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

1. Melanophores and xanthophores are pigment cell derivatives of the NC. In amphibian embryos they migrate from their original position on the neural tube dorsally (into the dorsal fin) as well as laterally (between somites and epidermis) and arrange themselves into typical pigment patterns of the skin. We investigated pigment pattern formation in two species of tailed amphibians, Triturus alpestris (alpine newt) and Ambystoma mexicanum (Mexican axolotl). In larvae of T. alpestris alternating longitudinal stripes or bands of melanophores and xanthophores develop, whereas in larvae of A. mexicanum a barred pattern with alternating transverse bands of melanophores and xanthophores is formed. Iridophores, a third type of pigment cell, are present later in both species and therefore play no role during early larval pigment pattern development. Visibly differentiated melanophores and xanthophores can be distinguished from each other under the light microscope by their contents of black melanins and yellow pterins respectively. With the dopa reaction (indicates tyrosinase in melanophores), and ammonia treatment (stimulates pterin fluorescence in xanthophores), the pigment cell phenotypes can be visualized even before their normal visible differentiation. In the TEM, melanophores and xanthophores can be distinguished from each other by their morphologically distinct pigment organelles and in the SEM by their different surface structure. 2. Because of the NC origin of melanophores and xanthophores and the ease with which these cells can be demonstrated even before they are visible from outside, their different arrangements in Triturus and axolotl embryos offer suitable model systems for studying the migration, interaction and localization of NC derivatives in relation to specific environmental influences. The environment of NC cells are the neural tube, epidermis, somites and lateral plate mesoderm, and the subepidermal ECM, a network of collagen fibrils associated with glycosaminoglycans, proteoglycans and glycoproteins. 3. Development of the pigment pattern in T. alpestris: Melanophores and xanthophores start to leave the NC at stage 28, melanophores slightly earlier than xanthophores. Both cell types become scattered in the dorsolateral trunk. In contrast to melanophores in the axolotl, melanophores in T. alpestris cannot be demonstrated with the dopa reaction before they become visibly black. From stage 29+ onwards, melanophores start to accumulate in zones alongside the dorsal and lateral somite edges, where they form compact stripes later. Xanthophores can be demonstrated from stage 28+ onwards only with the SEM (by means of their specific surface structures) or with the fluorescence microscope (by means of their fluorescing pterins). At state 34, xanthophores become visible externally as yellow cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The development of the larval pigment patterns in Triturus alpestris and Ambystoma mexicanum. 236 40

Thermal treatment of Zn(NH3)(4)2+ precursor in ethanol solvent led to the formation of the tubular ZnO which exhibited strong ultraviolet photoluminescence around 385 nm at room temperature; TEM images showed the hollow tubules with approximately 450 nm in diameter and approximately 4 microns in length were built up by ZnO polycrystals.
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PMID:A simple route towards tubular ZnO. 1212 Mar 95

The extraction behavior and phase behavior of TOPO (or TRPO)-kerosene/HCl-ZrOCl(2) systems have been investigated. The middle phase with bicontinuous structure is first used as both the Zr(IV) source and the template to prepare mesoporous material just by precipitation with aqua ammonia under low temperature. By this method, crystal mesoporous ZrO(2) powders with average d-values of 6.3 and 7.48 nm, respectively, have been obtained. TG-DTA, TEM, and XRD are adopted for the characterization of the synthesized sample.
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PMID:Preparation of mesoporous ZrO2 with the middle phase formed in a trioctyl (or alkyl) phosphinic oxide-kerosene/HCl-ZrOCl2 extraction system. 1292 70

