Compounds break bonds holding dangerous pollutants together

Everything from the manufacture of new materials to the creation of modern medications relies on chemicals known as metal-based catalysts. Catalysts pack a double punch: Even as they greatly increase the rate of chemical processes, they regenerate so they can be used again.

Catalysts also can be designed to break or make powerful chemical bonds at one end of a molecule while leaving the other end to sit quietly inactive. For this reason, many chemists — particularly, inorganic chemists who often study metals and their reactivity — are on a continuing quest for new catalysts.

At The Johns Hopkins University, researchers have developed a new set of molecules that has the potential to catalyze a wide variety of chemical reactions, including — but not limited to — the clean-up of common but quite dangerous groundwater pollutants called organohalides. Scientists will announce their results in late August at the American Chemical Society's annual summer meeting, held this year in Philadelphia.

"Organohalides comprise a high percentage of the priority pollutants as registered by the EPA, so this is a pretty important advance," said David P. Goldberg (pictured at right), associate professor in the Department of Chemistry in the Krieger School of Arts and Sciences at Johns Hopkins. "In addition, our molecules have the potential to catalyze a number of other reactions important in the synthesis of specialty chemicals for industry."

In the biological world, enzymes are the catalysts which function inside cells, and many enzymes depend on metal held inside specially built organic molecules called porphyrins. Using these as a model, Goldberg's team synthesized a variation that changed the properties of the reactive metal in the center.

Called a "corrolazine," the new ring contains one less atom than other, better-studied porphyrins. These molecules are fascinating from a fundamental perspective, Goldberg said. The tiny change made in their structure imparts some very different properties than the same system found in nature, and may allow scientists to catalyze reactions in very different ways from their natural counterparts.

"By studying these natural mimics, we can learn a great deal about why nature — actually, evolution — made certain choices in the design and development of enzymes," Goldberg said.

Though some of the molecules being investigated by Goldberg's team are important synthetic precursors that can ultimately be used in making specialty chemicals and pharmaceuticals, other recent work in the group, spearheaded by graduate students Joseph Fox and David Capretto, has focused on how to use the new catalysts to render the groundwater pollutants called organohalides harmless by way of a simple chemical reaction.

"Organohalides can be transformed into safer compounds by breaking the bonds between the halogen and carbon atoms they contain," Goldberg said.

Goldberg's work, funded largely by the National Science Foundation, has been recognized by the Dreyfus Foundation, which awarded him one of nine Dreyfus Postdoctoral Fellowships in Environmental Chemistry given out this year nationwide. These prestigious awards are intended to fund the salary and expenses of an outstanding post-doctoral fellow for two years in the lab of the sponsor.

"Though this work represents a step forward, there is still an enormous amount of work to be done, including finding what metals work best under what conditions," Goldberg said.