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排序方式: 共有329条查询结果,搜索用时 31 毫秒
251.
Molinaro A Lindner B De Castro C Nolting B Silipo A Lanzetta R Parrilli M Holst O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(7):1542-1548
From the lipopolysaccharides (LPSs) of the plant-pathogenic bacterium Burkholderia caryophylli, the complete structure of lipid A has been characterized. For the first time, a 4-amino-4-deoxy-L-arabinopyranose 1-phosphate residue was proven to be exclusively linked to the reducing end of lipid A from a wild-type LPS. The LPSs of B. caryophylli were degraded by mild acetate buffer hydrolysis at pH 4.4. The obtained lipid A was analyzed as such, and also after de-O-acylation or dephosphorylation. The structure of lipid A was identified mainly by means of matrix-assisted laser desorption/ionisation mass spectrometry, and by various 1D and 2D (1)H and (13)C NMR spectroscopic measurements. 相似文献
252.
Various strategies have been investigated for separating a group of nonsteroidal anti-inflammatory drugs (NSAIDs) by microemulsion electrokinetic capillary chromatography (MEEKC) using high-speed separations. The parameters that of affect the separation, such as the nature of the oil droplet and the buffer, and the surfactant concentration have been studied. In addition, several organic solvents were used to decrease the retention of the analytes in the oil droplet phase and to improve the resolution of the NSAIDs. The optimum microemulsion background electrolyte (BGE) solution made of 0.8% w/w ethyl acetate, 6.6% w/w butan-1-ol, 6.0% w/w acetonitrile, 1.0% w/w sodium dodecyl sulfate (SDS), and 85.6% w/w of 10 mM sodium tetraborate at pH 9.2 resolved the drugs within 8 min. The short-end injection procedure is an alternative for reducing the analysis time. When this procedure was used, the microemulsion BGE solution consisted of 0.8% w/w ethyl acetate, 6.6% w/w butan-1-ol, 17.0% w/w methanol, 1.0% w/w SDS, and 74.6% w/w of 10 mM sodium tetraborate, pH 9.2, and the NSAIDs were separated within 3 min. The reversed electrode polarity stacking mode (REPSM) technique was applied to the on-line concentration of the NSAIDs. In this technique, the sample matrix was pumped out of the capillary using a polarity-switching step. When this technique was applied, the sensitivity was enhanced up to 40-fold and the limits of detection (LODs) were in the low microg.L(-1) levels. 相似文献
253.
Alba E. Díaz-Álvarez Pascale Crochet Maria Zablocka Victorio Cadierno Laure Vendier José Gimeno Jean-Pierre Majoral 《Polyhedron》2007
The diastereoselective κ2-P,N-coordination of a chiral tricyclic β-iminophosphine ligand to the half-sandwich ruthenium(II) fragments [RuCl(η6-arene)]+ (arene = C6H6, p-cymene, 1,3,5-C6H3Me3, C6Me6), [Ru(η6-p-cymene)(NCMe)]2+ and [Ru(η5-C5H5)(NCMe)]+ is described. The structures of the resulting mono- and dicationic cymene derivatives have been confirmed by X-ray crystallography. Studies on the catalytic activity of these Ru(II) compounds in Diels–Alder cycloaddition processes are also reported. 相似文献
254.
Peptidoglycan and muropeptides from pathogens Agrobacterium and Xanthomonas elicit plant innate immunity: structure and activity 总被引:4,自引:0,他引:4
255.
Moss TA Alba A Hepworth D Dixon DJ 《Chemical communications (Cambridge, England)》2008,(21):2474-2476
N-Mesitylene sulfonyl and N-tosyl aziridines have been identified as effective electrophiles in alkylation reactions of carbon acids catalyzed by the organic phosphorine base BEMP; yields of up to 99% for a range of pro-nucleophiles under mild reaction conditions are reported. 相似文献
256.
We have successfully developed the first prototype of an electrochemical protein biosensor using polypyrrole as the substrate
and doped aptamer as the probe. The sensitivity for a specific target is 10 ng/ml. Two targets, platelet-derived growth factor
and immunoglobulin E, have been tested. In both cases the sensor exhibited high specificity and the signal was found to increase
as the target concentration increased. 相似文献
257.
