Recent progress has been made in the reductive debromination of polybrominated diphenyl ethers (PBDEs) by nanoscale zero-valent iron (nZVI). To better understand the mechanism of this reaction, seven selected BDE congeners and their anions were investigated at the density functional theory (DFT) level using four different methods, including B3LYP/6-31G(d), B3LYP/6-31+G(d), B3LYP/6-31G(d,p) and B3LYP/6-311G(d,p). The cleaved C–Br bonds observed in the equilibrium structures of anionic PBDEs were adopted as the probe of the susceptible debromination position of PBDEs in the presence of nZVI, and the proposed major reaction pathways based on our calculations can satisfactorily conform to the reported experimental results. The debromination preference is theoretically evaluated as meta-Br > ortho-Br > para-Br. In addition, both the calculated frontier orbital energies and adiabatic electronic affinities were found to be highly related to their experimental reductive debromination rate constants. The highest linear regression coefficient was observed in the case using the energy of lowest unoccupied molecular orbital as the molecular descriptor obtained from B3LYP/6-31G(d) ( R 2 = 0.961, n = 7) or B3LYP/6-31G(d,p) ( R 2 = 0.961, n = 7). The results clearly showed the evidence of an electron transfer mechanism associated with this reductive debromination reaction.
References
[1]
Chen, L.G.; Mai, B.X.; Bi, X.H.; Chen, S.J.; Wang, X.M.; Ran, Y.; Luo, X.J.; Sheng, G.Y.; Fu, J.M.; Zeng, E.Y. Concentration levels, compositional profiles, and gas-particle partitioning of polybrominated diphenyl ethers in the atmosphere of an urban city in South China. Environ. Sci. Technol 2006, 18, 1190–1196.
[2]
Hites, R.A. Polybrominated diphenyl ethers in the environment and in people: A meta-analysis of concentrations. Environ. Sci. Technol 2004, 38, 945–956.
[3]
Darnerud, P.O.; Eriksen, G.S.; Jóhannesson, T.; Larsen, P.B.; Viluksela, M. Polybrominated diphenyl ethers: occurrence, dietary exposure, and toxicology. Environ. Health Perspect 2001, 109(Suppl 1), 49–68.
[4]
Meerts, I.A.T.M.; Letcher, R.J.; Hoving, S.; Marsh, G.; Bergman, ？.; Lemmen, J.G.; Burg, B.V.; Brouwer, A. In vitro estrogenicity of polybrominated diphenyl ethers, hydroxylated PBDEs, and polybrominated bisphenol A compounds. Environ. Health Perspect 2001, 109, 399–407.
[5]
Sj？din, A.; Patterson, J.; Patterson, G.D.; Bergman, ？. A review on human exposure to brominated flame retardants—Particularly polybrominated diphenyl ethers. Environ. Int 2003, 29, 829–839.
[6]
Haglund, P.S.; Zook, D.R.; Buser, H.; Hu, J.W. Identification and quantification of polybrominated diphenyl ethers and methoxy-polybrominated diphenyl ethers in baltic biota. Environ. Sci. Technol 1997, 31, 3281–3287.
[7]
The European parliament and the council of the European Union. Directive 2002/95/EC of the European Parliament and of the Council of 27 January 2003 on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment; OJ L37; European Union: Brussels, Belgium, 2003.
[8]
Canton, R.F.; Scholten, D.E.; Marsh, G.; de Jong, P.C.; van den Berg, M. Inhibition of human placental aromatase activity by hydroxylated polybrominated diphenyl ethers (OH-PBDEs). Toxicol. Appl. Pharmacol 2008, 227, 68–75.
[9]
Ward, J.; Mohapatra, S.P.; Mitchell, A. An overview of policies for managing polybrominated diphenyl ethers (PBDEs) in the Great Lakes basin. Environ. Int 2008, 34, 1148–1156.
[10]
Li, X.Q.; Elliott, D.W.; Zhang, W.X. Zero-valent iron nanoparticles for abatement of environmental pollutants: Materials and engineering aspects. Crit. Rev. Solid State 2006, 31, 111–122.
[11]
Shih, Y.; Tai, Y. Reaction of decabrominated diphenyl ether by zerovalent iron nanoparticles. Chemosphere 2010, 78, 1200–1206.
[12]
Li, A.; Tai, C.; Zhao, Z.S.; Wang, Y.W.; Zhang, Q.H.; Jiang, G.B.; Hu, J.T. Debromination of decabrominated diphenyl ether by resin-bound iron nanoparticles. Environ. Sci. Technol 2007, 41, 6841–6846.
[13]
Zhuang, Y.; Ahn, S.; Luthy, R.G. Debromination of polybrominated diphenyl ethers by nanoscale zerovalent iron: Pathways, kinetics, and reactivity. Environ. Sci. Technol 2010, 44, 8236–8242.
