Boronic Acid-diol Research Articles

Molecular Design of Boronic Acid-Based Dye Receptors for Nucleosides

Abstract Chromophric receptors for nucleosides were designed utilizing the boronic acid–diol interaction which effectively operates in aqueous solution. Receptors consist of a boronic acid moiety and a dimethylaminophenylazo moiety. The boronic acid moiety forms a covalently-bonded ester linkage with the 2,3-diol group in nucleosides in a reversible manner and the anionic charge generated on the boron atom is stabilized intramolecularly by the pyridinium cation. The azo moiety can overlap with the heteroaromatic ring moiety in nucleosides to stabilize the complex. The complexation constants could be conveniently determined by the absorption spectral change. Comparison of the complexation constants with those of 2-deoxyadenosine without 2-OH and 1,4-anhydroerythritol without the heteroaromatic ring established that the complex formation is primarily due to the boronic acid–diol (2,3-diol) interaction and secondarily facilitated by the hydrophobic and/or π–π stacking interactions.

Chemical affinity systems—I: pH dependence of boronic acid-diol affinity in aqueous solution

A comprehensive theory of complex formation between boronic acids (RB(OH) 2) and organic diols is introduced and compared with experimental results for two exemplary systems using a direct spectrophotometric method over a wide range of pH values. The complexes of benzeneboronic acid with 4,5-dihydroxynaphthalene-2,7-disulfonate (4,5-diol) and with 2,3-dihydroxynaphthalene-6-sulfonate (2,3-diol) were found to dissociate to the extent of one part in 3.39 × 10 4 and 4.37 × 10 4, respectively, at optimal pH values. The conjugate acid form of a complex is observed for the first time in equilibria of this type.