A novel concept for the biodegradation mechanism of dianionic catechol with homoprotocatechuate 2, 3-dioxygenase: A non-proton-assisted process. (May 2020)

• Record Type: Journal Article
• Authors: Tu, Ningyu; Zhang, Dongmei; Niu, Xianchun; Du, Cheng; Zhang, Li; Xie, Wenyu; Niu, Xiaojun; Liu, Yang; Li, Youming
• Is Part Of: Chemosphere. Volume 246(2020)
• Publication Date: 2020-05
• Subjects: 2, 3-HPCD -- 4NC -- Alkylperoxo species -- Non-proton-assisted process -- Catalytic mechanism; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2019.125796
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: The theory of "proton-assisted process" can well explain the catalytic mechanism of homoprotocatechuate 2, 3-dioxygenase (2, 3-HPCD) with a monoanionic substrate (homoprotocatechuate, HPCA). Here a "non-proton-assisted process" is presented to interpret catalytic mechanism of 2, 3-HPCD with a dianionic substrate (4-nitrocatechol, 4NC). The ONIOM calculation is performed to investigate the reaction pathway of a wild-type 2, 3-HPCD with 4NC (H200H–4NC system). The catalytic reaction is comprised of four steps: (1) A dioxygen attacks the aromatic ring to produce an alkylperoxo species. (2) O–O bond cleavage and the formation of an epoxide species occur. (3) A seven-membered O-heterocyclic compound is generated by the extinction of the epoxy structure. (4) The seven-membered ring undergoes ring opening to form the final product (C2–C3 cleavage product). The effective free energy barrier of the catalytic reaction of the H200H–4NC system is 26.2 kcal mol −1, which is much higher than that of the H200H-HPCA system. Furthermore, two calculated electronic configurations (Fe(III)–O2 - and Fe(III)-SQ ) have a high similarity to previously detected ones, which demonstrates that the Asn200 variant (H200N–4NC variant system) employs a C4 (para-carbon) pathway to produce a C4–C5 cleavage product. Our findings provide an in-depth understanding of the catalytic mechanisms of dianionic catechol and its derivatives. Graphical abstract: Image 1 Highlights: "non-proton-assisted process" is advanced to interpret the catalytic mechanism of 2, 3-HPCD-4NC. The catalytic mechanisms of C3 and C4 pathways for H200N–4NC are illustrated by a DFT working. Two optimized electronic configurations of H200N–4NC coincide with the reported species.