排序方式: 共有39条查询结果,搜索用时 31 毫秒
21.
Lin LY Tiemann KM Li Y Pinkner JS Walker JN Hultgren SJ Hunstad DA Wooley KL 《Journal of the American Chemical Society》2012,134(9):3938-3941
Amphiphilic block copolymer nanoparticles are conjugated with uropathogenic Escherichia coli type 1 pilus adhesin FimH(A) through amidation chemistry to enable bladder epithelial cell binding and internalization of the nanoparticles in vitro. 相似文献
22.
Sofie Hultgren Niklas Larsson Bo F. Nilsson Jan Åke Jönsson 《Analytical and bioanalytical chemistry》2009,393(3):929-937
A two-phase hollow-fiber (HF) liquid-phase microextraction (LPME) method was developed for determination of a quaternary ammonium
compound surfactant, dicocodimethylammonium chloride, in aqueous samples. The porous HF was fixed on a metal rod support and
was impregnated with approximately 6.6 μL of organic extractant, which was immobilized in the HF pores. Surfactant extraction
was facilitated by addition of carboxylic acid to the sample forming neutral ion pairs with the quaternary ammonium compound.
After extraction, the analyte was transferred from the organic extractant in the fiber pores by dissolving the 1-octanol into
100 μL methanol. The methanol extract was analyzed by liquid chromatography–mass spectrometry. The method was optimized (with
optimized parameters in brackets) with regard to type of organic extractant (1-octanol), fiber length (2 cm), choice and concentration
of anionic carrier (600 μg L−1 octanoate), procedure of transfer to methanol (15-min sonication), sample volume (250 mL), extraction time (17 h), pH (10),
and ionic strength (50 mM carbonate). Aspects influencing repeatability in LPME of (quaternary ammonium) surfactants are discussed.
The enrichment factor achieved in 250-mL carbonate buffer was around 400. Due to matrix effects, the enrichment factors achieved
when industrial process water was analyzed were 120 or about 30% of that in carbonate buffer. Detection limits of 0.3 μg L−1 in carbonate buffer and 0.9 μg L−1 in industrial process water were obtained. If the studied compound is seen as a model substance representing quaternary dialkylated
dimethylated ammonium surfactants in general, the developed method may be applied to other quaternary ammonium surfactants. 相似文献
23.
We study a piecewise linear system approximating the behaviour of a switched DC/DC converter. We give conditions for a unique limit cycle in our different cases and give examples of complicated phenomena that might occur. The stability of a state space trajectory controlled converter is addressed. 相似文献
24.
Electromigration of hydrogen in YH(3-delta) is studied by exploiting the H concentration dependence of the optical transmission of YH(3-delta). We find the effective valence Z* of H in YH(3-delta) to be negative. Its value is dominated by a huge wind-force-like term, i.e., Z* approximately K/rho, with K approximately -60 mOmega cm. This value is 3 orders of magnitude larger than typical for H in metals. In an Arrhenius plot, the ratio of hydrogen and electron fluxes extrapolates to unity at infinite temperature, suggesting a one-to-one correlation of hydrogen and electron hopping. We discuss our results in the light of strong electron correlation theories which predict each proton to bind two electrons in a sort of Zhang-Rice singlet. 相似文献
25.
IA Simpson R Bol ID Bull RP Evershed K Petzke SJ Dockrill 《Rapid communications in mass spectrometry : RCM》1999,13(13):1315-1319
Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
26.
We have performed extensive small-angle neutron scattering (SANS) diffraction studies of the vortex lattice in single crystal
YNi2B2C for B‖c. High-resolution SANS, combined with a field-oscillation vortex lattice preparation technique, allows us to separate Bragg
scattered intensities from two orthogonal domains and accurately determine the unit cell angle, β. The data suggest that upon increasing field there is a finite transition width where both low- and high-field distorted
hexagonal vortex lattice phases, mutually rotated by 45°, coexist. The smooth variation of diffracted intensity from each
phase through the transition corresponds to a redistribution of populations between the two types of domains. 相似文献
27.
New first- and high-order centred methods for conservation lawsare presented. Convenient TVD conditions for constructing centredTVD schemes are then formulated and some useful results areproved. Two families of centred TVD schemes are constructedand extended to nonlinear systems. Some numerical results arealso presented. 相似文献
28.
Horvath I Weise CF Andersson EK Chorell E Sellstedt M Bengtsson C Olofsson A Hultgren SJ Chapman M Wolf-Watz M Almqvist F Wittung-Stafshede P 《Journal of the American Chemical Society》2012,134(7):3439-3444
Small organic molecules that inhibit functional bacterial amyloid fibers, curli, are promising new antibiotics. Here we investigated the mechanism by which the ring-fused 2-pyridone FN075 inhibits fibrillation of the curli protein CsgA. Using a variety of biophysical techniques, we found that FN075 promotes CsgA to form off-pathway, non-amyloidogenic oligomeric species. In light of the generic properties of amyloids, we tested whether FN075 would also affect the fibrillation reaction of human α-synuclein, an amyloid-forming protein involved in Parkinson's disease. Surprisingly, FN075 stimulates α-synuclein amyloid fiber formation as measured by thioflavin T emission, electron microscopy (EM), and atomic force microscopy (AFM). NMR data on (15)N-labeled α-synuclein show that upon FN075 addition, α-synuclein oligomers with 7 nm radius form in which the C-terminal 40 residues remain disordered and solvent exposed. The polypeptides in these oligomers contain β-like secondary structure, and the oligomers are detectable by AFM, EM, and size-exclusion chromatography (SEC). Taken together, FN075 triggers oligomer formation of both proteins: in the case of CsgA, the oligomers do not proceed to fibers, whereas for α-synuclein, the oligomers are poised to rapidly form fibers. We conclude that there is a fine balance between small-molecule inhibition and templation that depends on protein chemistry. 相似文献
29.
Aberg V Hedenström M Pinkner JS Hultgren SJ Almqvist F 《Organic & biomolecular chemistry》2005,3(21):3886-3892
Virulence-associated organelles, termed pili or fimbriae, are assembled via the highly conserved chaperone-usher pathway in a vast number of pathogenic bacteria. Substituted bicyclic 2-pyridones, pilicides, inhibit pilus formation, possibly by interfering with the active site residues Arg8 and Lys112 of chaperones in uropathogenic E. coli. In this article we describe the synthesis and evaluation of nine analogues of a biologically active pilicide. Derivatization was performed with respect to its C-terminal features and the affinities for the chaperone PapD were studied with 1H relaxation-edited NMR spectroscopy. It could be concluded that the carboxylic acid functionality and also its spatial location was important for binding. In all cases, binding was significantly reduced or even abolished when the carboxylic acid was replaced by other substituents. In addition, in vivo results from a hemagglutination assay are presented where the derivatives have been evaluated for their ability to inhibit pilus formation in uropathogenic E. coli. 相似文献
30.