In the present work we investigate the hydrogen sorption mechanism in a MgH(2)/Nb(2)O(5) composite and analyze why Nb(2)O(5) could strongly improve hydrogen sorption kinetics in magnesium. Hereby we make use of the fact that Nb(2)O(5) nanoparticles are able to reduce the milling time significantly with the achievement of excellent sorption kinetics, and can so exclude effects occurring at long-term milling that make difficult the study of the mechanism. On the basis of extensive chemical, crystalline, and microstructural characterization of the MgH(2)/Nb(2)O(5) nanopowder system, a "pathway model" is proposed, which explains the kinetic hydrogen sorption improvement by a formation of pathways of niobium oxide species with lower oxidation state that facilitate the hydrogen transport into the sample. This mechanism is shown to be supported by additional oxidation experiments, which indicate increased oxygen diffusion through these pathways. 相似文献
Using x-ray diffraction, a structural state consisting of two “isomorphous” phases was revealed in nanocrystalline powders of simple oxides Re2O3 (Re = Eu, Gd, La, Lu) and Y3Ga5O12 prepared by solvent thermolysis from simple-oxide solutions followed by annealing of obtained precursors at elevated temperatures. A model is proposed explaining such two-phase states in terms of the excess energy of nanograin surface layers which causes the formation of a surface phase isomorphous to the core phase having a smaller lattice parameter. Analogous two-phase states were also obtained in microcrystalline LuBO3 and Eu2(MoO4)3 powders subjected to long-term grinding. 相似文献
A flow injection hydride generation system with a metal furnace atomizer (Inconel 600® alloy) was employed for Bi and Se determination. The presented methods have linear ranges up to 200 and 500 μg L− 1 for Bi and Se, respectively, with good linearities (r2 = 0.9997 and 0.9974, respectively). The limits of quantification obtained according to IUPAC recommendations were 2.3 μg L− 1 for Bi and 6 μg L− 1 for Se, and the relative standard deviations (N = 6) based on Bi and Se analytical responses from real samples were 2.7% and 10%, respectively. Accuracy evaluations were based on certified materials such as SRM 361, SRM 363, and SRM 364 (steel alloys) for Bi, Mess-3 (marine sediment), SRM 397 (human hair), and Bio-Rad2 — 69042 (urine) for Se. Good agreements between the results were obtained at the 95% confidence level, according to the t-test. 相似文献
The application of the reporter molecule (Mrep) method for identifying nonspecific complexes in the ES-MS analysis of protein-ligand and DNA-ligand interactions in vitro
is described. To test the reliability of the method, it was applied to the ES-MS analysis of protein-carbohydrate complexes
originating from specific interactions in solution and from nonspecific interactions in the ES process. These control experiments
confirm the basic assumptions underlying the Mrep method, namely that nonspecific ligand binding is a random process, and that the ES droplet histories for specific and nonspecific
complexes are distinct. The application of the Mrep method to the ES-MS analysis of the sequential binding of the ethidium cation, a DNA intercalator, to single and double strand
oligodeoxynucleotides is also described, and highlights the general utility of the method. 相似文献
This study reports on the use of the catch-and-release electrospray ionization mass spectrometry (CaR-ESI-MS) assay, combined with glycomicelles, as a method for detecting specific interactions between water-soluble proteins and glycolipids (GLs) in aqueous solution. The B subunit homopentamers of cholera toxin (CTB5) and Shiga toxin type 1 B (Stx1B5) and the gangliosides GM1, GM2, GM3, GD1a, GD1b, GT1b, and GD2 served as model systems for this study. The CTB5 exhibits broad specificity for gangliosides and binds to GM1, GM2, GM3, GD1a, GD1b, and GT1b; Stx1B5 does not recognize gangliosides. The CaR-ESI-MS assay was used to analyze solutions of CTB5 or Stx1B5 and individual gangliosides (GM1, GM2, GM3, GD1a, GD1b, GT1b, and GD2) or mixtures thereof. The high affinity interaction of CTB5 with GM1 was successfully detected. However, the apparent affinity, as determined from the mass spectra, is significantly lower than that of the corresponding pentasaccharide or when GM1 is presented in model membranes such as nanodiscs. Interactions between CTB5 and the low affinity gangliosides GD1a, GD1b, and GT1b, as well as GD2, which served as a negative control, were detected; no binding of CTB5 to GM2 or GM3 was observed. The CaR-ESI-MS results obtained for Stx1B5 reveal that nonspecific protein-ganglioside binding can occur during the ESI process, although the extent of binding varies between gangliosides. Consequently, interactions detected for CTB5 with GD1a, GD1b, and GT1b are likely nonspecific in origin. Taken together, these results reveal that the CaR-ESI-MS/glycomicelle approach for detecting protein–GL interactions is prone to false positives and false negatives and must be used with caution.
