Theoretical Study on the Catalytic Oxidation of p‐Iodophenol by Horseradish Peroxidase in a Chemiluminescent System

Abstract

Oxidation of p-iodophenol (PIP) by horseradish peroxidase (HRP) is a key factor contributing to the enhancement effect of PIP in the luminol-HRP-H 2 O 2 chemiluminescent (CL) system. However, the mechanism of enhancement is still unproved to this day. Herein we use quantum mechanics (QM) calculations to study the process of PIP oxidation by HRP, compound I (HRPÀ I) and compound II (HRP-II), and try to uncover the enhancement mechanism. The calculations demonstrate that the oxidation process of PIP by HRPÀ I/HRP-II involve a protoncoupled electron-transfer step and reveal the crucial role of a bridging water molecule. Besides, the reaction of HRP with PIP shows remarkably lower barriers in comparison with the reaction with luminol. This suggests that the enhancer PIP accelerates the turnover of HRP enzyme, which may facilitate the enhancement effect of PIP in the luminol CL system.[a] Prof.