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501.
Far-field near-infrared fluorescence microscopy of single-walled carbon nanotubes (SWNTs) has been hampered by the diffraction limit to resolution. A new analysis method is presented that allows subwavelength (相似文献
502.
Gold nanoparticles were recently reported to reduce the formation of nonspecific products in polymerase chain reaction (PCR) at remarkably low temperatures, with hypothesized mechanisms including adsorption of DNA and heat-transfer enhancement. In contrast to these reports, we report that gold nanoparticles do not enhance the specificity of PCR but rather suppress the amplification of longer products while favoring amplification of shorter products, independent of specificity. Gold nanoparticles bearing a self-assembled monolayer of hexadecanethiol did not affect PCR, suggesting that surface interactions play an essential role. This role was further confirmed by experiments in which a similar effect on PCR was observed for the same total surface area of particles over a 100-fold range of per-particle surface area. The effect was seen with Taq and Tfl polymerases but not with Vent polymerase, and the effects of nanoparticles can be reversed by increasing the polymerase concentration or by adding bovine serum albumin (BSA). Transient high-temperature nanoparticle pre-exposure of PCR mix containing polymerase but not template or primers, followed by nanoparticle removal, modified subsequent nanoparticle-free PCR. Interaction between polymerase and gold nanoparticles was confirmed by changes in nanoparticle absorption spectrum and electrophoretic mobility in the presence of polymerase. Taken together, these results suggest that the nanoparticles nonspecifically adsorb polymerase, thus effectively reducing polymerase concentration. 相似文献
503.
Effect of Ce and La on microstructure and properties of a 6xxx series type aluminum alloy 总被引:1,自引:0,他引:1
The increase in iron content in secondary sources of aluminum has led to an increase in the amount of Fe-bearing intermetallic
phases in Al alloys. One of these intermetallics, β-AlFeSi, which is seen as the dominant phase in 6xxx series alloys, reduces
bendability of wrought alloys, which in turn, limits their usage in the automotive industry. It is known that small additions
of Sr prevent the formation of the β phase and facilitate the precipitation of a less detrimental intermetallic, α-AlFeSi,
in as-cast alloys. It is worth investigating whether other elements cause a similar effect. Cerium and lanthanum as the least
expensive representatives of rare-earth metals are tried as such elements. It is found that in alloys containing 0.1–0.2 wt.%
of lanthanum, the fraction of β particles is pronouncedly less than that in the reference alloy. In addition to this advantage,
much smaller grains are seen in the alloy with 0.2 wt.% La. Despite similarities between La and Ce, the latter metal neither
modifies the microstructure nor noticeably affects the grain size. Moderate thermo-mechanical processing nullifies the beneficial
effect of small La additions resulting in no improvement in the bendability of the alloy.
相似文献
Mehdi HosseinifarEmail: |
504.
Thermal conductivity of a crystalline solid at high temperature is dominated by the Umklapp process because the number of high frequency phonons increases with temperature. It is challenging to reduce the thermal conductivity of crystalline solids at high temperature although it is widely known that, by increasing the atomic defect concentration, thermal conductivity of crystalline solids can be reduced at low temperature. By increasing the concentration of ErAs nanoparticles in In 0.53Ga 0.47As up to 6 atom %, we demonstrate a thermal conductivity reduction by almost a factor of 3 below that of In 0.53Ga 0.47As at high temperature. A theoretical model suggests that the mean free path of the low frequency phonons is suppressed by increasing the ErAs nanoparticle concentration. 相似文献
505.
506.
Becker K Lupton JM Müller J Rogach AL Talapin DV Weller H Feldmann J 《Nature materials》2006,5(10):777-781
Bringing together compounds of intrinsically different functionality, such as inorganic nanostructures and organic molecules, constitutes a particularly powerful route to creating novel functional devices with synergetic properties found in neither of the constituents. We introduce nanophotonic functional elements combining two classes of materials, semiconductor nanocrystals and dyes, whose physical nature arises as a superposition of the properties of the individual components. The strongly absorbing rod-like nanocrystals focus the incident radiation by photopumping the weakly absorbing dye via energy transfer. The CdSe/CdS nanorods exhibit a large quantum-confined Stark effect on the single-particle level, which enables direct control of the spectral resonance between donor and acceptor required for nanoscopic F?rster-type energy transfer in single nanorod-dye couples. With this far-field manipulation of a near-field phenomenon, the emission from single dye molecules can be controlled electrically. We propose that this effect could lead to the design of single-molecule optoelectronic switches providing building blocks for more complex nanophotonic circuitry. 相似文献
507.
