Trovacenchemie. 13 [1] Weg und Irrweg zu Di([5]trovacenyl)keton

Trovacene Chemistry. 13 [1] On Being Lead and Mislead in the Synthesis of Di([5]trovacenyl)ketone Di([5]trovacenyl)ketone ( 3¨ ) has been prepared from lithio‐[5]trovacene and dimethylcarbamoyl chloride and studied by X‐ray diffraction, cyclic voltammetry, magnetic susceptometry and EPR spectroscopy. Slight variation of the synthetic protocol affords an unusual trinuclear complex 5 ? that is also fully characterized. Spin‐spin exchange interaction is smaller in 3¨ than in 1,1‐di([5]trovacenylethene ( 2¨ ), which differs from 3¨ by a replacement of O for CH₂. The novel trinuclear complex 5 ? , however, displays exchange coupling very similar to that observed in 1‐methoxy‐2,5,6‐tri([5]trovacenyl)benzene ( 7 ? ). In both cases, an unsymmetrical triangular arrangement of S = 1/2 centers is encountered. These findings are discussed in terms of the nature of the respective spacers.     

Ground-state dynamics of α-methylstyrene. I. Thermally induced oligomerization in bulk

α-Methylstyrene (α-Me-St) in bulk undergoes a variety of thermally induced processes which we investigated in detail by product-distribution analysis. The oligomeric products, shown by GC–MS coupling techniques and independent syntheses, consisted of nine dimers and nine trimers with no detectable higher oligomers or polymers. Two isomeric cyclobutanes and one of the open-chain unsaturated dimers were formed by a conventional two-step cycloaddition; a Flory-type diradical was the common intermediate. In contrast to these 2π + 2π products, the majority of the remaining oligomers could not be interpreted on the basis of π-electron interaction between closed shell molecules. Their structures, however, were compatible with a free radical process in which cumyl(MH·) and 1,4-dimethyl-1-phenyl-tetrahydronaphthalene-yl(THN·), which are consecutive products of 4π + 2π and 2π + 2π interactions, respectively, were involved in addition and transfer reactions. Because of the small rate of initiation and the obvious lack of free radical recombination products, a mechanism was suggested in which MH· and THN· radicals react predominantly in a closed sequence of elementary processes and to a rather small extent only by bimolecular free radical termination. Two sorts of stabilization steps, hydrogen transfer to monomer (R_nH· + M → R_n + MH·) and hydrogen abstraction from a hypothetical 4π + 2π intermediate I (R_nH· + I → R_nH₂ + THN·), are attributed to the high rates of unsaturated and saturated oligomer formation.     

Comparison between capillary electrophoresis and ion-chromatography for analysis of inorganic anions

Separation and detection of some selected inorganic anions with capillary electrophoresis are shown. The anions are separated in microbore capillaries (25 m* 0.2 m) and detected with a UV-detector. Results are compared with the method of ion exchange chromatography. In consideration of the most important physical and chemical parameters an easy kind of computer simulation for such electropherograms was developed.To get optimal results of separation and UV-detection in capillary electrophoresis some parameters of the device HPE 100, i.e. loading time in the electrokinetic sample injection mode and the running voltage are varied. The behaviour of absorption in the UV region of the chosen anions as well as the influence of pH values in retention behaviour are investigated. There is a simple way to calculate the electrophoretic mobilities from known retention times. Approximate limits of detection for all anions and for each technique are given.     

Response Characteristics of Arsenic-Sensitive Bioreporters Expressing the gfp Reporter Gene

This paper describes the development of an analytical technique for arsenic analyses that is based on genetically-modified bioreporter bacteria bearing a gene encoding for the production of a green fluorescent protein (gfp). Upon exposure to arsenic (in the aqueous form of arsenite), the bioreporter production of the fluorescent reporter molecule is monitored spectroscopically. We compared the response measured as a function of time and concentration by steady-state fluorimetry (SSF) to that measured by epi-fluorescent microscopy (EFM). SSF is a bulk technique; as such it inherently yields less information, whereas EFM monitors the response of many individual cells simultaneously and data can be processed in terms of population averages or subpopulations. For the bioreporter strain used here, as well as for the literature we cite, the two techniques exhibit similar performance characteristics. The results presented here show that the EFM technique can compete with SSF and shows substantially more promise for future improvement; it is a matter of research interest to develop optimized methods of EFM image analysis and statistical data treatment. EFM is a conduit for understanding the dynamics of individual cell response vs. population response, which is not only a matter of research interest, but is also promising in the practical terms of developing micro-scale analysis.