The Belousov-Zhabotinsky (BZ) reaction is the prototype chemical excitable medium. In the ferroin/ferriin-catalyzed reaction in a Petri dish one sees spontaneous formation of target patterns: outward-moving waves of oxidation (blue) generated by oscillatory pacemakers in an otherwise red, reduced, excitable medium (figure). In contrast, one typically sees phase waves (near synchronous behavior) in the Mn catalyzed reaction, even if targets form. We explored pacemaker dynamics and phase wave initiation using ferroin/ferriin, Mn2+/3+ and combinations as catalysts. BZ dynamics was modelled with the Oregonator, a relaxation oscillator with a fast activator (HBrO2) and a slow inhibitor (Br-), generated by the catalytic oxidation of brominated MA. A stoichiometric factor f parametrizes Br- generation; each molecule of catalyst reduced generates f/2 Br- ions. We stimulated oscillations in several ways. (1) Adding Ag+ to explore sensitivity of the ferroin-catalyzed reaction to reductions in [Br-]. Adding 0.3 μL of 10-7 M Ag+ generated targets; as a control adding 10-8 M Ag+ did not. (2) Adding Mn to the ferroin-catalyzed reaction reduced f because Mn3+ can oxidize un-brominated MA, generating no Br-, but ferriin cannot. This generated targets by destabilizing the reduced, high-[Br-] steady state of the background medium (f was reduced from ~2 towards ~1.5, where a steady state is least stable). (3) Similarly, adding ferroin to the Mn catalyzed reaction appeared to increase f towards ~1.5 from a lower value, again generating targets. We also explored the effects of mixed catalysts, frequently seeing a combination of pacemakers in an otherwise oscillatory medium. The transition from isolated pacemakers to large-scale phase waves might be a useful analog of the transition to epilepsy, in which decreasing f from ~2 corresponds to decreases in production of the inhibitory neurotransmitter GABA.

Effect of small perturbations on the Belousov-Zhabotinsky reaction

255th National Meeting (2018)

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