(bpy)(OH2] (1) and [Pd(Phenpip)(OH2)] (2) have been synthesized. ► The binding properties of the two complexes with CT-DNA were investigated. ► The intrinsic binding constants Kb have been calculated. ► The mode of binding is an electrostatic and/or groove one. ► Our complexes may act as model anticancer agents.