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排序方式: 共有491条查询结果,搜索用时 15 毫秒
1.
Abstract Under a suitable ellipticity condition, we show that classical SG-pseudodifferential operators of nonnegative order possess
complex powers. We show that the powers are again classical and derive an explicit formula for all homogeneous components.
Keywords: Complex power, Weighted symbols, Noncompact manifolds 相似文献
2.
A linear inequality system with infinitely many constraints is polynomial (analytical) if its index set is a compact interval
of the real line and all its coefficients are polynomial (analytical, respectively) functions of the index on this interval.
This paper provides an example of analytical system whose solution set cannot be the solution set of any polynomial system.
Research supported by DGES of Spain and FEDER of UE, Grant BFM2002-04114-C02-01.
Research supported by CONACyT of Mexico, Grant 130036.
Research partially supported by CONACyT of Mexico, Grant 44003. 相似文献
3.
Georgiy B. Shul’pin Camilla C. Golfeto Lidia S. Shul’pina 《Tetrahedron letters》2005,46(27):4563-4567
The H2O2-FeCl3-bipy system in acetonitrile efficiently oxidises alkanes predominantly to alkyl hydroperoxides. Turnover numbers attain 400 after 1 h at 60 °C. It has been assumed that bipy facilitates proton abstraction from a H2O2 molecule coordinated to the iron ion (these reactions are stages in the catalytic cycle generating hydroxyl radicals from the hydrogen peroxide). Hydroxyl radicals then attack alkane molecules finally yielding the alkyl hydroperoxide. 相似文献
4.
Villorbina G Roura L Camps F Joglar J Fabriàs G 《The Journal of organic chemistry》2003,68(7):2820-2829
The formation of methylenecyclopropanes by enzymatic desaturation of 11-cyclopropylundecanoic acid (1) and its disubstituted derivatives cis- and trans-3-5 has been investigated using the Delta(11) desaturase of Spodoptera littoralis as model enzyme. Gas chromatography coupled to mass spectrometry analyses of methanolyzed lipidic extracts from tissues incubated with each probe revealed that all the cyclopropyl fatty acids were transformed into the corresponding 11-cyclopropylidene acids, except for compound trans-5 (5b), which was not desaturated at C11. The formation of methylenecyclopropane 9 as the only reaction product from 1 indicates that a potential radical intermediate is too short-lived to allow rearrangement reactions. Information on the Delta(11) desaturase substrate binding domain is provided considering the cyclopropyl probes 3-5 as conformationally restricted analogues of the straight-chain substrates. 相似文献
5.
Amelichev SA Aysin RR Konstantinova LS Obruchnikova NV Rakitin OA Rees CW 《Organic letters》2005,7(25):5725-5727
[chemical reaction: see text]. Treatment of N-substituted 2,5-dimethylpyrroles 2 with an equilibrated mixture of disulfur dichloride and DABCO in chloroform at 0 degrees C gives pentathiepinopyrroles 3 in moderate yields; further reaction of 3 with the same mixture at room temperature leads, in an extensive reaction cascade, to bis(dithiolo)pyrroles 4 in high yield; 2 can be converted into 4 in a one-pot operation under unusually mild conditions. 相似文献
6.
While advances in protein design have made possible the construction of protein architectures with nativelike properties and predictable structures and function, there are as of yet no examples of functional, protein-based, solar energy conversion systems. This communication describes the design and characterization of an artificial reaction center (RC) protein that closely resembles the function of the natural photosynthetic RC. The synthetic protein, designed by the protein design program CORE, participates in multiple reduction/oxidation cycles with exogenous acceptors/donors following photoexcitation. The designed metalloprotein, aRC, consists of a tetrahelical bundle functionalized with two bis-histidine bound metal cofactors: a Ru(bpy)2 moiety and a heme group. Two distinct bis-histidine binding sites were engineered for each of these metal centers. Photoexcitation of aRC results in rapid ET from the RuII complex to the heme group (kET >/= 5 x 1010 s-1) yielding a long-lived (70 ns) charge-separated state (CSS), RuIII/FeII. This long-lived CSS participates in subsequent ET reactions with exogenous donors and acceptors in multiple photocycles, thus mimicking the basic function of native photosynthetic RCs. This study illustrates the successful design and construction of a protein-based functional charge separation device using a combination of automated computational protein design and knowledge of the engineering principles of biological electron tunneling extracted from natural electron-transfer systems. To our knowledge, this represents the first example of a functional protein-based artificial reaction center. 相似文献
7.
Juliana Vaz Bevilaqua Lidia M. Lima Aline Gomes Cunha Eliezer J. Barreiro Tito L. M. Alves Lucia Moreira Campos Paiva Denise M.Guimarães Freire 《Applied biochemistry and biotechnology》2005,121(1-3):117-128
The last step of the production of four phthalimide-derived acids, designed to act as antiasthma drugs, was performed by enzymatic hydrolysis of the respective methyl or ethyl esters. The esters 4-ethyl-[2-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)]-phenoxyacetic methyl ester (PHT-MET), 4-ethyl-[2-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)]-phenoxyacetic ethyl ester, 4-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)-phenoxyacetic ethyl ester, and 2-(1,3-dioxo-1, 3-dihydro-2-isoindoylyl)-phenoxyacetic ethyl ester were hydrolyzed by immobilized lipase. The enzymatic reaction could be used only to produce the desired 4-substituted compounds. The best result that was found to hydrolysis of PHT-MET, and, therefore, that ester was selected for optimization experiments in a three-phase system. Reactions were performed with solid biocatalyst (Lipozyme® RM IM), organic solvent phase (ethyl acetate), and aqueous phase (saturated Na2CO3 solution). To optimize the reaction conditions, an experimental design optimization procedure was used. The variables studied were the amount of enzyme, the temperature, and the volume of the aqueous solution. Time course experiments were then performed for different initial enzyme concentrations (0.5, 0.9, and 1.4 UH/mL of solvent). The optimized reaction conditions found were 20 mg of Lipozyme (0.9 UH/mLsolvent) and 5.0 mL of Na2CO3(sat) at 40°C for 6 h. 相似文献
8.
Marcin Marczak Lidia Wolska Wojciech Chrzanowski Jacek Namieśnik 《Mikrochimica acta》2006,155(3-4):331-348
Volatile organic compounds (VOCs), due to their toxicity and persistence in the environment, are particularly important pollutants.
Some of these compounds are mutagens, teratogens or carcinogens, while others are responsible for the degradation of organoleptic
parameters such as taste and odour of water. This review focuses on a number of key procedural steps in the analysis of volatile
organic compounds (VOCs) in water samples. A wide spectrum of techniques for the isolation and preconcentration of the aforementioned
pollutants for trace organic analysis by gas chromatography are presented and discussed. The advantages and disadvantages
of these techniques are discussed and novel developments are also taken into consideration. 相似文献
9.
10.
Andrew Wisel Irene Studentsova Abdurakhim Muslinkin Ramil Garaev Valeriy Danilov Lidia Schukina 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract The synthesis of dimephosphone (1) was carried out on Pudovik's reaction. 相似文献