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 21,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Three new aliphatic thiol surfactants were synthesized by reacting alkyl bromide with hexamethyldisilathiane under a mild condition. This approach provides an easy access for the direct synthesis of various different length thiol surfactants which play a crucial role in tuning the properties of gold nanoparticles. Gold nanoparticles encapsulated with one of our synthetic thiols were prepared and well characterized by H NMR, UV-vis, FT-IR, and TEM. The hybrid nanoparticles are very stable in both organic solvents and the solid state.
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PMID:A facile synthesis of aliphatic thiol surfactant with tunable length as a stabilizer of gold nanoparticles in organic solvents. 1729 18

The formation of a complex between an anionic spherical polyelectrolyte brush (SPB) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) is investigated. The SPB consists of long chains of the strong polyelectrolyte poly(styrene sulfonate) (PSS), which are bound chemically to a solid poly(styrene) core of 56 nm in radius. The SPB are dispersed in water, and the ionic strength is adjusted by addition of NaBr. The resulting complexes are investigated in dilute solution by dynamic light scattering, by electrophoretic light scattering, and by cryogenic transmission electron microscopy (cryo-TEM). The formation of the complex between the SPB and the surfactant can be monitored by a strong shrinking of the surface layer when adding CTAB to dilute suspensions (0.01 wt %) and by a decrease of the effective charge of the complexes. Complex formation starts at CTAB concentrations lower than the critical micelle concentration of this surfactant. If the ratio r of the charges on the SPB to the charge of the added surfactant is exceeding unity, the particles start to flocculate. Cryo-TEM images of the complexes at r = 0.6 measured in salt-free solution show that the surface layer composed of the PSS chains and the adsorbed CTAB molecules is partially collapsed: A part of the chains form a dense surface layer while another part of the chains or aggregates thereof are still sticking out. This can be deduced from the cryo-TEM micrographs as well as from the hydrodynamic radius, which is still of appreciable magnitude. The 1:1 complex (r = 1.0) exhibits a fully collapsed layer formed by the PSS chains and CTAB. If the complex is formed in the presence of 0.05 M NaBr, r = 0.6 leads to globular structures directly attached to the surface of the core particles. All structures seen in the cryo-TEM images can be explained by a collapse transition of the surface layer brought about by the hydrophobic attraction between the polyelectrolyte chains that became partially hydrophobic through adsorption of CTAB.
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PMID:Binding of oppositely charged surfactants to spherical polyelectrolyte brushes: a study by cryogenic transmission electron microscopy. 1731 35

In the present work, the assembly morphology changes during the solubilization process of the sonicated unilamellar vesicles from dimyristoyl phosphocholine (DMPC) by a cationic surfactant, n-dodecyl triethylammonium bromide (DTEAB) were well characterized with DSC, FF-TEM and DLS and fluorescence probes technique. Based on an analysis on the above results, a primary multi-stage model was brought forward to sketch the assembly morphology changes during the DMPC vesicle solubilization by DTEAB. In comparison with classical models, vesicles division, tubule-like structure formation and fission to vesicle were found in the middle stages of this model. Additionally, it is the first time that the transversally-cut profiles of tubule-like structures were observed during vesicle solubilization process.
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PMID:Characterizing assembly morphology changes during solubilization process of dimyristoyl phosphocholine vesicles by n-dodecyl triethylammonium bromide. 1737 71

A novel class of organic-inorganic hybrids, the so-called cerasomes, which have a bilayer vesicular structure and a silicate surface, has been synthesized by combination of sol-gel reaction and self-assembly of organoalkoxysilanes with a molecular structure analogous to lipids. We have synthesized two cerasome-forming organoalkoxysilanes, N-[N-(3-triethoxysilyl)propylsuccinamoyl]dihexadecylamine (1) and N,N-dihexadecyl-N (alpha)-[6-[(3-triethoxysilyl)propyldimethylammonio]hexanoyl]glycinamide bromide (2), and investigated the synthetic conditions of the cerasomes and their structural characteristics. For the proamphiphilic 1, the cerasome was obtained under restricted pH conditions where acid-catalyzed hydrolysis of the triethoxysilyl moiety proceeded without disturbing the vesicle formation. In contrast, the amphiphilic 2, additionally having a hydrophilic quaternary ammonium group, formed stable dispersions of the cerasome in a wide pH range. The hydrolysis behavior of the triethoxysilyl groups was monitored by (1)H NMR spectroscopy. Morphology of the cerasomes having the liposomal vesicular structure was confirmed by TEM observations. Extent of the development of siloxane networks through condensation among the silanol groups on the cerasome surface was evaluated by using MALDI-TOF-MS spectrometry. Formation of oligomers of the cerasome-forming lipids in the vesicle was clearly confirmed. Due to the siloxane network formation, the cerasome showed remarkably high morphological stability compared with a reference liposome, as evaluated by surfactant dissolution measurements.
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PMID:Preparation and characterization of a novel organic-inorganic nanohybrid "cerasome" formed with a liposomal membrane and silicate surface. 1740 15

