Slow Homogeneous Reaction Research Articles

Hyperbranched RCA-mediated construction of a dendritic DNA nanostructure for ratiometric fluorescence biosensing

As a robust isothermal strand amplification technique, rolling circle amplification (RCA) is popularly adopted for constructing various homogeneous fluorescence biosensing strategies. However, the limited functional unit decoration on linear RCA products and the slow homogeneous reaction kinetics usually restrict their performance. Herein, by designing a target biorecognition-triggered hyperbranched RCA reaction to construct an Mg2+-dependent DNAzyme (MNAzyme)-decorated dendritic DNA nanostructure, a novel ratiometric fluorescence biosensing method was proposed. The catalyzed cleavage of MNAzymes toward a short stand labeled with the FAM fluorophore and its quencher realized a “signal-on” fluorescence output. Meanwhile, a “signal-off” fluorescence output of 2-aminopurine (2-AP) labeled at a DNA hairpin was realized through the DNA hybridization with the nanostructure. Besides efficient acceleration of homogeneous reaction kinetics, these fluorescence responses were dramatically amplified by the high decoration of MNAzymes on the dendritic nanostructure and its strong signal suppression toward 2-AP. Together with the exonuclease III-amplified target biorecognition reaction, a very low detection limit of 0.53 fg mL–1 and a six-order magnitude linear range were endowed for kanamycin antibiotic assay. This excellent analytical performance and its high selectivity, and good operability determine promising prospect of the method for practical applications.

Oxidative Dehydrogenation of Ethylenediamine Coordinated to Ruthenium with Hexafluoroacetylacetonate, Induced by Electrochemical Oxidation of Ruthenium(II) to Ruthenium(III)

Abstract Two mixed-ligand complexes, [Ru(hfac)2(en)] and [Ru(hfac)(en)2]PF6 (en = ethylenediamine and hfac− = hexafluoroacetylacetonate ion), were synthesized. The oxidative dehydrogenation of their en ligand was studied in acetonitrile solutions. Each complex underwent a Nernstian one-electron oxidation at platinum electrodes. The resultant ruthenium(III) species was converted through a series of slow homogeneous reactions into the corresponding 1,2-diiminoethane ruthenium(II) species. Voltammograms recorded during the course of the reactions suggested the presence of 2-amino-1-iminoethane ruthenium(II) intermediates.

The Polarization of Molten Carbonate Fuel Cell Electrodes: II . Characterization by AC Impedance and Response to Current Interruption

AC impedance and current interruption measurements have been investigated as an in situ method for characterizing rate‐limiting processes in molten carbonate fuel cell porous electrodes. Analysis of the data for the fuel cell anode indicates that the anode is always under strong mass‐transfer control, in the temperature range of 600–700°C. Analysis of data for the cathode indicates that at 650°C the cathode is under mixed control. Charge‐transfer control is approached at lower temperature (600°C) and at high partial pressures. Control by mass transfer or slow homogeneous reactions (e.g.,) in the cathode tends to become dominant at higher temperature (700°C). The kinetic (exchange) reaction orders of the cathode reaction are approximately 0.85 and −0.45 for oxygen and carbon dioxide, respectively. The activation energy of oxygen reduction is approximately 230 kJ/g mol.

The Effect of the Tribromide Complex Reaction on the Oxidation/Reduction Current of the Br2 / Br − Electrode

The electrode reaction with tribromide complex formation reaction in the solution, a chemical‐electrochemical (C‐E) type reaction, has been investigated in order to determine the effect of the chemical reaction on the electrode kinetics. It is shown that the chemical reaction has little effect on the electrode kinetics at very slow homogeneous reaction rates, but has a more drastic effect on the electrode kinetics at faster homogeneous reaction rates. Also, the kinetics at the electrode are affected by changes in the concentrations of the active species (, Br−, and ) in the bulk solution as a consequence of the coupling effect of the chemical reaction on the electrode kinetics.

Extension of the improved “heterogeneous equivalent” method to the digital simulation of the slow psuedo-first order homogeneous reactions coupled to the electrode reaction

The improved “Heterogeneous Equivalent” method for simulation of very fast first and pseudo-first order homogeneous reactions coupled with electrode reaction has been extended for the treatment of moderately fast and slow homogeneous reactions. New algorithms have been developed avoiding the simulation of homogeneous kinetics through finite difference approximation. Instead, the analytical expression for the term containing the kinetic parameter has been included in combination with other constant parameters (such as the diffusion coefficient).

Thermochemical kinetics of anthracene pyrolysis

A theoretical analysis of chemical reactions in the early stages of anthracene pyrolysis is presented. This analysis makes extensive use of thermochemical and kinetic estimation methods as well as fundamental principles of free radical kinetics. The focus is on liquid-phase reactions near 500°C although reactions at higher temperatures and at lower densities are also discussed. Some noteworthy predictions concerning anthracene pyrolysis in the liquid phase near 500°C are: 1. (1) Decomposition is initiated by impurities, wall reactions and/or very slow homogeneous reactions. 2. (2) Products are expected to catalyze the reaction once a small amount of decomposition has taken place. 3. (3) Anthracene polymerization involves a step in which a resonance stabilized π-radical adds to the 9-position of an anthracene moiety. 4. (4) The first major molecular product is 9-(9'-anthryl)-9,10-dihydroanthracene. 5. (5) Radicals are generated primarily by molecular disproportionation reactions between 9,10-dihydroanthryl and anthryl structures. 6. (6) Hydrogen atoms released during C-C bond formation are held primarily in 9,10-dihydroanthryl structures. 7. (7) Phenyl-type radicals and free H atoms are not important intermediates at 500°C, although they are probably important in reactions at higher temperatures and in the gas phase.

Decomposition of pyrite in acids by pressure leaching and anodization: the case for an electrochemical mechanism

Abstract The oxygen pressure leaching of pyrite has been studied with regard to reaction mechanism by oxygen-18 tracer tests, electrochemical simulation and actual leaching experiments over a range of variables; temperature, 85 to 130°C; pressure, 0 to 976 psi O2 (66.4 atm); and acid concentration, 0.01 to 3M H2SO4. The dissolution mechanism has been found to be electrochemical and is a potentiostatically controlled steady state between sulphate-forming and elemental sulphur-forming anodic reactions:1. FeS2+8H2O→Fe+2+2SO4 =+16H++14e− 2. FeS2+Fe+2+2SOo+2e− Ferric ions are produced primarily by a slow homogeneous reaction:4Fe+2+O2+4H+→4Fe+3+2H2OThe cathodic reaction initially involves the reduction of oxygen:1/2O2+2H++2e−→H2OThis reaction is supplemented by cathodic reduction of ferric ions after these have built up to a significant concentrationThe electrochemical model has been cited to explain the effect of oxygen pressure on the system and acid production or consumption by pyrite during leaching. Resume...