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Forcing Reactants To Click

By pushing alkyne-coated elastomeric tips onto an azide-covered surface, chemists induce the Huisgen reaction and quantify the force needed to do so

by Bethany Halford
July 28, 2014 | A version of this story appeared in Volume 92, Issue 30

There is a disturbance in the force-induced reaction community. Chemists disagree as to whether it’s possible to spur on the Huisgen reaction—the most popular of the so-called click reactions—by forcing the azide and alkyne reactants into contact with each other. Seeking to clear up the matter, researchers led by Adam B. Braunschweig of the University of Miami created azide-coated monolayers on a surface of gold-covered glass and then used arrays of elastomeric tips to push alkyne-containing fluorescent inks into this surface (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja504137u). Fluorescence and electrochemical experiments show that the triazole-forming reaction does take place. “Our technique allows us to quantify the exact force being applied at the surface so we could extract important parameters, such as activation volume and reaction rate, which provided insight into the reaction mechanism,” Braunschweig says. His group found that the reaction rate is a function of applied force and, surprisingly, monolayer chain length. “The differences in reaction rate and yield observed by previous groups can be rationalized because the different groups applied different amounts of force to the surface, and this discrepancy explains the differences in observed products,” he adds.

Elastomeric tips coated with alkynes are pressed onto an azide-coated surface, forming a triazole.
A schematic showing a triangle with alkyne-R groups being shoved down on an azide SAM.
Elastomeric tips coated with alkynes are pressed onto an azide-coated surface, forming a triazole.


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