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The internal barriers of rotation for the 209 polychlorinated biphenyls
Umeå University, Faculty of Science and Technology, Department of Chemistry.
1997 (English)In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 4, no 2, 75-81 p.Article in journal (Refereed) Published
Abstract [en]

The internal barrier of rotation (Erot) was calculated for all 209 polychlorinated biphenyls (PCBs) by using a semi-empirical method, viz. the Austin Model 1 (AM1) Hamiltonian. The difference in total energy between a forced planar state and an optimised twisted structure was defined as Erot. The Erot values were in the range of 8.33 to 483 kJ/mol, and were significantly influenced by the number of chlorine atoms in ortho position. An additional structural characteristic of the PCBs influencing Erot of ortho substituted congeners was substitution by chlorine atoms in vicinal meta positions, which is assumed to prevent outward bending of ortho substituents. This so-called buttressing effect contributed with 4 to 31 kJ/mol per added chlorine atom. In conclusion, the internal barrier of rotation, calculated for all 209 PCBs, provides an important structure dependent physico-chemical parameter for multivariate modelling of future quantitative structure-activity and structure-property relationships (QSARs/QSPRs).

Place, publisher, year, edition, pages
1997. Vol. 4, no 2, 75-81 p.
Keyword [en]
PCBs, physico-chemical properties, semi-empirical calculations, AM1, substitution pattern, ortho-chlorines, dihedral angle, rotational barrier, buttressing effect, QSAR, QSPR
National Category
Chemical Sciences
URN: urn:nbn:se:umu:diva-3297DOI: 10.1007/BF02986283ISI: A1997XJ06700005OAI: diva2:141849
Available from: 2000-05-26 Created: 2000-05-26 Last updated: 2014-08-29Bibliographically approved
In thesis
1. Physico-chemical characteristics and quantitative structure-activity relationships of PCBs
Open this publication in new window or tab >>Physico-chemical characteristics and quantitative structure-activity relationships of PCBs
2000 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The polychlorinated biphenyls (PCBs) comprise a group of 209 congeners varying in the number of chlorine atoms and substitution patterns. These compounds tend to be biomagnified in foodwebs and have been shown to induce an array of effects in exposed organisms. The structural characteristics of the PCBs influence their potency as well as mechanism of action. In order to assess the biological potency of these compounds a multi-step quantitative structure-activity relationship (QSAR) procedure was used in the project described in this thesis.

The ultraviolet absorption (UV) spectra were measured for all 209 PCBs, and digitised for use as physico-chemical descriptors. Interpretations of the spectra using principal component analysis (PCA) showed the number of ortho chlorine atoms and para-para substitution patterns to be significant. Additional physico-chemical descriptors were derived from semi-empirical calculations. These included various molecular energies, the ionisation potential, electron affinity, dipole moments, and the internal barrier of rotation. The internal barrier of rotation was especially useful for describing the conformation of the PCBs on a continuous scale.

In total 52 physico-chemical descriptors were compiled and analysed by PCA for the tetra- to hepta-chlorinated congeners. The structural variation within these compounds was condensed into four principal properties derived from a PCA for use as design variables in a statistical design to select congeners representative for these homologue-groups. The 20 selected PCBs have been applied to study structure-specific biochemical responses in a number of bioassays, and to study the biomagnification of the PCBs in various fish species.

QSARs were established using partial least squares projections to latent structures (PLS) for the PCBs potency to inhibit intercellular communication, activate respiratory burst, inhibit dopamine uptake in synaptic vesicles, compete with estradiol for binding to estrogen receptors, and induce cytochrome P4501A (CYP1A) related activities. By the systematic use of the designed set of PCBs the biological potency was screened over the chemical domain of the class of compounds. Further, sub-regions of highly potent PCBs were identified for each response measured. For risk assessment of the PCBs potency to induce dioxin-like activities the predicted induction potencies (PIPs) were calculated. In addition, two sets of PCBs were presented that specifically represent congeners of environmental relevance in combination with predicted potency to induce estrogenic and CYP1A related activities.

Place, publisher, year, edition, pages
Umeå: Kemi, 2000. 70 p.
polychlorinated biphenyls, PCBs, physico-chemical properties, statistical design, multivariate, PCA, PLS, biomagnification, BMF, bioassay, CYP1A, SAR, QSAR, REPs, risk assessment, Chemistry, Kemi
National Category
Chemical Sciences
urn:nbn:se:umu:diva-17 (URN)91-7191-838-8 (ISBN)
Public defence
Available from: 2000-05-26 Created: 2000-05-26Bibliographically approved

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