Facile synthesis of silver chalcogenide (Ag2E; E=Se, S, Te) semiconductor nanocrystals

A general, one-pot, single-step method for producing colloidal silver chalcogenide (Ag(2)E; E = Se, S, Te) nanocrystals is presented, with an emphasis on Ag(2)Se. The method avoids exotic chemicals, high temperatures, and high pressures and requires only a few minutes of reaction time. While Ag(2)S and Ag(2)Te are formed in their low-temperature monoclinic phases, Ag(2)Se is obtained in a metastable tetragonal phase not observed in the bulk.     

High-quality manganese-doped zinc sulfide quantum rods with tunable dual-color and multiphoton emissions

We report a simple, fast and green phosphine-free colloidal chemistry to synthesize high-quality wurtzite-type Mn-doped ZnS quantum rods (QRs) with tunable diameters (1.6-5.6 nm), high aspect ratios (up to 50), variable Mn doping levels (0.18-1.60%), and high quantum yields (up to 45%). The electron paramagnetic resonance spectra with modeling reveal the successful doping of paramagnetic Mn(2+) ions in the host ZnS QRs. The Mn-doped ZnS QRs demonstrate tunable dual-color (orange and blue) emissions by tuning the doping levels and UV excitation wavelengths. The orange emission with long decay lifetime (3.3 ms) originates from the doped Mn(2+) states, while the blue emission with fast decay lifetime (0.31 ns) is attributed to the QR surface states. The bright two- and three-photon excitation upconversion luminescence from the Mn-doped ZnS QRs have been observed using tunable near-infrared femtosecond laser. Our strategy provides a versatile route to programmably control the optical properties of anisotropic semiconductor nanomaterials, which may create new opportunities for photonic devices and bioimaging applications.     

The role of spontaneous polarization in the negative thermal expansion of tetragonal PbTiO3-based compounds

PbTiO(3)-based compounds are well-known ferroelectrics that exhibit a negative thermal expansion more or less in the tetragonal phase. The mechanism of negative thermal expansion has been studied by high-temperature neutron powder diffraction performed on two representative compounds, 0.7PbTiO(3)-0.3BiFeO(3) and 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3), whose negative thermal expansion is contrarily enhanced and weakened, respectively. With increasing temperature up to the Curie temperature, the spontaneous polarization displacement of Pb/Bi (δz(Pb/Bi)) is weakened in 0.7PbTiO(3)-0.3BiFeO(3) but well-maintained in 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3). There is an apparent correlation between tetragonality (c/a) and spontaneous polarization. Direct experimental evidence indicates that the spontaneous polarization originating from Pb/Bi-O hybridization is strongly associated with the negative thermal expansion. This mechanism can be used as a guide for the future design of negative thermal expansion of phase-transforming oxides.     

Surface-initiated DNA self-assembly as an enzyme-free and nanoparticle-free strategy towards signal amplification of an electrochemical DNA sensor

Surface-initiated DNA polymerization has been employed in this work as an appealing signal amplification strategy for electrochemical DNA sensors. This strategy is especially superior in that enzymes, colloidal particles and other bulky structures are not involved in order to achieve amplified signals, and thus is highly promising in circumventing problems due to uncontrolled nucleation, adsorption, aggregation or disassembly of nanoparticles, liposomes and proteins, as well as enzyme deactivations. Our preliminary results have shown that a decrease (as compared to an amplification-free system) in detection limit by a factor greater than 300 can be easily achieved by cyclic voltammetry under still not optimized conditions, with an ability of differentiating a single base mutation.     

Convenient Synthesis of 3,5‐Biscarbamoyl‐pyridine Derivatives

An efficient and convenient method for synthesis of 3,5‐bis‐carbamoyl‐2,6‐dimethylpyridine derivatives was achieved in good to excellent yields by reaction of anilines with 3,5‐bis(3′,5′‐dimethyl‐1′‐pyrazolyl‐carbonyl)‐2,6‐dimethylpyridine, in which pyrazoles served as leaving groups. The structures of products were confirmed by spectra data and microanalysis.     

