Die Aluminiumoxidfluoreszenz von 3-Keto-Δ4-steroiden

Zusammenfassung Die blauen Fluoreszenzchromogene, die beim Erhitzen von auf einer Aluminiumoxid-Dünnschichtplatte gebildet werden [1], wurden als Oberfl?chen-verbindungen von . Das Aluminiumoxid reagiert hier als ein Oxydationskatalysator für eine aktivierte Methylengruppe. Bei einer Heizdauer von 20 Minuten bleibt die Empfindlichkeit im Bereich von 150–180°C konstant. Die Selektivit?t der Reaktion nimmt mit abnehmender Temperatur zu. Die intramolekulare Wasserstoffbrückenbindung der freien Chromogene führt auf Silicagel gegenüber den Ausgangssubstanzen zu einer Erh?hung der R _f -Werte.

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Fluorescence of 3-Keto-Δ⁴-steroids on alumina

Summary The blue-fluorescence chromogens which are formed on heating on a thin layer plate of alumina [1] were identified as surface compounds of . The alumina is acting here as an oxidation catalyst for an activated methylene group. With a heating time of 20 minutes the sensitivity remains constant in the range 150 to 180°C. The selectivity of the reaction increases with decreasing temperature. Owing to the intramolecular hydrogen bonding in the free chromogens an increased R _f -value on silica gel compared to the original substances is found.

     

Investigation of a Lithium–Halogen Exchange Flow Process for the Preparation of Boronates by Using a Cryo‐Flow Reactor

Conducting low‐temperature organometallic reactions under continuous flow conditions offers the potential to more accurately control exotherms and thus provide more reproducible and scalable processes. Herein, progress towards this goal with regards to the lithium–halogen exchange/borylation reaction is reported. In addition to improving the scope of substrates available on a research scale, methods to improve reaction profiles and expedite purification of the products are also described. On moving to a continuous system, thermocouple measurements have been used to track exotherms and provide a level of safety for continuous processing of organometallic reagents. The use of an in‐line continuous liquid–liquid separation device to circumvent labour intensive downstream off‐line processing is also reported.     

Near-Infrared Diffuse Reflection Spectroscopy and Multivariate Calibration Hyphenated with Thin-Layer Chromatography for Quality Control of a Phytomedicine and Simultaneous Quantification of Methoxylated Flavones

JPC – Journal of Planar Chromatography – Modern TLC - By use of near infrared (NIR) spectroscopy hyphenated to thinlayer chromatography (TLC) for analysis of methoxylated flavones in a...     

On the role of single regiodefects and polydispersity in regioregular poly(3-hexylthiophene): defect distribution, synthesis of defect-free chains, and a simple model for the determination of crystallinity

Identifying structure formation in semicrystalline conjugated polymers is the fundamental basis to understand electronic processes in these materials. Although correlations between physical properties, structure formation, and device parameters of regioregular, semicrystalline poly(3-hexylthiophene) (P3HT) have been established, it has remained difficult to disentangle the influence of regioregularity, polydispersity, and molecular weight. Here we show that the most commonly used synthetic protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with Ni(dppp)Cl(2) as the catalyst, leads to regioregular chains with one single tail-to-tail (TT) defect distributed over the whole chain, in contrast to the hitherto assumed exclusive location at the chain end. NMR end-group analysis and simulations are used to quantify this effect. A series of entirely defect-free P3HT materials with different molecular weights is synthesized via new, soluble nickel initiators. Data on structure formation in defect-free P3HT, as elucidated by various calorimetric and scattering experiments, allow the development of a simple model for estimating the degree of crystallinity. We find very good agreement for predicted and experimentally determined degrees of crystallinities as high as ～70%. For Ni(dppp)Cl(2)-initiated chains comprising one distributed TT unit, the comparison of simulated crystallinities with calorimetric and optical measurements strongly suggests incorporation of the TT unit into the crystal lattice, which is accompanied by an increase in backbone torsion. Polydispersity is identified as a major parameter determining crystallinity within the molecular weight range investigated. We believe that the presented approach and results not only contribute to understanding structure formation in P3HT but are generally applicable to other semicrystalline conjugated polymers as well.     

Use of fullerene‐, octadecyl‐, and triaconthyl silica for solid phase extraction of tryptic peptides obtained from unmodified and in vitro glycated human serum albumin and fibrinogen

SPE plays a crucial role in bioanalytical research. In the present work a novel fullerene(C60)‐derivatised silica material is compared with octadecyl(C18) – and triaconthyl(C30)‐silicas regarding recoveries of peptides and sequence coverage of HSA and fibrinogen digests. C30‐ and C60(30 nm)‐SPE materials were found to be the two most prominent SPE materials. At low peptide concentrations C60‐material prepared from a silica gel with a pore size of 30 nm has proven to be the best material with regards to recoveries. By increasing the amount of loaded peptides recoveries decrease due to its relative low binding capacity in contrast to C30‐silica particles, showing no changes. The best sequence coverages of Aα‐ and Bβ‐chains of 20 pmol fibrinogen digest can also be achieved using these two SPE materials, C60 (30 nm) demonstrates an outstanding value of sequence coverage (62.15%) achieved for the γ‐chain. After nonenzymatic glycation the digests of fibrinogen and HSA were also separated. This makes the detection of a considerably higher number of glycated peptides possible compared to the unfractionated digests and the use of boronate affinity chromatography in the case of fibrinogen. For HSA, ten new sites of glycation at lysine and arginine residues have been explored. Using the detailed SPE/off‐line MALDI method the glycation sites on fibrinogen are first described in this paper.