Changing the paradigm in modelling the Bray-Liebhafsky oscillatory chemical reaction.

The Bray-Liebhafsky (BL) reaction is one of the simplest chemical oscillators consisting initially of only three components. Despite this, its mechanism is unknown for more than 100 years due to the absence of selective, sensitive, and fast experimental techniques for following all of the involved intermediates. The modeling of the BL mechanism assumes presumably mass action kinetics "adjustable" to oscillatory solutions by the application of mathematical stability analysis and treating the system as homogeneous. Such a basically mathematical approach need not suggest physically realistic kinetic parameters and is not unique since a number of models can be proposed. Based on recent experimental and computational results, a new model of the BL oscillatory reaction mechanism is constructed by including heterogeneous processes occurring in the system. The same set of equations is able to demonstrate not only the oscillatory evolution but also mixing effects on the oscillatory dynamics, and non-oscillatory stepwise-iodine oxidation and can rationalize other effects described in literature. Thus, the paradigm of treating the BL oscillatory system as a homogeneous one, described by formal kinetics only, is extended for a better understanding of the chemistry of this apparently simple system. The introduced ideas of energy redistribution may contribute to establishing an improved conceptual base for considering other complex oscillators in various fields of science.

Coupling between nucleation and chemical reactions and its importance in understanding the oxidation of iodine by hydrogen peroxide.

We have investigated the reaction of iodine with hydrogen peroxide coupled to gas nucleation. A step-like increase in the nucleation rate with increasing amounts of dissolved oxygen can act as a trigger for the formation of highly reactive components and complete oxidation of iodine to iodate despite the large thermodynamic barrier for the whole process. Energetic coupling of nucleation with chemical reactions is based on local redistribution of energy by collapsing unstable nuclei. The developed model correctly describes the evolution of the measured reaction parameters. It offers a conceptual improvement of formal-kinetic models by drawing attention to important contributions of physical effects to the reaction mechanism.

Intermittent Chaos in the CSTR Bray-Liebhafsky Oscillator-Specific Flow Rate Dependence.

Dynamic states with intermittent oscillations consist of a chaotic mixture of large amplitude relaxation oscillations grouped in bursts, and between them, small-amplitude sinusoidal oscillations, or even the quiescent parts, known as gaps. In this study, intermittent dynamic states were generated in Bray-Liebhafsky (BL) oscillatory reaction in an isothermal continuously-fed, well-stirred tank reactor (CSTR) controled by changes of specific flow rate. The intermittent states were found between two regular periodic states and obtained for specific flow rate values from 0.020 to 0.082 min-1. Phenomenological analysis based on the quantitative characteristics of intermittent oscillations, as well as, the largest Lyapunov exponents calculated from experimentally obtained time series, both indicated the same type of behavior. Namely, fully developed chaos arises when approaching to the vertical asymptote which is somewhere between two bifurcations. Hence, this study proposes described route to fully developed chaos in the Bray-Liebhafsky oscillatory reaction as an explanation for experimentally observed intermittent dynamics. This is in correlation with our previously obtained results where the most chaotic intermittent chaos was achieved between the periodic oscillatory dynamic state and stable steady state, generated in BL under CSTR conditions by varying temperature and inflow potassium iodate concentration. Moreover, it was shown that, besides the largest Lyapunov exponent, analysis of chaos in experimentally obtained intermittent states can be achieved by a simpler approach which involves using the quantitative characteristics of the BL reaction evolution, that is, the number and length of gaps and bursts obtained for the various values of specific flow rates.

Scrutinizing microwave effects on glucose uptake in yeast cells.

Taking into account different literature reports on microwave (MW) effects on living organisms, we thoroughly investigated the influence of constant 2.45 GHz MW irradiation on glucose uptake in yeast cells. A Saccharomyces cerevisiae suspension of 2.9 × 108 cells/ml was used in all experiments. A large specific absorption rate of 0.55 W/g of suspension is compensated by efficient external cooling of the reaction vessel, which established a strong non-equilibrium flow of energy through the solution and enabled a constant bulk temperature of 30 °C to within 1 °C during glucose uptake. Comparison of MW effects with control experiments revealed insignificant changes of glucose uptake during the initial stages of the experiment (up to the 10th min). Statistically "notable" differences during the next 20 min of the irradiation were detected corresponding to thermal overheating of 2 °C. Possible specific thermal MW effects may be related to local temperature increase and a large flow of energy throughout the system. The obtained effects show that environmental MW pollution (fortunately) is of too low intensity to provoke metabolic changes in living cells. At the same time, a longer exposure of cells to electromagnetic irradiation may have impacts on biochemical applications and production of valuable biotechnological products.