Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C1275122 (TEM)
 21,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A high-temperature reductive sulfuration method is demonstrated to synthesize highly ordered mesoporous metal sulfide crystallites by using mesoporous silica as hard templates. H2S gas is utilized as a sulfuration agent to in situ convert phosphotungstic acid H3PW12O40.6H2O to hexagonal WS2 crystallites in the silica nanochannels at 600 degrees C. Upon etching silica, mesoporous, layered WS2 nanocrystal arrays are produced with a yield as high as 96 wt %. XRD, nitrogen sorption, SEM, and TEM results reveal that the WS2 products replicated from the mesoporous silica SBA-15 hard template possess highly ordered hexagonal mesostructure (space group, p6mm) and rodlike morphology, analogous to the mother template. The S-W-S trilayers of the WS2 nanocrystals are partially oriented, parallel to the mesochannels of the SBA-15 template. This orientation is related with the reduction of the high-energy layer edges in layered metal dichalcogenides and the confinement in anisotropic nanochannels. The mesostructure can be 3-D cubic bicontinuous if KIT-6 (Iad) is used as a hard template. Mesoporous WS2 replicas have large surface areas (105-120 m2/g), pore volumes ( approximately 0.20 cm3/g), and narrow pore size distributions ( approximately 4.8 nm). By one-step nanocasting with the H3PMo12O40.6H2O (PMA) precursor into the mesochannels of SBA-15 or KIT-6 hard template, highly ordered mesoporous MoS2 layered crystallites with the 2-D hexagonal (p6mm) and 3-D bicontinuous cubic (Iad) structures can also be prepared via this high-temperature reductive sulfuration route. When the loading amount of PMA precursor is low, multiwalled MoS2 nanotubes with 5-7 nm in diameter can be obtained. The high-temperature reductive sulfuration method is a general strategy and can be extended to synthesize mesoporous CdS crystals and other metal sulfides.
 ...
PMID:Synthesis of highly ordered mesoporous crystalline WS(2) and MoS(2) via a high-temperature reductive sulfuration route. 1762 61

Zinc oxide nanoparticle was obtained by zinc hydrate deposited on the silica nanoparticle surface and zinc hydrate was dispersed in starch gel. The structure of zinc oxide particle was characterized by nitrogen adsorption-desorption and XRD, the morphology was observed by TEM. The result showed that the zinc oxide nanoparticle deposited on the silica nanoparticle surface was well-dispersed and less than 50nm, displayed higher photocatalytic activity for methylene blue degradation. However, the zinc oxide nanoparticle in a size of 60nm was derived from starch gel and showed poorer photocatalytic activity. It provided a simple and effective route to prepare zinc oxide nanoparticle with higher photocatalytic activity through depositing zinc oxide on the silica particle surface, moreover, the catalyst is easier to recover due to its higher density.
 ...
PMID:Photocatalytic degradation for methylene blue using zinc oxide prepared by codeposition and sol-gel methods. 1768 8

The stability and oxidation of copper nanoparticles stabilized with various ligands have been studied. Lauric acid-capped copper nanoparticles were prepared by a modified Brust-Schiffrin method. Then, ligand exchange with an excess of different capping agents was performed. Oxidation and stability were studied by UV-vis, XRD, and TEM. Alkanethiols and oleic acid were found to improve air stability. The oxidation resistance of thiol-capped copper nanoparticles was found to increase with the chain length of the thiol. However, excess thiol caused etching of the particles under nitrogen. With oleic acid no etching was observed under nitrogen. After oxidation, no traces of the ligand-exchanged particles were found, suggesting their dissolution due to excess ligand. Oleic acid protected the particles against oxidation better than the tested thiols at large excess (ligand-copper ratio 20:1).
 ...
PMID:Influence of ligand structure on the stability and oxidation of copper nanoparticles. 1796 85

Nanocrystalline Lu2O3:Eu3+ was prepared by co-precipitation method using ammonium hydrogen carbonate and ammonium oxalic acid as precipitants, respectively. The crystal structure and morphology were analyzed by means of XRD and TEM. The resultant powders were sintered into transparent ceramics in vacuum and then in nitrogen without any additive. The surface morphology of the unpolished sintered specimens was characterized using SEM. The effect of different precipitants on microstructure of the nanopowders and transparency of the ceramics are compared. The excitation and emission spectra of Lu2O3:Eu3+ powders and ceramics were measured at room temperature by using synchrotron radiation as the light source. The fluorescence decay times of all specimens were analyzed. Luminescence of the ceramics decays faster than the corresponding nanopowders.
 ...
PMID:Effects of precipitant on microstructure and luminescent properties of Lu2O3:Eu3+ nanopowders and ceramics. 1798 Oct 80

