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991.
Carlo Bicchi Giuseppe Artuffo Angela D'Amato Anna Galli Mario Galli 《Journal of separation science》1992,15(10):655-658
This paper reports the chromatographic performance of columns coated with 2,3,6-trimethyl-α-, β-, and γ-cyclodextrins (2,3,6-TriMe-α,- β-, and γ-CD) and their derivatives 2,6-dimethyl-3-trifluoroacetyl-α-, β-, and γ-cyclodextrins (2,6-DiMe-3-TFA-α-, β-, and γ-CD), all six diluted in polysiloxane, for the separation of the enantiomers of volatile compounds. The influence of column length and film thickness on separation is reported. Phenomena related to reproducibility and consistency, over a period of time, of columns prepared with these CD derivatives are also discussed, and a possible solution to some drawbacks reported here is proposed. 相似文献
992.
Inexact spectral projected gradient methods on convex sets 总被引:9,自引:0,他引:9
Birgin Ernesto G.; Martinez Jose Mario; Raydan Marcos 《IMA Journal of Numerical Analysis》2003,23(4):539-559
A new method is introduced for large-scale convex constrainedoptimization. The general model algorithm involves, at eachiteration, the approximate minimization of a convex quadraticon the feasible set of the original problem and global convergenceis obtained by means of nonmonotone line searches. A specificalgorithm, the Inexact Spectral Projected Gradient method (ISPG),is implemented using inexact projections computed by Dykstra'salternating projection method and generates interior iterates.The ISPG method is a generalization of the Spectral ProjectedGradient method (SPG), but can be used when projections aredifficult to compute. Numerical results for constrained least-squaresrectangular matrix problems are presented. 相似文献
993.
994.
995.
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
996.
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
997.
998.
999.
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
1000.
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