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排序方式: 共有835条查询结果,搜索用时 15 毫秒
811.
Luis M. Molina Sungsik Lee Kristian Sell Giovanni Barcaro Alessandro Fortunelli Byeongdu Lee Soenke Seifert Randall E. Winans Jeffrey W. Elam Michael J. Pellin Ingo Barke Viola von Oeynhausen Yu Lei Randall J. Meyer Julio A. Alonso Arantxa Fraile Rodríguez Armin Kleibert Suzanne Giorgio Claude R. Henry Karl-Heinz Meiwes-Broer Stefan Vajda 《Catalysis Today》2011,160(1):965
812.
Aaron Gryzia Hans Predatsch Armin Brechling Veronika Hoeke Erich Krickemeyer Christine Derks Manfred Neumann Thorsten Glaser Ulrich Heinzmann 《Nanoscale research letters》2011,6(1):486
We report on the characterization of various salts of [MnIII6CrIII]3+ complexes prepared on substrates such as highly oriented pyrolytic graphite (HOPG), mica, SiO2, and Si3N4. [MnIII6CrIII]3+ is a single-molecule magnet, i.e., a superparamagnetic molecule, with a blocking temperature around 2 K. The three positive charges of [MnIII6CrIII]3+ were electrically neutralized by use of various anions such as tetraphenylborate (BPh4-), lactate (C3H5O3-), or perchlorate (ClO4-). The molecule was prepared on the substrates out of solution using the droplet technique. The main subject of investigation was how the anions and substrates influence the emerging surface topology during and after the preparation. Regarding HOPG and SiO2, flat island-like and hemispheric-shaped structures were created. We observed a strong correlation between the electronic properties of the substrate and the analyzed structures, especially in the case of mica where we observed a gradient in the analyzed structures across the surface. 相似文献
813.
Ursula Palm Christiane Askari Uwe Hener Eckhard Jakob Claudia Mandler Martin Geßner Armin Mosandl Wilfried A. König Petra Evers und Ralph Krebber 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1991,192(3):209-213
Zusammenfassung 5-Alkyl-substituierte-Lactone finden sich als aromarelevante Substanzen in tierischen Fetten, aber auch in einigen Früchten. Vor kurzem gelang die erste direkte gaschromatographische Stereodifferenzierung einiger-Lactone an der chiralen Phase Oktakis(3-O-butyryl-2,6-di-O-pentyl)--cyclodextrin [4]. Es wird nun die Enantiomerentrennung der-Lactone bis zu den langkettigen Verbindungen-Trideca-(-C13-)- und-Tetradeca-(-C14-)-lacton aufgezeigt. Über optisch reine Referenzsubstanzen konnte die Elutionsfolge S(I), R(II) der drei wichtigsten aromarelevanten Vertreter dieser-Lactonklasse bestimmt werden. Die Enantiomerenverteilung der C8-, C10-, C12--Lactone im Wasserdampfdestillat verschiedener Milchprodukte (Milch, Sahne, Butter), in Margarine sowie im Kokosnußfleisch wurde exemplarisch mit Hilfe der HRGC, auch unter Einsatz der multidimensionalen Gaschromatographie (MDGC), untersucht. Es zeigten sich charakteristische, substratspezifische Enantiomerenverteilungen. Die Verteilungsmuster der untersuchten Spiegelbildisomeren aus Kokosnüssen unterschieden sich wesentlich von denen der Milchprodukte.
Stereoisomeric flavour compoundsXLVII. Direct chirospecific HRGC-analysis of natural -lactones
Summary 5-Alkylated-lactones are well known flavour compounds in animal fats and also some special kinds of fruit. Recently, the first direct stereo-differentiation of chiral-lactones was reported using Oktakis(3-O-butyryl-2,6-di-O-pentyl)--cyclodextrin as the chiral stationary phase [4]. The enantiomeric separation of-lactones up to the long-chain compounds-trideca-(-C13–) and-tetradeca-(-C14–)-lactone is demonstrated. By means of optically pure references, the order of elution S(I), R(II) was determined for the important flavour compounds-octa-,-deca-, and-dodecalactone. Analysis of the steam distillate of some dairy products (milk, cream, butter), of margarine and of coconut has been carried out, in order to yield the enantiomeric distribution of C8-, C10- and C12--lactones by HRGC and multidimensional gas chromatography. Characteristic and product-specific ratios of-lactone enantiomers are detected. The pattern of enantiomeric composition of-octa-,-deca-,-dodecalactone in coconuts differs completely from that found in the dairy products.相似文献
814.