[14]
Arulmozhiraja, S.; Morita, M. Electron affinities and reductive dechlorination of toxic polychlorinated dibenzofurans: A density functional theory study. J. Phys. Chem. A 2004, 108, 3499–3508.
[15]
Zhao, Y.Y.; Tao, F.M.; Zeng, E.Y. Structures, reductive dechlorination, and electron affinities of selected polychlorinated dibenzo-p-dioxins: Density functional theory study. J. Phys. Chem. A 2007, 111, 11638–11644.
[16]
Keum, Y.; Li, Q.X. Reductive debromination of polybrominated diphenyl ethers by zerovalent iron. Environ. Sci. Technol 2005, 39, 2280–2286.
[17]
Zhao, Y.Y.; Tao, F.M.; Zeng, E.Y. Theoretical study on the chemical properties of polybrominated diphenyl ethers. Chemosphere 2008, 70, 901–907.
[18]
Hu, J.W.; Eriksson, L.; Bergman, ？.; Jakobsson, E.; Kolehmainen, E.; Knuutinen, J.; Suontamo, R.; Wei, X.H. Molecular orbital studies on brominated diphenyl ethers. Part I—Conformational properties. Chemosphere 2005, 59, 1033–1041.
[19]
Hu, J.W.; Eriksson, L.; Bergman, ？.; Jakobsson, E.; Kolehmainen, E.; Knuutinen, J.; Suontamo, R.; Wei, X.H. Molecular orbital studies on brominated diphenyl ethers. Part II—Reactivity and quantitative structure-activity (property) relationships. Chemosphere 2005, 59, 1043–1057.
[20]
Zhou, J.; Chen, J.W.; Liang, C.; Xie, Q.; Wang, Y.N.; Zhang, S.Y.; Qiao, X.L.; Li, X.H. Quantum chemical investigation on the mechanism and kinetics of PBDE photooxidation by ·OH: A case study for BDE-15. Environ. Sci. Technol 2011, 45, 4839–4845.
[21]
Vogel, T.M.; Criddle, C.S.; McCarty, P.L. ES Critical Reviews: Transformations of halogenated aliphatic compounds. Environ. Sci. Technol 1987, 21, 722–736.
[22]
Rienstra-Kiracofe, J.C.; Tschumper, G.S.; Schaefer, H.F., III; Nandi, S.; Ellison, G.B. Atomic and molecular electron affinities: Photoelectron experiments and theoretical computations. Chem. Rev 2003, 102, 231–282.
[23]
Zhuang, Y.; Ahn, S.; Seyfferth, A.L.; Masue-Slowey, Y.; Fendorf, S.; Luthy, R.G. Dehalogenation of polybrominated diphenyl ethers and polychlorinated biphenyl by bimetallic, impregnated, and nanoscale zerovalent iron. Environ. Sci. Technol 2011, 45, 4896–4903.
[24]
Fukui, K.; Yonezawa, T.; Nagata, C.; Shingu, H. Molecular orbital theory of orientation in aromatic, heteroaromatic and other conjugated molecules. J. Chem. Phys 1954, 22, 1433–1442.
[25]
Scherer, M.M.; Balko, B.A.; Gallagher, D.A.; Trantnyek, P.G. Correlation analysis of rate constants for dechlorination by zerov-alent iron. Environ. Sci. Technol 1998, 32, 3026–3033.
[26]
Lowry, G.V.; Johnson, K.M. Congener-specific dechlorination of dissolved PCBs by microscale and nanoscale zerovalent iron in a water/methanol solution. Environ. Sci. Technol 2004, 38, 5208–5216.
[27]
Agarwal, S.; Al-Abed, S.R.; Dionysiou, D.D.; Graybill, E. Reactivity of substituted chlorines and ensuing dechlorination pathways of select PCB congeners with Pd/Mg bimetallics. Environ. Sci. Technol 2009, 43, 915–921.
[28]
Kim, J.H.; Tratnyek, P.G.; Chang, Y.S. Rapid dechlorination of polychlorinated dibenzo-p-dioxins by bimetallic and nanosized zerovalent iron. Environ. Sci. Technol 2008, 42, 4106–4112.
Becke, A.D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys 1993, 98, 5648–5652.
[31]
Lee, C.; Yang, W.; Parr, R.G. Development of the colle–salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785–789.
[32]
Jon Baker, A.S.; Andzelm, J. Spin contamination in density functional theory. Chem. Phys. Lett 1993, 216, 380–388.
[33]
Zeng, X.; Simonich, S.L.M.; Robrock, K.R.; Korytar, P.; Alvarez-Cohen, L.; Barofsky, D.F. Application of a congener-specific debromination model to study photodebromination, anaerobic microbial debromination, and Fe0 reduction of polybrominated diphenyl ethers. Environ. Toxicol. Chem 2010, 29, 770–778.
