PHENOL DERIVATIVES AS ENHANCERS AND INHIBITORS OF LUMINOL-H2O2-HORSERADISH PEROXIDASE CHEMILUMINESCENCE

Systematic studies on phenol derivatives facilitates an explanation of the enhancement or inhibition of the luminol-H2O2-horseradish peroxid ase system chemiluminescence. Factors that govern the enhancement are the one-electron reduction potentials of the phenoxy radicals (PhO./Ph OH) vs. luminol radicals (L-./LH-) and the reaction rates of the pheno l derivatives with the compounds of horseradish peroxidase (HRP-I and HRP-II). Only compounds with radicals with a similar or greater reduct ion potential than luminol at pH 8.5 (0.8 V) can act as enhancers. Rad icals with reduction potentials lower than luminol behave in a differe nt way, because they destroy luminol radicals and inhibit chemilumines cence. The relations between the reduction potential, reaction rates a nd the Hammett constant of the substituent in a phenol suggest that 4- substituted phenols with Hammett constants (sigma) for their substitue nts similar or greater than 0.20 are enhancers of the luminol-H2O2-hor seradish peroxidase chemiluminescence. In contrast, those phenols subs tituted in position 4 for substituents with Hammett constants (sigma) lower than 0.20 are inhibitors of chemiluminescence. On the basis of t hese studies, the structure of possible new enhancers was predicted. ( C) 1998 John Wiley & Sons, Ltd.