Catalysis of the Electro-Oxidation of Carbon Monoxide by Cobalt Octaethylporphyrin

The electro-oxidation of cobalt (II) octaethylporphyrin adsorbed on graphite electrodes, Co^(II)(OEP)_(ads') to Co^(III)(OEP) ^+_(ads), in the presence of aqueous solutions of CO leads to catalytic oxidation of CO to CO_2. No such oxidation occurs with Co^(II)(OEP) and CO dissolved in nonaqueous solvents. Coordination of the CO to Co^(III)(OEP)^+ is the first step in the catalytic mechanism. Nucleophilic attack on the coordinated CO by H_2O is the probable rate-limiting step in the catalytic oxidation. A pseudo first-order rate constant of 0.3 s^(-1) was estimated for this reaction

Electrochemical Assessment of the Stability of [Os(NH_3)_5(OH_2)]^(2+) in Aqueous Solutions

The [Os(NH_3)_5(OH_2)]^(2+) complex in aqueous acid has been widely regarded as short-lived on the basis of results reported in an early pioneering electrochemical study.1 More recently, a much longer-lived Os(II) species generated by reduction of [Os(NH)3))5(OH)2)]^(3+) but of uncertain composition has been reported. In the present study the lifetime of [Os(NH_3)_5(OH_2)]^(2+) in aqueous acid was determined by steady-state voltammetry at a carbon microelectrode and by comparing experimental with simulated cyclic voltammograms obtained for solutions of [Os(NH_3)_5(OH_2)]^(3+). Rate constants for the oxidation of [Os(NH_3)_5(OH_2)]^(2+) by H^+, CH_3COOH (HA), and H_2O were evaluated as k_H = 17 M^(-1) s^(-1), k_(HA) = 1.2 M^(-1) s^(-1), and k_(H_2O) = 4.1 × 10^(-4) s^(-1). These values are shown to be compatible with the data in ref 1 and come close to accounting for the long-lived species described in ref 6 which may be [Os(NH_3)_5(OH_2)]^(2+) itself. A revised value of 4.85 was measured for the pKA of [Os(NH_3)_5(OH_2)]^(3+). Adsorption of an Os complex on the surface of mercury, but not glassy carbon, electrodes is shown to enhance greatly the rate with which protons undergo direct electroreduction

Electrochemical Assessment of the Stability of [Os(NH_3)_5(OH_2)]^(2+) in Aqueous Solutions

The [Os(NH_3)_5(OH_2)]^(2+) complex in aqueous acid has been widely regarded as short-lived on the basis of results reported in an early pioneering electrochemical study.1 More recently, a much longer-lived Os(II) species generated by reduction of [Os(NH)3))5(OH)2)]^(3+) but of uncertain composition has been reported. In the present study the lifetime of [Os(NH_3)_5(OH_2)]^(2+) in aqueous acid was determined by steady-state voltammetry at a carbon microelectrode and by comparing experimental with simulated cyclic voltammograms obtained for solutions of [Os(NH_3)_5(OH_2)]^(3+). Rate constants for the oxidation of [Os(NH_3)_5(OH_2)]^(2+) by H^+, CH_3COOH (HA), and H_2O were evaluated as k_H = 17 M^(-1) s^(-1), k_(HA) = 1.2 M^(-1) s^(-1), and k_(H_2O) = 4.1 × 10^(-4) s^(-1). These values are shown to be compatible with the data in ref 1 and come close to accounting for the long-lived species described in ref 6 which may be [Os(NH_3)_5(OH_2)]^(2+) itself. A revised value of 4.85 was measured for the pKA of [Os(NH_3)_5(OH_2)]^(3+). Adsorption of an Os complex on the surface of mercury, but not glassy carbon, electrodes is shown to enhance greatly the rate with which protons undergo direct electroreduction

(5,10,15,20-Tetramethylporphyrinato)cobalt(II): A Remarkably Active Catalyst for the Electroreduction of O_2 to H_2O

Unlike most simple, monomeric cobalt porphyrins, the cobalt tetramethylporphyrin identified in the title catalyzes the electroreduction of O_2 to H_2O instead of H_2O_2. On graphite electrodes, coatings of the porphyrin prepared by irreversible adsorption from chloroform solutions catalyze the electroreduction of O_2 in aqueous HClO_4 at unusually positive potentials. Both the title porphyrin and the corresponding unsubstituted cobalt porphine are argued to derive their activity as four-electron reduction catalysts from their propensity to form dimers (or higher aggregates) in solution and, presumptively, on the surface of graphite electrodes

(5,10,15,20-Tetramethylporphyrinato)cobalt(II): A Remarkably Active Catalyst for the Electroreduction of O_2 to H_2O

Unlike most simple, monomeric cobalt porphyrins, the cobalt tetramethylporphyrin identified in the title catalyzes the electroreduction of O_2 to H_2O instead of H_2O_2. On graphite electrodes, coatings of the porphyrin prepared by irreversible adsorption from chloroform solutions catalyze the electroreduction of O_2 in aqueous HClO_4 at unusually positive potentials. Both the title porphyrin and the corresponding unsubstituted cobalt porphine are argued to derive their activity as four-electron reduction catalysts from their propensity to form dimers (or higher aggregates) in solution and, presumptively, on the surface of graphite electrodes

Estimular o Aprendizado para Exame Nacional do Ensino Médio Utilizando o Sistema Tutor Inteligente MAZK

TCC (graduação) - Universidade Federal de Santa Catarina. Centro de Ciências Tecnologias e Saúde. Tecnologias da Informação e ComunicaçãoA tecnologia avança continuamente e cresce no âmbito de ser usada como ferramenta educacional. Este trabalho tem como objetivo estimular o aprendizado para o Exame Nacional do Ensino Médio por meio do tutor inteligente MAZK que foi usado como ferramenta de aplicação. O trabalho está fundamento em aspectos como as principais dificuldades na utilização dessas tecnologias a favor da educação por parte dos estudantes, professores e alunos; que as tecnologias digitais aplicadas de forma planejada atraem os estudantes e auxiliam os professores; que o sistema tutores inteligente são aliados da educação e do aluno por oferecer um ensino-aprendizagem personalizado; a partir disso, foi realizada uma competição entre escolas públicas dividida em duas fases que envolveram escola, professor e alunos

Electroreduction of O_2 to H_2O at Unusually Positive Potentials Catalyzed by the Simplest of the Cobalt Porphyrins

Simple cobalt porphine, adsorbed on graphite electrodes, catalyzes the direct reduction of O_2 to H_2O, while most other monomeric cobalt porphyrins do not. The surprising behavior of cobalt porphine suggests possible new strategies for the design of electrocatalysts for the reduction of O_2 to H_2O using structurally similar but more oxidation-resistant analogs

Electroreduction of O_2 to H_2O at Unusually Positive Potentials Catalyzed by the Simplest of the Cobalt Porphyrins

Simple cobalt porphine, adsorbed on graphite electrodes, catalyzes the direct reduction of O_2 to H_2O, while most other monomeric cobalt porphyrins do not. The surprising behavior of cobalt porphine suggests possible new strategies for the design of electrocatalysts for the reduction of O_2 to H_2O using structurally similar but more oxidation-resistant analogs