Factors affecting the affinity of boronic acid derivatives to linear polyols: The substituents of boronic acid derivatives and relative position of dihydroxyl group in polyols

The separation of 1,2,4-butanetriol (BT) through phenylboronate anion reactive extraction in fermentation broth has been proposed based on the process where the boronic acid groups specifically recognize the cis-dihydroxyl groups. To fully elucidate the affinity process of boronic acid group and polyols, here we have investigated the binding constant (Ka) and thermodynamic data of four phenylboronic acid derivates (PBADs) and four structurally similar linear polyols (BT, 1,2-butanediol (1,2-BD), 1,3-butanediol (1,3-BD), and 1,4-butanediol (1,4-BD)) through fluorescence spectroscopy, isothermal titration calorimetry (ITC), and computational chemistry. It can be concluded that the substituent group of boronic acid, the numbers and relative positions of the hydroxyl group in polyols affected the affinity of the boronic acid group to it. The ionized boronic acid group preferentially reacts with the 1,2-dihydroxy group to form a pentacyclic phenylboronate. Compared with other three butanediols, phenylboronic acid (PBA) has a larger binding constant and shows a smaller Gibbs free energy change with BT.