A group of scientists at The Scripps Research Institute (TSRI) were able to demonstrate complex system behavior among small, reacting organic molecules by putting them in and out of a nanocapsule.
In the current issue of the journal Nature, a report from a group led by Julius Rebek, Jr., Ph.D., demonstrated that they could achieve chemical amplification (speeding up the reaction as it proceeded) without the presence of an autocatalyst (a product of the reaction that acts as a catalyst for more product).
"[The findings] show a different way of controlling reactivity," says Rebek, who is Director and Professor of The Skaggs Institute for Chemical Biology. "This is a way of turning a reaction on and off."
The Rebek group's autoamplification was made possible by carrying out a reaction in the presence of dimeric nanocapsules, which are like two identical half eggs that can close around a reactant molecule, sequestering it from the rest of the molecules in solution. The nanocapsules encapsulate molecules of the proper size and shape and inhibit their reactivity.
In the reaction, the sequestered molecules are dicyclohexylcarbodiimide (DCC), one of the reactants.
When DCC molecules are mixed with molecules of ptoluic acid and p-ethyl-aniline, they react to form an amide and a urea molecule.
But when the DCC molecules are mixed with the nanocapsules first, the reaction proceeds much more slowly, since the nanoencapsulation effectively reduces the concentration of DCC in solution.
However, the reaction proceeds nonlinearly it speeds up over time because the products of the reaction fit inside the nanocapsules. And, as the amide and urea molecules are produced, they displace the DCC molecules, freeing them to react.
In fact, the reaction resembles a chain reaction as the reaction proceeds, more and more of the product is made, and the end result is exponential growth. One molecule makes two, and these both di
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Contact: Robin B. Goldsmith
rgoldsmi@scripps.edu
858-784-8134
Scripps Research Institute
24-Jan-2002