The impact of perchlorate ions and acetonitrile medium on copper redox couple was investigated. The acetonitrile solvent and perchlorate ions were found to synergistically increase the redox potential of Cu(II)-Cu(I) couple, thereby increasing its ability to oxidize more systems and expand the copper redoxi metric analysis window. The difference in the behavior of thiourea towards copper(II) salts in aqueous and non aqueous media was also explored. Based on the synergistic effect, an electroanalytical method for com position analysis of copper(I) thiourea complexes was proposed. Kinetic and quantum chemical studies have been used for mechanistic insight into synergistic effect of acetonitrile and perchlorate ions on copper redox couple.
Abstract. Transition metal ions in their free state bring unwanted biological oxidations generating oxidative stress. The ligand modulated redox potential can be indispensable in prevention of such oxidative stress by blocking the redundant bio-redox reactions. In this study we investigated the comparative ligand effect on the thermo-kinetic aspects of biologically important cysteine iron (III) redox reaction using spectrophotometric and potentiometric methods. The results were corroborated with the complexation effect on redox potential of iron(III)-iron(II) redox couple. The selected ligands were found to increase the rate of cysteine iron (III) redox reaction in proportion to their stability of iron (II) complex (EDTA < terpy < bipy < phen). A kinetic profile and the catalytic role of copper (II) ions by means of redox shuttle mechanism for the cysteine iron (III) redox reaction in presence of 1,10-phenanthroline (phen) ligand is also reported.
Herein, we report that the thermodynamic barrier for solution-phase electron transfer (ET) between Cu(II) and Fe(II) in aqueous acidic media can be overcome through the addition of 2,9-dimethyl-1,10-phenanthroline (Neocuproine [NC]) to the reaction mixture. A detailed discussion of the kinetic and mechanistic aspects of this coordination-inspired ET is presented. We attribute the observed change in the thermodynamic feasibility to the change in the reduction potential of Cu(II)-Cu(I) couple on its ligation with NC. The reaction was found to be slow, following firstorder kinetics with respect to each Cu(II) and Fe(II). In the presence of excess NC, the reaction was observed to proceed with a pseudo-second-order rate constant of 3.37 ± 0.05 dm 3 mol À1 s À1 at 298 K, with an activation barrier of ca. 26.22 kJ mol À1 . The slow reaction is attributed to the significant reorganization energy associated with large-scale changes in the coordination sphere of the oxidant. A two-step mechanism that explains the experimental observations is proposed for the investigated reaction.
IntroductionCoordination complexes of transition metal ions [1-3] have established roles as metalloproteins in life processes. Analytical and other applications of coordination complexes make studies related to redox properties, mechanistic, kinetic, and applied aspects of inner and outer sphere electron transfers in coordination complexes important [4,5]. Few reports [6-8] using transition metal ion complexes as model systems for understanding electrontransfer processes in metalloproteins have been demonstrated. A long-standing challenge related to electron-transfer processes in metalloproteins is to unravel the basic cause for the metal ion center in electron transfer proteins that allows them to mediate a huge number of electron transfer reactions with high sensitivity and accuracy [9,10]. XRD and other structural studies in blue copper proteins have established that this ability of metalloproteins can be partly attributed to a large variation in the redox potential of metal ion center (190-780 mV) due to the nature and complexation geometry specific to the redox tuning properties of ligands [11,12].In continuation to our work on coordination-inspired redox systems [13,14], we investigated redox titration between Fe(II) and Cu(II) in the presence of 2,9-dimethyl-1,
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