title: Rules of thumb for assessing reductive dechlorination pathways of PCDDs in specific systems.
abstract: This paper reports a theoretical validation and proposition of the reductive dechlorination pathways for polychlorinated dibenzo-p-dioxin (PCDD) congeners. Density functional theory (DFT) calculations were carried out at the B3LYP/6-31G(d) level for all PCDDs and Mulliken atomic charges on chlorine atoms were adopted as the probe of the dechlorination reaction activity. The experimentally substantiated dechlorination pathways of 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) and its daughter products in the presence of zero-valent zinc were validated and the complete pathway of dechlorination of octachlorodibenzo-p-dioxin (OCDD) was proposed. The proposed pathways were found to be consistent with anaerobic biotransformation of several PCDD congeners. Four rules of thumb arrived from this study include (1) the chlorine atoms in the longitudinal (1,4,6,9) positions are removed in preference to the chlorine atoms on lateral (2,3,7,8) positions; (2) the chlorine atom that has more neighboring chlorine atoms at ortho-, meta- and para-positions is to be eliminated; (3) reductive dechlorination prefers to take place on the benzene ring having more chlorine substitutions; and (4) a chlorine atom on the side of the longitudinal symmetry axis containing more chlorine atoms is preferentially eliminated. These rules of thumb can be conveniently used for rapidly predicting the major dechlorination pathway for a given PCDD in specific systems.
authors.affiliation: School of Environmental Science and Engineering, South China University of Technology, Guangzhou Higher Education Mega Center, Guangzhou 510006, PR China.
authors.forename: Gui-Ning
authors.initials: GN
authors.lastname: Lu
authors.forename: Zhi
authors.initials: Z
authors.lastname: Dang
authors.forename: Donna E
authors.initials: DE
authors.lastname: Fennell
authors.forename: Weilin
authors.initials: W
authors.lastname: Huang
authors.forename: Zhong
authors.initials: Z
authors.lastname: Li
authors.forename: Cong-Qiang
authors.initials: CQ
authors.lastname: Liu
mesh_terms: D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D001711:Biotransformation; D002713:Chlorine / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
chemical_list: D000072317:Polychlorinated Dibenzodioxins; D002713:Chlorine