Collective Behavior In Chemistry

Synchronized behavior seen in biology that leads to the rhythmic contraction of groups of heart muscle cells or the undulation of bacterial cilia occurs in chemistry, too. Kenneth Showalter and Mark R. Tinsley of West Virginia University; Annette F. Taylor of the University of Leeds, in England; and colleagues have shown that iron-impregnated particles can spontaneously undergo the exotic oscillating Belousov-Zhabotinsky (BZ) reaction that produces colored waves and spirals, but only once a collection of particles reaches a critical number (Phys. Rev. Lett. 2009, 102, 158301). This simple chemical system gives scientists a chance to probe "quorum sensing" behavior, which is ordinarily difficult to do with complex biological systems, Showalter says. The team's study builds on recent work from the Showalter and Taylor labs (Science 2009, 323, 614). Groups of particles containing the BZ catalyst ferroin sit quietly in an unstirred BZ reaction solution containing HBrO₃ and bromomalonic acid, unless the groups contain the key number of particles. The oscillating reaction then kicks off. Showalter says the collective behavior of the particles "is much like that of bacteria when they are growing in a medium on a surface."

A collection of catalyst-loaded particles undergoes the Belousov-Zhabotinsky oscillating reaction.