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排序方式: 共有492条查询结果,搜索用时 343 毫秒
61.
E Glaser E Cadenas S Andell L Ernster 《Acta chemica Scandinavica. Series B: Organic chemistry and biochemistry》1988,42(3):175-182
Rose Bengal mediated photooxidation of mitochondrial F1-ATPase and its beta-subunit resulted in inactivation and loss of about 50 and 60% of their histidine residues, respectively. The beta-subunit was not cleaved upon photooxidation. Photooxidation of histidine probably results in changes in the conformational stability of F1-ATPase leading to its inactivation. The participation of singlet molecular oxygen during the photooxidation process is suggested by the selective loss of histidine residues, while other amino acids, also sensitive to singlet oxygen attack, were not affected. Photochemical damage of F1-ATPase was prevented by various phenanthroline compounds, the order of efficiency being bathophenanthroline-Fe chelate greater than bathophenanthroline greater than orthophenanthroline-Fe chelate greater than bathophenanthroline-sulfonate-Fe chelate. The prevention by bathophenanthroline-Fe chelate of photochemical damage is interpreted on the basis of its interaction with the photosensitizer, Rose Bengal, probably implying a chemical reaction which decreases the actual concentration of the sensitizer and, thereby, the extent of photoinactivation. 相似文献
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63.
Zusammenfassung Eine Methode zur dünnschichtchromatographischen Trennung von acht Nitroalkanen wurde ausgearbeitet. Die Nitroverbindungen wurden mit Lauge in Nitronate, diese durch saure Hydrolyse in die entsprechenden Oxoverbindungen übergeführt, in Form ihrer 2,4-Dinitrophenylhydrazone gefällt, gelöst und chromatographiert. Die optimalen Reaktionsverhältnisse und die Möglichkeiten zur Zurückdrängung der Nebenreaktionen wurden besprochen.
Thin layer chromatographic separation of nitroalkanes
Summary A method has been developed for the thin layer Chromatographic separation of eight nitroalkanes. The nitro compounds were converted into nitronates by means of alkali, and these products then converted by acid hydrolysis to the corresponding oxo compounds which were precipitated as their 2,4-di-nitrophenyl hydrazones. The latter were dissolved and chromatographed. The optima] reaction proportions and the possibilities of suppressing side reactions are discussed.相似文献
64.
Douglas McHugh Sherry SJ Hu Neta Rimmerman Ana Juknat Zvi Vogel J Michael Walker Heather B Bradshaw 《BMC neuroscience》2010,11(1):44
Background
Microglia provide continuous immune surveillance of the CNS and upon activation rapidly change phenotype to express receptors that respond to chemoattractants during CNS damage or infection. These activated microglia undergo directed migration towards affected tissue. Importantly, the molecular species of chemoattractant encountered determines if microglia respond with pro- or anti-inflammatory behaviour, yet the signaling molecules that trigger migration remain poorly understood. The endogenous cannabinoid system regulates microglial migration via CB2 receptors and an as yet unidentified GPCR termed the 'abnormal cannabidiol' (Abn-CBD) receptor. Abn-CBD is a synthetic isomer of the phytocannabinoid cannabidiol (CBD) and is inactive at CB1 or CB2 receptors, but functions as a selective agonist at this Gi/o-coupled GPCR. N-arachidonoyl glycine (NAGly) is an endogenous metabolite of the endocannabinoid anandamide and acts as an efficacious agonist at GPR18. Here, we investigate the relationship between NAGly, Abn-CBD, the unidentified 'Abn-CBD' receptor, GPR18, and BV-2 microglial migration. 相似文献65.
Glaser T Liratzis I Kataeva O Fröhlich R Piacenza M Grimme S 《Chemical communications (Cambridge, England)》2006,(9):1024-1026
Two hydrogen-bonds from geometrically constrained OH groups to coordinated oxygen donors shift the reduction potential of a Cu(II) complex by +270 mV as compared to the structurally analogous reference complex missing the OH groups. 相似文献
66.
The results are reported of a theoretical study of the addition of small nucleophiles Nu(-) (HO(-), F(-)) to phenylboronic acid Ph-B(OH)(2) and of the stability of the resulting complexes [Ph-B(OH)(2)Nu](-) with regard to Ph-B heterolysis [Ph-B(OH)(2)Nu](-) --> Ph(-) + B(OH)(2)Nu as well as Nu(-)/Ph(-) substitution [Ph-B(OH)(2)Nu](-) + Nu(-) --> Ph(-) + [B(OH)(2)Nu(2)](-). These reactions are of fundamental importance for the Suzuki-Miyaura cross-coupling reaction and many other processes in chemistry and biology that involve phenylboronic acids. The species were characterized by potential energy surface analysis (B3LYP/6-31+G*), examined by electronic structure analysis (B3LYP/6-311++G**), and reaction energies (CCSD/6-311++G**) and solvation energies (PCM and IPCM, B3LYP/6-311++G*) were determined. It is shown that Ph-B bonding in [Ph-B(OH)(2)Nu](-) is coordinate covalent and rather weak (<50 kcal.mol(-1)). The coordinate covalent bonding is large enough to inhibit unimolecular dissociation and bimolecular nucleophile-assisted phenyl anion liberation is slowed greatly by the negative charge on the borate's periphery. The latter is the major reason for the extraordinary differences in the kinetic stabilities of diazonium ions and borates in nucleophilic substitution reactions despite their rather similar coordinate covalent bond strengths. 相似文献
67.
