The effect of boronic acid-positioning in an optical glucose-sensing ensemble

The quenching of the anionic dye 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (pyranine) with three different boronic acid-substituted benzyl viologens was determined, and the fluorescence signal modulation obtained upon addition of glucose to the dye/quencher system was also studied. The benzyl viologen that contains boronic acids in the ortho-position (o-BBV) was found to display unique behavior, which can be rationalized by a charge neutralization mechanism facilitated by an intramolecular interaction between sp(3) boronate and the quaternary nitrogen of the viologen. Potentiometric titration and B-11 NMR spectroscopy were used to generate pH profiles for the boronic acids, which provide additional evidence for the proposed mechanism. (c) 2006 Elsevier Ltd. All rights reserved.