Detailed Reaction Mechanism of Bis-(o-Aminomethylphenylboronic Acid)-based Receptors with Various Length Methylene-chain Linkers with D-Glucose

The detailed reaction mechanisms of several bis-(o-aminomethylphenylboronic acid)-based receptors, linked with methylene chains of different lengths (i. e., DBAn (n=2, 3, and 4) having 2n methylene groups), with D-glucose were kinetically investigated in methanolic aqueous solutions. The pK_a measurements showed that the two boronic acid moieties in DBAn were equivalent and had no electronic interaction between them. DBA2 reacted with D-glucose to form a 1 : 1 product, in which two boronic acid moieties in one molecule of DBA2 were bound to two reactive sites in one molecule of D-glucose. DBA3 and DBA4 reacted with D-glucose to form a 1 : 2 product, in which the two boronic acid moieties in one molecule of DBA3 or DBA4 were bound to two molecules of D-glucose simultaneously through one reactive site. Thus, in the recognition of D-glucose, the distance between the two boronic acid moieties in DBAn was optimal for n=2 and too long for n=3 or 4.