7 resultados para reversible potential
em Deakin Research Online - Australia
Resumo:
The reductive voltammetry of the photovoltaic sensitizer [(H2-dcbpy)2Ru(NCS)2] (H2-dcbpy=2,2′-bipyridine-4,4′-dicarboxylic acid) and [(H3-tctpy)Ru(NCS)3]− (H3-tctpy=2,2′:6′,2″-terpyridine-4,4′,4″-tricarboxylic acid) has been investigated in acetone. Significant surface interactions at both platinum and glassy carbon electrodes occur at 0.6 V prior to the reversible potential expected for ligand-based reduction process of the fully protonated acids. The origin of the surface interactions are attributed to the acid–base behaviour of the compounds, combined with overall deprotonation and reduction to hydrogen, since repetitive cycling of the potential reveals well-defined reversible reduction processes in the negative potential range, resulting from formation of doubly deprotonated [(H-dcbpy−)2Ru(NCS)2]2− and singly deprotonated [(H2-tctpy−)Ru(NCS)3]2−, respectively. The extent of the surface interactions has been estimated by electrochemical quartz crystal microbalance and chronocoulometric measurements. Under certain conditions, a thick conducting polymer consisting of several hundred monolayers is formed.
Resumo:
Reactions of CeCl3·7H2O and Ce(NO3)3·6H2O with Naacac or NH4acac in aqueous solution at 21 and 45 °C yielded the trihydrate [Ce(acac)3(H2O)2]·H2O and the dihydrate [Ce(acac)3(H2O)2], respectively, whereas similar treatment of (NH4)2[Ce(NO3)6] gave the trihydrate at both temperatures. Desiccation of the hydrates over silica gel left the dihydrate unchanged, whereas the trihydrate underwent decomposition rather than dehydration. Aerial oxidation of [Ce(acac)3(H2O)2] in CH2Cl2 and toluene yielded α-[Ce(acac)4] and β-[Ce(acac)4], respectively, the structure of the former being re-determined with improved precision. Careful treatment of aqueous (NH4)4[Ce(SO4)4] and Hacac (initially pH 1–2) with aqueous ammonia to pH 5 precipitated hydrated [Ce(acac)4], from which [Ce(acac)4]·10H2O was isolated as unstable, light-sensitive single crystals, and the structure was determined. The complex is a laminar clathrate containing layers of Ce(acac)4 molecules sandwiched between extensive hydrogen-bonded layers of water molecules which do not interact with the metal. Electrochemical experiments confirmed the unstable nature of hydrated CeIII(acac)3, while the reduction of [Ce(acac)4] yielded well-defined cyclic voltammograms in acetonitrile and acetone, corresponding to a quasi-reversible process. For the [CeIV(acac)4]/[CeIII(acac)4]−redox couple, a calculated reversible potential of 0.22±0.02 V versus SHE was obtained in acetone or acetonitrile (0.1 M Bu4NPF6) at both gold and glassy carbon electrodes. This potential is consistent with the ease of both oxidation and reduction of cerium acetylacetonate complexes as found in the synthetic studies.
Resumo:
The new ligand, [Fc(cyclen)2] (5) (Fc=ferrocene, cyclen=1,4,7,10-tetraazacyclododecane), and corresponding ZnII complex receptor, [Fc{Zn(cyclen)(CH3OH)}2](ClO4)4 (1), consisting of a ferrocene moiety bearing one ZnII-cyclen complex on each cyclopentadienyl ring, have been designed and prepared through a multi-step synthesis. Significant shifts in the 1H NMR signals of the ferrocenyl group, cf. ferrocene and a previously reported [Fc{Zn(cyclen)}]2+ derivative, indicated that the two ZnII-cyclen units in 1 significantly affect the electronic properties of the cyclopentadienyl rings. The X-ray crystal structure shows that the two positively charged ZnII-cyclen complexes are arranged in a trans like configuration, with respect to the ferrocene bridging unit, presumably to minimise electrostatic repulsion. Both 5 and 1 can be oxidized in 1:4 CH2Cl2/CH3CN and Tris-HCl aqueous buffer solution under conditions of cyclic voltammetry to give a well defined ferrocene-centred (Fc0/+) process. Importantly, 1 is a highly selective electrochemical sensor of thymidilyl(3′-5′)thymidine (TpT) relative to other nucleobases and nucleotides in Tris-HCl buffer solution (pH 7.4). The electrochemical selectivity, detected as a shift in reversible potential of the Fc0/+ component, is postulated to result from a change in the configuration of bis(ZnII-cyclen) units from a trans to a cis state. This is caused by the strong 1:1 binding of the two deprotonated thymine groups in TpT to different ZnII centres of receptor 1. UV-visible spectrophotometric titrations confirmed the 1:1 stoichiometry for the 1:TpT adduct and allowed the determination of the apparent formation constant of 0.89±0.10×106 M−1 at pH 7.4.
Resumo:
Characterization of the anticancer active compound trans-[PtII{(p-BrC
Resumo:
We demonstrate the complete, rapid, and reversible switching between the emissions from two electrogenerated chemiluminescence (ECL) systems contained within the same solution, controlled by simple modification of the applied potential. The fundamental bases of the approach are the ability to selectively 'switch on' luminophores at distinct oxidation potentials, and an intriguing observation that the emission from the well-known electrochemiluminescent complex, fac-Ir(ppy)3, (where ppy is 2-phenylpyridinato), can be selectively 'switched-off' at high overpotentials. The dependence of this phenomenon on high concentrations of the co-reactant implicates quenching of the excited [Ir(ppy)3]* state by electron transfer. Rapid spectral scanning during modulation of the applied potential reveals well resolved maxima for mixtures comprising either green and red or green and blue luminophores, illustrating the vast potential of this approach for multiplexed ECL detection.
Resumo:
Staging models are widely used in clinical medicine, and offer an insight into the progressive nature of many disorders. In general, the earlier stages of illness may be associated with a better prognosis and a higher treatment response. Once chronicity is reached, more complex and invasive treatments may be required, and the utility of treatments may decline. There is evidence that treatment response is greatest in the early phases of the disorder. There is also a progressive social and psychological burden of ongoing illness. This is paralleled by the twin notions of neuroprotection, which is supported by increasing evidence that structural changes in the disorder may be progressive and reversible with algorithm appropriate treatment, and that of early intervention, which posits that the optimal window for intervention is early in the illness course. A staging model compliments existing and proposed classifications of bipolar disorder, adding a temporal dimension to a cross sectional view. It may inform treatment choice and prognosis, and could have utility as a course specifier.
Resumo:
Mg has great potential as the basis for a safe, low cost energy storage technology, however, cycling of magnesium is difficult to achieve in most electrolytes. We demonstrate cycling of Mg from a novel alkoxyammonium ionic liquid. DFT calculations highlight the role that Mg coordination with [BH4](-) ions plays in the mechanism.