Synthesis, Kinetics, Reaction Mechanism, and Bioactivity Assays of a Dimeric Palladium Complex

A dimer of Pd(II), [(bpy)Pd(μ-OH)₂Pd(bpy)]²⁺, (complex 1) (where bpy = 2,2'-bipyridyl) has been synthesized at physiological pH (7.4) and characterized by electronic spectroscopy, electrospray ionization mass spectrometry (ESI-MS) spectroscopy, and Fourier transform infrared (FT-IR) analysis. Reaction kinetics of 1 with glycine (L¹H), l-glutamic acid (L²H), and l-arginine (L³H) were investigated in an aqueous medium at pH of 7.4 and constant ionic strength via a spectrophotometer as a function of temperature and different concentrations of substrate-complex and ligand. The interactions were supported by two discrete successive steps, i.e., ligand-dependent and ligand-independent steps. The equilibrium constant of complex formation (outer-sphere association) and the rate constant during complex-substrate-ligand interaction were calculated. The Eyring equation was applied to evaluate activation factors (ΔH^‡ and ΔS^‡), and associative mechanisms of all reactions were proposed. Thermodynamic parameters (ΔH° and ΔS°) were also estimated from the standard plot of ln K_E against 10³/T. Spectroscopic titration of 1 at pH 7.4 in Tris-HCl buffer with calf thymus DNA, electronic emission titration with ethidium bromide (EtBr), antimicrobial activities, and an agarose gel electrophoresis run of 1 on pBR322 plasmid DNA have shown strong evidence of anticancer activity. Moreover, it has nontoxic water molecules as leaving groups.