Prediction of endocrine disruptors based on a new structure-activity relationship for sex and environmental hormones using chemical hardness concept

On the use of electronic descriptors for QSAR modelling of PCDDs, PCDFs and dioxin-like PCBs

The electronic properties of 29 polychlorinated dibenzo-p-dioxins and dibenzofurans and dioxin-like polychlorinated biphenyls that have been included in the toxic equivalency factor system have been investigated and used to derive quantum mechanical (QM) chemical descriptors for QSAR modelling. Their utility in this context was investigated alongside descriptors based on ultraviolet absorption data and traditional 2D descriptors including log K(ow), polarizability, molecular surface properties, van der Waals volume and selected connectivity indices. The QM descriptors were calculated using the semi-empirical AM1 method and the density functional theory method B3-LYP/6-31G**. Atom-specific and molecular quantum chemical descriptors were calculated to compare the electronic properties of dioxin-like compounds regardless of their chemical class, with particular emphasis on the lateral positions. Multivariate analysis revealed differences between the chemical classes in terms of their electronic properties and also highlighted differences between congeners. The results obtained demonstrated the importance of considering molecular orbital energies, but also indicated that the ratios of the coefficients of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) at the lateral carbons were important. In addition, the digitalized UV spectra contained chemical information that provided crucial insights into dioxin-like activity.

Legume-grass intercropping phytoremediation of phthalic acid esters in soil near an electronic waste recycling site: a field study

A field experiment was conducted to study the phytoremediation of phthalic acid esters (PAEs) by legume (alfalfa, Medicago sativa L.)-grass (perennial ryegrass, Lolium perenne L. and tall fescue, Festuca arundinacea) intercropping in contaminated agricultural soil at one of the largest e-waste recycling sites in China. Two compounds, DEHP and DnBP, were present in the soil and in the shoots of the test plants at much higher concentrations than the other target PAEs studied. Over 80% of 'total' (i.e., all six) PAEs were removed from the soil across all treatments by the end of the experiment. Alfalfa in monoculture removed over 90% of PAEs and alfalfa in the intercrop of the three plant species contained the highest shoot concentration of total PAEs of about 4.7 mg kg(-1) DW (dry weight). Calculation of phytoextraction efficiency indicated that the most effective plant combinations in eliminating soil PAEs were the three-species intercrop (1.78%) and the alfalfa monocrop (1.41%). Phytoremediation with alfalfa was effective in both monoculture and intercropping. High bioconcentration factors (BCFs) indicated the occurrence of significant extraction of PAEs by plants from soil, suggesting that phytoremediation may have potential for the removal of PAEs from contaminated soils.

Stereo structure-controlled and electronic structure-controlled estrogen-like chemicals to design and develop non-estrogenic bisphenol A analogs based on chemical hardness concept

The aim of this study was to elucidate the structure-activity relationship of bisphenol A (BPA) analogs using absolute hardness (eta) and absolute electronegativity (chi) (chemical hardness) and to design a non-estrogen active BPA. To determine the structure-activity relationships of BPA analogs, we investigated MCF-7 cell proliferation stimulated by BPA analogs and an eta-chi diagram based on the electronic structure of the BPA analogs. The results show that the actions of the environmental hormones BPA analogs have two chemical properties; (i) 'stereo structure-controlled' and (ii) 'electronic structure-controlled' estrogen-like chemical activities. Therefore, we designed and synthesized BPA analogs which do not possess these 2 characteristics, ((i) and (ii)), and demonstrate the non-estrogen activity of the analog.

Studies on photochemical reactions of air pollutants. XV. Photoreactivity of heptachloro-3'-cyclopentenyldioxy heptachloro-2-cyclopentene formed by exposure of hexachlorocyclopentadiene to ultraviolet light in air

Hexachlorocyclopentadiene (HCCP, 1), one of the starting materials in the synthesis of aldrin (3), was found to be able to epoxidize aldrin (3) to give dieldrin (4) when exposed to artificial light at wavelengths longer than 290 nm. In this photochemical reaction, heptachloro-3'-cyclopentenyldioxy heptachloro-2-cyclopentene (2) was isolated as a key intermediate, which appears to be derived from the interaction between the triplet state of photo-excited HCCP (1) and triplet oxygen (3sigma(g)-), but not from that between the ground state of HCCP (1) and singlet oxygen (1delta(g)). The peroxide (2) plays an important role in the formation of dieldrin (4), because it utilized oxygen atom derived from oxygen in air for the epoxidation.