Chemical waves curl around tiny globe.

Chemical waves curl around tiny globes

A barely visible streak of blue chemicals appears spontaneously at the north pole of a red, translucent globe the size of a small peppercorn. It winds southward behind the globe and emerges at the front just of the equator. The spiraling blueness then dips into the southern hemisphere as it crosses the tiny orb's front, once again disappearing to the other side. Even before the streak spirals into itself and vanishes at the south pole, another one pierces the red-again north pole and begins its own twisting journey south.

Through a microscope, chemists Kenneth Showalter and Jerzy Maselko of West Virginia Univeristy in Morgantown spy these and even more exotic periodic chemical happenings on the surfaces of polymeric beads immersed in unusual chemical solutions. "It's a psychedelic effect," Showalter says.

The bead surfaces harbor systems of oscillating reactions that alternate between two colors. By getting the reactions to occur on spherical surfaces for the first time, the researchers can elicit behaviors impossible for such chemical systems in their more common experimental condition -- spread onto a flat petri dish. The scientists report their observations in the June 22 NATURE.

For years researchers have studied these odd series of chemical reactions, which produce concentric-circular and spiral patterns that oscillare both in space and in time. The mathematical equations describing the reaction dynamics are nearly the same ones describing such phenomena as propagating flame fronts inside an engine's piston, the complex and contrary motions of a heart teetering toward cardiac arrest and the ebbs and flows of animal populations, notes Arthur T. Winfree of the University of Arizona in Tucson.

Showalter adds that studying these oscillating reactions on nonflat geometries could lead to insights about biological processes that operate according to the same dynamical rules that govern the oscillating reactions. "It's just a lot easier to study the chemical systems than the biological systems," he says.

The most studied chemical oscillator--named the Belousov-Zhabotinsky or B-Z reaction after is Russian discoverer and developer, respectively--involves a complex interplay in acidic solutions of organic molecules like malonic acid, inorganic ingredients such as the negatively charged bromate ions, and a metal-containing catalyst that doles out or takes back an electron at different phases of the oscillation. The rapidity of the oscillations depends on the relative concentrations of the solution components, and the specific behavior at a point in the solution reflects variations in the local chemical environment.

Instead of allowing the catalyst to roam the solution freely, the Morgantown scientists load ferroin, and iron-containing catalyst, onto the roughly 1-millimeter beads. The beads' overall negative charge also keeps a major B-Z reactant--bromate ions -- from penetrating the beads' interiors. "This forces the reaction to occur at the surface," Showalter explains. "We go from bead to bead looking for interesting behavior."