The results of an investigation into the influence of sulfolane, a commonly used supercharging agent, on electrospray ionization mass spectrometry (ESI-MS) measurements of protein–ligand affinities are described. Binding measurements carried out on four protein–carbohydrate complexes, lysozyme with β-d-GlcNAc-(1→4)-β-d-GlcNAc-(1→4)-β-d-GlcNAc-(1→4)-d-GlcNAc, a single chain variable fragment and α-d-Gal-(1→2)-[α-d-Abe-(1→3)]-α-d-Man-OCH3, cholera toxin B subunit homopentamer with β-d-Gal-(1→3)-β-d-GalNAc-(1→4)[α-d-Neu5Ac-(2→3)]-β-d-Gal-(1→4)-β-d-Glc, and a fragment of galectin 3 and α-l-Fuc-(1→2)-β-d-Gal-(1→3)-β-d-GlcNAc-(1→3)-β-d-Gal-(1→4)-β-d-Glc, revealed that sulfolane generally reduces the apparent (as measured by ESI-MS) protein–ligand affinities. To establish the origin of this effect, a detailed study was undertaken using the lysozyme–tetrasaccharide interaction as a model system. Measurements carried out using isothermal titration calorimetry (ITC), circular dichroism, and nuclear magnetic resonance spectroscopies reveal that sulfolane reduces the binding affinity in solution but does not cause any significant change in the higher order structure of lysozyme or to the intermolecular interactions. These observations confirm that changes to the structure of lysozyme in bulk solution are not responsible for the supercharging effect induced by sulfolane. Moreover, the agreement between the ESI-MS and ITC-derived affinities indicates that there is no dissociation of the complex during ESI or in the gas phase (i.e., in-source dissociation). This finding suggests that supercharging of lysozyme by sulfolane is not related to protein unfolding during the ESI process. Binding measurements performed using liquid sample desorption ESI-MS revealed that protein supercharging with sulfolane can be achieved without a reduction in affinity.
Tubulin, which is the building block of microtubules, plays an important role in cell division. This critical role makes tubulin an attractive target for the development of chemotherapeutic drugs to treat cancer. Currently, there is no general binding assay for tubulin–drug interactions. The present work describes the application of the catch-and-release electrospray ionization mass spectrometry (CaR-ESI-MS) assay to investigate the binding of colchicinoid drugs to αβ-tubulin dimers extracted from porcine brain. Proof-of-concept experiments using positive (ligands with known affinities) and negative (non-binders) controls were performed to establish the reliability of the assay. The assay was then used to screen a library of seven colchicinoid analogues to test their binding to tubulin and to rank their affinities.
Microtermolides A (1) and B (2) were isolated from a Streptomyces sp. strain associated with fungus-growing termites. The structures of 1 and 2 were determined by 1D- and 2D-NMR spectroscopy and high-resolution mass spectrometry. Structural elucidation of 1 led to the re-examination of the structure originally proposed for vinylamycin (3). Based on a comparison of predicted and experimental (1)H and (13)C NMR chemical shifts, we propose that vinylamycin's structure be revised from 3 to 4. 相似文献
Electrospray ionization mass spectrometry (ESI-MS) measurements were performed under a variety of solution conditions on a highly acidic sub-fragment (B3C) of the C-terminal carbohydrate-binding repeat region of Clostridium difficile toxin B, and two mutants (B4A and B4B) containing fewer acidic residues. ESI-MS measurements performed in negative ion mode on aqueous ammonium acetate solutions of B3C at low ionic strength (I?<?80?mM) revealed evidence, based on the measured charge state distribution, of protein unfolding. In contrast, no evidence of unfolding was detected from ESI-MS measurements made in positive ion mode at low I or in either mode at higher I. The results of proton nuclear magnetic resonance and circular dichroism spectroscopy measurements and gel filtration chromatography performed on solutions of B3C under low and high I conditions suggest that the protein exists predominantly in a folded state in neutral aqueous solutions with I?>?10?mM. The results of ESI-MS measurements performed on B3C in a series of solutions with high I at pH 5 to 9 rule out the possibility that the structural changes are related to ESI-induced changes in pH. It is proposed that unfolding of B3C, observed in negative mode for solutions with low I, occurs during the ESI process and arises due to Coulombic repulsion between the negatively charged residues and liquid/droplet surface charge. ESI-MS measurements performed in negative ion mode on B4A and B4B also reveal a shift to higher charge states at low I but the magnitude of the changes are smaller than observed for B3C. 相似文献