Crystalline vanadium pentoxide with hierarchical mesopores was synthesized by using a CTAB/BMIC cotemplate (CTAB = cetyltrimethylammonium bromide, BMIC = 1-butyl-3-methylimidazolium chloride). The material was fully characterized by SEM, TEM, N2 adsorption-desorption, XRD, XPS, and CV methods. By elaborate adjustment of the template proportions, the distribution and size of the hierarchical pores were tuned successfully. CTAB cationic surfactant contributed more to the larger mesopores, whereas BMIC ionic liquid was beneficial in forming the smaller nanopores. The vanadium-containing anions combined with CTA+ micelles and BMI+ rings through electrostatic interactions. The CTA(+)-O(VO)O(-)-BMI(+) entities built up an orderly array, which finally formed the hierarchical mesoporous framework during thermal treatment. The mesoporous vanadium pentoxide directed by the cotemplate of CTAB/BMIC = 1:1 showed many orderly crystalline structures and demonstrated a large capacitance (225 F g(-1)); it is thus a promising material for electrochemical capacitors. Two alternative solutions to the disappearance of capacitance due to insertion of K+ are proposed in view of possible future applications.
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PMID:Crystalline vanadium pentoxide with hierarchical mesopores and its capacitive behavior. 1744 Nov 11

The phase behavior and structure of aqueous-in-n-heptane microemulsions, stabilized by surfactant mixtures of di-n-didodecyldimethylammonium bromide, DDAB, and Brij(R)35 were studied by small angle (neutron or X-ray) scattering techniques. The aqueous nanodroplets contain either a precursor reactive salt or a precipitating agent, so that simple mixing induces nanoparticle formation. These formulated microemulsions display good phase stability against added polar additives such as monovalent, divalent, trivalent metal ions, ammonia solution, tetrabutylammonium hydroxide, and their mixtures. Nanoparticle formation was demonstrated via precipitation of metal oxides inside the water nanodroplets, affording control over the resulting particle size. Nanoparticle characteristic size (XRD- and HR-TEM derived sizes) and specific surface areas (S(BET) (m(2)g(-1))) for iron oxide and CeO(2) prepared in these mixed microemulsions, are compared with those stabilized by single surfactants DDAB and Pure AOT.
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PMID:Generation of metal oxide nanoparticles in optimised microemulsions. 1754 27

Silver carboxylates can be made by the reaction of silver nitrate and the corresponding sodium carboxylates. The length of the alkyl chain has a significant impact on the product behavior. In this study, 18, 20, and 22 carbon chains (stearate, arachidate, and behenate, respectively) have been selected. All three sodium carboxylates are very insoluble in water at room temperature. Solutions are obtained above the Krafft temperature, which precipitates lamellar crystals if cooled at the proper cooling rate. Depending on the chain length, metastable morphologies, such as vesicles and tiny fibers, can be seen consecutively before hexagonal plates form. The carboxylate with the shorter chain length reaches equilibrium more quickly. All three silver carboxylates also take on a lamellar structure. Small-angle X-ray scattering (SAXS) shows that the d spacing of the crystals increases as the chain length increases. Cryo-TEM illustrates that the crystallites are the result of micelle nucleation and micelle aggregation. In addition, the crystallization process in the presence of silver bromide nanocrystals has been investigated. In the initial stage, an epitaxial interface is formed between the silver carboxylate crystallites and the cubic silver bromide grains. Budlike and strandlike structures grow because of it. The consequent strand enclosure restrains the crystal growth, which reduces the size and changes the morphology of the crystals.
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PMID:Crystallization of silver carboxylates from sodium carboxylate mixtures. 1756 57

