Wlodzimierz Kutner

Stability and electrocatalytic activity of the oxo-bridged dimer [(bpy)2(H2O)RuORu(OH2)(bpy)2]4+ in basic solutions

Abstract Rotating disk electrode and cyclic voltammetry experiments with glassy carbon electrodes were applied to study the electrocatalytic properties of the oxo-bridged dimer, [(bpy)2(H2O)-RuIIIORuIII(H2O)(bpy)2]4+, I, (bpy = 2,2′-bipyridine) in basic solutions. When generated by electro-oxidation of I, the Ru(IV)Ru(V) form of the dimer electrocatalytically oxidizes alcohols, sugars and amino acids in reactions that the first order in catalyst and in substrate. The rate constants, kcat, for oxidation of glycine, L(+)arginine, D(+)glucose and benzyl alcohol by the Ru(IV)Ru(V) form of I were measured in 0.2, 0.1, 0.1 and 1.0 M NaOH, respectively, as equal to 12.0±1.3, 11.2±0.8, 63.2±4.0 and 6.2±0.5 × 103M−1 s−1, respectively. The electrocatalytic reaction involves prior proton dissociation from the complex [(bpy)2(HO)RuIIIORuIV(OH)(bpy)2]3+ (pKa3=13.7) in the course of electrogenerating the Ru(IV)Ru(V) dimer. The pseudo-first order rate constant of this step was measured as 20±5 s−1 in 1.0 M NaOH. The proton dissociation reaction is too rapid to limit the electrocatalytic rate of oxidation of glycine, which is pH independent from pH 13 to 14. The rate constant for the more rapidly oxidizable benzyl alcohol is, on the other hand, strongly pH dependent and this reaction can be quantitatively shown to be proton dissociation rate-limited. In experiments supporting the main electrocatalytic objectives, the complex I in homogeneous 0.1 M NaOH solutions was found to oxidize D(+)glucose with a rate constant of 1.4±0.1×10−2M−1 s−1. The Ru(III)-Ru(IV) dimer spontaneously self-reduces with a pseudo-first order rate constant of 8.6×10−4 s−1 in 1.0 M NaOH, apparently by oxidation of a bpy ligand.

Electrochemical and electrocatalytic reactions of a ruthenium oxo complex in solution and in cation exchange beads in carbon paste electrodes

Abstract A strategy for electrode immobilization of an ionic reagent as a counterion of an ion exchange matrix is described along with an electrocatalytic application of the reagent. Carbon paste electrodes, CPE, were prepared which contain microparticle beads of a strong cation exchanger, Dowex 50W×8, that had been loaded with the electrocatalytic oxidant reagent, [Ru II (trpy)(phen)(OH)] + ( I ) (trpy = 2,2′, 2″-terpyridine, phen = 1,10-phenanthroline). At pH 13 I is reversibly electro-oxidized by one two-electron, one-proton step to produce the Ru(IV) oxidant, [Ru IV (trpy)(phen)O] 2+ ( oxI ). At lower loadings of I in the Dowex resin, semi-infinite molecular diffusion of the reagent within the microparticle beads is the major means of charge transport. Benzyl alcohol oxidation by oxI , with electrochemical regeneration of I , served in basic solution as a system to probe electrocatalysis. On very slow experimental time scales, the electrochemical process is controlled solely by the rate of reaction of oxI with benzyl alcohol inside the ion exchanger. An electrocatalytic rate constant, k 1 = 10.8 ± 4 M −1 s −1 was measured in 0.1 M NaOH. The electrocatalytic rate constant measured at naked glassy carbon electrodes and at CPE containing no ion exchanger, and with I and benzyl alcohol dissolved in the solution, was within a factor of three of the above k 1 .

Preparation and properties of insoluble films of cyclodextrin condensation polymers

The preparation and properties of smooth and stable films of cyclodextrin polymers are described. The commercially available water soluble prepolymers ofα-, β-, andγ-cyclodextrin of low molecular masses were crosslinked with glutaric dialdehyde. Side-chain unreacted aldehyde groups were reduced with sodium borohydride. For theα-cyclodextrin polymer, optimum film performance was found for a 1:10 mass ratio of glutaric dialdehyde to prepolymer, which corresponds to a molar ratio of glutaric dialdehyde to cyclodextrin units of about 1.75: 1. Such films, of thickness 2.4 µm, were prepared on metallic or glassy-carbon substrates for characterization by scanning-electron microscopy, and for studies with the electrochemical quartz-crystal microbalance.

Derivatization of fullerenes by electrosynthesis

Abstract In this paper the electrochemical derivatization of fullerenes in the case of C 60 is described. The property of fullerenes to form di- or tri-anions by electrochemical reduction at less cathodic potentials is used for chemical derivatization. These anions react with alkyl or aryl halides, e.g. iodomethane, iodobenzene, 1-iodonaphthalene and 1,2-diiodobenzene in benzonitrile solution. Depending on the electrochemical conditions and the chemical structure, di- or tetra-alkyl and aryl fullerenes, respectively, are formed. The electrosynthesis is followed by cyclic voltammetry. The reaction products are isolated by high performance liquid chromatography (HPLC) and characterized by 1 H NMR spectroscopy and mass spectrometry.