Moenuronic acid: synthetic studies and absolute configuration

The absolute configuration of the moenuronic acid moiety of the antibiotic moenomycin A has been established by a partial synthesis starting from D-galactose. The relation between the absolute conformation of α-hydroxy lactones and their chiroptical properties is discussed in detail.     

Kristallachsenlagen in Hagelkörnern

Summary The big single crystals of a shell of a hailstone are mostly arranged in palisades, directed to a certain point. This preferred orientation of shape of single crystals is identical to the direction of growth of the hailstone at the place of the crystallite refered to. If we look at the statistical deviation of the direction of thec-axis — determined by a Replica method — of the crystallites of a whole shell from the local direction of growth, we find that thec-axis looks mainly in the direction of growth (Figures 7, 10, 12) but the relative height of the maximum of the distribution may vary from one shell to another (Figures 7 and 10). Although in one case no rule of orientation could be found (Figures 14 and 15) and in another thec-axis was perpendicular to the direction of growth (Figure 16). Results of some primary investigations, based upon experiments in the hail tunnel, leed us to the conclusion that the arrangement of the crystallographic axis of the different single crystals depends very much on the growing conditions of the ice deposits. Therefore one may expect, that in the near future an interpretation of the icing conditions of natural hailstones is possible on behalf of their crystallographic structure. Icing experiments in the hail tunnels will give us the rules one has to observe for this procedure.     

Das Gaußsche Lemma ist Beispiel einer Verlagerung

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