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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Native MA-10 mouse Leydig tumor cell mitochondrial preparations were examined by transmission electron (TEM) and atomic force (AFM) microscopic procedures in order to investigate the topography and organization of the peripheral-type benzodiazepine receptor (PBR). Mitochondria were immunolabeled with an anti-PBR antiserum coupled to gold-labeled secondary antibodies. Results obtained indicate that the 18,000 MW PBR protein is organized in clusters of 4-6 molecules. Moreover, on many occasions, the interrelationship among the PBR molecules was found to favor the formation of a single pore. Taking into account recent observations that the 18,000 MW PBR protein is functionally associated with the pore forming 34,000 MW voltage-dependent anion channel (VDAC) these results suggest that (i) the mitochondrial PBR complex could function as a pore, thus allowing the translocation of cholesterol and other molecules to the inner mitochondrial membrane, and (ii) the native receptor is a multimeric complex of an approximate 140,000 MW composed on an average of five 18,000 PBR subunits, one 34,000 VDAC subunit, and associated lipids.
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PMID:Topography of the Leydig cell mitochondrial peripheral-type benzodiazepine receptor. 782 99

Amelogenin proteins are the principal constituents of the extracellular organic matrix associated with the nucleation and growth of the carbonated calcium hydroxyapatite (HAP)-containing mineral phase of dental enamel. Amelogenins are believed to function in controlling the sizes and organization of the developing enamel crystals. Previous studies have shown that enamel proteins exhibit unusual reversible aggregation properties. The present studies were designed to test the hypothesis that self-assembly of recombinant amelogenin generates supramolecular structures that are indistinguishable from the electron-dense particles associated with HAP crystal growth in vivo. A recombinant amelogenin analog of the murine 180-residue protein was analyzed by high-resolution size exclusion chromatography, atomic force (AFM), and transmission electron (TEM) microscopy. It was found that the amelogenin formed supramolecular aggregates which were in a concentration-dependent equilibrium with protein monomers. Imaging of the amelogenin by both AFM and TEM techniques revealed spherical aggregate structures of about 18 nm diameter which were seen to be similar to electron-dense enamel structures observed in vivo. We interpret these results to suggest that, in vivo, the amelogenin protein self-assembles through functional motifs of the protein primary structure, generating specific supramolecular aggregates which we hypothesize function to control the ultrastructural organization of the developing enamel crystallites.
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PMID:Self-assembly of a recombinant amelogenin protein generates supramolecular structures. 806 Jul 28

Polymer encapsulation of small silica particles, using dispersion polymerization of styrene in aqueous ethanol medium with poly(N-vinyl pyrrolidone) (PVP) as stabilizer, is described. Silica particles, directly synthesized by the Stober process in an aqueous ethanol medium, are either unreacted (hydrophilic character) or coated with 3-(trimethoxysilyl)propyl methacrylate (MPS) (hydrophobic character), which is grafted at the silica particle surface. When the bare silica particles are used as the seed, there is a strong tendency of the silica beads to cover the surface of the polystyrene particles and obviously encapsulation does not occur. On the contrary, when the silica surface is made hydrophobic by coating, the inorganic particles are entirely contained in the polystyrene particles as evidenced by microscopy techniques (TEM, SEM, AFM). It is shown that some polystyrene chains are then chemically bonded to the silica particles, through the coupling agent MPS, and that only a small amount of bonded polystyrene, compared to the total polystyrene synthesized, is sufficient to obtain encapsulation of the silica particles with the entire amount of polystyrene synthesized during the polymerization. Under our experimental conditions, each polystyrene latex particle contains, on average, 4 to 23 silica beads depending, in particular, on the size of the silica. We believe that it is possible to control the composite particle size and morphology by a convenient choice of the composition of the system. Moreover, this new polymer-encapsulation process could be used to synthesize other organic-inorganic composite particles, using, for example, other monomers or minerals. Copyright 1998 Academic Press. Copyright 1998Academic Press
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PMID:Encapsulation of Inorganic Particles by Dispersion Polymerization in Polar Media 946 71

