Acta Phys. -Chim. Sin. ›› 2017, Vol. 33 ›› Issue (3): 620-626.doi: 10.3866/PKU.WHXB201612011

• ARTICLE • Previous Articles     Next Articles

Radical Mechanism of Laccase-Catalyzed Catechol Ring-Opening

Ming CHEN1,Lin WANG2,Tian TAN1,Xue-Cai LUO2,Zai ZHENG2,Ruo-Chun YIN2,Ji-Hu SU1,*(),Jiang-Feng DU1   

  1. 1 CAS Key Laboratory of Microscale Magnetic Resonance, Department of Modern Physics, University of Science and Technology of China, Hefei 230026, P. R. China
    2 Inspiration Center for Bio-manufacture, School of Life Sciences, Anhui University, Hefei 230601, P. R. China
  • Received:2016-09-29 Published:2017-03-07
  • Contact: Ji-Hu SU E-mail:sujihu@ustc.edu.cn
  • Supported by:
    the National Key Basic Research Program of China (973)(2013CB921802);Fundamental Research Funds for the Central Universities, China, State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, China(KSL-CUSAb-2012-03)

Abstract:

Enzyme-catalyzed reactions are a prominent field of research in green chemistry. Laccase is a multicopper oxidase, which we used to study the oxidation of catechol. A mechanism for this ring-opening reaction is also proposed. A o-benzosemiquinone radical was the initial nascent product of catechol oxidation during the catalytic reaction. This radical underwent two reaction pathways:(1) formation of an intramolecular adduct, which gave a carbon-centered furan-derived radical trapped by 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO); (2) formation of an intermolecular adduct producing dimeric and trimeric oligomers, as resolved by mass spectrometry. Products of the furan-like intermediate were also characterized by 1H-NMR. Simultaneously, a hydroxyl radical (·OH) originating from the water solvent was identified by 17O-isotope tracing. The kinetics of this radical were also evident with substrates including 3-and 4-methyl catechol, but not with resorcinol and hydroquinone isomers, 3-and 4-nitro catechol, and 2, 3-dihydroxynaphthalene. The mechanism of selective activation and ring-opening at the C4-C5 site is discussed. This reaction is distinct from intra-and extra-diol ringcleavages catalyzed by catechol dioxygenase. These results are meaningful for mimicking laccase catalysis to further protein design.

Key words: Laccase, Radical oxidation, Aromatic ring cleavage, Electron paramagnetic resonance spectroscopy, Spin trapping

MSC2000: 

  • O643