Rounding Out the Understanding of ACD Toxicity with the Discovery of Cyclic Forms of Actin Oligomers
Harper Smith Nick Pinkerton David B. Heisler Elena Kudryashova Aaron R. Hall Kelly R. Karch Andrew Norris Vicki Wysocki Marcos Sotomayor Emil Reisler Dimitrios Vavylonis Dmitri S. Kudryashov 《International journal of molecular sciences》2021,22(2)
Actin is an essential element of both innate and adaptive immune systems and can aid in motility and translocation of bacterial pathogens, making it an attractive target for bacterial toxins. Pathogenic Vibrio and Aeromonas genera deliver actin cross-linking domain (ACD) toxin into the cytoplasm of the host cell to poison actin regulation and promptly induce cell rounding. At early stages of toxicity, ACD covalently cross-links actin monomers into oligomers (AOs) that bind through multivalent interactions and potently inhibit several families of actin assembly proteins. At advanced toxicity stages, we found that the terminal protomers of linear AOs can get linked together by ACD to produce cyclic AOs. When tested against formins and Ena/VASP, linear and cyclic AOs exhibit similar inhibitory potential, which for the cyclic AOs is reduced in the presence of profilin. In coarse-grained molecular dynamics simulations, profilin and WH2-motif binding sites on actin subunits remain exposed in modeled AOs of both geometries. We speculate, therefore, that the reduced toxicity of cyclic AOs is due to their reduced configurational entropy. A characteristic feature of cyclic AOs is that, in contrast to the linear forms, they cannot be straightened to form filaments (e.g., through stabilization by cofilin), which makes them less susceptible to neutralization by the host cell. 相似文献
508.
Formic acid and formates are often produced by hydrogenation of CO2 with hydrogen over homogeneous catalysts. The present review reports recent achievements in utilization of heterogeneous catalysts. It shows that highly dispersed supported metal catalysts are able to carry out this reaction by providing activation of hydrogen on the metal sites and activation of CO2 or bicarbonate on the support sites. Important advances have recently been achieved through utilization of catalysts using CxNy materials as supports. The high activity of these catalysts could be assigned to their ability to stabilize the active metal in a state of single-metal atoms or heterogenized metal complexes, which may demonstrate a higher activity than metal atoms on the surface of metal nanoparticles. 相似文献
509.
Dmitri Sharifulin Dr. Elena Babaylova Dr. Olga Kossinova Dr. Yulia Bartuli Dr. Dmitri Graifer Prof. Galina Karpova 《Chembiochem : a European journal of chemical biology》2013,14(16):2136-2143
A key step of translation initiation in eukaryotes is formation of the 48S preinitiation complex (PIC) containing the 40S ribosome, a set of eukaryotic initiation factors (eIFs), mRNA, and initiator Met‐tRNA interacting with mRNA start codon; however, the PIC structure remains substantially unknown. Here, we apply formaldehyde‐induced protein–protein crosslinks to identify contacts between ribosomal protein S5e (rpS5e, “e” stands for “eukaryotic”) and eIFs within the mammalian PIC, assembled on either model canonical or IRES‐containing mRNA. Using immunoblotting and mass spectrometry, we show that with both types of mRNA, rpS5e crosslinks to eIF2α. Comparative analysis of peptides resulting from trypsinolysis of the crosslinked proteins before and after crosslink reversal reveals crosslinked peptides in the N‐terminal parts of rpS5e and eIF2α. Application of these data to a model PIC structure obtained with the use of available structures indicates that eIF2α undergoes major conformation rearrangements to enable contacts of the factor with rpS5e. These contacts are suggested to maintain the correct positioning of eIF2α relative to other PIC components; this could be essential for start‐codon selection by the PIC. 相似文献
510.
Transient kinetics in the toluene oxidation over V/Ti oxide catalysts prepared by grafting and impregnation have been compared. V4+ cations are supposed to be the sites for the formation of electrophilic oxygen species participating in deep oxidation. Another oxygen species (probably nucleophilic) present on the oxidised catalyst surface are responsible for benzaldehyde formation. Selectivity of 80–100% can be obtained during the initial period of the reaction on the grafted catalysts in the presence of gaseous oxygen and during the interaction of toluene (without O2 in the mixture) with partially reduced catalysts. 相似文献