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Electron Microscopy Data (electron + microscopy_data)
Selected AbstractsFunctional role of B,-chain N-terminal fragment in the fibrin polymerization processFEBS JOURNAL, Issue 17 2007E. V. Lugovskoy Four mAbs of the IgG1 class to the thrombin-treated N-terminal disulfide knot of fibrin, secreted by various hybridomas, have been selected. Epitopes for two mAbs, I-3C and III-10d, were situated in human fibrin fragment B,15,26, and those for two other mAbs, I-5G and I-3B, were in fragment B,26,36. Three of these mAbs, I-5G, I-3B and III-10D, as well as their Fab-fragments, decreased the maximum rate of fibrin desAA and desAABB polymerization up to 90,95% at a molar ratio of mAb (or Fab-fragment) to fibrin of 1 or 2. The fourth mAb, I-3C, did not influence the fibrin desAABB polymerization and inhibited by 50% the maximum rate of fibrin desAA polymerization. These results suggest that these mAb inhibitors block a longitudinal fibrin polymerization site. As the mAbs retard both fibrin desAABB and fibrin desAA polymerization, one can conclude that the polymerization site does not coincide with polymerization site ,B' (B,15,17). To verify this suggestion, the polymerization inhibitory activity of synthetic peptides B,SARGHRPLDKKREEA(12,26), B,LDKKREEA(19,26), B,APSLRPAPPPI(26,36), B,APSLRPAPPPISGGGYRARPA(26,46) and B,GYRARPA(40,46), which imitate the various sequences in the N-terminal region of the fibrin B,-chain, have been investigated. Peptides B,12,26 and B,26,46, but not B,40,46, B,19,26, and B,26,36, proved to be specific inhibitors of fibrin polymerization. The IC50 values for B,12,26 and B,26,46 were 2.03 × 10,4 and 2.19 × 10,4 m, respectively. Turbidity and electron microscopy data showed that peptides B,12,26 and B,26,46 inhibited the fibrin protofibril formation stage of fibrin polymerization. The conclusion was drawn that fibrin fragment B,12,46 took part in fibrin protofibril formation simultaneously with site ,A' (A,17,19) prior to removal of fibrinopeptide B. A model of the intermolecular connection between fragment B,12,46 of one fibrin desAA molecule and the D-domain of another has been constructed. [source] Composite suspended sediment particles and flocculation in glacial meltwaters: preliminary evidence from Alpine and Himalayan basinsHYDROLOGICAL PROCESSES, Issue 9 2002J. C. Woodward Abstract Research over the last decade has shown that the suspended sediment loads of many rivers are dominated by composite particles. These particles are also known as aggregates or flocs, and are commonly made up of constituent mineral particles, which evidence a wide range of grain sizes, and organic matter. The resulting in situ or effective particle size characteristics of fluvial suspended sediment exert a major control on all processes of entrainment, transport and deposition. The significance of composite suspended sediment particles in glacial meltwater streams has, however, not been established. Existing data on the particle size characteristics of suspended sediment in glacial meltwaters relate to the dispersed mineral fraction (absolute particle size), which, for certain size fractions, may bear little relationship to the effective or in situ distribution. Existing understanding of composite particle formation within freshwater environments would suggest that in-stream flocculation processes do not take place in glacial meltwater systems because of the absence of organic binding agents. However, we report preliminary scanning electron microscopy data for one Alpine and two Himalayan glaciers that show composite particles are present in the suspended sediment load of the meltwater system. The genesis and structure of these composite particles and their constituent grain size characteristics are discussed. We present evidence for the existence of both aggregates, or composite particles whose features are largely inherited from source materials, and flocs, which represent composite particles produced by in-stream flocculation processes. In the absence of organic materials, the latter may result solely from electrochemical flocculation in the meltwater sediment system. This type of floc formation has not been reported previously in the freshwater fluvial environment. Further work is needed to test the wider significance of these data and to investigate the effective particle size characteristics of suspended sediment associated with high concentration outburst events. Such events make a major contribution to suspended sediment fluxes in meltwater streams and may provide conditions that are conducive to composite particle formation by flocculation. Copyright © 2002 John Wiley & Sons, Ltd. [source] Nondestructive characterization of ferrofluids by wide-angle synchrotron light diffraction: crystalline structure and size distribution of colloidal nanoparticlesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2008Alexei Vorobiev The combination of magnetic and nonmagnetic interactions between the colloidal particles in ferrofluids results in various local inter-particle correlations that, in turn, change the macroscopic properties of the whole system. Therefore, characterization of the particle ensemble is a crucial point, allowing optimization of a ferrofluid for a particular application. Here it is shown how the crystal structure of the particles can be easily obtained in a fast synchrotron light diffraction experiment without any special treatment of the ferrofluid sample. Moreover, from the same diffraction patterns, such important parameters as particle mean size and dispersion are retrieved; these are compared with the corresponding parameters obtained from electron microscopy data. A particular problem of magnetite,maghemite transformation in nanoparticles stabilized by the surfactant shell is pointed out. [source] Single-Source Sol-Gel Synthesis of Nanocrystalline ZnAl2O4: Structural and Optical PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001Sanjay Mathur Nanometer-sized zinc aluminate (ZnAl2O4) particles were synthesized from heterometal alkoxides, [ZnAl2(OR)8], possessing an ideal cation stoichiometry for the ZnAl2O4 spinel. ZnAl2O4 is formed at 400°C, which is the lowest temperature reported for the formation of monophasic ZnAl2O4. 27Al magic-angle spinning nuclear magnetic resonance spectroscopy revealed that ZnAl2O4 possesses an inverse structure at <900°C, while the normal spinel phase is observed at higher temperatures. The homogeneity of the in-depth composition and Zn:Al stoichiometry (1:2) was confirmed by electron spectroscopy for chemical analysis. Evaluation of the valence-band spectra of ZnAl2O4 and ZnS suggested that the hybridization of O 2p and Zn 3d orbitals is responsible for lowering the bandgap in the latter. The average crystallite size showed an exponential relationship to the calcination temperature (X-ray diffractometry and transmission electron microscopy data). The optical spectra of different spinel powders (average particle sizes, 20,250 nm) showed that the absorption edge exhibits a blue shift as particle size decreases. [source] Cu(In,Ga)Se2 thin films grown with a Cu-poor/rich/poor sequence: growth model and structural considerationsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2003J. Kessler Thin films of Cu(In,Ga)Se2 are grown by a co-evaporation process in which the In, Ga, and Se fluxes, as well as the substrate temperature, are constant and the only variable is the Cu flux. This Cu flux varies in three steps in such a way that the growing film evolves from Cu-poor to Cu-rich and then back to Cu-poor. The film growth is monitored by the ,end point detection' method, and film thicknesses of the order of 2,,m are deposited in less than 20,min. Quality devices (efficiencies above 15%) are produced in our baseline processes for all of the other synthesis steps. The Cu(In,Ga)Se2 layers are studied from a (112) versus (220) (204) orientation and recrystallization point of view. Including the results from a previous study on the influence of the substrate temperature to the present X-ray diffraction and scanning as well as tunneling electron microscopy data, a five-stage growth model for the films is described. The specific features of these films are that they are weakly (220) (204) oriented and exhibit crevices in their top fractions. The growth model hypothesizes about the origins of these crevices and on how to avoid them. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||