Oscillating to a copper beat.

Oscillating to a copper beat

Start with an alkaline potassium-thiocyanate solution, mix it with hydrogen peroxide and add a pinch of copper sulfate. The result is a solution that oscillates in color between dark yellow and pale yellow or colorless. This recipe is the most recent addition to the growing family of oscillating chemical recent addition tot he growing family of oscillating chemical reactions. It may represent, says Hungarian chemist Miklos Orban of L. Eotvos University in Budapest, "a member of a fundamentally new group" of oscillating reactions. His report appears in the Oct. 29 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.

Simple chemical oscillators are of interest because they provide insight into biochemical systems that regulate the heartbeat and other periodic biological processes. until a few years ago, all of the known, nonbiological oscillators involved iodate, bromate or chlorite compounds (SN: 9/19/81, p. 188). "It was a little confining that these were all oxyhalogen systems," says Irving R. Epstein of Brandeis University in Waltham, Mass. In 1984, two chemists at the University in Waltham, Mass. In 1984, two chemists at the University of Montana in Missoula found an oscillator using only sulfide and sulfite ions with methylene blue as a catalyst. Later, Epstein and Orban reported a simple oscillating system involving only sulfide ions and hydrogen peroxide. The new thiocyanate oscillator, says Epstein, "extends that work into another sulfur-based system."

The new system is noteworthy because it is one of the few that oscillates while sitting around in a stirred beaker. "The vast majorityof oscillators now known require a flow in order to keep them oscillating," says Epstein. Fluctuations are seen in the color, the potential at a platinum electrode and the amount of oxygen produced.

Even in a flow system, in which fresh reactants are continually fed into a reaction chamber while products are removed, the thiocyanate oscillator shows unusual behavior. Depending on the flow rates of the different incoming solutions, the system may take on one of two steady states or an oscillating state. Moreover, slight perturbations can shift the system out of any one state into either of the remaining two.