Relative reactivity of phenylboronic acid to phenylboronate ion toward L-lactate and mandelate at physiological pH

Abstract

Abstract Kinetic studies were performed on the reactions of phenylboronic acid with L -lactic acid and mandelic acid in acidic aqueous and alkaline solutions in order to specify reactive species in these reactions. It was confirmed that the diprotonated ligand (H 2 L: L -lactic acid or mandelic acid) is less reactive than the monoprotonated ligand (HL − : L -lactate ion or mandelate ion), which made possible direct determination of the rate constants of phenylboronic acid (PhB(OH) 2 ) and its conjugate base, phenylboronate ion (PhB(OH) 3 − ). It was found that PhB(OH) 2 is more reactive than PhB(OH) 3 − . On the basis of kinetic results, it was concluded that the most reactive species are PhB(OH) 2 and HL − at physiological pH 7.4, so the reaction in the boronic acid-based sensor for L -lactate mainly would occur between these species.