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181.
JuvenileAplysia dactylomela were found feeding in abundance on the tropical brown algaStypopodium zonale, a seaweed previously shown to contain numerous unique terpene-quinone natural products. Lipid extracts of these herbivorous mollusks were shown by TLC and HPLC-NMR analyses to contain appreciable quantities of twoS. zonale metabolites as well as one new but closely related compound. Spectroscopic analyses of the new compound in concert with functional group modifications identified this new compound as 3-keto epitaondiol. A careful analysis of the seaweed extract failed to locate this ketone, and thus, it most likely represents anAplysia-biotransformed compound. This is the first clear reported observation of metabolite transfer between an alga of the phylum Phaeophyta and a sea hare. 相似文献
182.
Walter J. Jakubas Bernard C. Wentworth William H. Karasov 《Journal of chemical ecology》1993,19(10):2353-2377
Various plant secondary metabolites related to cinnamic acid are of interest because of their repellency to birds and their occurrence in ecologically important food items. Coniferyl benzoate (CB), a phenylpropanoid ester that occurs in quaking aspen (Populus tremuloides) is of particular ecological interest because of its effect on ruffed grouse (Bonasa umbellus) feeding behavior and its possible influence on the population dynamics of this bird. During detoxification processes, CB and other analogous compounds are metabolized into by-products, such as ferulic acid (FA), that can cause anti-reproductive effects. We tested whether consumption of CB produces antire-productive effects similar to FA using male and female Japanese quail (Coturnix coturnix) as avian models for ruffed grouse. The parameters we investigated included: the production, morphology, and development of eggs; reproductive characteristics influenced by estrogen; serum prolactin levels; and male reproductive behavior. Dietary CB did not produce antireproductive effects similar to FA at intake levels that Japanese quail and ruffed grouse would freely consume. Consumption of CB by Japanese quail significantly reduced egg production and body mass but did not affect male reproductive performance. Coniferyl benzoate's effect on egg production may be explained by lower energy acquisition and retention rather than endocrine changes per se. Contrary to previous reports, it is unlikely that FA, or similar compounds act directly as estrogen mimics or antagonists. Although, CB did reduce egg production in quail, it is unlikely that it would affect egg production in wild ruffed grouse. Detoxification costs and the effects of CB on nutrient utilization may explain why ruffed grouse avoid high dietary levels of CB. 相似文献
183.
Gang Yao William Yi Wang Chengxiong Zou Ke Ren Peixuan Li Xingyu Gao Deye Lin Jun Wang Shufeng Yang Yiguang Wang Haifeng Song Jinshan Li 《Journal of the American Ceramic Society》2022,105(6):4260-4276
High-entropy carbides (HECs) are regarded as potential candidate structural materials with attractive mechanical properties due to their ultra-high hardness. It is essential to reveal the atomic and electronic basis for strengthening mechanism in order to develop the advanced HECs. In the present work, C (M = Nb, Ti, V) are selected as case studies. The effects of transition metals (M) on the lattice parameters, bulk modulus, enthalpy of formation, electron work function (EWF), and bonding morphology/strength of HECs are comprehensively studied by first-principles calculations. It is found that the lattice parameters, equilibrium volumes, and bulk modulus of HECs are improved with the increase of M atomic volumes. The atomic-size differences among various groups of elements not only result in the lattice mismatch/distortion but also contribute to the formation of weak spots. In the view of bonding charge density, the electron redistributions caused by the coupling effect of the lattice distortion and valance electron differences can be revealed obviously, which identify the different bonding strength. Moreover, in terms of EWF, the proposed power-law-scaled hardness of HECs is validated and matches well with those reported theoretical and experimental results, providing a strategy to design advanced HECs with excellent mechanical properties. 相似文献
184.
Preparation of Silicon Carbide/Aluminum Nitride Ceramics Using Organometallic Precursors 总被引:1,自引:0,他引:1
Corinna L. Czekaj Michael L. J. Hackney William J. Hurley Jr. Leonard V. Interrante Gary A. Sigel Paul J. Schields Glen A. Slack 《Journal of the American Ceramic Society》1990,73(2):352-357
Solid solutions of 2H -SiC/AlN can be prepared at temperatures less than 1600°C by rapid pyrolysis ("hot drop") of mixtures of [(Me3 Si)0.80 ((CH2 =CH)MeSi)1.0 (MeHSi)0.35 ] n (VPS) or [MeHSiCH2 ] n (MPCS) with [R2 AlNH2 ]3 , where R=Et, i -Bu or simply by slow pyrolysis of the precursor mixture in the case of [Et2 AlNH2 ]3 . In contrast, slow pyrolysis of mixtures of VPS or MPCS with [ i -Bu2 AlNH2 ]3 yields a composite of 2 H -AlN and 3 C -SiC at 1600°C, which transforms into a single 2 H -SiC/AlN solid solution on heating to 2000°C. The influences of the nature of the precursor and processing conditions on the structure, composition, and purity of the SiC/AlN materials are discussed. 相似文献
185.