Enhancement of epithelial cell attachment to laminin-5-coated titanium alloy (Ti-6Al-4V) implant material was evaluated in vitro. Protein analysis showed that Ti-6Al-4V has a high affinity for laminin-5 and adsorbed significantly more laminin-5 than laminin-1. DNA analysis showed that laminin-5 enhanced attachment of normal human epidermal keratinocytes (NHEK) to Ti-6Al-4V significantly more than did laminin-1 or uncoated controls. The effect of passivation on laminin-5 adsorption and activity on Ti-6Al-4V also was evaluated. Passivation had no significant effect on the amount of protein adsorbed; however, AFM, ESCA, and ToF-SIMS analyses suggested that passivation affects the conformation of adsorbed laminin-5. Although laminin-5 coating significantly enhanced rapid attachment of epithelial cells to both passivated and unpassivated Ti-6Al-4V, surface area measurements showed that cells spread on laminin-5-coated passivated Ti-6Al-4V covered a significantly larger surface area than cells spread on laminin-5-coated unpassivated samples. TEM analysis showed that cells formed significantly more hemidesmosomes on the surface of laminin-5 coated passivated than on the surface of laminin-5 coated unpassivated titanium alloy. The enhancement of rapid cell attachment, spreading, and hemidesmosome assembly on laminin-5-coated passivated samples may reflect better integration between epithelial cells and titanium alloy and thus may be predictive of long-term implant stability.
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PMID:Laminin-5 coating enhances epithelial cell attachment, spreading, and hemidesmosome assembly on Ti-6A1-4V implant material in vitro. 964 21

A novel approach is proposed for studying tooth-biomaterial interactions with high resolution. Thus far, polished interfaces examined by AFM have not disclosed much detail, mainly due to the destruction of soft surface texture and the smearing of polishing debris across the interface that obscures the actual ultra-structure. Therefore the practical utility of diamond-knife microtomy as a sample preparation technique for imaging tooth-biomaterial interfaces by AFM with high resolution was tested in this study and compared to that of ultra-fine mechanical polishing techniques. The AFM images clearly demonstrated the enhanced potential of diamond-knife microtomy for nondestructively producing clean cross-sections through interfaces that allow the interfacial ultra-structure to be imaged by AFM with a resolution equaling that of TEM. This novel approach opens the field to the full range of scanning probe microscopy, including physical and chemical surface characterization of interfaces with a mix of soft and hard substrates.
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PMID:A novel approach to AFM characterization of adhesive tooth-biomaterial interfaces. 1040 Aug 85

The excimer laser irradiation of thin film amorphous silicon (a-Si) precursors on glass is a suitable method for obtaining high-performance polycrystalline silicon (p-Si) active layers for devices and circuits. By changing the experimental conditions, the recrystallization method generates a variety of microstructures that have direct impact on the material performance. An additional reason for microstructural characterization is introduced by the methods for spatially locating the recrystallization nuclei, used in more ergonomic concepts of device fabrication. Metal and SiO2 strip overlayers have been applied here, on a-Si to fix the position of the solidification seeds after laser melting. The control of many aspects of the thin film microstructure can be achieved with a collection of a few inspection techniques like AFM, SEM, EC contrast, TEM, X-ray diffraction (XRD), some of which require preliminary grain decoration treatment, and some do not. The results of different irradiation experiments, are herein illustrated, enlightened by the above characterization techniques, for providing information on surface morphology, grain arrangement, preferred orientation.
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PMID:Morphological and structural effects of excimer laser treatment of amorphous silicon 1070 80