Preparation and characterization of polymeric particles ultrafine on Hb-SDS-Ag have been reported. (Taking fixed quantity of Hb, SDS to be putting in a beaker, then Ag(NH3)2NO3 solution, pH--12 buffer, n-heptane and iso-amyl-alcohol were added. And fixed quantity formaldehyde, n-heptane and iso-amyl-alcohol were added in another beaker. They were stirred emulsification respectively, both of mixture were mixed in a three-well flask and which were reacted for 1.5 h at 60 +/- 0.5 degrees C. After cooling, the precipitation was separated and washed once and again, it was dried) The structure of surface have been investigated by XRD, TEM and FT-IR for this polymeric ultrafine particles, and size of diameter is about 120 nm. It is shown that Ag+ ion first formed chemical binding with Hb, then reduced to Ag particles and finally collected to a network polymers of coated by Hb.
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PMID:[Preparation and characterization of polymeric ultrafine particles on Hb-SDS-Ag hydrogeles (I)]. 1293 49

Chemically unaltered melanosomes from black hair were isolated using a mild enzymatic procedure reported by Novellino et al. involving sequential treatment of a homogenized hair sample with different protease enzymes. Time-dependent fluorescence studies show, under identical conditions, that the rate of bleaching upon NH3/H2O2 treatment of hair melanosomes is twice that of Sepia melanosomes. The structure and morphology of hair melanosomes are compared to Sepia eumelanin using ESEM and TEM imaging studies. Black hair melanosomes are aggregates of rice-shaped ellipsoidal particles (0.8-1.0 microm in length and 0.2-0.6 microm in width) surrounded by an amorphous material suspected to be made of non-proteinacious materials. Sepia eumelanin aggregates are larger (2-5 microm) particles with a "doughnut" shape comprised of 100-150-nm spherical particles. Time-dependent TEM imaging studies of ammonia-treated (pH 10) hair melanosomes showed an initial breakdown of melanosomal aggregates followed by rupture of the melanosomal membrane, releasing melanin nanoparticles and leaving a ghost membrane behind. After prolonged treatment with aqueous NH3, a total loss of characteristic melanosome morphology was observed leading to an amorphous material. By contrast, Sepia melanosomes under identical conditions of ammonia treatment did not show such changes, probably due to different surface properties and aggregation behavior. Sodium hydroxide or sodium carbonate at identical pH did not show similar changes to ammonia, suggesting that the changes are not merely due to alkaline pH, but, rather, are specific to ammonia. Co-treatment with ammonia and peroxide induced a faster disintegration of the melanosomes, resulting in a complete dissolution and discoloration of melanin in 30 minutes. The data suggest that ammonia helps to release melanin nanoparticles out of melanosomes, making them more susceptible to oxidative attack by H2O2.
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PMID:New insights into the physicochemical effects of ammonia/peroxide bleaching of hair and Sepia melanins. 1452 91

Use of a dialkoxysilane-containing, condensable alanine amphiphile with a cleavable hexadecyl ester tail (1) as a "lizard" template for sol-gel synthesis results in the formation of a mesoporous silicate (2) whose channels are filled with an organic group of the template. Treatment of 2 with aqueous HCl allows selective cleavage of the ester moiety to leave nanochannels (3) whose surface is densely covered with alanine-CO2H. According to XRD and TEM, 2, on conversion into 3, can preserve its regular hexagonal structure. 3 displays a clear N2 adsorption/desorption isotherm with a BET surface area of 536 m2 g-1. 3 can also adsorb a basic guest such as NH3 up to 0.7 mmol g-1, which is 7 times greater than that observed for mesoporous silica obtained by calcination of 2.
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PMID:A condensable amphiphile with a cleavable tail as a "Lizard" template for the sol-gel synthesis of functionalized mesoporous silica. 1474 44

Pure metallic Cu nanoparticles at a high concentration (up to 0.2 M) have been synthesized by the reduction of cupric chloride with hydrazine in the aqueous CTAB solution. The input of extra inert gases was not necessary. The use of ammonia solution for the adjustment of solution pH up to 10 and the use of hydrazine as a reducing agent in a capped reaction bottle are crucial for the synthesis of pure Cu nanoparticles. The reaction solution finally became wine-reddish and its UV/vis absorption spectrum exhibited an absorption band at 574 nm, revealing the formation of metallic Cu nanoparticles. By the analysis of electron diffraction pattern, EDS, XRD, and XPS, the resultant particles were confirmed to be pure Cu with a face-centered cubic (fcc) structure. From the TEM analysis, it was found that the mean diameter of Cu nanoparticles first decreased and then approached a constant with the increase of hydrazine concentration. In addition, the CTAB concentration had not significant influence on the size of Cu nanoparticles. Also, TG analysis indicated that there were two weight-loss steps for the CTAB-capped Cu nanoparticles. It was suggested that a bilayer structure of CTAB was formed on the surface of Cu nanoparticles to prevent from the particle agglomeration. The synthesis method reported in this work might be helpful for the large-scale production of Cu nanoparticles.
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PMID:Synthesis of high-concentration Cu nanoparticles in aqueous CTAB solutions. 1505 47