Eicosa-5,8,11,14-tetraynoic acid or arachidonic acid or no supplement (controls) was given orally to rats maintained on a
fat free diet and the fatty acid composition of total lipids of several organs determined. No changes were noted in the total
fatty acid concentrations of the organs examined in the various groups. A decrease in the amount of arachidonic acid, 22∶4ω6
and 22∶5ω6 (as percent of total fatty acids), and an increase in the amount of 20∶3ω6 and linoleate were observed in total
lipids of several organs. In the group receiving the arachidonate supplement, there was less linoleate and 20∶3ω6 and more
arachidonate than in the controls. Both eicosa-5,8,11,14-tetraynoic acid and arachidonate supplements resulted in a decrease
in 20∶3ω9 in most organs studied. Generally, the most marked changes were seen in liver but, of the other organs examined
(heart, kidney, testis, brain, and adrenals), only the adrenals failed to show any significant differences between the controls
and each of the two supplemented groups. Although the experimental conditions preclude conclusive interpretation of the changes
observed, it is suggested that eicosa-5,8,11,14-tetraynoic acid was effective in inhibiting the conversion of linoleate to
arachidonate and the conversion of arachidonate to 22∶4 and 22∶5. 相似文献
186.
Policy flight simulators are designed for the purpose of exploring alternative management policies at levels ranging from individual organizations to national strategy. This article focuses on how such simulators are developed and on the nature of how people interact with these simulators. These interactions almost always involve groups of people rather than individuals, often with different stakeholders in conflict about priorities and courses of action. The ways in which these interactions are framed and conducted are discussed, as well as the nature of typical results. 相似文献
187.
Taylor William R.; Orengo Christine A. 《Protein engineering, design & selection : PEDS》1989,2(7):505-519
A method of protein structure comparison developed previouslyis extended to incorporate other aspects of protein structurein addition to the inter-atomic vectors on which it was originallybased. Each additional aspect, which included hydrogen bonding,solvent exposure, torsional angles and sequence, was introducedseparately and evaluated for its ability to improve alignmentquality. The components were then combined, suitably weighted,to produce a more holistic comparison method. The method wastested on a group of remotely related ß/ type proteinsthat share a common feature in their overall chain fold. Theresults indicated that while the original inter-atomic vectorcomponent was sufficient to give the correct alignment of mostpairs of topologically equivalent proteins, the inclusion ofhydrogen bonds, torsion angles and a measure of solvent exposureled to improvements in the more difficult comparisons. Considerationof amino acid properties, including hydrophobicity, had no beneficialeffect. The failure of the latter component was not unexpectedconsidering the almost total lack of sequence similarity amongthe proteins considered. 相似文献
188.
G. William Chase Jr. Casimir C. Akoh Ronald R. Eitenmiller 《Journal of the American Oil Chemists' Society》1994,71(11):1273-1276
A high-performance liquid chromatographic method is described to determine the sucrose polyester (SPE) content in seven blends
of cooking oils. Four gel-permeation chromatography (GPC) columns were used in series with an evaporative light scattering
mass detector to separate the SPE from the acylglycerols in the final chromatogram. The SPE fraction was collected off the
GPC column and injected onto a reverse-phase C-18 column for quantitation with sucrose octaacetate as an internal standard
and a gradient of nonaqueous solvents as mobile phase. The chromatograms were interference-free, with only two sharp peaks
appearing. The standards were linear from 500 to 5000 μg/mL with a correlation coefficient of r=0.999. The mean percent recovery
(n=9) and standard deviation were 102±6.7. The detector could detect amounts as low as 5 μg SPE. 相似文献
189.
John T. Budin William M. Breene Daniel H. Putnam 《Journal of the American Oil Chemists' Society》1996,73(4):475-481
Grain of 21Amaranthus accessions (eight species) was analyzed for crude fat, fatty acid profiles (FAP), and vitamin E (tocopherols and tocotrienols).
Contents of (1→3), (1→4) β-glucan were determined in 12 accessions (four species), and trypsin inhibitor activity (TIA) in
20 accessions (six species). FAP and vitamin E profiles were compared to those of barley, buckwheat, corn, lupin, oat, and
wheat oils. Crude fat content ranged from 5.2 to 7.7%, and of the oils examined, amaranth oil was most similar in FAP to corn
and buckwheat oils. Amaranth was higher than all but wheat and lupin in tocopherol content but was virtually devoid of tocotrienols,
which have been shown to have hypocholesterolemic activity. Amaranth grain did not contain (1→3), (1→4) β-glucans and was
low in trypsin inhibitor activity (≤4.3 trypsin units inhibited/mg). Any hypocholesterolemic effects of dietary amaranth are
apparently due to substances other than (1→3), (1→4) β-glucans or tocotrienols. 相似文献
190.
Byrdwell WC 《Lipids》2001,36(4):327-346
Atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) has proven to be a very valuable technique for analysis
of lipids from a variety of classes. This instrumental method readily produces useful ions with gentle fragmentation from
large neutral molecules such as triacylglycerols and carotenoids, which are often difficult to analyze using other techniques.
Molecules that are easily ionized, such as phospholipids, produce molecular ions and diagnostically useful fragment ions that
are complementary to those produced by methods such as electrospray ionization MS with collision-induced dissociation. The
simplicity and versatility of APCI-MS make it an ideal tool for use in solving hitherto very difficult analytical problems. 相似文献