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 78,556 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Silver-nanoparticle-embedded aminosilica colloids synthesized via aminosilane-induced spontaneous reduction reaction exhibit selective adhesion properties on hydrophobic surfaces and have been utilized as a simple and one-step procedure to create patterned nanocomposite film with silver to aminosilica mole ratio at 0.9:1. Substrates that enable self-assembly of the colloids include silicon wafer, polydimethylsiloxane, and microscope slide, where patterns of hydrophilic surface were either created using oxygen plasma treatment or stamped with chemical ink using microcontact printing. Upon substrates being immersed in a solution containing silver-aminosilica colloids, particles attach to hydrophobic surfaces and continuously self-assemble onto the deposited film, allowing us to fabricate nanocomposite patterns with controllable thickness (approximately 200 nm).
ACS Appl Mater Interfaces 2009 Dec
PMID:Self-assembly of silver-aminosilica nanocomposites through silver nanoparticle fusion on hydrophobic surfaces. 2035 56

Water-dispersible aminoclay synthesized in a single step process was used as an inorganic filler for preparing polyvinyl alcohol (PVA)-clay hybrid films. The PVA-clay hybrid films with different weight percentages of aminoclay were obtained by simple mixing and casting of aqueous solutions of clay and polymer. The composite films show excellent retention of ductile behavior of the polymer, PVA, even at higher loadings (20 wt %) of aminoclay. Introduction of aminoclay stabilized Ag nanoparticles significantly improved the mechanical properties of the composite film. The oxygen barrier property of the composite film was improved with the increase in composition of the clay.
ACS Appl Mater Interfaces 2009 Dec
PMID:Aminoclay: a designer filler for the synthesis of highly ductile polymer-nanocomposite film. 2035 59

Polymer electrolytes based on mixtures of poly(ethylene oxide-co-propylene oxide) and 1-methyl-3-propyl-imidazolium iodide (MPII) were investigated, aiming at their application in dye-sensitized solar cells (DSSC). The interactions between the copolymer and the ionic liquid were analyzed by infrared spectroscopy and (1)H NMR. The results show interactions between the ether oxygen in the polymer and the hydrogen in the imidazolium cations. The ionic conductivities, electrochemical behaviors, and thermal properties of the electrolytes containing different concentrations of MPII were investigated. The electrolyte containing 70 wt % MPII presented the highest ionic conductivity (2.4 x 10(-3) S cm(-1)) and a diffusion coefficient of 1.9 x 10(-7) cm(2) s(-1). The influence of LiI addition to the electrolytes containing different concentrations of MPII was also investigated. The DSSC assembled with the electrolyte containing 70 wt % MPII showed an efficiency of 3.84% at 100 mW cm(-2). The stability of the devices for a period of 30 days was also evaluated using sealed cells. The devices assembled with the electrolyte containing less ionic liquid showed to be more stable.
ACS Appl Mater Interfaces 2009 Dec
PMID:Electrochemical and structural characterization of polymer gel electrolytes based on a PEO copolymer and an imidazolium-based ionic liquid for dye-sensitized solar cells. 2035 69

The mechanisms of technologically important atomic layer deposition (ALD) processes, trimethylaluminium (TMA)/ozone and tetrakis(ethylmethylamino)hafnium (TEMAH)/ozone, for the growth of Al(2)O(3) and HfO(2) thin films are studied in situ by a quadrupole mass spectrometer coupled with a 300 mm ALD reactor. In addition to released CH(4) and CO(2), water was detected as one of the reaction byproduct in the TMA/O(3) process. In the TEMAH/O(3) process, the surface after the ozone pulse consisted of chemisorpted active oxygen and -OH groups, leading to the release of H(2)O, CO(2), and HNEtMe during the metal precursor pulse.
ACS Appl Mater Interfaces 2010 Feb
PMID:In situ reaction mechanism studies on ozone-based atomic layer deposition of Al(2)O(3) and HfO(2). 2035 79

