Redox Behavior and DNA Binding Studies of Some Electroactive Compounds

Abstract

The redox behavior of four biologically important compounds; Na-salt of 2-methyl -3-(4-nitrophenyl)acrylate, dimethyl-2-oxoglutarate, camptothecin and lumazine was studied by cyclic, square wave and differential pulse voltammetry on a glassy carbon electrode in different pH media. The voltammetric response of Na-salt of 2-methyl -3-(4-nitrophenyl)acrylate revealed 2e - , 2H + pH dependent reduction process leading to the formation of an electroactive reduction product that strongly adsorbed at the electrode surface. The electrochemical reduction of dimethyl-2-oxoglutarate followed 1e - , 1H + irreversible diffusion-controlled process that occurred in cascade mechanism. The redox signals of camptothecin and lumazine were also examined in a wide pH range. On the basis of the results obtained the redox mechanisms were proposed with the objective of providing useful insights into the pathways by which such compounds exert their biochemical actions. Cyclic voltammetry (CV) and UV-Vis spectroscopy were used to probe the interaction of some potential anticancer ferrocenes and organotins with DNA. The ferrocene moiety serves as spectroscopically active chromophore, biological marker and redox active site with accessible potential range, established antiproliferative effects, thermodynamic and kinetic characteristics. In the present work four ferrocene derivatives i.e., protonated ferrocene, 4-nitrophenylferrocene, 1-ferrocenyl-3-phenyl-2-propen-1-one and 1-ferrocenyl-3-(4-nitrophenyl)-2-propen-1-one were investigated with the objective of understanding the mechanism by which they interact with DNA and exercise their biological effects. Spurred by the anti-tumor activity, structural diversity and biological applications of organotin(IV) complexes the mode of interaction and binding strength of diorganotin(IV) complexes [Cl(C 4 H 9 ) 2 Sn(L)], [Cl(C 2 H 5 ) 2 Sn(L)] and [(C 6 H 5 ) 2 Sn(L) 2 ], where L is 4-(4-nitrophenyl)piperazine-1-carbodithioate, with DNA were examined by CV and UV-Vis absorption titration. The results revealed that the binding constant, binding site size and Gibbs free energy vary in the sequence: [(C 6 H 5 ) 2 Sn(L) 2 ]> [Cl(C 4 H 9 ) 2 Sn(L)]>[Cl(C 2 H 5 ) 2 Sn(L)]. The electrochemical, kinetic and thermodynamic parameters of diorganotin(IV) derivatives of ONO tridentate Schiff base, [(C 6 H 5 ) 2 Sn(L) 2 ], [(CH 3 ) 2 Sn(L) 2 ] and ii[(C 4 H 9 ) 2 Sn(L) 2 ] where L = [N-(2-oxidobenzylidene)-N-(oxidomethylene)hydrazine] interacting with DNA were also evaluated by CV and UV-Vis spectroscopy. The results revealed the following order of binding strength: [(C 4 H 9 ) 2 Sn(L) 2 ]>[(C 6 H 5 ) 2 Sn(L) 2 ]>[(CH 3 ) 2 Sn(L) 2 ] with binding affinity more than penta and hexa-coordinated diorganotin(IV) 4-(4-nitrophenyl) piperazine-1-carbodithioate. The mode of interaction and binding strength of organotin (IV) carboxylates and three organotin (IV) dicarboxylates with DNA were also examined. The organotin (IV) carboxylates were found to have better anticancer activities than organotin (IV) dicarboxylates.