The aim of this model is to analyse quality management systems from the standpoint of the organization of complex systems introduced by Robert Rosen. The concept that an organized system, under certain conditions, can be modelled as a living system introduces unsuspected tools to analyse its behaviour. The model is oriented towards the understanding of the implications of modifications introduced in laboratories working with a quality organization following the ISO/IEC 17025 standard.This standard establishes management and technical requirements concerning the documental organization, control of the management and technical records, personnel, equipments, test or calibration methods, etc. The objective of the quality system implementation is to assure the quality of the product, the special consideration being the customer’s satisfaction with all aspects of the service the laboratory offers.The improper use of the quality system tools has an impact on the laboratory activity. The perception of this fact can be negligible at the moment it happens. The model allows us to realize that this alteration always has a negative impact on the customer and it specially affects the continuous improvement that the laboratory must implement. 相似文献
258.
Guardiola F Tres A Codony R Addis PB Bergmann SD Zavoral JH 《Analytical and bioanalytical chemistry》2007,389(1):277-289
A gas chromatographic method was successfully applied to determine cholesterol oxidation products (COPs) in human plasma.
The linearity, precision, recovery and sensitivity of the method were determined. Oral supplementation with a combination
of vitamin E (800 IU), C (1 g) and β-carotene (24 mg), given for 21 days to 21 patients, did not significantly decrease plasma
COP content. No correlations (n = 26) were found between initial plasma COP content and the following parameters: age, body mass index, plasma content of
α-tocopherol, cholesterol, high-density lipoprotein cholesterol and triglycerides, and fat, natural antioxidant and oxidized
lipid intake. Differences in plasma COP content between type 2 diabetic (n = 6) and nondiabetic (n = 20) patients were not statistically significant. The results from this study lead us to hypothesize that the nonenzymatic
oxidation of cholesterol in plasma is negligible compared to COPs originating from the diet. This article also includes a
comprehensive review of the drawbacks of the analytical methods of COP determination in plasma and serum. 相似文献
259.
Silipo A Molinaro A Ieranò T De Soyza A Sturiale L Garozzo D Aldridge C Corris PA Khan CM Lanzetta R Parrilli M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(12):3501-3511
Members of genus Burkholderia include opportunistic Gram-negative bacteria that are responsible for serious infections in immunocompromised and cystic fibrosis (CF) patients. The Burkholderia cepacia complex is a group of microorganisms composed of at least nine closely related genomovars. Among these, B. cenocepacia is widely recognized to cause epidemics associated with excessive mortality. Species that belong to this strain are problematic CF pathogens because of their high resistance to antibiotics, which makes respiratory infections difficult to treat and impossible to eradicate. Infection by these bacteria is associated with higher mortality in CF and poor outcomes following lung transplantation. One virulence factor contributing to this is the pro-inflammatory lipopolysaccharide (LPS) molecules. Thus, the knowledge of the lipopolysaccharide structure is an essential prerequisite to the understanding of the molecular mechanisms involved in the inflammatory process. Such data are instrumental in aiding the design of antimicrobial compounds and for developing therapeutic strategies against the inflammatory cascade. In particular, defining the structure of the LPS from B. cenocepacia ET-12 clone LMG 16656 (also known as J2315) is extremely important given the recent completion of the sequencing project at the Sanger Centre using this specific strain. In this paper we address this issue by defining the pro-inflammatory activity of the pure lipopolysaccharide, and by describing its full primary structure. The activity of the lipopolysaccharide was tested as a stimulant in human myelomonocytic U937 cells. The structural analysis was carried out by compositional analysis, mass spectrometry and 2D NMR spectroscopy on the intact lipooligosacchride (LOS) and its fragments, which were obtained by selective chemical degradations. 相似文献
260.
Xin Luo Daniel Saliba Tianxiao Yang Serena Gentile Keita Mori Patricia Islas Trishalina Das Neda Bagheri Alessandro Porchetta Alba Guarne Gonzalo Cosa Hanadi F. Sleiman 《Angewandte Chemie (International ed. in English)》2023,62(44):e202309869
DNA nanotubes (NTs) have attracted extensive interest as artificial cytoskeletons for biomedical, synthetic biology, and materials applications. Here, we report the modular design and assembly of a minimalist yet robust DNA wireframe nanotube with tunable cross-sectional geometry, cavity size, chirality, and length, while using only four DNA strands. We introduce an h-motif structure incorporating double-crossover (DX) tile-like DNA edges to achieve structural rigidity and provide efficient self-assembly of h-motif-based DNA nanotube ( H-NT ) units, thus producing programmable, micrometer-long nanotubes. We demonstrate control of the H-NT nanotube length via short DNA modulators. Finally, we use an enzyme, RNase H, to take these structures out of equilibrium and trigger nanotube assembly at a physiologically relevant temperature, underlining future cellular applications. The minimalist H-NTs can assemble at near-physiological salt conditions and will serve as an easily synthesized, DNA-economical modular template for biosensors, plasmonics, or other functional materials and as cost-efficient drug-delivery vehicles for biomedical applications. 相似文献