Electron Affinity for the Most Toxic 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD): A Density Functional Theory Study

Quantum Chemical Investigation of Polychlorinated Dibenzodioxins, Dibenzofurans and Biphenyls: Relative Stability and Planarity Analysis

All the possible polychlorinated aromatic compounds in the classes of dibenzodioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) were studied by the quantum chemical methods of HF/6-311++G(d,p), B3LYP/6-311++G(d,p), and MP2/cc-pVTZ. The calculated stabilities and structures of these compounds were compared with the available data on their abundance and toxicity. Prediction models for trends in energy and planarity among these congeners were proposed. The results discussed here can help contribute to the understanding of the role of dioxin-like compounds (DLCs) in the environment.

Molecular Polarization Potential as a Molecular Descriptor to Predict Biological Activity of Dioxins and Dibenzofurans

Molecular interaction potential (MIP) maps are a powerful tool to develop structure-activity relationships of a series of compounds. In the present study we have studied the effect of molecular polarization on the description of the toxicity of a series of dioxins and benzofurans using their MIPs. Specifically, we have used principal component analysis in an exploratory way to understand the common structural features that describe the toxicity of these molecules through the analysis of their MIPs and each of their components, i.e.; molecular electrostatic and polarization potentials. Moreover, we have developed a predictive model using PLS that permits to evaluate the toxicity of compounds belonging to any of the families of compounds studied in the present work on the basis of their molecular electrostatic and interaction potentials.

Dehalogenation of persistent halogenated organic compounds: A review of computational studies and quantitative structure-property relationships

Dehalogenation is one of the highly important degradation reactions for halogenated organic compounds (HOCs) in the environment, which is also being developed as a potential type of the remediation technologies. In combination with the experimental results, intensive efforts have recently been devoted to the development of efficient theoretical methodologies (e.g. multi-scale simulation) to investigate the mechanisms for dehalogenation of HOCs. This review summarizes the structural characteristics of neutral molecules, anionic species and excited states of HOCs as well as their adsorption behavior on the surface of graphene and the Fe cluster. It discusses the key physiochemical properties (e.g. frontier orbital energies and thermodynamic properties) calculated at various levels of theory (e.g. semiempirical, ab initio, density functional theory (DFT) and the periodic DFT) as well as their connections to the reactivity and reaction pathway for the dehalogenation. This paper also reviews the advances in the linear and nonlinear quantitative structure-property relationship models for the dehalogenation kinetics of HOCs and in the mathematical modeling of the dehalogenation processes. Furthermore, prospects of further expansion and exploration of the current research fields are described in this article.

Theoretical study of the quantitative structure-activity relationships for the toxicity of dibenzo-p-dioxins

Density functional theory calculations of polychlorinated dibenzo-p-dioxins (PCDDs) were carried out to obtain the electronic descriptors, polarizabilities, and traceless quadrupole moments of 76 PCDD congeners. No simple relationships were found for the electronic descriptors with the relevant aryl hydrocarbon receptor (AhR) binding affinities of PCDDs, which suggests that they alone may not be sufficient to explain the variation in toxicity. However, quantitative structure-activity relationships (QSARs) were developed with the polarizabilities and traceless quadrupole moments, explaining about 74% and 59% of variation in AhR binding affinities of PCDDs, respectively. To explain the nature of toxic interaction, a mathematical model based on the ligand-receptor binding and solute-solvent interaction was presented, and then a multiple regression analysis of all the above parameters was performed to evaluate the contributions of the parameters to the bonding affinities. Other data for PCDFs found in the literature were also included in the regression analysis to minimize data over-fitting. The results suggest that dispersion and electrostatic interactions are equally important for the interaction of PCDD/Fs with the AhR.

Theoretical study on the chemical properties of polybrominated diphenyl ethers

Density functional theory calculations at the B3LYP/6-31+G(d) and B3LYP/aug-cc-pVDZ levels were performed to obtain the equilibrium structures, thermodynamic properties, and electron affinities (EA) of 14 polybrominated diphenyl ether (PBDE) congeners in the gas phase. All congeners except for those of symmetric BDE are found to have two or more conformational isomers. The optimized geometries of the most stable conformational isomers are in agreement with recently published X-ray crystallographic data. The thermodynamic properties of the congeners with a given number of bromine substitutions are strongly dependent on the substitution pattern, whereas the EA values also depend on the number of bromine substitutions. The vertical electron affinities (EA(Ver)) calculated for the selected BDE congeners at the B3LYP/aug-cc-pVDZ level are all positive except for di-BDEs, and are correlated with the initial reductive debromination rate constants obtained recently [Keum, Y.-S., Li, Q.X., 2005. Reductive debromination of polybrominated diphenyl ethers by zerovalent iron. Environ. Sci. Technol. 39, 2280]. All adiabatic electron affinities (EA(Ada)) are positive, and suggest that the BDE congeners act as electron acceptors when reacting with receptors in living cells. The calculated EA(Ada) values differ considerably from those of EA(Ver) because of the large geometrical relaxation from the neutral to the anionic BDE congeners, highlighted by the lengthening of a C-Br bond. The elongated C-Br bond, which occurs at the alpha position, is directly involved in the debromination of n-bromodiphenyl to (n-1)-bromodiphenyl ethers in the reductive debromination experiments.

Aryl Hydrocarbon Receptor-Mediated Effects of Chlorinated Polycyclic Aromatic Hydrocarbons

Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) with 3-5 rings are ubiquitous environmental contaminants. However, toxicities of ClPAHs remain unclear. In this study, aryl hydrocarbon receptor (AhR)-mediated activities of ClPAHs were investigated by using a yeast assay system. All environmentally relevant 18 ClPAHs showed the AhR activities in the test; the activities were elevated with the number of chlorine atoms on the lower molecular weight PAH ( approximately three-ring and fluoranthene derivatives) but not for higher molecular weight ClPAHs (>four-ring). The similar trends were also observed in certain ClPAHs-induced cytochrome P450 1A1 expression in MCF-7 cells. The structure-activity relationship between the AhR activity and the corresponding solvent accessible surface area of ClPAHs revealed a parabolic relationship, with approximately 350 A (2)/molecule as the optimal dimensions as the ligand for binding to AhR. These findings indicate that the spatial dimensions of ClPAHs apparently influence their ability to activate the AhR. Finally, we discussed the toxicity of exposure to ClPAHs based on the AhR activities, estimated that it would be approximately 30-50 times higher than that of dioxins.

Electrophilicity index as a possible descriptor of biological activity

The purpose of this study is to probe the suitability of DFT based chemical reactivity parameter, electrophilicity index as a possible biological activity descriptor in the development of QSAR. Testosterone derivatives with activity described in terms of various biological activity parameters and the estrogen derivatives by relative binding affinity (RBA) values have been selected as model systems. The implications for the ability of electrophilicity to describe the biological activities are discussed. From the results it is possible to observe that electrophilicity index may be suitable to effectively describe the biological activity.