The activity and selectivity of carbon-supported Pt-decorated PdFe nanoparticles in the oxygen reduction reaction (ORR) were investigated in the presence and absence of methanol. The Pt-decorated PdFe nanoparticles, which consist of a PdPt surface and a PdFe interior, were prepared by the galvanic reaction between PdFe/C alloy nanoparticles and PtCl4(2-) in aqueous solution. The presence of a Pt-enriched surface after the replacement reaction was independently confirmed by several microstructural characterization techniques and cyclic voltammetry. The catalyst with such heterogeneous architecture is catalytically more active than a bulk PdFePt alloy catalyst with the same overall composition. The observed enhancements in catalyst performance can be attributed to the lattice strain effect between the shell and core components. The Pt-decorated PdFe (PdFe@PdPt/C) catalyst also compares favorably with a commercial Pt/C catalyst with four times as much Pt in terms of ORR activity, cost, and methanol tolerance.
ACS Appl Mater Interfaces 2010 Jan
PMID:Pt-decorated PdFe nanoparticles as methanol-tolerant oxygen reduction electrocatalyst. 2035 28

We show that ligand exchange with short-chain carboxylic acids (formic, acetic, and oxalic acid) can quantitatively remove oleic acid from the surface of PbSe and PbS quantum dot (QD) films to yield p-type, carboxylate-capped QD solids with field-effect hole mobilities in the range of 10(-4)-10(-1) cm(2) V(-1) s(-1). For a given chemical treatment, PbSe devices have 10-fold higher mobilities than PbS devices because of stronger electronic coupling among the PbSe QDs and possibly a lower density of surface traps. Long-term optical and electrical measurements (i) show that carboxylate-capped PbSe QD films oxidize much more gradually in air than do thiol-capped PbSe films and (ii) quantify the slower and less extensive oxidation of PbS relative to PbSe QDs. We find that whereas the hole mobility of thiol-capped samples decreases continuously with time in air, the mobility of carboxylate-capped films first increases by an order of magnitude over several days before slowly decreasing over weeks. This behavior is a consequence of the more robust binding of carboxylate ligands to the QD surface, such that adsorbed oxygen and water initially boost the hole mobility by passivating surface states and only slowly degrade the ligand passivation to establish an oxide shell around each QD in the film. The superior hole mobilities and oxidation resistance of formic- and acetic-treated QD solids may prove useful in constructing efficient, stable QD photovoltaic devices.
ACS Nano 2010 Apr 27
PMID:p-Type PbSe and PbS quantum dot solids prepared with short-chain acids and diacids. 2035 35

We report the preparation of alpha-Fe2O3 electrodes using a technique known as reactive ballistic deposition in which iron metal is evaporatively deposited in an oxygen ambient for photoelectrochemical (PEC) water oxidation. By manipulating synthesis parameters such as deposition angle, film thickness, and annealing temperature, we find that it is possible to optimize the structural and morphological properties of such films in order to improve their PEC efficiency. Incident photon to current conversion efficiencies (IPCE) are used to calculate an AM1.5 photocurrent of 0.55 mA/cm(2) for optimized films with an IPCE reaching 10% at 420 nm in 1 M KOH at +0.5 V versus Ag/AgCl. We also note that the commonly observed low photoactivity of extremely thin hematite films on fluorine-doped tin oxide substrates may be improved by modification of annealing conditions in some cases.
ACS Nano 2010 Apr 27
PMID:Reactive ballistic deposition of alpha-Fe2O3 thin films for photoelectrochemical water oxidation. 2036 56

