We have synthesized a series of azobenzene boronic acids that have isomerism-dependent binding affinities with diols. The thermodynamically-favored E isomer binds weakly with diols to form boronic esters. Visible light-mediated E-Z isomerization of the azobenzene boronic acid enhances diol binding between 2- and 20-fold depending on azobenzene and diol structure. Competition experiments and computed geometry-optimized structures suggest that the changes in binding affinity originate from destabilization of the E boronic esters. We can tune the E:Z ratio with different wavelengths of irradiation, enabling wavelength-dependent binding. The observed changes in binding affinity are preserved for a variety of diols, from simple ethylene glycol to cyclic diols, catechol, and biologically relevant drugs and polyols. Furthermore, we show that switchable diol binding occurs in both organic and aqueous environments, and can be used to bind and release a fluorescently tagged diol. By tethering this photoswitch to multi-arm poly (ethylene glycol) polymers, we can realize phototunable dynamic covalent hydrogels. We envision that photoswitchable equilibria will serve as a tool for the reversible ligation of molecular and macromolecular species.

Using light to control boronic-acid- ester equilibria

ACS Fall 2020 Virtual Meeting

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