Quaternized chitosan/layered silicate nanocomposite was prepared by simple solution-mixing in aqueous media. Montmorillonite (MMT) modified with cetyltrimethyl ammonium bromide was used as an organically modified layered silicate. XRD and TEM analyses respectively confirmed that silicate layers of MMT were intercalated and nicely distributed in quaternized chitosan matrix in despite of the high content of MMT (25-50 wt %). The interactions between the quaternized chitosan macromolecules and MMT in aqueous media were analyzed using FTIR, XRD, and zeta-potential measurements. Antimicrobial studies showed that the nanocomposites could strongly inhibit the growth of a wide variety of microorganisms, including Gram-positive bacteria, Gram-negative bacteria, and fungi; more importantly, they exhibited good antimicrobial capacity in whichever medium, in weak acid, water, or weak base. As the amount of MMT increased, the nanocomposites had better inhibitory effect on microorganisms, especially Gram-positive bacteria. The lowest minimum inhibition concentration (MIC) value of the nanocomposites against Staphylococcus aureus and Bacillus subtilis were less than 0.00313% (w/v) under all the conditions. The adsorption action of MMT on bacteria was simply discussed via SEM images. The results revealed that the strong antimicrobial of the nanocomposites may be attributed to the fine dispersion and the interaction between quaternized chitosan and MMT.
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PMID:Preparation, characterization, and antimicrobial activity of quaternized chitosan/organic montmorillonite nanocomposites. 1761 81

Adhesive materials extracted from the brown algae Fucus Serratus were studied. These adhesives are composed of cross-linked alginate and polyphenols oxidized in the presence of KI or KBr. All formulations were capable of adhering to a variety of surfaces, however the adhesion properties were influenced by the halide used. SAXS and TEM experiments revealed that oxidized polyphenols self-assemble into chain-like objects, irrespective of the oxidation conditions. Yet, slight differences in the aggregate size were detected. QCM-D results showed that the kinetics of the oxidation was faster with iodide than with bromide. Moreover, oxidation with iodide generates stiffer networks, suggesting that the interaction between the alginate and the polyphenol could be the cause of the reduced adhesion.
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PMID:The influence of halide-mediated oxidation on algae-born adhesives. 1772 88

In this work, a novel sol-gel coating of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPTS)-silica was prepared for capillary microextraction (CME) of trace Cu, Zn, Ni, Hg and Cd followed by on-line ICP-MS detection. This organic-inorganic hybrid coating was in situ created on the inner walls of fused silica capillary using a sol solution containing tetramethoxysilane (TMOS) as a precursor, AAPTS as a co-precursor, ethanol as the solvent and cetyltrimethylammonium bromide (CTAB) as the template. The structure of the capillary coating was characterized by IR, SEM and TEM. Various experimental parameters affecting capillary microextraction of the target analytes have been investigated carefully, and the optimized extraction conditions were established. It was found that the AAPTS-silica coating with a terminal functional group of -NH-CH2-CH2-NH2 exhibited a high selectivity towards the selected metal ions. With a consumption of 1.0 mL sample solution and 80 microL eluent, the detection limits (3sigma) were found to be 1.8, 11.8, 1.1, 3.3 and 1.4 pg mL(-1) for Cu, Zn, Ni, Hg and Cd, respectively. A sampling frequency of 14 h(-1) and an enrichment factor of 12.5 were obtained under the optimized experimental conditions. The relative standard deviations (RSDs) for the target analytes were less than 3.6% (C = 1 ng mL(-1), n = 7, sample volume = 1 mL). Two certified reference materials of NIES No.10-c rice flour and BCR-CRM 278 mussel flesh were analyzed to validate the proposed method, and the determined values were in good agreement with the certified values. The developed method had also been applied to the determination of trace target elements in human hair, serum and urine, and the recoveries for the spiked samples were in the range of 89.2-101.8%. The AAPTS-silica coated capillary showed an excellent pH resistance and could be used for more than 120 times without decreasing adsorption efficiency.
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PMID:Preparation of a high pH-resistant AAPTS-silica coating and its application to capillary microextraction (CME) of Cu, Zn, Ni, Hg and Cd from biological samples followed by on-line ICP-MS detection. 1802 4


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