Theoretical Investigation of Impurities and Intercain Coupling in Polyacetylene

In this work we study the efect of the interchain coupling on the electronic density of states in polyacetylene. First we show that a localized interchain coupling can be simulated by a single substitutional impurity scattering and introduces four symmetrical bound levels at the band edges. We then study the evolution of these levels in the presence of a soliton on the chains. Finally we consder a two- dimensional distribution of interchain interwactions and study its effect on the broadening of the band edges. It is found that, when this coupling is taken into acount, the semi conductormetal transition found in charged soliton-Lattices may occur at a concentration of solitons c ～ 5%.     

Soliton Interaction and Soliton Lattice in Poyace Tyklene

We report here an analysis of the electronic properties of a periodic lattice of solitons in infinite chains of polyacetylene. The method used is a Green's function recursive mjethod which allows an exact determination of the density of states of the system. We have also determined the energy per soliton of this lattice as a function of the concentraton of dopants. A semiconductor-metal transition is found to occur at a doping level C ～ 7%.     

Development of a liquid chromatography/atmospheric pressure photo-ionization high-resolution mass spectrometry analytical method for the simultaneous determination of polybrominated diphenyl ethers and their metabolites: application to BDE-47 metabolism in human hepatocytes

Polybrominated diphenyl ethers (PBDEs) are flame retardants widely used in electronic and domestic goods. These persistent pollutants are present in the environment and in humans, and their toxicological properties are of growing concern. PBDEs can be metabolised into compounds suspected to be responsible for their toxicity. These metabolites have been characterised quite well in rodents and fish, but available information in humans remains scarce. For their identification, an efficient method for the simultaneous analysis of PBDEs, hydroxylated PBDEs (OH-PBDEs), and other PBDE metabolites in a single run was needed and has been developed in this work. Atmospheric pressure ionisation modes were compared, and Atmospheric Pressure Photo-Ionization (APPI) was selected. After careful setting of APPI parameters such as dopant and operating temperature, the optimised method was based on APPI ionization coupled to High-Resolution Mass Spectrometry operating in the full scan mode at a resolution of 60 000. This provided excellent sensitivity and specificity, allowing the discrimination of signals which could not be resolved on a triple quadrupole used as a reference. The full-scan high-resolution acquisition mode allowed monitoring of both parent PBDEs and their metabolites, including hydroxylated PBDEs, with detection limits ranging from 0.1?pg to 4.5?pg injected on-column based on the investigated standard compounds. The method was applied to the study of BDE-47 metabolism after incubation with human primary cultures of hepatocytes, and proved to be efficient not only for monitoring the parent compound and expected hydroxylated metabolites, but also for the identification of other non-targeted metabolites. In addition to hydroxy-BDE-47, several conjugated metabolites could be located, and the formation of a dihydrodiol derivative was evidenced for the first time in the case of PBDEs in this work.     

Defect states in trans-polyacetylene

The interaction of a dopant molecule with the π electrons of a single (CH)_x chain is studied within a model potential which incorporates the core repulsive effects. The soliton type defects are found to be energetically favoured upon doping whereas the position of the induced levels inside the gap are strongly affected by the interaction.     

Probing new approaches using atmospheric pressure photo ionization for the analysis of brominated flame retardants and their related degradation products by liquid chromatography-mass spectrometry

Atmospheric pressure photo ionisation has been evaluated for the analysis of brominated flame retardants and their related degradation products by LC-MS. Degradation mixtures obtained from the photochemical degradation of tetrabromobisphenol A and decabromodiphenylether were used as model systems for the assessment of the developed methodology. Negative ion mode gave best results for TBBPA and its degradation compounds. [M - H]- ions were formed without the need of using a doping agent. MS and MS/MS experiments allowed the structural identification of new TBBPA "polymeric" degradation compounds formed by attachment of TBBPA moieties and/or their respective cleavage products. In the case of polybromodiphenylethers, the positive mode provided M*+ ions and gave better results for congeners ranging from mono- to pentabromodiphenylethers whereas for higher bromination degrees, the negative ion mode (providing [M - Br + O]- ions) was best suited. Under both positive and negative ionisation modes, the use of toluene as doping agent gave better results. Liquid chromatography-mass spectrometry by means of atmospheric pressure photo-ionisation was applied to the analysis of aromatic brominated flame retardants and their degradation products. This methodology proved to be particularly useful, for the characterisation and structural identification of some compounds which are not amenable to GC-MS, especially in the case of apolar "polymeric" degradation products of tetrabromobisphenol A investigated in this work.