Facile synthesis : Pt nanosponges, nanonetworks, and nanodendrites (see figure) are synthesized through a unique galvanic replacement reaction between Te nanowires and PtCl62? ions in the presence of sodium dodecyl sulfate. The three Pt nanomaterials all have large active surface areas and highly electrocatalytic activities for the oxidation of methanol.
This study analyzes the varying electrophoretic mobility and zeta potential of bone marrow stromal cells (BMSCs) during their differentiation towards neurons. Electrophoresis of primary BMSCs and neuron growth factor (NGF)‐induced neuron‐like cells with the uptake of heparin‐functionalized poly(lactide‐co‐glycolide) (PLGA) nanoparticles (NPs) are also investigated. Immunofluorescent images revealed that a high concentration of NGF accelerated the differentiation of BMSCs into neurons. When the concentration of NGF increased, the absolute values of electrophoretic mobility and zeta potential of the differentiating BMSCs increased. In addition, a longer inductive period yielded higher charge of the differentiating BMSCs and a smaller uptake amount of heparin‐functionalized PLGA NPs. However, an increase in the loading efficiency of heparin on PLGA NPs enhanced the uptake and reduced the electrical characteristics of the primary and differentiating BMSCs. Hence, a general rule is drawn that an increase in the uptake of heparin‐functionalized PLGA NPs decreased the electrophoretic mobility and zeta potential of BMSCs during differentiation towards neurons. 相似文献
Human embryonic stem (ES) cells have far-reaching applications in the areas of tissue engineering, regenerative medicine, pharmacology and basic scientific research. Although the culture conditions can maintain the human ES cells in an undifferentiated state for a transient period, spontaneous differentiation has also been observed during the routine culturing of ES cells. However, the maintenance of ES cells in the undifferentiated, pluripotent state for extended periods of time will be required in many areas of scientific research. Cryopreservation is a technology with potentially far reaching implication for the development and widespread use of such cell lines. This study was undertaken to develop and optimize a protocol for cryopreservation of human ES cells through programmed cooling. The effects of the seeding temperature, the cooling rate and the sub-zero temperature to which the samples were cooled before plunging into liquid nitrogen(the terminal temperature), all significantly affected the recovery of cryopreserved ES cells. After studying these factors, an improved protocol was obtained: the sample was cooled from 0 degree C to -35 degree C at a cooling rate of 0.5 degree per min, with seeding was set at -10 degree C, before being plunged immediately into the liquid nitrogen. Using this protocol, 9 of 11 colony fragments survived freezing and thawing and could be cultured for prolonged periods. They retained the properties of pluripotent cells, had a normal karyotype and showed histochemical staining for alkaline phosphatase. 相似文献
In this article, we address in situ synthesis of polyethylene terephthalate (PET) nanocomposites using the bis (2‐hydroxyethyl) phthalate monomer and inorganic layered materials (sulfanilic acid salt‐modified magnesium aluminum‐layered double hydroxides [MgAl LDH‐SAS] and Dimethyloctadecyl [3‐(trimethoxysilyl) propyl] ammonium chloride [DTSACl] and tetraethyl orthosilicate [TEOS]‐ modified clay [CL120‐DT]). The dispersion morphology of the synthesized nanocomposites was evaluated using XRD and TEM, from these results, it was confirmed that 0.5 wt% loaded PET/MgAl LDH‐SAS and PET/CL120‐DT nanocomposites have flocculated and intercalated morphologies, respectively. Thermomechanical analyses were performed by thermogravimetric analysis, dynamic mechanical analysis, and differential scanning calorimetry, respectively. Moreover, the water vapor transmission rate (WVTR) values of a pure PET, PET/CL120‐DT 0.5 wt%, and PET/MgAl LDH‐SAS 0.5 wt% nanocomposites were found to be 49, 45, and 46 g·m?2·day?1, respectively. Furthermore, the gas barrier properties of PET composite films containing various amounts of inorganic nanoparticles were investigated using Gas permeability analysis (GPA). 相似文献
