Yota Suzuki, M. Shimizu, T. Okamoto
Oct 1, 2016
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Abstract
A detailed kinetic study of the reactions of phenylboronic acid (PhB(OH)2), 2-methylphenylboronic acid (2-MePhB(OH)2), 2-isopropylphenylboronic acid (2-iPrPhB(OH)2), and 1-hydroxy-3H-2,1-benzoxaborole (BxB(OH)) with D-fructose was carried out to clarify the nature of the reactive boron species in D-fructose sensing and investigate the corresponding reaction mechanism. Both the boronic acids (RB(OH)2) and boronate ions (RB(OH)3−) were reactive toward D-fructose, while out of the five D-fructose anomers only α-D-fructofuranose was reactive toward boron species. The reactions of all substrates proceeded consecutively in two steps (steps 1 and 2). We concluded that the first intermolecular step (step 1) corresponds to the parallel reactions (two parallel reactions for 2-iPrPhB(OH)2 and three for the other systems) of the boronic acid and the boronate ion with α-D-fructofuranose to form bicoordinate complexes (mixture of exo- and endo-isomers), and the second intramolecular step (step 2) corresponds to the formation of a tricoordinate α-D-fructofuranose complex from the bicoordinate complexes. It was found that both the boronic acid and the boronate ion were kinetically reactive toward D-fructose, with the latter being more reactive.