Novel dendritic polyphenylazomethines (DPAs), which consist of a pi-conjugated backbone, were synthesized up to the fourth generation by the convergent method via dehydration of aromatic ketones with aromatic amines in the presence of titanium(IV) tetrachloride. The obtained dendrimers, DPA G1-4 (designated as GX, where X is the generation number), show high thermostability (Td(10%) 521 degrees C in DPA G4) and high solubility for the common solvents such as chloroform, THF, and DMSO unlike the conventional linear polyphenylazomethines, which have very low solubilities. The DPA G4 molecule was confirmed to have a spherelike structure by GPC measurement and a molecular model based on the crystal structure of DPA G2. Crystal data for DPA G2: monoclinic space group P2(1)/a, a = 25.352(4) A, b = 8.577(2) A, c = 16.151(2) A, beta = 106.25(1) degrees, V = 3371.6(10) A(3), Z = 2, D(calc) = 1.168 g/cm(3), mu(Cu Kalpha) = 0.536 cm(-1), final R = 0.089, and R(w) = 0.287. The molecular modeling reveals that a DPA G4 molecule has a spherelike structure, in which the height, width, and depth are 2.3, 2.9, and 2.5 nm, respectively. The TEM and AFM pictures show the DPA G4 molecules to have a spherelike structure (the diameter: 2.3 nm) and are regularly assembled on a plate by casting. The occupied area of one DPA G4 molecule in a monolayer on water was estimated by pi-A measurements to be 3.8-4.2 nm(2) (the calculated diameter 2.2-2.3 nm, which agreed with the TEM result). NMR studies (1H NMR at 130 degrees C and T(1) measurements) supported a conformational rigidity of DPA G4 in solution.
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PMID:First synthesis of phenylazomethine dendrimer ligands and structural studies. 1145 26

MBE growth of ZnS(x)Se(1 - x) thin films on ITO coated glass substrates were carried out using ZnS and Se sources with the substrate temperature ranging from 270 degrees C to 330 degrees C . The XRD theta/2theta spectra resulted from these films indicated that the as-grown polycrystalline ZnS(x)Se(1 - x) thin films had a preferred orientation along the (111) planes. The evaluated crystal sizes as deduced from the FWHM of the XRD layer peaks showed strong growth temperature dependence, with the optimized temperature being about 290 degrees C. Both AFM and TEM measurements of these thin films also indicated a similar growth temperature dependence. High quality ZnS(x)Se(1 - x) thin film grown at the optimized temperature had the smoothest surface with lowest RMS value of 1.2 nm and TEM cross-sectional micrograph showing a well defined columnar structure.
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PMID:Polycrystalline ZnS(x)Se(1 - x) thin films deposited on ITO glass by MBE. 1265 24

Star polymers containing ruthenium complex in the core were prepared by ruthenium-catalyzed living radical polymerization, where the metal catalysts were directly encapsulated on linking reactions of living poly(MMA) in the presence of ethylene glycol dimethacrylate as a linker and diphenyl-4-styrylphosphine as a ligand incorporated in the core. The products were characterized by SEC/MALLS, UV-vis, NMR, AFM, TEM, and ICP-AES and were employed as polymer catalysts for the oxidation reaction of alcohol.
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PMID:Polymer catalysts from polymerization catalysts: direct encapsulation of metal catalyst into star polymer core during metal-catalyzed living radical polymerization. 1272 Apr 36

Particles of linear polyethylene (M(n) = (2-3) x 10(3) g x mol(-)(1); M(w)/M(n) = 2-4) obtained by catalytic emulsion polymerization of ethylene possess a nonspherical, lentil-like shape with an average aspect ratio of ca. 10 and diameters from 30 to >300 nm, as determined by TEM and AFM. The particle structure results from a stacking of the lamellae along the one shorter axis of the lentils (i.e., their height, by contrast to the diameter). In addition to these multilamellae particles, remarkably, a considerable number of the particles consist of only a single lamella. The thickness of the lamellae (spacing) as determined by TEM is only 9-11 nm, depending on the polymerization temperature during the synthesis of the dispersions. Crystallization in the dispersions during emulsion polymerization differs dramatically from the usual heterogeneous nucleation of bulk polyethylene samples. Each submicron droplet crystallizes individually, independently from the other droplets, resulting in large supercoolings of around 55 degrees C.
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PMID:Submicron polyethylene particles from catalytic emulsion polymerization. 1286 79


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