Unser 10. Leibniz Plant Biochemistry Symposium am 7. und 8. Mai war ein großer Erfolg. Thematisch ging es in diesem Jahr um neue Methoden und Forschungsansätze der Naturstoffchemie. Die exzellenten Vorträge über Wirkstoffe…
Omanische Heilpflanze im Fokus der Phytochemie IPB-Wissenschaftler und Partner aus Dhofar haben jüngst die omanische Heilpflanze Terminalia dhofarica unter die phytochemische Lupe genommen. Die Pflanze ist reich an…
Geschmack ist vorhersagbar: Mit FlavorMiner. FlavorMiner heißt das Tool, das IPB-Chemiker und Partner aus Kolumbien jüngst entwickelt haben. Das Programm kann, basierend auf maschinellem Lernen (KI), anhand der…
Drosihn, S.; Porzel, A.; Brandt, W.;Determination of preferred conformations of brassinosteroids by means of NMR investigations and Boltzmann statistical analysis of simulated annealing calculationsJ. Mol. Model.734-42(2001)DOI: 10.1007/s008940100009
Brassinosteroids are a class of steroidal phytohormones with high growth-promoting properties. The preferred side-chain conformations of 10 brassinosteroids were determined by means of detailed NMR investigations and molecular-modeling studies. Vacuum conformations obtained by simulated annealing calculations and Boltzmann statistical analysis were compared with solution conformations derived from NOE experiments and molecular dynamic simulations, and with X-ray structures. In general, results from simulated annealing calculations and NMR-supported molecular dynamics simulations are in good agreement. For some of the compounds investigated the conformation was less well-defined at the end of the side-chain. It could be shown that the energetically most favorable and most probable conformations also include the conformations obtained by NMR supported molecular-dynamics calculations and by X-ray analysis. For the most bioactive compound brassinolide (1) the majority of conformations show a side-chain bent towards the β-face of the steroid skeleton, whereas for the less bioactive brassinosteroids, conformations with straight side-chains or side-chains bent towards the α-face are more frequent.
Publikation
Cai, Y.; Sun, M.; Schliemann, W.; Corke, H.;Chemical Stability and Colorant Properties of Betaxanthin Pigments from Celosia argenteaJ. Agr. Food Chem.494429-4435(2001)DOI: 10.1021/jf0104735
The chemical stability and colorant properties of three betaxanthins recently identified from Celosia argentea varieties were evaluated. Lyophilized betaxanthin powders from yellow inflorescences of Celosia exhibited bright yellow color and high color purity with strong hygroscopicity. The aqueous solutions containing these betaxanthins were bright yellow in the pH range 2.2−7.0, and they were most stable at pH 5.5. The betaxanthins in a model system (buffer) were susceptible to heat, and found to be as unstable as red betacyanins (betanin and amaranthine) at high temperatures (>40 °C), but more stable at 40 °C with the exclusion of light and air. The three betaxanthins had slightly higher pigment retention than amaranthine/isoamaranthine in crude extracts at 22 °C, as verified by HPLC analysis. Lyophilized betaxanthins had much better storage stability (mean 95.0% pigment retention) than corresponding aqueous solutions (14.8%) at 22 °C after 20 weeks. Refrigeration (4 °C) significantly increased pigment retention of aqueous betaxanthins to 75.5%.