68.
Beamforming array techniques for acoustic emission monitoring of large concrete structures 总被引:1,自引:0,他引:1
Gregory C. McLaskey Steven D. Glaser Christian U. Grosse 《Journal of sound and vibration》2010,329(12):2384-2394
This paper introduces a novel method of acoustic emission (AE) analysis which is particularly suited for field applications on large plate-like reinforced concrete structures, such as walls and bridge decks. Similar to phased-array signal processing techniques developed for other non-destructive evaluation methods, this technique adapts beamforming tools developed for passive sonar and seismological applications for use in AE source localization and signal discrimination analyses. Instead of relying on the relatively weak P-wave, this method uses the energy-rich Rayleigh wave and requires only a small array of 4–8 sensors. Tests on an in-service reinforced concrete structure demonstrate that the azimuth of an artificial AE source can be determined via this method for sources located up to 3.8 m from the sensor array, even when the P-wave is undetectable. The beamforming array geometry also allows additional signal processing tools to be implemented, such as the VESPA process (VElocity SPectral Analysis), whereby the arrivals of different wave phases are identified by their apparent velocity of propagation. Beamforming AE can reduce sampling rate and time synchronization requirements between spatially distant sensors which in turn facilitates the use of wireless sensor networks for this application. 相似文献
69.
Michael Zech Marianne Benesch Johannes Hepp Steven Polifka Bruno Glaser 《Isotopes in environmental and health studies》2013,49(4):394-403
ABSTRACTInspired by a previous ‘Sauna, sweat and science’ study [Zech et al. Isot Environ Health Stud. 2015;51(3):439–447] and out of curiosity and enthusiasm for stable isotope and sauna research we aimed at answering the question ‘do we sweat (isotopically) what we drink’? We, therefore, pulse-labelled five test persons in a sauna experiment with beverages that were 2H-enriched at about +25,600?‰. Sweat samples were collected during six sauna rounds and the hydrogen isotope composition δ2Hsweat was determined using an isotope ratio mass spectrometer. Before pulse labelling, δ2Hsweat – reflecting by approximation body water – ranged from –32 to –22?‰. This is ~35?‰ enriched compared to usual mid-European drinking water and can be explained with hydrogen-bearing food as well as with the respiratory loss of 2H-depleted vapour. The absence of a clearly detectable 2H pulse in sweat after pulse labelling and δ2Hsweat results of ≤+250?‰ due to a fast 2H equilibration with body water are moreover a clearly negative answer to our research question also in a short-term consideration. Given that the recovery of the tracer based on an isotope mass balance calculation is clearly below 100?%, we finally answer the question ‘where did the rest of the tracer go?’ 相似文献
70.
Qing Wang Mingxing Fu Xiaojun Li Runfeng Huang Rainer E. Glaser Lili Zhao 《Journal of computational chemistry》2019,40(16):1599-1608
Density functional theory calculations were performed to understand the detailed reaction mechanism of aluminum alkoxy-catalyzed conversion of glucose to 5-hydroxymethylfurfural (HMF) using Al(OMe)3 as catalyst. Potential energy surfaces were studied for aggregates formed between the organic compounds and Al(OMe)3 and effects of the medium were considered via continuum solvent models. The reaction takes place via two stages: isomerization from glucose to fructose (stage I) and transformation of fructose to HMF (stage II). Stage II includes three successive dehydrations, which begins with a 1,2-elimination to form an enolate (i.e., B), continues with the formation of the acrolein moiety (i.e., D), and ends with the formation of the furan ring (i.e., HMF). All of these steps are facilitated by aluminum alkoxy catalysis. The highest barriers for stage I and stage II are 23.9 and 31.2 kcal/mol, respectively, and the overall catalytic reaction is highly exothermic. The energetic and geometric results indicate that the catalyzed reaction path has feasible kinetics and thermodynamics and is consistent with the experimental process under high temperature (i.e., 120 °C). Remarkably, the released water molecules in stage II act as the product, reactant, proton shuttle, as well as stabilizer in the conversion of fructose to HMF. The metal–ligand functionality of the Al(OMe)3 catalyst, which combines cooperative Lewis acid and Lewis base properties and thereby enables proton shuttling, plays a crucial role in the overall catalysis and is responsible for the high reactivity. © 2019 Wiley Periodicals, Inc. 相似文献