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(582n) Kinetic Study of Enzyme-Catalyzed Phenol and Its Derivatives Oxidative Coupling Products

Authors: 
Wang, K., Department of Chemical Engineering, Key Lab of Industrial Biocatalysis, Ministry of Education, Tsinghua University
Jiang, G., Key Lab of Industrial Biocatalysis, Ministry of Education, Tsinghua University
Liu, Z., Key Lab of Industrial Biocatalysis, Ministry of Education, Tsinghua University
Human derived pharmaceuticals in water have attracted great attention over the past decade. The employment of enzymes for biotransformation of pharmaceutical contaminants has become an increasingly attractive alternative approach. A large class of pharmaceuticals contained the moieties of phenol derivatives, which can be removed by the laccase-catalyzed oxidative coupling, i.e., the phenol derivatives are oxidized into radicals which are further polymerized into biologically inactivity polymers that precipitate from the water. The kinetics of enzyme-catalyzed oxidative coupling process was studied to remove products effectively based on higher enzyme activity. The higher enzyme activity was acquired by adjustment of the concentration of enzyme and the microenvironment (e.g. pH) for enzyme. The enhancement of radicals formation rate catalyzed by laccase with higher activity accelerated the generation of products with higher degree polymerization and further improved the removal performance of phenol derivatives. The change of UV absorbance over time was compared using phenol, 2,2-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), p-aminophenol or acetaminophen as different substrate. The contents of oxidative coupling products of varied coupling degree were analyzed by LC-MS. The mechanism of coupling reaction process was conducive to the further study of kinetics. The precipitation caused by coupling reaction was analyzed by dynamic light scattering (DLS) measurements. The results showed that the formation time of polymerized products which could naturally precipitated became earlier and precipitation rate was also faster under higher enzyme activity. The micron-grade products were increasing with time increasing. The generation of micron-grade products (precipitation easily) could explain the decline of absorbance over time well. The kinetics is helpful for understanding the reaction process of enzyme-catalyzed coupling of phenol and its derivatives in depth and finding the way to removal of them from water with high performance.