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The Design of Boronic Acid Spectroscopic Reporter Compounds by Taking Advantage of the pKa-Lowering Effect of Diol Binding:  Nitrophenol-Based Color Reporters for Diols

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journal contribution
posted on 19.03.2004, 00:00 by Weijuan Ni, Hao Fang, Greg Springsteen, Binghe Wang
The complex that forms between a boronic acid and a diol is often much more acidic than the starting boronic acid. In conditions where the solution pH is between the two pKa values, the boron atom will convert from a neutral trigonal form to an anionic tetrahedral form upon complexation. Such a change is likely to dramatically alter the electron density of neighboring groups. Utilizing this effect, we have designed and synthesized two nitrophenol-based boronic acid reporter compounds that change ionization states and therefore spectroscopic properties upon diol binding. Both compounds show significant UV changes upon addition of saccharides. For example, a blue shift of the absorption max from 373 to 332 nm was observed with the addition of d-fructose to 2-hydroxy-5-nitrophenylboronic acid at neutral pH. Such a reporter compound can be used as a recognition and signaling unit for the construction of polyboronic acid sensors for the selective and specific recognitions of saccharides of biological significance.