Design of a Fluorescent Boronic Acid‐Functionalized Pyranoflavylium Receptor to Host and Release Diol‐Rich Bioactive Analytes in a pH‐Dependent Manner

ABSTRACT Smart materials composed of bioactive compounds and stimuli‐responsive dyes are currently of great interest in different disciplines, from the food industry to biomedical applications in sensing, theranostics, imaging, and drug/gene delivery. This work synthesized a new symmetrical pyranoflavylium‐boronic acid derivative, structurally characterized and complexed with relevant diol‐based biological molecules such as (+)‐catechin, L‐lactic acid, and D‐glucose. The model systems were studied by fluorescence technique in the presence and absence of those ligands and were able to recognize those analytes with different association constants and in a pH‐controlled fashion. Overall, (+)‐catechin revealed the greatest affinity with the dye with an association binding constant ( K a ) of 48895 ± 1 M −1 rather than with L‐lactic acid ( K a 595 ± 2 M −1 ) or D‐glucose ( K a 7 ± 2 M −1 ). The covalent interaction between (+)‐catechin and the pyranoflavylium receptor was demonstrated to be pH‐dependent, occurring near of the dye p K a (pH∼8), while for acidic pH values the (+)‐catechin is released from the dye, recovering the initial fluorescence of its free flavylium cation species. The formation of the diol‐boronate ester complex was confirmed by 11 B NMR spectroscopy in the presence of (+)‐catechin only at a neutral pH value.