Suppression mechanism of model humic constituents on laccase-enabled 17β-estradiol oxidation and oligomerization

• Published in: Chemosphere (Oxford) 2022-03, Vol.290, p.133356-133356, Article 133356
• Main Authors: Li, Shunyao, Sun, Kai
• Format: Article
• Language: English
• Subjects: 17β-estradiol conversion; Ecosystem; Estradiol; Humic Substances - analysis; Inhibition mechanism; Laccase; O-quinone intermediates; Small humic constituents; Trametes; Trametes versicolor laccase
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2021.133356

Humic constituents (HCs) are ubiquitous in the aquatic ecosystems, and contain various functional groups that seriously impact the conversion of 17β-estradiol (17β-E2) by fungal laccase. The purpose of this study was to explore the influencing mechanism of HCs on Trametes versicolor laccase-enabled 17β-E2 oxidation and oligomerization. Herein, T. versicolor-secreted laccase could rapidly convert 99.2% of 17β-E2 (rate constant = 3.7 × 10−2 min−1, half-life = 18.7 min) into multifarious oligomers at 25 °C and pH 5.0, by phenolic radical-caused C–C and/or C–O self-linking routes, whereas HCs with O-phenolic hydroxyl groups (O-p-OH, i.e., catechol, pyrogallol, gallic acid, and caffeic acid) dramatically suppressed 17β-E2 oligomerization. Compared with HC-free, 17β-E2 rate constants weakened 6.3–15.8 fold in the presence of HCs containing O-p-OH. It is largely because the O-p-OH was preferentially oxidized by T. versicolor laccase to create the electrophilic O-quinone monomers/oligomers. These unstable reactive O-quinone intermediates strongly reversed 17β-E2 phenolic radicals to their monomeric molecules via two proton-transfer versus two electron-transfer channels, thus intercepting 17β-E2 oxidation and oligomerization. These findings highlight new insights into the effect of HCs containing O-p-OH on T. versicolor laccase-started 17β-E2 conversion, which is beneficial to re-understanding the fate and geochemical behavior of 17β-E2 in water. [Display omitted] •Trametes versicolor laccase-started bioremediation could rapidly convert 17β-estradiol.•Multifarious oligomers of 17β-estradiol and humic constituents were identified.•Inhibition mechanism of humic constituents on 17β-estradiol oxidation was illustrated.