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排序方式: 共有168条查询结果,搜索用时 15 毫秒
1.
Berit OlofssonPeter Somfai 《Tetrahedron letters》2003,44(6):1279-1281
A large set of syn- and anti-1,2-amino alcohols has been synthesized. Upon comparison of the CH?O and CH?N 1H NMR shifts a general trend has been observed, making it possible to determine the relative configuration of 1,2-amino alcohols without derivatization or shift reagents. 相似文献
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3.
Jensen BP Smith CJ Bailey CJ Rodgers C Wilson ID Nicholson JK 《Rapid communications in mass spectrometry : RCM》2005,19(4):519-524
Inductively coupled plasma mass spectrometry (ICPMS) has been used to determine the rate and routes of excretion of bromine following the intraperitoneal administration (50 mg kg(-1)) of 2-, 3- and 4-bromobenzoic acids to male bile-duct-cannulated rats. Analysis of urine and bile for (79/81)Br using ICPMS showed that all three bromobenzoic acids were rapidly excreted (82-98%) within 48 h of dosing, primarily via the urine. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS) was then used to obtain metabolite profiles for bile and urine. These profiles revealed that extensive metabolism had taken place, with the unchanged bromobenzoic acids forming a minor part of the total of compound-related material detected. Concomitant MS studies, supplemented by alkaline hydrolysis, enabled the identification of the major metabolite of all three of the bromobenzoic acids as a glycine conjugate. Ester glucuronide conjugates were also identified, but formed only a small proportion of total. 相似文献
4.
Campa C Oust A Skjåk-Braek G Paulsen BS Paoletti S Christensen BE Ballance S 《Journal of chromatography. A》2004,1026(1-2):271-281
The average degree of polymerisation (DP) and distribution of oligosaccharides in partially acid hydrolysed mannuronans were quantitatively evaluated by 1H NMR, electrospray ionisation mass spectrometry (ESI-MS), micellar electrokinetic capillary chromatography with UV detection (MEKC-UV), and high-pressure anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Our investigation shows that 1H NMR, MEKC-UV and, in particular, HPAEC-PAD can be used as quantitative tools to aid the investigation of polysaccharide structure, function and synthesis. For the latter two techniques, especially, this represents a significant new development as it enables calculation of the quantity of individual oligomers of nominal DP by direct analysis of a defined oligomer mixture. Appropriate statistical averages of number and weight distributions were also calculated and found to fit very well to predicted Kuhn distributions that assume random depolymerisation. 相似文献
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DIFFERENT PHOTOINACTIVATION MECHANISMS IN Propionibacterium acnes FOR NEAR-ULTRAVIOLET and VISIBLE LIGHT 总被引:1,自引:0,他引:1
The light sensitivity of Propionibacterium acnes was investigated when the cells were exposed to anoxia, sodium azide, D2 O or superoxide dismutase in combination with visible light (broad band red light and 415 nm) and near-ultraviolet irradiation (360 and 320 nm). During anoxia the cells became less sensitive when the irradiation wavelength increased. Oxygen increased the photodamage to a greater extent in the case of visible light than of near-UV light. The photosensitization effects were, however, more or less oxygen dependent at all wavelengths used. An effect of azide and D2 O on the light sensitivity was observed for visible light, while superoxide dismutase was effective only at 320 nm.
The results support the hypothesis that inactivation of P. acnes with near-UV and visible light is based on different mechanisms. Porphyrin photosensitization, accomplished by singlet oxygen, is the most important mechanism when visible light is used. At shorter wavelengths (320 and 360 nm) singlet oxygen is not involved and for 320 nm the destruction might occur via superoxide anion formation. 相似文献
The results support the hypothesis that inactivation of P. acnes with near-UV and visible light is based on different mechanisms. Porphyrin photosensitization, accomplished by singlet oxygen, is the most important mechanism when visible light is used. At shorter wavelengths (320 and 360 nm) singlet oxygen is not involved and for 320 nm the destruction might occur via superoxide anion formation. 相似文献
7.
Asymmetric additions of alkyl radicals, generated from R3B, to chiral 2H-azirine-3-carboxylates offer a new entry to enantio-enriched aziridines, and proceed with high diastereoselectivity when using 8-phenylmenthol as chiral auxiliary. 相似文献
8.
This paper presents analyses of teachers?? discussions within mathematics teaching developmental research projects, taking mediation as the central construct. The relations in the so-called ??didactic triangle?? form the basic framework for the analysis of two episodes in which upper secondary school teachers discuss and prepare tasks for classroom use. The analysis leads to the suggestion that the focus on tasks places an emphasis on the task as object and its resolution as goal; mathematics has the role of a mediating artefact. Subject content in the didactic triangle is thus displaced by the task and learning mathematics may be relegated to a subordinate position. 相似文献
9.
The asymmetric transfer hydrogenation of β-amido-α-keto esters providing the corresponding anti-β-amido-α-hydroxy esters via dynamic kinetic resolution is reported. The use of a commercially available, or simply prepared, chiral ruthenium catalyst results in good yields as well as high diastereoselectivities and enantioselectivities. 相似文献
10.
Dr. Bernd M. Schmidt Berit Topolinski Dr. Mihoko Yamada Dr. Shuhei Higashibayashi Prof. Dr. Mitsuhiko Shionoya Prof. Dr. Hidehiro Sakurai Prof. Dr. Dieter Lentz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13872-13880
The syntheses and properties of corannulenes carrying electron‐withdrawing groups (F, CF3, C6F5) are reported. Direct fluorination of corannulene (C20H10) was carried out with xenon difluoride, and the crystal structure of the product was confirmed by the X‐ray analysis. Novel trifluoromethylated corannulenes, including the versatile 4,9‐dibromo‐1,2‐bis(trifluoromethyl)corannulene, were obtained by various established ring‐closing reactions. Besides the use of hexafluorobutyne for the construction of fluoranthenes by Diels–Alder reaction as precursor molecules to form 1,2‐disubstituted corannulenes, bis(pentafluorophenyl)acetylene was employed as dienophile. The molecular structure and crystal packing of a trifluoromethylated corannulene was determined by single‐crystal X‐ray analysis and compared with those known brominated and trifluoromethylated corannulenes. The general electron‐acceptor properties of corannulenes bearing substituents introduced in particular positions by liquid‐phase synthesis are discussed together with published computational results. 相似文献