Synthetic "locks" that can bind straight, skinny molecules but block out bent or fat ones have been created by researchers at the University of Illinois (Champaign). These synthetic receptors may be used as molecular sensors and selective catalysts.
"Molecules are the messengers between cells and even between whole organisms," says Ken Suslick, a chemistry professor at the University of Illinois. "The cells understand these by recognizing messenger molecules, often on the basis of their shape."
At the heart of Suslick's synthetic receptor is a metalloporphyrin (a metal ion bound in the middle of a molecular ring), much like the iron compound found in the hemoglobin in blood. To this core are attached dendrimers (branching polymers) that spread out like limbs on a tree.
Depending on where the dendrimers are placed, the resulting receptor has either a round hole or a narrow chimney above and below the metal ion, Suslick says. The shape of these pockets determines the shape of molecules that can bind to the metal. Suslick and his colleagues have altered the binding strength of various molecules to the metal at the center of these artificial receptors.
"Just the shape of an incoming molecule can change its binding by almost a million-fold," Suslick says. "Such exquisite selectivity is very much the way that living systems control chemical reactions."
Industrial chemists use a similar technique when manipulating chemical feedstocks. For example, improving octane ratings in gasoline often uses shape-selective catalysts called zeolites. Based on their molecular shapes, these can select for the formation of high-octane molecules during the reforming of crude oil.
Suslick and his research group are interested in using synthetic receptors as shape-selective catalysts and sensors. For example, by controlling the access of certain molecules by their shapes, oxidation can be carefully directed to specific sites in complex molecules. As another example, the ability to detect molecules on the basis of their shapes is extremely important when developing artificial noses and other chemical sensors.
This research was reported in the Jan. 12, 1999, issue of the Journal of the American Chemical Society.
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