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991.
Lipid determination by the Smedes method was tested in an interlaboratory trial performed by nine laboratories from seven countries belonging to the West European Fish Technologists Association Analytical Methods Working Group. Five samples of fish and fishery products with different lipid contents, including two blind duplicates, were distributed among the participants. All laboratories applied a slightly modified Smedes method, which included extraction of lipids by cyclohexane and isopropanol, transfer of lipids to the cyclohexane phase by addition of water, phase separation by centrifugation, and gravimetric lipid determination. The results indicate that the RSD for reproducibility (RSD(R)) was between 4.11 and 6.31% for samples with moderate (7%) and high (14%) lipid content, depending on the sample. Larger SDs among the laboratories were obtained for a cod sample with low lipid content of 0.5%. The method is judged to be suitable as a routine method for lipid determination in fish and fishery products.  相似文献   
992.
The mixed ruthenium(II) complexes trans-[RuCl2(PPh3)2(bipy)] (1), trans-[RuCl2(PPh3)2(Me2bipy)](2), cis-[RuCl2(dcype)(bipy)](3), cis-[RuCl2(dcype)(Me2bipy)](4) (PPh3 = triphenylphosphine, dcype = 1,2-bis(dicyclohexylphosphino)ethane, bipy = 2,2′-bipyridine, Me2bipy = 4,4′-dimethyl-2,2′-bipyridine) were used as precursors to synthesize the associated vinylidene complexes. The complexes [RuCl(CCHPh)(PPh3)2(bipy)]PF6 (5), [RuCl(CCHPh)(PPh3)2(Me2bipy)]PF6 (6), [RuCl(CCHPh)(dcype)(bipy)]PF6 (7), [RuCl(CCHPh)(dcype)(bipy)]PF6 (8) were characterized and their spectral, electrochemical, photochemical and photophysical properties were examined. The emission assigned to the π–π1 excited state from the vinylidene ligand is irradiation wavelength (340, 400, 430 nm) and solvent (CH2Cl2, CH3CN, EtOH/MeOH) dependent. The cyclic voltammograms of (6) and (7) show a reversible metal oxidation peak and two successive ligand reductions in the +1.5-(?0.64) V range. The reduction of the vinylidene leads to the formation of the acetylide complex, but due the hydrogen abstraction the process is irreversible. The studies described here suggest that for practical applications such as functional materials, nonlinear optics, building blocks and supramolecular photochemistry.  相似文献   
993.
[(18)F]-5-Fluoro-5-deoxyribose ([(18)F]-FDR) conjugates much more rapidly than [(18)F]-FDG under mild reaction conditions to peptides and offers new prospects for mild and rapid bioconjugation for fluorine-18 labelling in PET imaging.  相似文献   
994.
The use of essential oils as chemotaxonomic markers could be useful for the classification of Artemisia species and to caracterize biodiversity in the different populations. An analysis of the chemical composition of four essential oils from Italian populations of Artemisia alba Turra (collected in Sicily, Marche and Abruzzo) was investigated. In this paper an in depth study of the significant differences observed in the composition of these oils is reported.  相似文献   
995.
A phytochemical analysis of the dichloromethane extract from the flowers of a subspecies of Tanacetum vulgare growing in Sicily was carried out. Five known sesquiterpene lactones with the eudesmane skeleton have been isolated and the cytotoxic activity of these compounds was tested in vitro on A549 (human lung carcinoma epithelial-like) and V79379A (Chinese hamster lung fibroblast-like) cells using the tetrazolium salt reduction (MTT) assay. All of tested compounds induced high time- and concentration-dependent cytotoxic effects.  相似文献   
996.
The photostability of quercetin in alcoholic solutions was studied. Both UVA and UVB light induced degradation of quercetin, yielding a single product 1 deriving from oxidation and addition of an alcohol molecule to the 2,3 double bond. The same mechanism operated when quercetin was dissolved in alkaline solutions, and again a product 2 due to oxidation and addition of water was characterized. Comparison with quercetin analogs confirmed that, despite the presence of five hydroxy groups in quercetin, those in positions 3, 3', and 4' are mainly involved in the antioxidant activity of the compound , as well as in its photolability.  相似文献   
997.
