pH dependent equilibria of poly(anilineboronic acid)-saccharide complexation in thin films

The complexation of saccharides with poly(anilineboronic acid) as a function of pH has been studied with simultaneous measurements of open-circuit potential and mass change. This study provides an insight into this reaction as well as the relationship between complexation and open-circuit potential and the optimum pH for complexation of D-fructose and D-glucose. The optimum pH values for poly(anilineboronic acid)-D-fructose and -D-glucose complexation are near the pK(a) values of the complex reported in homogeneous solution. At physiological pH (7.4), the apparent binding constant Of D-fructose and D-glucose with poly(anilineboronic acid) is 19.2 and 0.2 m(-1), respectively. In contrast, at pH 9.0, the apparent binding constant of D-glucose with poly(anilineboronic acid) is 12 m-1, double than that Of D-fructose. The decrease in complexation in the polymer films at pH values above the pK(a) of the complexes is in contrast to the behavior in homogeneous solutions. This trend is observed for both D-fructose and D-glucose using open-circuit potential, mass change and polarization modulated infrared reflection absorption spectroscopic measurements. Also, the complexation is limited in the polymer film, i.e., <= 23% boron is involved. These results suggest that steric and/or electrostatic interactions may play an important role in complexation within polymer films.