Quantum interference in nanotube electron waveguides

We have calculated the quantum conductance of single-walled carbon nanotube (SWNT) waveguide by using a tight binding-based Greens function approach. Our calculations show that the slow conductance oscillations as well as the fast conductance oscillations are manifestations of the intrinsic quantum interference properties of the conducting SWNTs, being independent of the defect and disorder of the SWNTs. And zigzag type tubes do not show the slow oscillations. The SWNT electron waveguide is also found to have distinctly different transport behavior depending on whether or not the length of the tube is commensurate with a (3N+1) rule, with N the number of basic carbon repeat units along the nanotube length.     

Anisotropic metal nanoparticles: Synthesis, assembly, and optical applications

This feature article highlights work from the authors' laboratories on the synthesis, assembly, reactivity, and optical applications of metallic nanoparticles of nonspherical shape, especially nanorods. The synthesis is a seed-mediated growth procedure, in which metal salts are reduced initially with a strong reducing agent, in water, to produce approximately 4 nm seed particles. Subsequent reduction of more metal salt with a weak reducing agent, in the presence of structure-directing additives, leads to the controlled formation of nanorods of specified aspect ratio and can also yield other shapes of nanoparticles (stars, tetrapods, blocks, cubes, etc.). Variations in reaction conditions and crystallographic analysis of gold nanorods have led to insight into the growth mechanism of these materials. Assembly of nanorods can be driven by simple evaporation from solution or by rational design with molecular-scale connectors. Short nanorods appear to be more chemically reactive than long nanorods. Finally, optical applications in sensing and imaging, which take advantage of the visible light absorption and scattering properties of the nanorods, are discussed.     

Complexation of thorium(IV) with acetate at variable temperatures

The complexation between Th(IV) and acetate in 1.05 mol kg(-1) NaClO4 was studied at variable temperatures (10, 25, 40, 55 and 70 degrees C). The formation constants of five successive complexes, Th(Ac)j(4-j)+ where Ac = CH3COO- and j = 1-5, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. Extended X-ray absorption fine structure spectroscopy (EXAFS) provided additional information on the complexes in solution. The effect of temperature on the stability of the complexes is discussed in terms of the electrostatic model.     

Chemoselective and enantioselective transfer hydrogenation of β,β-disubstituted nitroalkenes catalyzed by a water-insoluble chiral diamine–rhodium complex in water

Asymmetric transfer hydrogenation of β,β-disubstituted nitroalkenes catalyzed by a chiral diamine–rhodium complex in combination with HCO₂Na–HCO₂H as a hydrogen source in water was successfully realized with high reactivity, excellent chemoselectivity and good enantioselectivity. The metal precursor and pH value of the aqueous solution have a large influence on the reactivity and chemoselectivity. The substituents on the benzene rings and the sulfonyl groups of TsDPEN have significant effects on the enantioselectivity. This catalytic asymmetric transformation is one of the most practical pathways to obtain optically active nitroalkanes.     

羟丙基-β-环糊精对1-羟基芘与牛血清白蛋白相互作用的影响

在模拟生理条件下,利用荧光光谱、圆二色光谱和紫外-可见吸收光谱探究了羟丙基-β-环糊精(HPCD)对1-羟基芘(1-OHPyr)与牛血清白蛋白(BSA)相互作用的影响及其相关机制.结果表明,291 K下HPCD可使1-OHPyr与BSA的结合常数降低为1.45×10~5L/mol;导致1-OHPyr-BSA体系中BSA的α-螺旋含量恢复,色氨酸(TRP)残基周围微环境的极性变化减弱;致使1-OHPyr及BSA的荧光寿命均延长,且二者的结合距离增大.初步研究结果表明,HPCD与1-OHPyr的包络作用是HPCD影响BSA与1-OHPyr结合的主要原因.     

