Size-controlled syntheses and hydrophilic surface modification of Fe3O4, Ag, and Fe3O4/Ag heterodimer nanocrystals

High-quality, monodisperse, and size-controlled Fe(3)O(4), Ag, and bifunctional Fe(3)O(4)/Ag heterodimer nanocrystals (NCs) have been synthesized successfully. In the synthesis of Fe(3)O(4) NCs, dodecanol was chosen as the substitute of 1,2-hexadecanediol and "size control" was achieved by simply adjusting the proportion among the ligands instead of utilizing seed-mediated growth. In the synthesis of Ag NCs, organometallic silver acetylacetonate (Agacac) was used as precursors and tunable particle size could be easily obtained by adjusting the reaction temperatures. By using different sized Fe(3)O(4) NCs as seeds, Fe(3)O(4)/Ag heterodimer NCs with particle sizes tuned from 5 to 16 nm for Fe(3)O(4) and 4 to 8 nm for Ag were successfully synthesized and superparamagnetism were maintained. We found that the size of Ag attached on the Fe(3)O(4) NCs relied on the size of Fe(3)O(4) seed. UV-vis absorption spectra and TEM investigations revealed that the bigger the Fe(3)O(4) NCs seed used, the bigger the Ag NCs that were obtained from the heterodimer NCs. In addition, we demonstrated that all of these NCs were successfully transferred into water by surface modification with biocompatible carboxylic acid groups, which made them meet the basic requirement for biolabeling and biomedical applications.     

Electronic and magnetic properties of copper-family-element atom adsorbed graphene nanoribbons with zigzag edges

We have investigated the electronic and magnetic properties of copper-family-element (CFE) atom adsorbed graphene nanoribbons (GNRs) with zigzag edges using first-principles calculations based on density functional theory. We found that CFE atoms energetically prefer to be adsorbed at the edges of nanoribbons. Charges are transferred between the CFE atom and carbon atoms at the edge, which reduce the local magnetic moment of carbon atoms in the vicinity of adsorption site and change the electronic structure of GNRs. As a result, Cu adsorbed zigzag GNR is a semiconductor with energy band gap of 0.88 eV in beta-spin and energy gap of 0.22 eV in alpha-spin, while Ag adsorbed zigzag GNR and Au adsorbed zigzag GNR are both half-metallic with the energy gaps of 0.68 eV and 0.63 eV in beta-spin, respectively. These results show that CFE atom adsorbed zigzag GNRs can be applied in nanoelectronics and spintronics.     

Metal-binding properties of an Hpn-like histidine-rich protein

The Hpn-like protein (Hpnl), a histidine- and glutamine-rich protein, is critical for Helicobacter pylori colonization in human gastric muscosa. In this study, the thermodynamic properties of Ni(II), Cu(II), Co(II), and Zn(II) toward Hpnl were studied by isothermal titration calorimetry (ITC). We found that Hpnl exhibits two independent binding sites for Ni(II) as opposed to one site for Cu(II), Co(II), and Zn(II). Protease digestion and chemical denaturation analysis further revealed that Ni(II) confers a higher stability upon Hpnl than other divalent metal ions. The potential Ni(II) binding sites are localized in the His-rich domain of Hpnl as confirmed by mutagenesis in combination with modification of histidine residues of the protein. We also demonstrated that the single mutants (H29A and H31A) and tetrameric mutant (H29-32A) cut nearly half of the binding capacity of Hpnl towards nickel ions, whereas other histidine residues (His30, 32, 38, 39, 40, and 41) are nonessential for nickel coordination. Escherichia coli cells that harbored H29A, H31A, and H29-32A mutant genes exhibited less tolerance toward high concentrations of extracellular nickel ions than those with the wild-type gene. Our combined data indicated that the conserved histidine residues, His29 and His31 in the His-rich domain of Hpnl, are critical for nickel binding, and such a binding is important for Hpnl protein to fulfill its biological functions.     

A new fractional equivalent linearization method for nonlinear stochastic dynamic analysis

Nonlinear Dynamics - In this paper, a novel fractional equivalent linearization (NFEL) approach is developed by introducing fractional derivative term into the conventional equivalent linear...     