Dietz M Mohr P Kuhn B Maerki HP Hartman P Ruf A Benz J Grether U Wright MB 《ChemMedChem》2012,7(6):1101-1111
Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors that control the expression of genes involved in a variety of physiologic processes, through heterodimerization with retinoid X receptor and complex formation with various cofactors. Drugs or treatment regimens that combine the beneficial effects of PPARα and γ agonism present an attractive therapeutic strategy to reduce cardiovascular risk factors. Aleglitazar is a dual PPARα/γ agonist currently in phase III clinical development for the treatment of patients with type 2 diabetes mellitus who recently experienced an acute coronary event. The potency and efficacy of aleglitazar was evaluated in a head-to-head comparison with other PPARα, γ and δ ligands. A comprehensive, 12-concentration dose-response analysis using a cell-based assay showed aleglitazar to be highly potent, with EC(50) values of 5 nM and 9 nM for PPARα and PPARγ, respectively. Cofactor recruitment profiles confirmed that aleglitazar is a potent and balanced activator of PPARα and γ. The efficacy and potency of aleglitazar are discussed in relation to other dual PPARα/γ agonists, in context with the published X-ray crystal structures of both PPARα and γ. 相似文献
815.
Background
The potential of diesel soot aerosol particles to break up into smaller units under mechanical stress was investigated by a direct impaction technique which measures the degree of fragmentation of individual agglomerates vs. impact energy. Diesel aerosol was generated by an idling diesel engine used for passenger vehicles. Both the aerosol emitted directly and aerosol that had undergone additional growth by Brownian coagulation ("aging") was investigated. Optionally a thermo-desoption technique at 280°C was used to remove all high-volatility and the majority of low-volatility HC adsorbates from the aerosol before aging. 相似文献816.
Frank Eulenstein Armin Werner Matthias Willms Radosław Juszczak Sandro Luis Schlindwein Bogdan H. Chojnicki Janusz Olejnik 《Nutrient Cycling in Agroecosystems》2008,82(1):33-49
Oxidation of pyrite by nitrate (autotrophic denitrification) was identified as the main cause for sulfate increase in drinking
water wells in an agriculturally used watershed, located in the north of Lower Saxony (Germany). Nitrate, which inducts this
microbial catalyzed process, is drained into ground water predominantly from agricultural fertilization. The increase of sulfate
in the ground water can only be stopped by reducing nitrate leaching into the ground water. To analyze the negative influence
of agricultural fertilization on the quality of ground water different fertilization strategies were deducted for an investigated
area of 890 ha. Calculated on the basis of nutrient balance of soil surface, the current average nitrogen balance in the investigated
area amounts to 91 kg N ha-1 a−1. Farm-gate balance of nutrients is a strong indicator for assessing potential nutrient losses caused by leaching. This indicator
shows comparable accuracy to the calculated nutrient balance of soil surface which demands, however, much more data input
for calculations. Nitrate concentrations in seepage water in 2 m depth layer of the soil from agricultural fields were simulated
with the model HERMES for the whole investigated area (agricultural land + forest). The nitrate concentration in seepage water
was calculated for the whole area on the basis of farm-gate nutrient balance as an annual average, which amounts to 14.0 mg NO3–N l−1 (62 mg NO3 l−1). In order to keep the nitrate concentration of the ground water below the threshold value for drinking water (EU-water directive:
11.3 mg NO3–N l−1 (50 mg NO3 l−1) and to limit pyrite oxidation, different scenarios with simulation studies to optimize fertilization measures were developed.
Only those scenarios which assured reduction of an average nitrate concentration in the drainage water below 11.3 mg NO3–N l−1 (50 mg NO3 l−1) without profit cuts for the farms were analyzed.
相似文献
Janusz OlejnikEmail: |
817.
