SEM investigations established the tubular crystalline microstructure of the epicuticular wax of W. nobilis leaves. GC-MS and NMR experiments showed that nonacosan-10-ol is the major constituent of the epicuticular wax of W. nobilis leaves.

A series of zwitterionic lambda(5)Si-silicates with a (2,2,6,6-tetramethylpiperidinio)methyl group and two identical bidentate ligands derived from glycine, (S)-alanine, (S)-phenylalanine, glycolic acid, (S)-lactic acid, (S)-3-phenyllactic acid, or (S)-mandelic acid were synthesized and structurally characterized (solution and solid-state NMR spectroscopy; single-crystal X-ray diffraction). The chiral lambda(5)Si-silicates with ligands derived from optically active alpha-amino acids or alpha-hydroxycarboxylic acids were isolated as enantiomerically and diastereomerically pure compounds that undergo a (Lambda)/(Delta)-epimerization in solution.

The chemistry of higher-coordinate silicon compounds is currently one of the main areas of research in silicon chemistry. [1] We have contributed to this field by systematic studies on zwitterionic l 5 Si-silicates that contain a pentacoordinate (formally negatively charged) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom.[1d] The zwitterions 1, [2] 2, [3] 3, [4] 4, [5] 5, [6] 6, [7] 7, [8] 8, [9] and 9 [10] are examples of this type of compound. Generally, these zwitterionic l 5 Si-silicates are quite sensitive to water and easily undergo hydrolytic SiÀOC, SiÀSC, and SiÀNC bond cleavage. We have now succeeded in synthesizing a zwitterionic l 5 Si-silicate, namely, bis[meso-oxolane-3,4-diolato(2À)][(morpholinio)methyl]silicate (10), that shows remarkable stability in water.[11] Surprisingly, this pentacoordinate silicon compound could even be prepared in aqueous solution by SiÀC bond cleavage. We report herein on the synthesis of 10 and its hydrate 10·H 2 O and their structural characterization in the solid state and in solution.Compound 10 was synthesized according to Scheme 1, either through cleavage of three SiÀO bonds (method a) or through cleavage of two SiÀO bonds and one SiÀC bond (method b), starting with trimethoxy[(morpholino)methyl]-silane (11) [12] (yield 87 %) and dimethoxy[(morpholino)-methyl]phenylsilane (12) [12] (yield 53 %), respectively. As the synthesis according to method b involves a relatively slow SiÀC cleavage reaction as the rate-determining step, [13] product formation was significantly slower than with method a (see Experimental Section). The hydrate 10·H 2 O was synthesized analogously to 10 (Scheme 1, method a) by using water instead of acetonitrile as the solvent and was isolated, after crystallization from water, in 93 % yield as a colorless crystalline solid.The chiral l 5 Si-silicates crystallize in the space groups P2 1

The present study describes fine structure and chemical composition of the epicuticular leaf waxes of three Araucariaceae species. The leaf surfaces of samples from greenhouse-grown juvenile trees of Araucaria araucana K.Koch and Agathis robusta F.Muell. were investigated by scanning electron microscopy (SEM) and compared with data for a young greenhouse-grown Wollemia nobilis W.G.Jones, K.D.Hill & J.M.Allen cutting characterised earlier. The chemical compositions of the epicuticular waxes selectively removed from the adaxial and abaxial leaf surfaces of A. araucana, A. robusta and W. nobilis were studied by gas chromatography combined with mass spectroscopy (GC–MS). The main components of the leaf cuticular waxes of A. araucana, A. robusta and W. nobilis are members of the following three major compound classes: n-alkanes, secondary alcohols and alkane diols. It was shown earlier that the latter two classes contribute to the formation of the tubular epicuticular-wax crystals on the leaf surfaces. The present comparative study also revealed differences in the crystalline microstructure and chemical composition of the epicuticular leaf waxes among the three species.

The zwitterionic λ5 Si-silicates (Λ,S,S)-4·CH2Cl2, (Λ,S,S)-5·CH2Cl2, (Λ,S,S)-6·2CH2Cl2, and (Λ,S,S)-6·1/2CH2Cl2, with a (2,2,6,6-tetramethylpiperidinio)methyl group and two identical bidentate chelate ligands derived from (S)-valine, (S)-tert-leucine, or (S)-proline bound to the silicon(IV) coordination center, were synthesized and structurally characterized (solution and solid-state NMR spectroscopy; single-crystal X-ray diffraction). All compounds were isolated as diastereo- and enantiomerically pure crystalline solids, and the λ5 Si-silicates (Λ,S,S)-4, (Λ,S,S)-5, and (Λ,S,S)-6 were demonstrated to exist as diastereo- and enantiomerically pure zwitterions in solution as well (CD2Cl2, temperature range −100 to 23 °C). The experimental investigations were complemented by computational studies of related model species.