结构可靠性分析高效自适应重要抽样方法

提出了一种基于自适应Metropolis算法和快速高斯变换技术的结构可靠性分析高效自适应重要抽样方法. 该方法首先利用自适应Metropolis算法高效生成结构失效域样本, 然后运用自适应宽核密度估计方法构造重要抽样密度函数, 最后采用快速高斯变换加速重要抽样过程中核函数的计算. 与传统方法相比, 自适应Metropolis算法能够在相同计算量下提供更多结构失效域信息从而改善计算精度, 即为求得给定精度问题的解, 可有效减少样本生成过程中的结构分析次数, 提高方法的计算效率; 快速高斯(Gauss)变换大幅降低核密度估计的计算复杂度从而大幅缩减重要抽样的计算耗时. 通过数值算例可以看出该方法具有较高的计算精度和效率.      

Synthesis,characterization, and photocatalytic properties of Ni<Subscript>12</Subscript>P<Subscript>5</Subscript> hollow microspheres

Ni₁₂P₅ hollow microspheres were prepared by a simple mixed cetyltrimethyl ammonium bromide/sodium dodecyl sulfate surfactant-assisted hydrothermal route. The as-prepared Ni₁₂P₅ microstructures were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). It was interesting to find that cetyltrimethyl ammonium bromide/sodium dodecyl sulfate could form a micro-reactor by the mixed micelles in the aqueous solution, which served as a soft template for Ni₁₂P₅ hollow microspheres with a diameter of 2~6 μm. Moreover, the as-prepared Ni₁₂P₅ hollow microspheres exhibited a good photocatalytic degradation activity for some organic dyes (such as Rhodamine B, Methylene Blue, Pyronine B, and Safranine T), and the degradation ratio could achieve more than 80%.     

Co/CNF catalysts tailored by controlling the deposition of metal colloids onto CNFs: preparation and catalytic properties

Carbon nanofiber-supported Co nanocomposites were prepared by means of a modified ethylene glycol (EG) process, in which the Co salts are reduced in EG and are subsequently deposited onto carbon nanofibers (CNFs). It has been found that the deposition of cobalt colloids onto CNFs can be tailored by simply adjusting the pH of the EG and by heating the mixture of CNFs and colloidal solution at 100 degrees C for some time. The pH value (<7) and the temperature (at least 100 degrees C) for heating the mixture of CNFs and colloidal solution are found to be the key factors for depositing Co particles onto CNFs. The obtained Co/CNFs have a high and homogeneous dispersion of spherical Co metal particles with a narrow size distribution of 10-15 nm with a peak around 13.5 nm; this result is consistent, to a certain degree, with the value of 12.8 nm obtained from the XRD study. The different states of the stabilizer including carboxylates (pH>7) and carboxylic acids (pH<7) as well as the decomposition of carboxylic acids during heat treatment were monitored by using FTIR and UV-visible spectroscopy. On the basis of experimental results, the mechanism of depositing cobalt colloids onto CNFs is also addressed. The as-synthesized Co/CNF catalysts show excellent activity and regioselectivity for the 1-octene hydroformylation.     

Phase Behavior of Aqueous Biphasic Systems with Choline Alkanoate Ionic Liquids and Phosphate Solutions: The Influence of pH

Aqueous biphasic systems (ABS) composed of the choline alkanoate ionic liquids (ILs) choline acetate [Cho][OAc], choline propanoate [Cho][Pro], choline butyrate [Cho][But], and choline hexanoate [Cho][Hex], mixed with K₃PO₄ solutions at pH 7.2 and 14.5, were prepared and their phase diagrams were compared. The ability to form ABS with alkaline K₃PO₄ solutions decreased in the order [Cho][OAc] ≈ [Cho][Pro] > [Cho][But] > [Cho][Hex], while with neutral K₃PO₄ solutions, [Cho][OAc] could not form an ABS, and the other three ILs performed similarly. All of the biphasic regions of the ABS decreased with the increase in pH. ¹H-NMR data indicated anion exchange between phases in ABS at neutral pH. The ABS at neutral pH were evaluated to extract the triazine herbicides simazine, cyanazine, and atrazine, and the ABS formed by [Cho][Pro] and the pH 7.2 K₃PO₄ solution has shown extraction recoveries higher than 90%.     

Interactions between bromophenol blue and cetyl- trimethylammonium bromide in aqueous solutions and microemulsions

The UV-Vis light absorption spectroscopy of bromophenol blue (BPB) in a series of cetyltrimethylammonium bromide (CTAB) aqueous solutions and microemulsions has been determined. There exist association interactions between the BPB and cationic surfactant CTAB. By establishing the appropriate association models and measuring the absorbance in different concentrations of BPB aqueous solutions and microemulsions that have different R values, the association constants K were obtained and the values of thermodynamics functions of association Δ_rG_m were calculated. It shows that the formation of microemulsion has inhibitory effects on the association reaction.