Highly hydrated poly(allylamine)/silica magnetic resin

The creation of multifunctional nanomaterials by combining organic and inorganic components is a growing trend in nanoscience. The unique size-dependent properties of magnetic nanoparticles (MNPs) make them amenable to numerous applications such as carriers of expensive biological catalysts, in magnetically assisted chemical separation of heavy metals and radionuclides from contaminated water sources. The separation of minor actinides from high-level radionuclide waste requires a sorbent stable in acidic pH, with ease of surface functionalization, and a high capacity for binding the molecules of interest. For the described experiments, the MNPs with 50 nm average size were used (size distribution from 20 to 100 nm and an iron content of 80–90 w/w%). The MNPs that have been double coated with an initial silica coating for protection against iron solubilization and oxidation in nitric acid solution (pH 1) and a second silica/polymer composite coating incorporating partially imbedded poly(allylamine) (PA). The final product is magnetic, highly swelling, containing >95% water, with >0.5 mmol amines g^?1 available for functionalization. The amine groups of the magnetic resin were functionalized with the chelating molecules diethylenetriaminepentaacetic acid (DTPA) and N,N-dimethyl-3-oxa-glutaramic acid (DMOGA) for separation of minor actinides from used nuclear fuel.     

Three‐Arm Branched Microporous Organic Nanotube Networks

Here, a novel method is demonstrated for the preparation of three‐arm branched microporous organic nanotube networks (TAB‐MONNs) based on molecular templating of three‐arm branched core–shell bottlebrush copolymers and Friedel–Crafts alkylation reaction. The unique three‐arm branched bottlebrush copolymers are synthesized by a combination of atom transfer radical polymerization, reversible addition‐fragmentation chain transfer polymerization, and ring‐opening polymerization techniques. In this approach, the length and diameter of branched tube units can be well‐controlled by rational molecular design. Moreover, the as‐prepared TAB‐MONNs possess a high surface area and exhibit a superior adsorption capacity for Rhodamine 6G (R6G) and p‐cresol.

     

Trace analysis of uranyl ion (UO2) in aqueous solution by fluorescence turn-on detection via aggregation induced emission enhancement effect

A sensitive fluorescence turn-on method for trace amounts of uranyl ion (UO₂²⁺) in solution has been developed in this study, based on aggregation induced emission enhancement (AIEE) characteristics of 4-pethoxycarboxyl salicylaldehyde azine (PCSA) induced by complex interaction between UO₂²⁺ and PCSA. Under optimized conditions, a fluorescence enhancement at 540 nm could be observed, which was linearly related to the concentration of UO₂²⁺ in the range of 1–25 ppb (part per billion). Analytical data showed that a detection limit of 0.2 ppb was achieved with the relative standard deviation (R.S.D.) 1.3% (n = 5). The proposed method was successfully utilized in quantifying UO₂²⁺ in fuel processing wastewaters.     

Guiding, distribution, and storage of trains of shape-dependent droplets

We present a simple method of guiding, distributing, and storing of a train of shape-dependent droplets by using side flows, cavity guiding tracks, and storage chambers. The squeezing flow makes a train of flattened droplets to align to one side of the wall and the pushing flow guides it to one of the designated guiding tracks. Then the guided droplets move along the guiding track due to the lowered surface energy when they flow along the track. In addition, simultaneous droplet guiding and storing process has been demonstrated. An array of storage chambers placed in each track could store each train containing differently concentrated droplets. The proposed method will be useful for distribution of droplets for further processes or storing for multiplex, large-scale, dynamic assays over time.     

Measurements of pressure induced self-broadening and frequency shift coefficients of methane R9 manifold of 2v3 band

An external-cavity diode laser (ECDL) has been used to investigate pressure-induced self-broadening as well as frequency shift of 2v3 band R9 manifold of methane. A phase sensitivity detection technology has been employed to determine the pressure induced frequency shift coefficient, however, which is obtained by line shape analyses of the recorded absorption spectrum. F1 and F2 unresolved double lines near 6105.626 cm-1 were measured as an object because they are often used to the high sensitivity detection of trace methane. The results show that the self-broadening and pressure induced frequency shift coefficients are 0.0232±0.003 and 0.0055±0.0007 MHz/Pa, respectively.