4-Dimethylaminopyridine (DMAP)-stabilized palladium nanoparticles with a mean diameter of 3.4 +/- 0.5 nm are prepared from the aqueous phase reduction of Na2PdCl4 using NaBH4 in the presence of DMAP. TEM and UV-vis spectroscopy characterization of the nanoparticle dispersion shows no obvious change in the nanoparticles several months after preparation. 1H NMR spectroscopy of the nanoparticles shows that the nanoparticle dispersion also contains a boron/DMAP complex and two palladium/DMAP complexes. One of the palladium complexes crystallizes out of the dispersion and is identified as Pd(DMAP)4(OH)2 by X-ray crystallography. Following extensive analysis, it is believed that the palladium/DMAP complexes are formed following the oxidation of the palladium nanoparticles. The prepared nanoparticle dispersion promotes selective hydrogen/deuterium (H/D) exchange on the carbon atoms alpha to the endocyclic nitrogen atom on the DMAP-stabilizing ligands through reaction with D2O. This activity is attributed to the presence of the nanoparticles rather than to the presence of the oxidized palladium/DMAP complexes.
 ...
PMID:Preparation and characterization of 4-dimethylaminopyridine-stabilized palladium nanoparticles. 1798 37

The incorporation of organic moieties into siliceous frameworks leads to a wide variety of adsorbate-adsorbent interactions including weak van-der-Waal attractions as well as strong interactions such as Coulomb forces. Depending on the desired properties of such substituted highly porous matrix materials, optimized synthesis routes can be established to enhance the desired internal pore surface-affinity toward certain volatile compounds. On the basis of a fundamental knowledge of the host-guest system, sorption-related applications may benefit from individually fine-tuned and modified sample materials. The sorption isotherms of vaporized toluene on nonmodified and phenyl-functionalized mesoporous silica samples were determined on an acoustic wave device at different temperatures. The mesoporous silica was modified by in situ co-condensation and postsynthesis grafting approaches, respectively. All samples were thoroughly characterized by nitrogen sorption, thermogravimetric analysis (TGA), scanning and transmission electron microscopy (SEM, TEM), solid-state nuclear magnetic resonance (29Si NMR), dynamic light scattering (DLS), Raman spectroscopy, and toluene adsorption on a quartz crystal microbalance (QCM). The different heats of adsorption of toluene on the various modified silica surfaces obtained by the sorption data make it possible to gain additional information about the degree and type of surface functionalization. It is thus demonstrated that QCM studies can be a powerful and convenient tool for efficient investigations of functionalized mesoporous silica particles that yield valuable quantitative information on molecule-surface interactions.
 ...
PMID:Probing the intrapore surface of phenyl-substituted nanoscale mesoporous silica-piezoelectric sorption measurements in thin films. 1800 Oct 67

We present a detailed study of the growth mechanism of single-walled boron nitride nanotubes synthesized by laser vaporization, which is the unique route known to the synthesis of this kind of tube in high quantities. We have performed a nanometric chemical and structural characterization by transmission electron microscopy (high-resolution mode (HRTEM) and electron energy loss spectroscopy) of the synthesis products. Different boron-based compounds and other impurities were identified in the raw synthesis products. The results obtained by the TEM analysis and from the synthesis parameters (temperature, boron, and nitrogen sources) combined with phase diagram analysis to provide identification of the fundamental factors determining the nanotube growth mechanism. Our experiments strongly support a root-growth model that involves the presence of a droplet of boron. This phenomenological model considers the solubility, solidification, and segregation phenomena of the elements present in this boron droplet. In this model, we distinguish three different steps as a function of the temperature: (1) formation of the liquid boron droplet from the decomposition of different boron compounds existing in the hexagonal boron nitride target, (2) reaction of these boron droplets with nitrogen gas present in the vaporization chamber and recombination of these elements to form boron nitride, and (3) incorporation of the nitrogen atoms at the root of the boron particle at active reacting sites that achieves the growth of the tube.
 ...
PMID:Root-growth mechanism for single-walled boron nitride nanotubes in laser vaporization technique. 1805 51

