Development of Supramolecular Saccharide Sensors Based on Cyclodextrin Complexes and Self-assembling Systems

Cyclodextrins (CDs) are water-soluble host compounds having nano-size hydrophobic cavities that enable them to incorporate organic molecules in water. Optically inert CDs can be efficiently combined with various types of chromoionophores and fluoroionophores. In this study, using diverse combinations of phenylboronic acid fluorescent sensors and azoprobes with CDs, the unique saccharide recognition functions of CD, chemically modified CD, and CD gel complexes based on their synergistic function are clarified, thereby confirming their use as supramolecular saccharide sensors. To realize novel supramolecular chirality, the twisted structure of two ditopic azoprobes inside the γ-CD chiral cavity is controlled by multi-point recognition of guest ions in water. As different types of supramolecular saccharide sensors, phenylboronic acid-based self-assembling systems are also reviewed.

Saccharide Recognition Based on Self-Assembly of Amphiphilic Phenylboronic Acid Azoprobes

We designed amphiphilic phenylboronic acid azoprobes (B-Azo-Cn) and evaluated their saccharide recognition function in relation to the micelle formation changes of the self-assembled B-Azo-Cn. First, we evaluated B-Azo-C8 in a 1% methanol-99% water solution under basic conditions. The wavelength of maximum absorption in the ultraviolet-visible (UV-vis) spectra of B-Azo-C8 was shifted, and the solution showed a color change with the addition of saccharides. The morphology of B-Azo-C8 was evaluated using dynamic light scattering (DLS) measurements and transmission electron microscopy (TEM) observations. B-Azo-C8 formed aggregates in the absence of saccharides and in the presence of glucose. In the presence of fructose, micelle-formed B-Azo-C8 was dispersed, indicating that B-Azo-C8 changed its dispersion state by recognizing fructose. The effect of alkyl chain length on the saccharide recognition ability was examined as well. B-Azo-C4 and B-Azo-C12 did not recognize saccharides in a 1% methanol-99% water solution under basic conditions, indicating that an appropriate alkyl chain length was required for recognizing saccharides. The control of the hydrophilic-lipophilic balance (HLB) was a key factor for saccharide recognition.

The design of phenylboronic acid azoprobe–polyamidoamine dendrimer complexes as supramolecular sensors for saccharide recognition in water

Phenylboronic acid azoprobe–PAMAM dendrimer complex responded to saccharides and exhibited selective aggregation particularly with glucose at neutral pH.