Dual Control Mechanism in a Belousov−Zhabotinskii (B−Z) Oscillator with Glucose and Oxalic Acid as a Double Substrate

Effects of Selenium Species on the Belousov-Zhabotinsky Reaction

The effects of selenium species on the Belousov-Zhabotinsky (B-Z) reaction were investigated by adding them to the system before and during oscillation. When selenium species were added into the system before oscillation, sodium selenite prolonged the induction period, whose effect was strong as sodium selenite could consume malonic acid to prohibit the accumulation of bromomalonic acid. For selenomethionine and selenocystine, their effects were derived from their reaction with ^•CH₂COOH and ^•Br₂^- producing a radical cation of selenoamino acids, which prohibited the accumulation of bromomalonic acid. Here, the selenium atoms in selenoamino acids, as reactive centers, took part in the redox reaction. As a result, the induction period was prolonged. However, as a diselenide, selenocystine can reduce bromate in acidic medium, which led to shortening of the induction period. Therefore, the effect of selenocystine on the induction period was the result of two opposite effects. Nanoselenium shortened the induction period in a certain concentration range because bromate was directly reduced by nanoselenium and the accumulation of bromomalonic acid was promoted. Furthermore, the dose perturbation effect was investigated by the injection of nanoselenium during oscillation. It was found that the amplitude was increased or decreased in a dose-dependent fashion when nanoselenium was injected at peak or trough of the time-dependent redox potential curve.

Mapping Sequential Oscillations in the Bromate-Oxalic Acid-Acetone-Ce(IV) Reaction

Oscillating reactions are reactions in which it is possible to observe oscillations in the concentrations of some reaction intermediates. The reaction studied here is composed of acetone, sulfuric acid, bromate, oxalic acid, and Ce(IV). Chemical oscillators may have different behaviors in batch, for example, the presence of an induction period and change of oscillations' pattern. A much rarer event is the presence of a break, or pause, between two groups of oscillations, which is shown by this system. To better determine the conditions under which this behavior occurs, we built several phase diagrams for the initial concentrations of reactants. These phase diagrams show that there is a well-defined range of concentrations that produce a pause in the oscillations. The initial bromate concentration is special because increasing this concentration eliminates the pause in the oscillations, but a further increase can make a pause appear again. These results can be interpreted considering that the reaction mechanism is controlled by at least two intermediates. In addition, this work presents a representative set of data that must be acknowledged by any detailed proposal of mechanism for this oscillating reaction.

Complex dynamical behavior in the highly photosensitive cerium-bromate-1,4-benzoquinone reaction

Experimental and numerical investigations are carried out on the nonlinear dynamics of the cerium-bromate-1,4-benzoquinone reaction in which a unique kinetic feature is that the reduction of Ce(IV) is through bromide ions rather than by organic substrates. Nonlinear phenomena including both simple and sequential oscillations have been observed, and the system could oscillate for longer than a week. Significantly, fluorescent ceiling light with an intensity of less than 20 μW/cm(2) exhibited strong influence on the frequency, lifetime, and complexity of the spontaneous oscillations. The transient oscillations lasted for a longer period of time at a low light intensity, were quenched by a moderate illumination, and then became long-lived again at a higher light intensity. Characterizations with (1)H NMR and GC/MS spectroscopy and ion selective electrode suggest that 2-bromo-1,4-benzoquinone is an important unstable intermediate product that undergoes photoaccelerated decomposition to produce hydroxy-1,4-benzoquinone and bromide ions. Simulations successfully reproduced the occurrence of oscillatory behavior in the studied system.