Due to limitations of the existing preparative methods of hollow nanoparticles by either heating at high temperature (>600 degrees C) or by using strong acid, alkali, or an organic solvent, it was not possible up till now to encapsulate any sensitive organic molecule like enzyme or others inside the cavity of hollow nanoparticles. We have demonstrated a much softer method of preparing hollow silica nanoparticles with horseradish peroxidase (HRP) inside the cavity by synthesizing HRP-doped core-shell silica-coated silver chloride nanoparticles and finally leaching out silver chloride with dilute ammonia at low temperatures. TEM pictures showed the hollow cavity inside the nanoparticles. The enzyme entrapped in these particles was active. The turnover number of HRP entrapped into these hollow particles and dispersed in aqueous buffer (pH 7.2) (k(cat) = 2.56 x 10(6) s(-1)) was found to be less than that of free enzyme in aqueous buffer (k(cat) = 6.133 x 10(7) s(-1)) but higher than that of HRP entrapped in solid-core silica nanoparticles and dispersed in aqueous buffer (k(cat) = 1.05 x 10(5) s(-1)). The result showed that hollow nanoparticles could be prepared using soft chemical methods and sensitive chemicals like active enzyme could be entrapped in the cavities and it retains its activity.
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PMID:Enzymes in the cavity of hollow silica nanoparticles. 1575 25

An intrachannel surface of host silica was functionalized through the reaction of surface silanol groups with silanes to generate a monolayer of positively charged groups, and together with the strongly adsorbed and negatively charged PtCl6(2-), resulting in nanostructured platinum-mesoporous silica composites. The highly dispersed Pt nanoparticles and nanonetworks are fabricated from (CH3O)3Si(CH2)3N(CH3)3+Cl- functionalized mesoporous silica MCM-48 with H2PtCl6 in ethanol and water solvent, and characterized by PXRD, XAS, TEM, and N2 adsorption. The solvent of H2PtCl6 solution is found to affect the mobility of Pt precursors and the resulting morphology of nanostructured metallic Pt. The effect of the intrachannel surface properties on the incorporation and the morphology of nanostructured Pt on the deposition of Pt(NH3)4Cl2 and H2PtCl6 on Al-doped or C-coated mesoporous silica MCM-41 is also studied relative to that on pure silica MCM-41.
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PMID:Morphology of nanostructured platinum in mesoporous materials-effect of solvent and intrachannel surface. 1647 27

Mesoporous nanocrystalline TiO2-xNx and TiO2-xNx/ZrO2 visible-light photocatalysts have been prepared by a sol-gel method. The photocatalysts were characterized by XRD, N2 adsorption-desorption, TEM, XPS, UV/Vis, and IR spectroscopy. The photocatalytic activity of the samples was evaluated by the decomposition of ethylene in air under visible light (lambda > 450 nm) illumination. Results revealed that nitrogen was doped into the lattice of TiO2 by the thermal treatment of NH3-adsorbed TiO2 hydrous gels, converting the TiO2 into a visible-light responsive catalyst. The introduction of ZrO2 into TiO2-xNx considerably inhibits the undesirable crystal growth during calcination. Consequently, the ZrO2-modified TiO2-xNx displays higher porosity, higher specific surface area, and an improved thermal stability over the corresponding unmodified TiO2-xNx samples.
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PMID:ZrO2-modified mesoporous nanocrystalline TiO2-xNx as efficient visible light photocatalysts. 1664 76


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