Effects of air exposure on surface properties, electronic structure, and carrier relaxation dynamics in colloidal PbSe nanocrystals (NCs) were studied using X-ray photoelectron spectroscopy, transmission electron microscopy, and steady-state and time-resolved photoluminescence (PL) spectroscopies. We show that exposure of NC hexane solutions to air under ambient conditions leads to rapid oxidation of NCs such that up to 50% of their volume is transformed into PbO, SeO2, or PbSeO3 within 24 h. The oxidation is a thermally activated process, spontaneous at room temperature. The oxidation-induced reduction in the size of the PbSe "core" increases quantum confinement, causing shifts of the PL band and the absorption onset to higher energies. The exposure of NC solutions to air also causes rapid (within minutes) quenching of PL intensity followed by slow (within hours) recovery during which the PL quantum yield can reach values exceeding those observed prior to the air exposure. The short-term PL quenching is attributed to enhanced carrier trapping induced by adsorption of oxygen onto the NC surface, while the PL recovery at longer times is predominantly due to reduction in the efficiency of the "intrinsic" nonradiative interband recombination caused by the increase of the band gap in oxidized NCs. Although the analysis of subnanosecond relaxation dynamics in air-exposed NCs is complicated by a significant enhancement in fast carrier trapping, our picosecond PL measurements suggest that air exposure likely has only a weak effect on Auger recombination and also does not significantly affect the efficiency of carrier multiplication. We also show that the effects of air exposure are partially suppressed in PbSe/CdSe core/shell structures.
ACS Nano 2010 Apr 27
PMID:Effect of air exposure on surface properties, electronic structure, and carrier relaxation in PbSe nanocrystals. 2036

Growing evidence points toward a very dynamic role for metals in biology. This suggests that physiological circumstance may mandate metal ion redistribution among ligands. This work addresses a critical need for technology that detects, identifies, and measures the metal-containing components of complex biological matrixes. We describe a direct, user-friendly approach for identifying and quantifying metal-protein adducts in complex samples using native- or SDS-PAGE, blotting, and rapid synchrotron X-ray fluorescence mapping with micro-XANES (X-ray absorption near-edge structure) of entire blots. The identification and quantification of each metal bound to a protein spot has been demonstrated, and the technique has been applied in two exemplary cases. In the first, the speciation of the in vitro binding of exogenous chromium to blood serum proteins was influenced markedly by both the oxidation state of chromium exposed to the serum proteins and the treatment conditions, which is of relevance to the biochemistry of Cr dietary supplements. In the second case, in vivo changes in endogenous metal speciation were examined to probe the influence of oxygen depletion on iron speciation in Shewanella oneidensis.
ACS Chem Biol 2010 Jun 18
PMID:Imaging metals in proteins by combining electrophoresis with rapid x-ray fluorescence mapping. 2055 40

Isoprenoid compounds are ubiquitous in nature, participating in important biological phenomena such as signal transduction, aerobic cellular respiration, photosynthesis, insect communication, and many others. They are derived from the 5-carbon isoprenoid substrates isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP). In Archaea and Eukarya, these building blocks are synthesized via the mevalonate pathway. However, the genes required to convert mevalonate phosphate (MP) to IPP are missing in several species of Archaea. An enzyme with isopentenyl phosphate kinase (IPK) activity was recently discovered in Methanocaldococcus jannaschii (MJ), suggesting a departure from the classical sequence of converting MP to IPP. We have determined the high-resolution crystal structures of isopentenyl phosphate kinases in complex with both substrates and products from Thermoplasma acidophilum (THA), as well as the IPK from Methanothermobacter thermautotrophicus (MTH), by means of single-wavelength anomalous diffraction (SAD) and molecular replacement. A histidine residue (His50) in THA IPK makes a hydrogen bond with the terminal phosphates of IP and IPP, poising these molecules for phosphoryl transfer through an in-line geometry. Moreover, a lysine residue (Lys14) makes hydrogen bonds with nonbridging oxygen atoms at P(alpha) and P(gamma) and with the P(beta)-P(gamma) bridging oxygen atom in ATP. These interactions suggest a transition-state-stabilizing role for this residue. Lys14 is a part of a newly discovered "lysine triangle" catalytic motif in IPKs that also includes Lys5 and Lys205. Moreover, His50, Lys5, Lys14, and Lys205 are conserved in all IPKs and can therefore serve as fingerprints for identifying new homologues.
ACS Chem Biol 2010 May 21
PMID:X-ray structures of isopentenyl phosphate kinase. 2040 38


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