Palladium(II) and platinum(II) complexes of deprotonated N,N′-bis(2-pyridinecarboxamide)-1,2-benzene: Synthesis, structural characterization and binding interactions with DNA and BSA

Two neutral complexes [ML] (where M = Pd (1a) and Pt (1b), L = bis(pyridine-2-carboxamide)benzene dianion) have been synthesized and characterized by physico-chemical and spectroscopic tools along with the detailed structural analysis by single crystal X-ray crystallography and theoretical (DFT) study. In solid state the compounds are isomorphous and isostructural showing the formation of [ML]3.3H2O trimeric species. Electrochemical study of 1a showed a quasi-reversible reductive response at E1/2 = -1.148 V assignable to the Pd(II)/Pd(I) couple, while a metal centered irreversible oxidative peak centred at +0.977 V was observed in the voltammogram of 1b. The interaction of the complexes with CT-DNA has been investigated using spectroscopic tools and viscosity measurement. In each case the association constant (Kb) was deduced from the absorption spectral study and the number of binding sites (n) and the binding constant (K) were calculated from relevant fluorescence quenching data, suggesting a non-covalent interaction between the metal complex and DNA, which could be assigned to an intercalative binding. In addition, the interaction of 1a and 1b was ventured with bovine serum albumin (BSA) with the help of absorption and fluorescence spectroscopy measurements. Through these techniques, the apparent association constant (Kapp) and the binding constant (K) could be calculated for each complex.