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author:("luther, G.")
2.  Electrostatic and aspheric influence of the fluoro-substitution of 4-bromodiphenyl ether (PBDE 3) 
Accurate structure determinations by X-ray crystal analysis and computation using semi-empirical self-consistent field molecular orbital calculations are described and compared for 4-bromodiphenyl ether (PBDE 3), the 13C6-isotopic labeled PBDE 3 (13C6-PBDE 3) and its five corresponding monofluorinated analogues (F-PBDEs 3): 2-fluoro-4-bromodiphenyl ether (F-PBDE 3-2F), 2′-fluoro-4-bromodiphenyl ether (F-PBDE 3-2′F), 3-fluoro-4-bromodiphenyl ether (F-PBDE 3-3F), 3′-fluoro-4-bromodiphenyl ether (F-PBDE 3-3′F) and 4′-fluoro-4-bromodiphenyl ether (F-PBDE 3-4′F). The synthesis and full characterization by means of 1H, 13C, 19F nuclear magnetic resonance spectroscopy and mass spectrometry of the F-PBDEs 3 are presented for the first time. Intermolecular interactions for PBDE 3 and the F-PBDEs 3 isomers were dominated by weak C-H(F,Br) ····π and C-H····F interactions. The bond lengths of C-F varied between 1.347(2) Å and 1.362(2) Å, C4-Br between 1.880(3) Å and 1.904(19) Å. Both correlated with electron-density differences as determined by 13C shifts, but not with the strength of C-F couplings. The interior ring angles at ipso-fluoro-substitution increased to 121.95° due to hyperconjugation by p-π-orbital overlapping, a phenomenon that was also computed. An attraction between the vicinal fluoro-and bromo-substituents was not determined, as seen in fluoro-substituted chlorobiphenyls. The torsion angles measured and computed for the series of PBDE 3 and F-PBDEs 3 differed strongly from each other. Since the ether linkage (an average of 2.76 Å) provides more distance and the bonds are flexible up to a certain range, the influence of a fluoro-substituent is only detectable in PBDEs with high ortho-substitution. A concordance of computed and measured torsion angles can be observed with increasing size and/or grade of substitution comparing mono- to tetra- fluoro-, chloro-, bromo- and methyl-substitutions in the ortho-positions of diphenyl ether. Differences between computational versus measured data demonstrates a strong need to evaluate the results against independent techniques to conclude structure receptor activity relationships of PBDEs. Any discussion of the Ah or other biological receptor activity of certain PBDEs should take this in consideration. For the first time a complete overview of known and hypothetical biological activities of PBDEs is presented.
PMCID: PMC3120100  PMID: 18204217
3.  Receptor interactions by polybrominated diphenyl ethers versus polychlorinated biphenyls: a theoretical Structure-activity assessment 
The extensive body of literature regarding the interaction of polychlorinated biphenyls (PCBs) with transcription factors (receptors) has great value to understand similarities and distinctions and in formulating hypotheses regarding the activity of polybrominated diphenyl ethers (PBDEs) toward those same receptors. Our goal is to present the most comprehensive overview of PBDE effects on AhR, CAR, PXR, ER, AR, PR, DHT, TH, T3, T4 and IGF, as well as hypothetical biological activities of PPAR, RyR, GR and GABA. Aside the influence of the conformation of the ligand, we discuss its constitution influencing the binding affinity: size and polarizability, hydrophilicity, Gibbs free energy of solvation, inductive and mesomeric effects. We evaluate the techniques to determine the biologically relevant conformation of these halogenated hydrocarbons, including computation methods, X-ray and microwave spectroscopy. A novel fluoro-tagged ligand approach holds promise as tools for illuminating the steric and electronic effects in ligand-receptor interaction. Based on our assessment, we predict that PBDEs do not exhibit AhR activity themselves, but impurities are responsible for these effects.
PMCID: PMC2746664  PMID: 19768137
polybrominated diphenyl ethers; PBDEs; polychlorinated biphenyls; PCBs; AhR; CAR; PXR; ER; AR; PR; DHT; TH; T3; T4; IGF; PPAR; RyR; GR; GABA; Conformation; Constitution; Binding affinity; Polarizability; Hydrophilicity; Gibbs free solvation energy; Inductive effects; Mesomeric effects

Results 1-3 (3)