Theo Plesser

The Structure of the Core of the Spiral Wave in the Belousov-Zhabotinskii Reaction

The quantitative structure of the core of the spiral-shaped traveling wave of chemical activity appearing in a thin excitable layer of the Belousov-Zhabotinskii reaction, in which the oxidation and decarboxylation of malonic acid by bromate ions is catalyzed by ferroin, was analyzed experimentally. Light absorption by ferroin as the reduced reaction catalyst and indicator was measured by means of a video-and computer-based two-dimensional spectrophotometer with 10-micrometer spatial, 2-second temporal, and 256-digital units intensity resolution. The spiral core is a singular site (diameter, 30 micrometers or less) at which intensity modulations due to ferroin-ferriin distributions are at least ten times smaller than in the surrounding area of spiral propagation. Archimedian spirals were fitted to isoconcentration lines.

Two-dimensional spectrophotometry and pseudo-color representation of chemical reaction patterns

The formation of spatio-temporal patterns in layers of chemical and biochemical media is observed and quantified by a two-dimensional spectrophotometer based on a computerized video equipment with high spatial, temporal, and intensity resolution. Images are shown, to some extent, in pseudo-colors. The use of pseudo-colors and three-dimensional perspective representations enhances the perception of the information contained in an image and the inherent order of the spatial structures.

Two-dimensional spectrophotometry with high spatial and temporal resolution by digital video techniques and powerful computers

A two-dimensional spectrophotometer having a spatial raster resolution of 512 X 512 picture elements with 256 grey levels and a time resolution of 30 images per min is assembled by combination of digital video techniques and a powerful computer system. The instrument is applied to the analysis of pattern formation processes in cytoplasmic media.

Periodic heat production by oscillating glycolysis in a cytoplasmic medium extracted from yeast

The rate of heat production in a periodically glycolysing cell‐free cytoplasmic medium extracted from yeast Saccharomyces cerevisiae is measured with a batch calorimeter. The rate exhibits periodic variations of approx. 10% of the average heat production rate of about 54 per minute. From this rate and the enthalpy change fro glycolysis a glucose degradation rate of 0.43 is calculated. The value fits into the ‘oscillatory window’ determined by a glucose injection technique.

Heat production in oscillating chemical reactions: three examples

Abstract Microcalorimetric measurements are reported for the metal-ion catalyzed Belousov-Zhabotinskii and the Briggs-Rauscher reactions as well as for the uncatalyzed reaction of phenol, bromate, and sulfuric acid. The rate of heat production and either optical or potentiometric signals are recorded simultaneously.

Interaction of chemical waves with convective flows induced by density gradients. A comparison between experiments and computer simulations

Abstract Experimentally observed hydrodynamic flows generated by chemical waves propagating in thin solution layers of the Belousov-Zhabotinsky (BZ) reaction have been analyzed by computer simulation of a simplified time-independent model of the experimental conditions. The assumption of density differences between the bulk of the solution and the wave is sufficient for an explanation of most of the features arising from the hydrodynamic flow induced by chemical waves. The calculations show that proper adjustment of only one parameter describing the density distribution is necessary to reproduce the experimental observations.

Simultaneous measurements of heat production and optical density in oscillating reactions

Abstract A device is presented which can be inserted into a calorimetric vessel to enable a simultaneous measurement of optical density and heat production. It consists mainly of a quartz rod and a photodiode which is sensitive from the near ultraviolet to the infrared. Specific wavelengths are selected by glass or interference filters placed between the light source and the rod. Homogeneity of the medium in the vessel can be achieved by a gentle but effective pneumatic stirring. The applicability of the whole set-up is demonstrated for two oscillating chemical reactions (Belousov-Zhabotinskii and Briggs-Rauscher reactions) and for the oscillating glycolysis of a cell-free cytoplasmic extract from yeast.

Distinctive sites in chemical waves: The spiral core and the collision area of two annuli

Dynamical and structural details of traveling chemical waves in an excitable solution layer of the Belousov-Zhabotinskii reaction are sensitively detected by measurements with a two-dimensional spectrophotometer and application of perspective display techniques for data analysis. Concentration gradients of the redox couple ferroin/ferriin catalyzing the reaction are determined to a resolution of about 10μm. In solutions of identical chemical composition the gradients reach peak values of 8 mM/mm in a front of a spiral and 15 mM/mm in a front of a circular wave. Variation of ferroin concentration in the center of spiral rotation is less than 6% of that outside the core region. The degree of oxidation of ferroin at which the steepest concentration gradients occur is higher inside the core than at the outward-moving fronts. The core structure and the collision area between two circular fronts are represented by three-dimensional orthographic projections.

Three-dimensional representation of chemical gradients

Perspective display techniques are applied to chemical and biochemical data sets. These represent spatially distributed gradients of reactive compounds that participate in pattern-formation processes due to reaction-diffusion or reaction-convection coupling. The patterns form in thin solution layers and are observed as chemical waves in the Belousov-Zhabotinskii reaction, as convection-induced stationary structures during oscillating glycolysis in yeast cytoplasm, and as the diffusive spreading of enzyme-catalyzed metabolic turnover in a substrate layer. The digital data are measured with a two-dimensional spectrophotometer based on a computerized video equipment with high spatial, temporal and intensity resolution. By application of three-dimensional procedures detailed structural properties of chemical and biochemical model systems will be presented yielding localization of reaction and transport events.

CHEMICAL WAVES AND NATURAL CONVECTION

The nonlinear dynamics of chemical systems evolving sufficiently far from thermodynamic equilibrium leads to many remarkable phenomena. For instance, in homogeneous reactive solutions bistability and hysteresis, periodic oscillations or chaotic behaviour may occur [1]. Without stirring the coupling of complex reaction kinetics to diffusion can lead to the propagation of chemical waves, that is concentration gradients move through space, as best observed in thin excitable solution layers in a petri dish [2–4]. Spatial patterns in solution layers can also be stationary or transient [5–10]. For several systems it has been established that such structures are generated by reaction-convection coupling [11] without necessarily involving excitable or oscillatory kinetics [12].