We present a new assay based on total internal reflection fluorescence (TIRF) to quantify the catalytic activity of adsorbed enzyme monolayers on macroscopically flat surfaces. The need for such an assay derives from a general shortage of assay methods that are sufficiently sensitive to measure reaction kinetics for just a single monolayer of enzymes. The assay is based on the enzymatic conversion of a soluble, nonfluorescent fluorogenic substrate reagent to a soluble, highly fluorescent product. The reaction occurs at the solid-liquid interface where the enzymes are adsorbed. Fluorogenic substrates are introduced to the adsorbed layer by convective diffusion from solutions undergoing steady laminar slit flow. The exponentially decaying evanescent wave that is produced by total internal reflection serves as a "spectroscopic ruler" to resolve the spatial concentration profile of fluorescent products in solution near the interface. By measuring the steady-state fluorescence signal as a function of the Peclet number that characterizes mass transfer conditions in the experiment, it is possible to determine the enzymatic reaction rate. Here we present the development of the method and its application to a test system of beta-galactosidase adsorbed to methylated silica surfaces. Compared to the enzymatic rate constants for this enzyme in free solution, adsorption decreased the Michaelis-Menten rate constant kcat by a factor of 10 and increased the equilibrium binding constant Km by a factor of 4.5. Thus the intrinsic activity of the enzyme, as represented by the ratio kcat/Km, decreased 45-fold due to adsorption. Copyright 1999 Academic Press. 相似文献
A three‐dimensional (3D) 3d‐4f complex, [Cu(en)2][Sm2(C5O5)(C2O4)3(H2O)2] · 8H2O ( 1 ) (en = ethylenediamine, C5O52– = dianion of 4,5‐dihydroxycyclopent‐4‐ene‐1,2,3‐trione), were prepared via the in‐situ ring‐opening oxidation reaction of croconate in the presence of the template‐directed complex, [Cu(en)2]2+ cation. The structural characterization determined by X‐ray diffraction determination reveals that the 3D anionic coordination polymer of [Sm2(C2O4)3(C5O5)(H2O)2]2– in 1 can be describe in terms of in‐plane 2D honeycomb‐like [Sm2(C2O4)3] layered frameworks bridged by oxalate with bis‐chelating mode, being mutually interlinked via the bridge of μ1,2,3,4‐croconate ligands with bis‐chelating coordination mode to complete the 3D open framework, which gives rise to 1D channels with pore size of 14.023 × 11.893 Å (longest atom–atom contact distances) along the b axis. The structure‐directing complex, [Cu(en)2]2+, and solvated water molecules are resided into these honeycomb‐type hexagonal channels. The thermal stability of 1 was further studied by TGA and in‐situ powder X‐ray diffraction measurement. 相似文献
Gold nanorods and bipyramids have been synthesized using the seed-mediated approach in aqueous cetyltriethylammonium bromide (CTEAB) solutions in the presence of silver nitrate. Gold nanoparticle seeds that are stabilized with either CTEAB or sodium citrate have been used. The use of the CTEAB-stabilized seeds gives gold nanorods in high yield in one step with the longitudinal plasmon wavelength ranging from 750 to 1030 nm, depending on the amount of the seeds. The longitudinal plasmon wavelength can be extended to 1100 nm by the use of a two-step growth method. The growth of gold nanorods in CTEAB solutions takes 5-10 h, more than 5 times slower than that in cetyltrimethylammonium bromide solutions at the same concentration of surfactants. The use of the citrate-stabilized seeds gives both gold bipyramids and a small percentage of gold nanorods. The longitudinal plasmon wavelength of the bipyramids is tunable from 700 to 1100 nm by varying the amount of the citrate-stabilized seeds. The growth of gold bipyramids takes more than 1 day. Transmission electron microscopy characterizations reveal that the gold nanorods grown from both types of gold nanoparticle seeds are single-crystalline and that the gold bipyramids are penta-twinned. 相似文献