DESIGN OF A VISUALIZED SUGAR SENSING SYSTEM UTILIZING A BORONIC ACID AZOPYRIDINE INTERACTION

The boronic acid-amine (B-N) interaction was applied to the molecular design of a visualized sensing system for saccharides. 3-Nitrophenyl-b oronic acid (3b) interacts with the pyridine nitrogen of 4-(4-dimethyl aminophenyl-azo) pyridine (2) in methanol and changes its color from y ellow to orange. Added saccharides form complexes with 3b and enhance the acidity of the boronic acid group. As a result, the B-N interactio n becomes stronger and the intensified intramolecular charge-transfer band changes the solution color to red. By combined H-1-NMR and absorp tion spectroscopic studies, four association constants governing the p resent ternary complex system have been determined. In case of D-fruct ose, the 3b.D-fructose complex can interact with 2240 times more stron gly than 3b and the 2.3b complex can associate D-fructose 241 times mo re strongly than 3b. Clearly, the B-N interaction not only enables the colorimetric saccharide sensing but also enhances the association abi lity (i.e., sensitivity). Thus, the present paper offers a novel basic concept for molecular design of visualized saccharide sensing systems .