Diarylboronic Receptor with Lyotropic Acidity for Monosaccharide Recognition in Aqueous Solution: Binding Thermodynamics and Interaction Mechanism

Tailoring of the arylboronic acid structures is essential for developing specific monosaccharide (MS) recognition receptors, in which the designed boronic acid derivative should have an appropriate p<i>K</i>_a, a stereostructure matched with the target MS, and an easily detectable method. Herein, we report a novel bis(<i>m</i>-benzylammonium) boronic acid with an ethyl spacer (BTEAB) as the receptor molecule to MS. Owing to its unique lyotropic acidity and intrinsic fluorescence characteristics in aqueous solution, BTEAB provides a new strategy for the design of MS sensors. The cation-π interaction promotes the self-assembly behavior of BTEAB and the lyotropic acidity and fluorescence quenching induced by aggregation. The aggregation behavior of BTEAB was confirmed by Rayleigh light scattering, fluorescence, and ¹H NMR, and its lyotropic acidity is quantified by the decrease in its acid dissociation constant p<i>K</i>_a. It was found that the esterification of BTEAB with three model MSs (fructose, glucose, and galactose) does not destroy the aggregates, indicating that the lyotropic acidity is an applicable characteristic for regulating the pH value of MS recognition. The affinity of BTEAB with MS and the structures of BTEAB-MS ester were studied mainly by isothermal titration calorimetry (ITC), fluorescence and NMR. The interaction mechanism of BTEAB with different MS was proposed. This work provides new insights into MS recognition under about physiological pH adjusted by diarylboronic acid aggregation.