Spectrofluorometric study of complexation of some amino derivatives of 9,10-anthraquinone with beta-cyclodextrin

Complexation reactions between 1-amino-9,10-anthraquinone (AA1), 1-amino-2-methyl-9,10-anthraquinone (AA2), 1-amino-2,4-dimethyl-9,10-anthraquinone (AA3) and 1-amino-2-ethyl-9,10-anthraquinone (AA4) and beta-cyclodextrin were studied spectrofluorometrically, under optimized experimental conditions. The formation constants of the resulting 1:1 beta-cyclodextrin complexes were evaluated and found to decrease in the order AA4>AA1>AA3>AA2. Possible reasons for the observed stability sequence are discussed based on the structures proposed for the resulting inclusion complexes.

Renewable-surface sol-gel derived carbon ceramic electrode fabricated by [Ru(bpy)(tpy)Cl]PF6 and its application as an amperometric sensor for sulfide and sulfur oxoanions

A highly sensitive and fast responding sensor for the determination of thiosulfate, sulfite, sulfide and dithionite is described. It consists of a chemically modified carbon ceramic composite electrode (CCE) containing [Ru(bpy)(tpy)Cl]PF6 complex that was constructed by the sol-gel technique. A reversible redox couple of Ru(II)/Ru(III) was observed as a solute in acetonitrile solution and as a component of carbon based conducting composite electrode. Electrochemical behavior and stability of modified CCE were investigated by cyclic voltametry, the apparent electron transfer rate constant (kappa(S)) and transfer coefficient (a) were determined by cyclic voltametry which were about 28 s(-1) and 0.43 respectively. Electrocatalytic oxidation of S(2-), SO3(2-), S2O4(2-) and S2O3(2-) were effective at the modified electrode at significantly reduced overpotentials and in the pH range 1-11. Optimum pH values for amperometric detection of thiosulfate, dithionite, sulfide and sulfite are 7, 9, 2 and 2. Under the optimized conditions the calibration curves are linear in the concentration ranges 1-500, 3-80, 2-90 and 1-100 microM for S2O3(2-), SO3(2-), S2- and S2O4(2-) determination. The detection limit (signal to noise is 3) and sensitivity are 0.5 and 12, 2.8 and 6, 1.6 and 8, and 0.65 microM and 80 nA microM(-1) for thiosulfate, sulfite, sulfide and dithionite detection. The modified carbon ceramic electrode doped with Ru-complex shows good reproducibility, a short response time (t < 2 s), remarkable long term stability (> 6 month) and especially good surface renewability by simple mechanical polishing (RSD for eight successive polishing is 2%). The advantages of this sulfur compound amperometric detector based on ruthenium doped CCE are high sensitivity, inherent stability at a broader pH range, excellent catalytic activity, less expense and simplicity of preparation in comparison with recently published papers. This sensor can be used as a chromatographic detector for analysis of sulfur derivatives.

Electrocatalytic reduction of dioxygen on a glassy carbon electrode modified with adsorbed cobaloxime complex

The preparation and electrochemical properties of a glassy carbon (GC) electrode modified with cobaloxime complex were investigated. The complex of the type [CoIII(DO)(DOH)pn)Cl2] where (DO)(DOH)pn = N2,N2'-propanediylbis-2,3-butanedione-2-imine-3-oxime) was adsorbed irreversibly and strongly on the surface of preanodized glassy carbon electrode. Electrochemical behavior and stability of modified GC electrode were investigated by cyclic voltammetry. The electrocatalytic reduction of dioxygen has been studied using this modified glassy carbon electrode by cyclic voltammetry, chronoamperometry and rotating disk electrode voltammetry as diagnostic techniques. The modified electrode showed excellent eletrocatalytic ability for the reduction of dioxygen to hydrogen peroxide in acetate buffer (pH 4.0) with overpotential 1.0 V lower than the plain glassy carbon electrode. The formal potential for this modified electrode is not shifted to more negative potentials by repeated reduction-oxidation cycles in oxygen-saturated supporting electrolyte solution. The apparent electron transfer rate constant (kS), the transfer coefficent (alpha) and the catalytic rate constant of O2 reduction at a GC modified electrode were determined by cyclic voltammetry and rotating disk electrode voltammetry and were found to be around 2.6 s(-1), 0.33 and 2.25 x 10(4) M(-1) s(-1). Based on the results, a catalytic mechanism is proposed and discussed.