The rate constants for the reactions of horseradish peroxidase compound 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 at pH 8.6, total ionic strength 0.11 M, using stopped-flow kinetic measurements. For comparison, the rate constants of the reactions of 4-iodophenol with compounds I and II were also determined under the same experimental conditions. The three arylboronic acid derivatives and their rate constants are: 4-biphenylboronic acid, k 1 = (1.21 ± 0.08) × 10 6 M −1 s −1 , k 2 = (4.6 ± 0.2) × 10 5 M −1 s −1 ; 4-bromophenylboronic acid, k 1 = (5.5 ± 0.2) × 10 4 M −1 s −1 , k 2 = (3.6 ± 0.2) × 10 4 M −1 s −1 ; and 4-iodophenylboronic acid, k 1 = (1.1 ± 0.2) × 10 5 M −1 s −1 , k 2 = (1.3 ± 0.1) × 10 4 M −1 s −1 . 4-Biphenylboronic acid, which shows comparable luminescent enhancement to 4-iodophenol, has the highest reactivity in the reduction of both compounds I and II among the three arylboronic acid derivatives tested.
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Sun et al. (1994) studied this question.