This study aims to evaluate the in vivo performance of ordered mesoporous silica (OMS) as a carrier for poorly water soluble drugs. Itraconazole was selected as model compound. Physicochemical characterization was carried out by SEM, TEM, nitrogen adsorption, DSC, TGA and in vitro dissolution. After loading itraconazole into OMS, its oral bioavailability was compared with the crystalline drug and the marketed product Sporanox in rabbits and dogs. Plasma concentrations of itraconazole and OH-itraconazole were determined by HPLC-UV. After administration of crystalline itraconazole in dogs (20mg), no systemic itraconazole could be detected. Using OMS as a carrier, the AUC0-8 was boosted to 681+/-566 nM h. In rabbits, the AUC0-24 increased significantly from 521+/-159 nM h after oral administration of crystalline itraconazole (8 mg) to 1069+/-278 nM h when this dose was loaded into OMS. Tmax decreased from 9.8+/-1.8 to 4.2+/-1.8h. No significant differences (AUC, Cmax, and Tmax) could be determined when comparing OMS with Sporanox in both species. The oral bioavailability of itraconazole formulated with OMS as a carrier compares well with the marketed product Sporanox, in rabbits as well as in dogs. OMS can therefore be considered as a promising carrier to achieve enhanced oral bioavailability for drugs with extremely low water solubility.
 ...
PMID:Increasing the oral bioavailability of the poorly water soluble drug itraconazole with ordered mesoporous silica. 1816 30

Swollen polymer networks exhibit multiscale pores filled with solvent. Such porosity, inherent to cross-linked polymers, determines some of their most relevant physical properties and applications. In this research, several samples of chemically crosslinked poly(N-vinylimidazole) were synthesized with the same permanent crosslinking density at two different conversions, and their inherent porosity was characterized on freeze-dried specimens by SEM, TEM and nitrogen physisorption. It was thus found that all of the samples showed pores, both on the nanometer and the micrometer scales, whose dimensions were mostly equal to or larger than the mesh size of the primary polymer network (22 nm) and whose volume and specific surface decreased with increasing conversion. Micropores have, in all cases, a very minor contribution. Samples synthesized with the largest comonomer concentrations show quasi-spherical mesopores (90 nm average diameter at any conversion) and macropores (from 5 to 10 microm with increasing conversion), whereas the mesopores of samples synthesized with the largest crosslinker ratios were channel-like (150 nm) and the macropores were interconnected contiguous voids (3 microm). Samples with intermediate compositions exhibit the lowest porosity due, mostly, to interconnected mesopores. The differences in shape were ascribed to the mechanism of phase separation, taking place during polymerization, even for samples that are transparent following polymerization. The inherent porosity is a significant source of spatial inhomogeneity, which contributes to the increase in turbidity. Light scattering decreases with increasing ionization when the degree of protonation is greater than 10%. An important consequence of the inherent porosity is that the degrees of swelling determined either gravimetrically or through size measurements are not equivalent.
 ...
PMID:Porosity inherent to chemically crosslinked polymers. Poly(N-vinylimidazole) hydrogels. 1828 79

The facile synthesis of highly ordered mesoporous aluminas with high thermal stability and tunable pore sizes is systematically investigated. The general synthesis strategy is based on a sol-gel process associated with nonionic block copolymer as templates in ethanol solvent. Small-angle XRD, TEM, and nitrogen adsorption and desorption results show that these mesoporous aluminas possess a highly ordered 2D hexagonal mesostructure, which is resistant to high temperature up to 1000 degrees C. Ordered mesoporous structures with tunable pore sizes are obtained with various precursors, different acids as pH adjustors, and different block copolymers as templates. These mesoporous aluminas have large surface areas (ca. 400 m2/g), pore volumes (ca. 0.70 cm3/g), and narrow pore-size distributions. The influence of the complexation ability of anions and hydro-carboxylic acid, acid volatility, and other important synthesis conditions are discussed in detail. Utilizing this simple strategy, we also obtained partly ordered mesoporous alumina with hydrous aluminum nitrate as the precursor. FTIR pyridine adsorption measurements indicate that a large amount of Lewis acid sites exist in these mesoporous aluminas. These materials are expected to be good candidates in catalysis due to the uniform pore structures, large surface areas, tunable pore sizes, and large amounts of surface Lewis acid sites. Loaded with ruthenium, the representative mesoporous alumina exhibits reactant size selectivity in hydrogenation of acetone, D-glucose, and D-(+)-cellobiose as a test reaction, indicating the potential applications in shape-selective catalysis.
 ...
PMID:Facile synthesis for ordered mesoporous gamma-aluminas with high thermal stability. 1828 38


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>