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A reversal of regioselectivity of LiAlH4 or LiBH4 reduction of 2-cyclohexenone induced by addition of [2.1.1]-cryptand to the reaction medium is accompanied by a rate decrease. In the absence of the cryptand, carbonyl attack predominates (C1:C3 = 86:14 with LiAlH4 in THF). In the presence of the cryptand, double bond attack is favoured (C1:C3= 14:86). This effect is larger with LiAlH4 than with LiBH4. This trend is general in the case of five substituted 2-cyclohexenones. Using 12-crown-4 as a Li+ coordinator, a change in regioselectivity occurs but it is less pronounced than with the cryptand. 相似文献
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First, sufficient conditions of minimal character are given which guarantee the sequential closedness of the set-valued function
defined by the parametric weak-multicriteria Nash equilibria of a parametric multicriteria game, that is to say: a convergent
sequence of parametric weak-multicriteria Nash equilibria, corresponding to an approximate value of the parameter xn, converges to a weak-multicriteria Nash equilibrium corresponding to the limit value x of the sequence (xn)n. Then, approximating sequences and parametrically well-posedness for a multicriteria game are introduced and investigated. 相似文献
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Jacqueline A Sobota William A Mohler Ann E Cowan Betty A Eipper Richard E Mains 《BMC neuroscience》2010,11(1):32
Background
Peptidergic neurons store and secrete the contents of large dense core vesicles (LDCVs) from axon terminals and from dendrites. Secretion of peptides requires a highly regulated exocytotic mechanism, plus coordinated synthesis and transport of LDCVs to their sites of release. Although these trafficking events are critical to function, little is known regarding the dynamic behavior of LDCVs and the mechanisms by which their transport is regulated. Sensory neurons also package opiate receptors in peptide-containing LDCVs, which is thought to be important in pain sensation. Since peptide granules cannot be refilled locally after their contents are secreted, it is particularly important to understand how neurons support regulated release of peptides. 相似文献119.
Two isomeric 4-methylumbelliferyl-alpha-D-N-acetylneuraminylgalactopyranosides (1 and 2) were synthesised. These compounds contain either the natural alpha-2,3 or alpha-2,6 sialyl-galactosyl linkages, as well as an attached 4-methylumbelliferone for convenient detection of their hydrolyses. These compounds were designed as natural sialoside analogues to be used in a continuous assay of sialidase activity, where the sialidase-catalysed reaction is coupled with an exo-beta-galactosidase-catalysed hydrolysis of the released galactoside to give free 4-methylumbelliferone. The kinetic parameters for 1 and 2 were measured using the wild-type and nucleophilic mutant Y370G recombinant sialidase from Micromonospora viridifaciens. Kinetic parameters for these analogues measured using the new continuous assay were in good agreement with the parameters for the natural substrate, 3'-sialyl lactose. Given the selection of commercially available exo-beta-galactosidases that possess a variety of pH optima, this new method was used to characterise the full pH profile of the wild-type sialidase with the natural sialoside analogue 1. Thus, use of these new substrates 1 and 2 in a continuous assay mode, which can be detected by UV/Vis or fluorescence spectroscopy, makes characterisation of sialidase activity with natural sialoside linkages much more facile. 相似文献
120.
The use of microwave-assisted extraction has gained wide acceptance as a powerful tool for the recovery of environmental contaminants
and their subsequent analysis. This paper reviews the historical and fundamental basis of the technology. It also provides
a cursory review of the current state-of-the-art and literature (2000–2006) in the area of environmental analysis in addition
to providing a critical review of the level of efforts being devoted to its further development.
MAP is a Trademark of Her Majesty the Queen in Right of Canada as represented by the Minister of the Environment. 相似文献