Based on results of a former study in 2005, this investigation aimed at quantifying UV- and cold temperature stress-induced
changes within the secondary metabolite production of the cultured mycobiont of the lichen Heterodea muelleri (Hampe) Nyl. The chemical profiles of the mycobiont cultures and the lichen thallus were determined by high-performance liquid
chromatography (HPLC) and thin layer chromatography (TLC) analyses. The voucher specimen of H. muelleri produced diffractaic acid as a major polyketide and barbatic acid as a satellite compound, whereas the untreated mycobiont
did not contain any detectable secondary metabolites. While UV-C stress caused a general increase in substance formation,
cold temperature stress resulted in a strong activation of barbatic acid biosynthesis. A further series of experiments focused
on the effect of diffractaic and barbatic acids on the growth of the symbiotic photobiont Trebouxia jamesii; usnic acid was similarly tested. Pure substances were obtained from mycobiont cultures by performing preparative TLC. A
determined quantity of algae was incubated on BBM plates that contained three different concentrations of the pure lichen
metabolites. The growth of the photobionts was monitored over a period of 1 mo to evaluate the impact of each substance on
the cultured algae. While diffractaic and usnic acid had no noticeable effect, barbatic acid strongly inhibited algal growth
and resulted in cell death. 相似文献
818.
Wisthaler A Strøm-Tejsen P Fang L Arnaud TJ Hansel A Märk TD Wyon DP 《Environmental science & technology》2007,41(1):229-234
Four different air purification conditions were established in a simulated 3-row 21-seat section of an aircraft cabin: no air purifier; a photocatalytic oxidation unit with an adsorptive prefilter; a second photocatalytic unit with an adsorptive prefilter; and a two-stage sorption-based air filter (gas-phase absorption and adsorption). The air purifiers placed in the cabin air recirculation system were commercial prototypes developed for use in aircraft cabin systems. The four conditions were established in balanced order on 4 successive days of each of 4 successive weeks during simulated 7-h flights with 17 occupants. Proton-transfer reaction mass spectrometry was used to assess organic gas-phase pollutants and the performance of each air purifier. The concentration of most organic pollutants present in aircraft cabin air was efficiently reduced by all three units. The photocatalytic units were found to incompletely oxidize ethanol released by the wet wipes commonly supplied with airline mealsto produce unacceptably high levels of acetaldehyde and formaldehyde. 相似文献
819.
Genetic transformation of auxotrophic mutants of the filamentous yeast Trichosporon cutaneum using homologous and heterologous marker genes 总被引:1,自引:0,他引:1
Urs A. Ochsner Virpi Glumoff Markus Klin Armin Fiechter Jakob Reiser 《Yeast (Chichester, England)》1991,7(5):513-524
A transformation system for the filamentous yeast Trichosporon cutaneum based on auxotrophic markers is presented and techniques for the induction, isolation and characterization of mutants are described. A number of auxotrophic mutants were isolated and characterized by using biosynthetic precursors and/or inhibitors. A mutant unable to grow in the presence of ornithine could be complemented successfully by spheroplast transformation experiments using the cloned Aspergillus nidulans ornithine transcarbamoylase gene (argB gene) as selection marker with an efficiency of 5-100 transformants per microgram of DNA. In these transformants the heterologous argB gene was present in multiple tandem copies and the transforming DNA was found to remain stable after more than 50 generations in non-selective media. The same mutant could be complemented by a T. cutaneum cosmid gene library and a complementary cosmid was subsequently isolated from this library by a sib-selection strategy. This cosmid transformed T. cutaneum spheroblasts with an efficiency of 50-200 colonies per microgram of DNA. Southern blot analyses were consistent with the view that the transforming sequences became stably integrated into the host genome at the homologous site. 相似文献
820.
In this review article, techniques for sodium (23Na) magnetic resonance imaging (MRI) are presented. These techniques can also be used to image other nuclei with short relaxation times (e.g., 39K, 35Cl, 17O). Twisted projection imaging, density-adapted 3D projection reconstruction, and 3D cones are preferred because of uniform k-space sampling and ultra-short echo times. Sampling density weighted apodization can be applied if intrinsic filtering is desired. This approach leads to an increased signal-to-noise ratio compared to postfiltered acquisition in cases of short readout durations relative to T 2 * relaxation time. Different MR approaches for anisotropic resolution are presented, which are important for imaging of thin structures such as myocardium, cartilage, and skin. The third part of this review article describes different methods to put more weighting either on the intracellular or the extracellular sodium signal by means of contrast agents, relaxation-weighted imaging, or multiple-quantum filtering. 相似文献