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Research Highlight: KALOW

Using Visible Light to Tune Boronic Acid–Ester Equilibria

Dynamic covalent reactions are widely exploited for the discovery and manipulation of new compounds, reactions, and materials. When incorporated into polymer networks, these reversible reactions enable dynamic properties, such as self-healing and stimuli-responsiveness. Professor Julia Kalow and coworkers have developed a series of compounds that can photoregulate the dynamic equilibrium between boronic acids and diol-containing compounds, such as catechols and saccharides, to form boronic esters. By tethering an azobenzene photoswitch to a boronic acid, the thermodynamics of the esterification reaction could be controlled by the azobenzene’s isomerism, which in turn can be controlled by light. This system can be thought of as molecular “catch and release” with light. Experimental and computational studies suggest that the E azobenzene discourages the boronic acid from reacting with diols. Photoisomerization to the Z isomer with red or green light favors boronic ester formation, which is reversed upon blue light irradiation. The reversibility of these processes and the exclusive use of visible light represent significant advances in the control of dynamic covalent reactions, while their marriage with azobenzenes expands the utility of this well-known photoswitch.

 This work was published as an article in J. Am. Chem. Soc. and highlighted in the December 4, 2020 issue of Science. Current work in the Kalow lab employs this chemistry to construct responsive hydrogels to study the way that cells respond to mechanical changes in their environment. 

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