Recognition of <scp>d</scp>-Glucose in Water with Excellent Sensitivity, Selectivity, and Chiral Selectivity Using γ-Cyclodextrin and Fluorescent Boronic Acid Inclusion Complexes Having a <i>Pseudo</i>-diboronic Acid Moiety

Abstract

Fluorescence recognition of d-glucose in water with excellent sensitivity, selectivity, and chiral selectivity is desired because d-glucose is an essential component in biological and pathological processes. We report an innovative approach that exploits the 1:2 stoichiometric inclusion complexes of γ-cyclodextrin (γ-CyD) with two molecules of fluorescent monoboronic acid-based receptors, which form a <i>pseudo</i>-diboronic acid moiety as the recognition site for d-glucose in water. Two monoboronic acids (<b>1F</b> and <b>2N</b>) were easily synthesized without heating or column purification. The 1:2 stoichiometric inclusion complexes (<b>1F/γ-CyD</b> and <b>2N/γ-CyD</b>) were prepared in a mixture of dimethyl sulfoxide/water (2/98 in v/v) by mixing γ-CyD and the corresponding monoboronic acids. Both <b>1F/γ-CyD</b> and <b>2N/γ-CyD</b> exhibited strong turn-on response to d-glucose with excellent selectivity over nine other saccharides in the water-rich solvent at pH 7.4 owing to the ditopic recognition of d-glucose by the <i>pseudo</i>-diboronic acid moieties. The limits of detection of <b>1F/γ-CyD</b> and <b>2N/γ-CyD</b> for d-glucose were 1.1 and 1.8 μM, respectively, indicating the remarkable sensitivity for the detection of d-glucose at μM levels. <b>1F/γ-CyD</b> and <b>2N/γ-CyD</b> also demonstrated chiral-selective recognition of d-glucose, which is apparent from the 2.0- and 6.3-fold enhancement of fluorescence by the addition of d-glucose relative to l-glucose addition, owing to the chiral <i>pseudo</i>-diboronic acid moieties produced by the chiral γ-CyD cavity. To the best of our knowledge, <b>2N/γ-CyD</b> has the highest d/l selectivity among hitherto reported fluorescent diboronic acid-based receptors.