May 4, 2009 Volume 87, Number 18 | p. 45 | first appeared online May 1

Collective Behavior In Chemistry

Scientists note that the oscillating Belousov-Zhabotinsky reaction requires a requisite number of particles to get started

Video Chemical Undulation A collection of catalyst-loaded particles undergoes the Belousov-Zhabotinsky oscillating reaction. Launch Video Zhaoyang Huang * Macromedia Flash Player 8 is required to view video.

Zhaoyang Huang The number of particles in a group dictates the start of a colorful spiraling oscillation (blue), as shown in this microscope photo.

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 HBrO 3 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."

Chemical Undulation

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