Tricky Transformation: Bubbling gases tighten, then loosen, the grip of novel molecules on grime

Imagine if detergent could not only pick up grease from your clothes but also let it go on command. You might then prevent the detergent from going down the drain with the dirt.

A new class of compounds created by researchers in Canada and the United States switches between clingy and nonclingy forms upon exposure to common gases, including air.

Although not yet being considered for laundry, such switchable substances might serve as improved degreasers for heavy equipment, the compounds’ developers say. Perhaps more important, the compounds might aid in recovery of crude oil from oil sands and lead to more-efficient and less-polluting ways to manufacture polymers.

The team, led by Philip G. Jessop of Queen’s University in Kingston, Ontario, unveils the new work in the Aug. 18 Science. The group included researchers at the Georgia Institute of Technology in Atlanta.

Soaps, detergents, and the clingy versions of the new compounds are categorized as surfactants. One end of a typically threadlike surfactant molecule consists of a long, waxy tail that attracts oil and repels water. At the other end of the molecule, an electrically charged head does the opposite. While the head associates with water, the tail of a surfactant typically binds to oil globules or particles of dirt, enabling them to dissolve or become suspended in water.

Jessop and his colleagues have synthesized two new, nitrogen-containing organic compounds that can transform into surfactants. These amidines are electrically neutral in undisturbed water, but when carbon dioxide bubbles through, the compounds transform into amidinium bicarbonate salts that act as surfactants.

Moreover, when the researchers turned off the carbon dioxide, heated the liquid, and bubbled in air, nitrogen, or argon, the chemicals reverted to their nonsurfactant forms. This convertibility might make it possible to recover and reuse the compounds, according to the researchers’ report.

In an experiment with crude oil mixed in water, the researchers were “shocked” when turning off an amidine surfactant didn’t just stop the mixing process but also accelerated oil-water separation, Jessop says.

Other researchers have made switchable surfactants that were prohibitively expensive or toxic. The new ones promise to be cheap, notes Jessop, but their toxicity isn’t yet known.

“These are clearly exciting findings,” comments chemical engineer Vijay T. John of Tulane University in New Orleans. “The full reversibility and ease of switching indicate relevance and value to the chemical industry.”

Materials chemist James R. McElhanon of Sandia National Laboratories in Livermore, Calif., applauds the method of switching because it doesn’t require added chemicals that would stay in the solution.

Not everyone is so sanguine. Bubbling of gases to switch the state of the compounds would be “extremely cumbersome,” contends Manilal Dahanayake of the chemical company Rhodia in Cranbury, N.J. Moreover, he says that the new amidines may be toxic to aquatic organisms.

Mainak Ghosh of Imperial Oil Resources in Calgary, Alberta, says that it’s too soon to know how well the new compounds might aid oil recovery, but that they could prove to be “a breakthrough invention.”

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