耐辐照玻璃成分分析标准物质的研制

采用高温熔融方法制备了玻璃成分分析标准物质.对标准物质的制备技术、均匀性检验、稳定性考察及定值不确定度进行了分析.研制的耐辐照成分分析标准物质具有良好的均匀性和稳定性,各组分不确定度均小于5％.     

A novel ion‐imprinted hydrogel for recognition of potassium ions with rapid response

A novel ion‐imprinted strategy is developed for synthesizing responsive hydrogels with rapid response to potassium ions. With potassium ions as templates, ion‐imprinted poly(N‐isopropylacrylamide‐co‐benzo‐15‐crown‐5‐acrylamide) (P(NIPAM‐co‐B15C5Am)) hydrogels are synthesized with 15‐crown‐5 crown ethers mounted on the polymer networks in pairs; therefore, it is very easy and fast for the crown ethers to capture potassium ions again by their Venus flytrap action and form stable 2:1 “host–guest” complexes with potassium ions in the ion‐recognition process. As a result, the response rate of the ion‐imprinted hydrogels to potassium ions is significantly faster than that of normal P(NIPAM‐co‐B15C5Am) hydrogels in which 15‐crown‐5 crown ethers are randomly pendent on the polymeric networks. Copyright © 2010 John Wiley & Sons, Ltd.     

Structure and wettability relationship of coelectrospun poly (L‐lactic acid)/gelatin composite fibrous mats

Coelectrospun polylactide(PLA)/gelatin (GE) composite fibrous matrixes have been identified to exhibit much improved performances compared to the respective components; however, the reasons for their water contact angles decreasing to zero at proper PLA/GE ratios remain unclear. To get a deep understanding of the phenomenon, PLA and GE were coelectrospun with different PLA/GE ratios in this study. Although the resulting composite fibers were homogeneous in appearance, they were detected different microscopic structures by transmission electron mircroscope (TEM) and via morphological observations after selective removal of either PLA or GE component. Together with the results of degradation study in phosphate buffered solution, a kind of cocontinuous phase separation microstructure could be identified for the PLA(50 wt%)/GE(50 wt%) composite fibers, which also showed the water contact angle of 0°. This value was far lower than those of electrospun PLA (～123°) and GE (～42°) fibrous matrixes. The X‐ray photoelectron spectrometry (XPS) data revealed that the polar side groups of protein macromolecules have moved toward composite fiber surface with solvent evaporation during electrospinning, due to the hydrophobic interaction between PLA and GE. Then the excellent hydrophilicity of PLA(50 wt%)/GE(50 wt%) composite fibers could be suggested as the consequence of: (1) the cocontinuous phase separation structure could provide more interface and void for water molecules penetrating; and (2) the accumulation of polar groups on composite fiber surface significantly increased the surface wettability. Copyright © 2010 John Wiley & Sons, Ltd.     

Dual carbamoylations on the polyketide and glycosyl moiety by asm21 result in extended ansamitocin biosynthesis

Carbamoylation is one of the post-PKS modifications in ansamitocin biosynthesis. A novel ansamitocinoside with carbamoyl substitution at the C-4 hydroxyl group of the N-β-D-glucosyl moiety was identified from the ansamitocin producer, Actinosynnema pretiosum. Through biotransformation, the carbamoyltransferase gene asm21 was suggested to be responsible for the carbamoylation of the glucosyl moiety. Three new derivatives without the backbone carbamoyl group were isolated from an asm21 mutant and characterized by NMR spectroscopy. Among them, 18-O-methyl-19-chloroproansamitocin was the major product and the preferred substrate for macrolactam C-7 carbamoylation by Asm21. However, Asm21 exhibited higher catalytic efficiency toward the glucosyl moiety. Furthermore, the dual carbamoylations and N-glycosylation were precisely demonstrated in vivo. This work represents the first biochemical characterization of an O-carbamoyltransferase performing dual actions on both a polyketide backbone and a glycosyl moiety during ansamitocin biosynthesis.