B/Z Reaction

B/Z reaction

Chemical reactions do not generally display dynamic patterns or spatial order. The Belousov-Zhabotinsky reaction, discovered in 1951, may be the first completely understandable laboratory example of pattern formation in a chemical system that involves nothing more than chemical reaction and molecular diffusion. That same year, in 1951, Alan Turing investigated the theoretical possibilities of pattern formation by reaction/diffusion as "The chemical basis of Morphogenesis." The B/Z reaction is an example of a chemical system that shows spatial, periodic and wave properties that suggests that morphogenetic self-organization might follow similar pathways in both inorganic and organic systems. (cf. Slime Mold)
from Arthur T. Winfree, When Time Breaks Down, p. 168


The B/Z reaction generates concentric rings like target patterns that slowly travel outwards from centers that spontaneously arise. .The reactions that produce the patterns have the following characteristics: First, there is a positive feedback effect so that a substance (Bromous acid) stimulates its own production, and a wave of production spreads out. But Carbon Dioxide is also produced, which inhibits the production of Bromous acid. The B/Z reaction is sufficiently complex that it oscillates rather than settling down to equilibrium, and in a flat petri dish, which is essentially a two-dimenstional space, propagating waves of bromous acid production are initiated from regions where the process gets a head start, often due to a bit of dust on whose surface the reactions are slightly accelerated, followed by a wave of inhibition.When expanding rings enounter one another they disappear -- They do not form interference patterns-- because bromous acid is inhibited behind the wave front and cannot immediately switch to production again. If a slight shear is introduced by tipping the petri dish gently to one side, spiral waves will get started and will tend to take over, displacing the concentric circles. The period at the generating center of the spiral wave is slightly smaller than that of the target pattern. Its initiator is a wave propagating around in a little circle at the center whose cycling time is the minimum time there can be between initiations. If the reagents are kept well-mixed by stirring, the whole system can change periodically from one state to another, so that changes occur in time but are spatially homogeneous. In this case, the BZ reaction settles into oscillations that make it a chemical clock, and is referred to by Prigogine and Stengers as an example of self-organization.

(Other examples include Liesagang patterns, Benard convection cells, viscous "salt fingers" and precipate "needles" and Osmotic growths.) (see Zeleny, Klir, and Hufford "Precipitation Membranes, Osmotic Growths, and Synthetic Biology" In Artificial Life 2) 

Investigations into the origins of life have concentrated on systems that might provide transitions from the inorganic to the organic. See, for example, A.G. Cairns-Smith's theories about clays in Genetic Takeover and the Mineral Origins of Life. The clay theory for the origin of life begins with the necessity of liquid water, whose major effect on a planet such as the earth is to weather rocks to clays. Clays are two-dimensional crystals, that store information in the distribution of ions like silicon, aluminum, iron, and magnesium in the crystal lattice. Replication is the process by which the distribution of the ions from the mother clay is copied into the daughter clay.