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排序方式: 共有309条查询结果,搜索用时 343 毫秒
211.
Tandem mass spectrometry has been applied to differentiate three sets of o-, m- and p-methyl, -methoxy and -nitro-substituted-6-phenyl-dibenzo(d,f)(1,3)dioxepines. Collision-induced dissociation (CID) experiments have been carried out on 2-phenylbenzo[b]furan fragment ions, which originate from the decomposition of the molecular ions after their EI-induced isomerization to spirocyclic structures. With the exception of m- and p-methylphenylbenzo[b]furan isomers, which display identical CID mass spectra, the three isomeric methoxy- and nitrophenylbenzo[b]furan fragment ions display very characteristic CID behavior which allows unequivocal differentiation of the 6-phenyl-dibenzo(d,f)(1,3)dioxepine isomers. 6-(o-nitrophenyl)-dibenzo(d,f)(1,3)dioxepine isomer, does not form a 2-(o-nitrophenyl)benzo[b]furan ion and, therefore, it can be differentiated from the m- and p- isomers based on the mere EI mass spectra. Furthermore, it shows a characteristic ion most likely due to an ortho effect between the nitro group and the dioxepine ring. Multiple stage mass spectrometric techniques (MSn), labeled derivatives and reference compounds were used in order to gain additional information on the structures of product ion from the CID fragmentation. 相似文献
212.
In the present Letter we discuss the role of different boundary conditions on the Casimir effect between parallel lines in a planar (2+1) system, specifically in the context of a Maxwell theory with a Chern-Simons mass term. We consider parallel lines of a different nature, namely a perfectly conducting line and an infinitely permeable one. We also discuss the case of two infinitely permeable lines. We compare our results with those found in the literature for the case of two perfectly conducting lines. 相似文献
213.
Cordeiro RS Scarano WR Campos SG Santos FC Vilamaior PS Góes RM Taboga SR 《Micron (Oxford, England : 1993)》2008,39(8):1312-1324
The normal growth, differentiation and maintenance of the morphofunctional integrity of the prostate gland are dependent on the interaction of constant levels of androgens with their receptors. The need to study the responses to hormones under several conditions and the effect of their blockage is due to the fact that the human prostate is the site of a great number of age-related diseases, and the ones with a major medical importance are prostate cancer (CaP) and benign prostatic hyperplasia (BPH), which can both be treated with androgen suppression. Seventy-five male gerbils were divided, randomly, into 3 groups of 25 animals each, where each group corresponded to one phase of postnatal development. In each phase, it was possible to morphologically and stereologically analyze the compartments of prostatic ventral lobe, as well as to immunohistochemically analyze the degree of expression of androgen receptors (ARs) after the androgen blockage therapies. In addition, it was possible to establish the hormonal dosage of serum testosterone levels given the comparative approach of the expression of androgen receptors. There is a pattern of AR distribution in the prostatic ventral lobe throughout postnatal development, in which the younger the animal is the higher, the interaction of circulating androgens that stimulate the AR expression in both the epithelial and stromal compartments. The androgen blockage therapies decreased AR expression in the prostatic compartments, but the androgen reposition after these blockages was not sufficient to recover the glandular structure or stimulate the AR expression up to normal physiological conditions. Both the regulation and distribution of androgen receptors along the gerbil prostatic tissues are complex mechanisms that are likely to be genetically regulated by androgens prenatally or by other factors that are still unknown. This rodent species seems to be a valuable model in the attempt to improve the understanding of the morphophysiological and pathological behavior of this important gland in humans throughout aging and to stimulate new therapeutic ideas to fight prostate cancer. 相似文献
214.
Mario Cetina Ante Nagl Svjetlana Prekupec Silvana Rai‐Mali Mladen Mintas 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(3):o158-o160
In the title compound, C10H14N2O3, a pyrimidine ring is fused with a piperidine ring. The pyrimidine ring is planar, whereas the piperidine ring adopts a half‐chair conformation. The molecules of the title compound are connected via O—H⋯O intermolecular hydrogen bonds into infinite zigzag chains. The pyrimidine ring is involved in three C—H⋯π interactions, which link the hydrogen‐bonded chains into a three‐dimensional framework. 相似文献
215.
Caputo R De Nisco M Festa P Guaragna A Palumbo G Pedatella S 《The Journal of organic chemistry》2004,69(21):7033-7037
4-Deoxy-l-hexoses were synthesized starting from our previously reported reagent 1 and (R)-benzyl glycidyl ether, which led in few steps to a substituted dihydropyran 6. The stereocontrolled hydroxylation of the latter afforded the corresponding 4-deoxy-l-hexoses 7a, 9, and 11. The same procedure, starting from (S)-benzyl glycidyl ether, enabled the preparation of their d-series enantiomers. 相似文献
216.
The author recently proved that 1-cotilting modules are pure-injective;however, the problem of determining whether n-cotilting modulesare pure-injective remained open. In this paper, necessary andsufficient conditions are given for the pure-injectivity ofn-cotilting modules. 2000 Mathematics Subject Classification16D90 (primary), 16D30 (secondary). 相似文献
217.
Silvana Bernasconi Giancarlo Jommi Roberto Pagliarin Paolo Tavecchia 《Journal of heterocyclic chemistry》1988,25(3):725-729
Eight compounds containing N- or N′-alkylated imidazole rings have been synthesized and their structures have been chemically and spectroscopically demonstrated. These molecules, submitted to biological tests in order to evaluate their activity as juvenile hormones, provoke morphological changes in the pupae of Tenebrio Molitor. 相似文献
218.
Riassunto In questo lavoro sono studiati gli isomorfismi tra reticoli di sottogruppi normali di gruppi nilpotenti senza torsione. Si
prova che ogni gruppo iperciclico con la struttura normale di gruppo nilpotente senza torsione è un gruppo nilpotente sanza
torsione.
Summary Lattice isomorphisms between the normal structures of torsion-free nilpotent groups are studied in this paper. We prove that every hypercyclic group with the normal structure of a torsion-free nilpotent group is a torsion-free nilpotent group.相似文献
219.
Silvana Modena Pierangelo Calini Guglielmo Gregorio Giovanni Moggi 《Journal of fluorine chemistry》1988,40(2-3):349-357
Liquid phase fluorination of diethyleneglycol dimethyl ether tetraethyleneglycol dimethyl ether, 2[1,2-dichloro-1,2-difluoroethyl] tetrahydrofuran and 2[1,2-dichloro-1,2-difluoroethyl] dioxane 1,4 produce the corresponding perfluoroethers in 56, 43, 67 and 74 % yields respectively.
The by-products are partially fluorinated compounds and no fragmentation is observed.
The simplicity of the reactions and method of preparation make this approach to fluorinated fluids and oils industrially attractive. 相似文献
220.
Silvia Bradamante Silvana Colombo Giorgio A. Pagani Stefano Roelens 《Helvetica chimica acta》1981,64(2):568-571
Phenylglycine esters react with pyruvic acid to give α-methylsuccinic amides 9 instead of the expected Schiff bases 8 , analogously to p-anisidine but unlike aniline. 相似文献