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 K₃[Co(ox)₃]·3H₂O (I), [Cu(phen)₂Cl]Cl·6.5H₂O (II), [Zn(phen)₃]Cl₂ (III) and [Pd(phen)₂](NO₃)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 (¹H-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.

Nonionic but water soluble, [Glycine-Pd-Alanine] and [Glycine-Pd-Valine] complexes. Their synthesis, characterization, antitumor activities and rich DNA/HSA interaction studies

Two novel, neutral and water soluble Pd(II) complexes of formula [Pd(Gly)(Ala)] (1) and [Pd(Gly)(Val)] (2) (Gly, Ala, and Val are anionic forms of glycine, alanine, and valine amino acids, respectively) have been synthesized and characterized by FT-IR, UV-Vis, ¹H-NMR, elemental analysis, and molar conductivity measurement. The data revealed that each amino acid binds to Pd(II) through the nitrogen of -NH₂ and the oxygen of -COO^- groups and acts as a bidentate chelate. These complexes have been assayed against leukemia cells (K₅₆₂) using MTT method. The results indicated that both of the complexes display more cytotoxicity than the well-known anticancer drug, cisplatin. The interaction of the compounds with calf thymus DNA (CT-DNA) and human serum albumin (HSA) were assayed by a series of experimental techniques including electronic absorption, fluorescence, viscometry, gel electrophoresis, and FT-IR. The results indicated that the two complexes have interesting binding propensities toward CT-DNA as well as HSA and the binding affinity of (1) is more than (2). The fluorescence data indicated that both complexes strongly quench the fluorescence of ethidium bromide-DNA system as well as the intrinsic fluorescence of HSA via static quenching procedures. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) calculated from the fluorescence studies showed that hydrogen bonds and van der Waals interactions play a major role in the binding of the complexes to DNA and HSA. We suggest that both of the Pd(II) complexes exhibit the groove binding mode with CT-DNA and interact with the main binding pocket of HSA. Communicated by Ramaswamy H. Sarma.

Palladium(II) complexes of biorelevant ligands. Synthesis, structures, cytotoxicity and rich DNA/HSA interaction studies

In this work, a pair of new palladium(II) complexes, [Pd(Gly)(Phe)] and [Pd(Gly)(Tyr)], (where Gly is glycine, Phe is phenylalanine, and Tyr is tyrosine) were synthesized and characterized by UV-Vis, FT-IR, elemental analysis, ¹H-NMR, and conductivity measurements. The detailed ¹H NMR and infrared spectral studies of these Pd(II) complexes ascertain the mode of binding of amino acids to palladium through nitrogen of -NH₂ and oxygen of -COO^- groups as bidentate chelates. The Pd(II) complexes have been tested for in vitro cytotoxicity activities against cancer cell line of K₅₆₂. Interactions of these Pd(II) complexes with CT-DNA and human serum albumin were identified through absorption/emission titrations and gel electrophoresis which indicated significant binding proficiency. The binding distance (r) between these synthesized complexes and HSA based on Forster's theory of non-radiation energy transfer were calculated. Alterations of HSA secondary structure induced by complexes were confirmed by FT-IR measurements. The results of emission quenching at three temperatures have revealed that the quenching mechanism of these Pd(II) complexes with CT-DNA and HSA were the static and dynamic quenching mechanism, respectively. Binding constants (K_b), binding site number (n), and the corresponding thermodynamic parameters were calculated and revealed that the hydrogen binding and hydrophobic forces played a major role when Pd(II) complexes interacted with DNA and HSA, respectively. We bid that [Pd(Gly)(Phe)] and [Pd(Gly)(Tyr)] complexes exhibit the groove binding with CT-DNA and interact with the main binding pocket of HSA. The complexes follow the binding affinity order of [Pd(Gly)(Tyr)] > [Pd(Gly)(Phe)] with CT-DNA- and HSA-binding.