2 + 2 + 2] Cycloaddition reactions belong to the not even large class of reactions, which can be catalyzed or mediated by a significant number of different transition metals. Cobalt complexes belong to the catalysts that paved the way for the extensive use and profound mechanistic knowledge on this particular transformation. Beside the established role, cyclopentadienyl (Cp) cobalt complexes inherit in synthetic applications of the cyclotrimerization reaction, modification of the precatalysts opened up novel reactivities and versatility for such catalytic initiators. At the same time the development of in situ generated cobalt catalysts allowed the conversion of novel substrates as well as novel reaction modes to be realized. In this personal account recent developments will be presented and the possibilities of catalysts containing cobalt atoms in different oxidation states be discussed.
The present study demonstrates the suitability of direct UV detection for saccharide analysis in HPLC. Under highly alkaline conditions, the non-UV absorbing saccharides are converted by a photo-initiated chemical reaction in the detection cell into malonenolate, which can be detected at 266 nm. A straightforward method for such direct UV detection of saccharides after their separation by anion-exchange chromatography was developed and successfully applied to several beverage samples. Investigation and optimization of the influencing factors using design of experiment resulted in a baseline separation of glucose, fructose, and sucrose within 6 min and LOD values below 0.2 mg L(-1). In addition, a fast, simple and cost-effective flow injection method was developed to estimate the total saccharide concentration. The results of this method applied to beverage samples are in good agreement with the chromatographic method as well as to the saccharide concentration stated by the manufacturer. Finally, a comparison of different commercially available UV detectors and detector cells revealed that sensitive detection requires the use of recently introduced flow cells with extended path length.
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