Sugar Recognition with a Dihydroxyborane Derivative Layer Assembled on Gold Electrode

Abstract

Properties of dihydroxy[3-(3-mercaptopropanamido)phenyl]borane(1) in the form of self-assembled monolayer on a gold electrode were studied by quartz crystal microbalance(QCM) method. The monolayer of 1 with surface coverage of 7.6×10^-10mol/cm² was obtained by immersing the gold electrode in aqueous solution of 1. The monolayer was found to bind D-fructose reversibly to form sugar/boran complexes in alkaline media. Selectivity of sugars(association constantsK=100, 4000, ≈0 and ≈0M^-1 for D-glucose, D-fructose, sucrose and methyl α-D-xylopyranoside, respectively) was consistent with the previous works concerning homogeneous solution of dihydroxyboranes. Although pH dependence of the sugar-binding ability of the dihydroxyborane in monolayer resembled that in homogeneous solution, the following remarkable characteristics were found for the assembled dihydroxyborane: (1) The dihydroxyborane in monolayer exhibited a greater pK_a value than that in homogeneous solution, which was explained by the interaction between neighboring trihydroxoborates RB(OH)₃^-. (2) The sugar-binding ability of the assembled dihydroxyborane was noticeably sensitive to pH depending on the square of [trihydroxoborate]/[dihydroxyborane] ratio.