Down with Metals

With their eyes on the public health hazards and economic implications of metal contaminants in the environment and in industrial reaction media such as those used to make pharmaceuticals, chemist Craig S. Wilcox of the University of Pittsburgh and graduate student Mark R. Ams report what they assess as a "significant step" toward new types of metal-scavenging agents dubbed "precipitons" (J. Am. Chem. Soc., published online Dec. 13, dx.doi.org/10.1021/ja0561340).

Wilcox and Ams have synthesized new precipiton structures that in solution undergo a swift bent-to-straight conformational change when illuminated with visible light captured by a light-absorbing appendage. That shape change can lead to precipitation of metal-containing complexes.

They demonstrate the principle with a ruthenium-hubbed cluster of bipyridine molecules attached to a linear multiring ligand, as shown. Transfer of energy captured by the ruthenium complex to the bent ligand causes it to straighten up.

The next step is to expand this model system so that it can grab the metals that need to be scavenged. It's worth the effort, Wilcox explains, because products and contaminants alike "can be isolated in high purity without extraction, distillation, or chromatography."