RATE CONSTANTS FOR REACTIONS OF HORSERADISH-PEROXIDASE COMPOUND-I ANDCOMPOUND-II WITH 4-SUBSTITUTED ARYLBORONIC ACIDS

The rate constants for the reactions of horseradish peroxidase compoun d I (k(1)) and compound II (k(2)) with three 4-substituted arylboronic acids, which enhance chemiluminescence in the horseradish peroxidase catalyzed oxidation of luminol by hydrogen peroxide, were determined a t pH 8.6, total ionic strength 0.11 M, using stopped-flow kinetic meas urements. For comparison, the rate constants of the reactions of 4-iod ophenol with compounds I and II were also determined under the same ex perimental conditions. The three arylboronic acid derivatives and thei r rate constants are: 4-biphenylboronic acid, k(1) = (1.21 +/- 0.08) x 10(6) M(-1) s(-1), k(2) = (4.6 +/- 0.2) x 10(5) M(-1) s(-1) 4-bromoph enylboronic acid, k(1) = (5.5 +/- 0.2) x 10(4) M(-1) s(-1), k(2) = (3. 6 +/- 0.2) x 10(4) M(-1) s(-1); and Ciodophenylboronic acid, k(1) = (1 .1 +/- 0.2) x 10(5) M(-1) s(-1), k(2) = (1.3 +/- 0.1) x 10(4) M(-1) s( -1). 4-Biphenylboronic acid, which shows comparable luminescent enhanc ement to 4-iodophenol, has the highest reactivity in the reduction of both compounds I and II among the three arylboronic acid derivatives t ested.