Direct spectroscopic observation of binding of sugars to polymers having phenylboronic acids substituted with an ortho-phenylazo group.

A novel vinyl monomer, 3-dimethylamino-6-(p-methacrylamidophenylazo)phenylboronic acid (AzoPBA), which had been prepared by the coupling of p-aminophenyl methacrylamide hydrochloride with m-dimethylaminophenylboronic acid in the presence of sodium nitrite, was polymerized with 3-dimethylaminopropylacrylamide (DMAPAA). The copolymer obtained (Poly(DMAPAA/AzoPBA)) bound to sugars such as fructose and glucose in a weakly alkaline region (8 < pH), which was indicated by the absorbance change of the diphenylazo group at 557 nm. In contrast with this, a copolymer of N,N-dimethylacrylamide (DMAA) and the AzoPBA (Poly(DMAA/AzoPBA)) bound to sugars in a more alkaline region (9 < pH). The larger sensitivity of the former copolymer to the sugars than the latter in a weakly alkaline region is due to the supporting effect of tertiary amino group in the DMAPAA residue to the binding of sugar to the phenylboronic acid moiety. The association constant (K) of boronic acid residue in these copolymers with fructose was larger than that with glucose. These results indicated the usefulness of the DMAPAA/AzoPBA copolymer for the sensing of sugars in the weakly alkaline region near the physiological pH.