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991.
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Mario O. Carignan Karina H.M. Cardozo Diogo Oliveira-Silva Pio Colepicolo José I. Carreto 《Journal of photochemistry and photobiology. B, Biology》2009,94(3):191-200
Using a high-resolution reverse-phase liquid chromatography method we found that the tissues of the hermatypic coral Pocillopora capitata (collected in Santiago Bay, Mexico) contain a high diversity of primary and secondary mycosporine-like amino acids (MAAs) typical of some reef-building coral species: mycosporine–glycine, shinorine, porphyra-334, mycosporine–methylamine–serine, mycosporine–methylamine–threonine, palythine–serine, palythine and one additional novel predominant MAA, with an absorbance maximum of 320 nm. Here we document the isolation and characterization of this novel MAA from the coral P. capitata. Using low multi-stage mass analyses of deuterated and non deuterated compounds, high-resolution mass analyses (Time of Flight, TOF) and other techniques, this novel compound was characterized as palythine–threonine. Palythine–threonine was also present in high concentrations in the corals Pocillopora eydouxi and Stylophora pistillata indicating a wider distribution of this MAA among reef-building corals. From structural considerations we suggest that palythine–threonine is formed by decarboxylation of porphyra-334 followed by demethylation of mycosporine–methylamine–threonine. 相似文献
994.
The paper proposes a numerical procedure for evaluating the geometrical and electromagnetic properties of the microstructure of a heterogeneous medium starting from the material effective characteristics. The identification process is developed by applying an inverse homogenisation technique, based on multiple scale expansion theory. The Newton–Raphson scheme and the Rosenbrock algorithm are tested. The efficiency of the second approach is proved by reporting several numerical results. 相似文献
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López-Cortina S Basiulis DI Marsi KL Muñoz-Hernández MA Ordoñez M Fernández-Zertuche M 《The Journal of organic chemistry》2005,70(19):7473-7478
[reaction: see text] The synthesis of pure cis- and trans-3-methoxy-2,2,6-trimethyl-3-phenyl-1,3-oxaphosphorinanium tetrafluoroborate salts 3a and 3b, respectively, molecules designed to evaluate the effect of oxygen on the steric course of base-induced nucleophilic displacement of the methoxy group at phosphorus, was accomplished. It was found that these isomeric salts react with aqueous sodium hydroxide to produce the corresponding phosphine oxides 7a and 7b with complete retention of configuration at phosphorus. 相似文献
999.
Starting from chiral 3,4-trans-disubstituted pyrrolidin-2-ones 11a and 11b, obtained from a Baylis-Hillman adduct, conformationally restricted analogues of both (S)-β-homoserine, 17, and (S)-aspartic acid, 21, were synthesized, respectively, and these compounds are suitable either for introduction in peptidomimetics or for synthesis of novel β-foldamers. 相似文献
1000.
Solid state (13)C NMR and FT-IR spectroscopy of the cocoon silk of two common spiders 总被引:2,自引:0,他引:2
Bramanti E Catalano D Forte C Giovanneschi M Masetti M Veracini CA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(1-3):105-111
The structure of the silk from cocoons of two common spiders, Araneus diadematus (family Araneidae) and Achaearanea tepidariorum (family Theridiidae) was investigated by means of (13)C solid state NMR and FT-IR spectroscopies. The combined use of these two techniques allowed us to highlight differences in the two samples. The cocoon silk of Achaearanea tepidariorum is essentially constituted by helical and beta-sheet structures, whereas that of Araneus diadematus shows a more complex structure, containing also beta-strands and beta-turns. Moreover, the former silk is essentially crystalline while the latter contains more mobile domains. The structural differences of the two cocoon silks are ascribed to the different habitat of the two species. 相似文献