Application Of Aggregation-induced Emission Phenomenon In Saccharides Recognition And Detection

Recently boronic acids have attracted considerable research attention for their promising applications in the area of carbohydrate receptors and artificial lectins. However, those artificial receptors' selectivity is tightly dependent on its binding affinity to sugars and thus constricted as a result of conventional signal transduction mechanisms. The essences of the present work are to design and synthesize boronic acid decorated tetraphenylethene (TPE) fluorophore, in an attempt to apply "restricted intramolecular rotation" mechanism of "aggregation-induced emission (AIE)" phenonmenon into saccharides recognition and make fundamental contribution to the design of saccharide receptor.Firstly, a conceptually new "light-up" biosensor with a high specificity for D-glucose in aqueous media has been developed based on the AIE effect. The emission from a tetraphenylethene-cored diboronic acid (TPEDB) was greatly boosted when the fluorogen was oligomerized with Glu because of restriction of the intramolecular rotations of the aryl rotors of TPE by formation of the oligomer. However, little change in the light emission was observed when TPEDB was mixed with D-fructose, D-galactose, or D-mannose, as these saccharides are unable to oligomerize with the fluorogen. This sensing mechanism regarding "oligomerization induced emission enhancement" provides a new approach to design fluorescent receptors with high selectivity to D-glucose.Secondly, an unexpected recognition of β-cyclodextrin (CD) from α-and γ-CDs based on boronic acid/diol interaction, rather than normal host-guest interaction, was achieved. The emission from a diboronic acid-containing tetraphenylethene (TPEDB) was amplified upon addition of β-CD, whereas there was almost no response for its analogues, α-and γ-CDs. TPEDB is proposed and verified to be anchored onto the wide rim of β-CD through cooperative interaction between dual boronic acid groups and alternative diols sites of β-CD, which lead to the restriction of intramolecular rotations of its phenyl rings and enhancement of fluorescent emission. This conceptually new binding model sheds a light on the design strategy for oligosaccharide receptors, and paves a new vanue toward construction of cyclodextrin based supramolecular assemblies.