Salicylate synthase from Mycobacterium tuberculosis, MbtI, is a highly promiscuous Mg(2+) dependent enzyme with up to four distinct activities detected in vitro: isochorismate synthase (IS), isochorismate pyruvate lyase (IPL), salicylate synthase (SS) and chorismate mutase (CM). In this paper, Molecular Dynamic (MD) simulations employing hybrid quantum mechanics/molecular mechanics (QM/MM) potentials have been carried out to get a detailed knowledge of the IS and the IPL activities at the molecular level. According to our simulations, the architecture of the MbtI active site allows catalyzing the two reactions: the isochorismate formation, by means of a stepwise mechanism, and the salicylate production from isochorismate, that appears to be pericyclic in nature. Findings also explain the role of the magnesium cation and the pH dependence activity experimentally observed in MbtI. Mg(2+) would be polarizing and pre-organizing the substrate and active site, as well as shifting the pK(a) values of key active site residues.  相似文献   
998.
The synthesis and characterization (mainly by (19)F NMR and X-ray diffraction) of highly fluorinated aryl-4,5,6,7-tetrafluoroindazoles and their corresponding thallium hydrotris(indazolyl)borate complexes are reported [aryl = phenyl, pentafluorophenyl, 3,5-dimethylphenyl, 3,5-bis(trifluoromethyl)phenyl]. Thanks to N-H···N hydrogen bonds, the indazoles crystallize as dimers that pack differently depending on the nature of the aryl group. The thallium hydrotris(indazolyl)borate complexes Tl[Fn-Tp(4Bo,3aryl)] resulting from the reaction of aryl-4,5,6,7-tetrafluoroindazoles [aryl = phenyl, 3,5-dimethylphenyl, 3,5-bis(trifluoromethyl)phenyl] with thallium borohydride adopt overall C(3v) symmetry with the indazolyl groups bound to boron via their N-1 nitrogen in a conventional manner. When the perfluorinated pentaphenyl-4,5,6,7-tetrafluoroindazole is reacted with thallium borohydride, a single regioisomer of C(s) symmetry having one indazolyl ring bound to boron via its N-2 nitrogen, TlHB(3-pentafluorophenyl-4,5,6,7-tetrafluoroindazol-1-yl)(2)(3-pentafluorophenyl-4,5,6,7-tetrafluoroindazol-2-yl) Tl[F27-Tp((4Bo,3C6F5)*)], is obtained for the first time. Surprisingly, the perfluorinated dihydrobis(indazolyl)borate complex Tl[F(18)-Bp(3Bo,3C6F5)], an intermediate on the way to the hydrotris(indazolyl)borate complex, has C(s) symmetry with two indazolyl rings bound to boron via N-2. The distortion of the coordination sphere around Tl and the arrangement of the complexes in the crystal are discussed.  相似文献   
999.
The possibility to extract the quark transverse-momentum distributions in the neutron from semi-inclusive deep inelastic electron scattering off polarized 3He is illustrated through an impulse approximation analysis in the Bjorken limit. The generalization of the analysis at finite momentum transfers in a Poincaré covariant framework is outlined. The definition of the light-front spin-dependent spectral function of a J = 1/2 system allows us to show that within the light-front dynamics only three of the six leading twist T-even transverse-momentum distributions are independent.  相似文献   
1000.
A set of simplified and rigorous electromagnetic vector theories is used for analyzing the transmittance characteristics of diffraction phase gratings. The scalar diffraction theory and the effective medium theory are validated with the exact results obtained via the rigorous coupled-wave theory and the finite-difference time-domain method. The effects of surface profile parameters and also the angle of incidence is demonstrated to be a limiting factor in the accuracy of these theories. Therefore, the error of both simplified theories is also analyzed in non-paraxial domain with the intention of establishing a specific range of validity for both simplified theories.  相似文献   
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