Sugar Recognition with a Dihydroxyborane Derivative Layer Assembled on Gold Electrode
Kenji OSHIMA*, Kouta KOBAYASHI†, Takeshi YAMAUCHI, Masato SHIMOMURA and Shinnosuke MIYAUCHI
Department of Bioengineering, Faculty of Engineering, Nagaoka University of Technology; 1603-1, Kamitomioka, Nagaoka-shi 940-2188 Japan
† Present address: Hokuto Denko Corporation; 4-22-13, Himonya, Meguro-ku, Tokyo 152-0003 Japan
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 7.6×10−10 mol/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 constants K=100, 4000, 0 and 0 M−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 pKa 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.
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