Copper(I)-Catalyzed Aryl Bromides To Form Intermolecular and Intramolecular Carbon-Oxygen Bonds

A highly efficient Cu-catalyzed C-O bond-forming reaction of alcohol and aryl bromides has been developed. This transformation was realized through the use of copper(I) iodide as a catalyst, 8-hydroxyquinoline as a ligand, and K3PO4 as a base. A variety of functionalized substrates were found to react under these reaction conditions to provide products in good to excellent yields.

Implantation of Nafion (R) ionomer into polyvinyl alcohol/chitosan composites to form novel proton-conducting membranes for direct methanol fuel cells

A series of cost-effective, proton-conducting composite membranes, comprising of Nafion (R) ionomer, chitosan (CS). and polyvinyl alcohol (PVA), is successfully prepared. By taking advantage of the strong electrostatic interactions between Nafion (R) ionomer and CS component, Nafion ionomer is effectively implanted into the PVA/CS composite membranes, and improves proton conductivity of the PVA/CS composite membranes. Furthermore, this effect dramatically depends on the composition ratio of PVA/CS, and the optimum conductivity is obtained at the PVA/CS ratio of 1:1. The developed composite membranes exhibit much lower methanol permeability compared with the widely used Nafion (R) membrane, indicating that these novel membranes have great potential for direct methanol fuel cells (DMFCs).

Enhanced crystallization of the gamma-form of propylene-ethylene copolymer in its miscible blends with propylene homopolymer

BACKGROUND: How to promote the formation of the gamma-form in a certain propylene-ethylene copolymer (PPR) under atmospheric conditions is significant for theoretical considerations and practical applications. Taking the epitaxial relationship between the alpha-form and gamma-form into account, it is expected that incorporation of some extrinsic alpha-crystals, developed by propylene homopolymer (PPH), can enhance the crystallization of the gamma-form of the PPR component in PPR/PPH blends.RESULTS: The PPH component in the blends first crystallizes from the melt, and its melting point and crystal growth rate decrease with increasing PPR fraction. On the other hand, first-formed alpha-crystals of the PPH component can induce the lateral growth of PPR chains on themselves, indicated by sheaf-like crystal morphology and positive birefringence, which is in turn responsible for enhanced crystallization of the gamma-form of the PPR component.

Effect of the gamma-form crystal on the thermal fractionation of poly(propylene-co-ethylene)

The effect of the gamma-form crystal on the thermal fractionation of a commercial poly(propylene-co-ethylene) (PPE) has been studied by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) techniques. Two thermal fractionation techniques, stepwise isothermal crystallization (SIC) and successive self-nucleation and annealing (SSA), have been used to characterize the molecular heterogeneity of the PPE. The results indicate that the SSA technique possesses a stronger fractionation ability than that of the SIC technique. The heating scan of the SSA fractionated sample exhibits 12 endothermic peaks, whereas the scan of the SIC fractionated sample only shows eight melting peaks. The WAXD observations of the fractionated PPE samples prove that the content of the gamma-form crystals formed during the thermal treatment of the SIC technique is much higher than that of the SSA treatment. The former is 57.4%, whereas the later is 12.6%. The effect of they-form crystals on thermal fractionation ability is discussed.

In situ circular dichroic electrochemical study of bilirubin and bovine serum albumin complex

The electrooxidation of bilirubin (BR) and bovine serum albumin (BSA) complexes was studied by in situ circular dichroism (CD) spectroelectrochemistry. The result showed that the mechanism of the whole electrooxidation process of this complex corresponded to electrochemical processes (EE mechanism) in aqueous solution. Some parameters of the process were obtained by double logarithm method, differential method and nonlinear regression method. In visible region, CD spectra of the two enantiomeric components of the complex and their fraction distribution against applied potentials were obtained by singular value decomposition least-square (SVDLS) method. Meanwhile, the distribution of the five components of secondary structure was also obtained by the same method in far-UV region. The peak potential gotten from EE mechanism corresponds to a turning point for the component transition, beyond which the whole reaction reaches a new equilibrium. Under applied positive potentials, the enantiomeric equilibrium between M and P form is broken and M form transfers to its enantiomer of P, while the fraction of alpha-helix increases and that improves the transition to P form.

Pt nanoparticles: Heat treatment-based preparation and Ru(bpy)(3)(2+)-mediated formation of aggregates that can form stable films on bare solid electrode surfaces for solid-state electrochemiluminescence detection

A simple thermal process for the preparation of small Pt nanoparticles is presented, carried out by heating a H-2-PtCl6/3- thiophenemalonic acid aqueous solution. The following treatment of such colloidal Pt solution with Ru( bpy)(3)(2+) causes the assembly of Pt nanoparticles into aggregates. Most importantly, directly placing such aggregates on bare solid electrode surfaces can produce very stable films exhibiting excellent electrochemiluminescence behaviors.

Reversible B/Z-DNA transition under the low salt condition and non-B-form polydApolydT selectivity by a cubane-like europium-L-aspartic acid complex

We report here that a cubane-like europium-L-aspartic acid complex at physiological pH can discriminate between DNA structures as judged by the comparison of thermal denaturation, binding stoichiometry, temperature-dependent fluorescence enhancement, and circular dichroism and gel electrophoresis studies. This complex can selectively stabilize non-B-form DNA polydApolydT but destabilize polydGdCpolydGdC and polydAdTpolydAdT. Further studies show that this complex can convert B-form polydGdCpolydGdC to Z-form under the low salt condition at physiological temperature 37 degrees C, and the transition is reversible, similar to RNA polymerase, which turns unwound DNA into Z-DNA and converts it back to B-DNA after transcription. The potential uses of a left-handed helix-selective probe in biology are obvious. Z-DNA is a transient structure and does not exist as a stable feature of the double helix. Therefore, probing this transient structure with a metal-amino acid complex under the low salt condition at physiological temperature would provide insights into their transitions in vivo and are of great interest.

How to form regular polymer microstructures by surface-pattern-directed dewetting

The substrates with regular patterns of self-assembly monolayers (SAMs) produced by microcontact printing with octadecyltrichlorosilane (OTS) was employed to direct thin polystyrene dewetting to fabricate ordered micrometer scale pattern. The pattern sizes and pattern fashion can be manipulated by controlling the experimental parameters. The pattern formation mechanisms have been discussed. The dewetting pattern can be transferred to form PDMS stamp for future microfabrication process.

Direct formation of form I poly(1-butene) single crystals from melt crystallization in ultrathin films

The morphologies and crystalline structures of melt-crystallized ultrathin isotactic poly(1-butene) films have been studied with transmission electron microscopy and electron diffraction. It is demonstrated that a bypass of form II crystallization can be achieved with an increase in its crystallization temperature. Electron microscopy observations show that melt-grown isotactic poly(1-butene) single crystals have a well-shaped hexagonal form, whereas form I crystals converted from form II display the morphologies of their tetragonal precursors. Electron diffraction results indicate that, instead of the twinned hexagonal pattern of the converted form I crystal, the directly formed form I single crystals exhibit an untwinned hexagonal pattern.

Synthesis and crystal structure of the dimeric, Ti-O-Ti bridged hydrid form polyoxoanion [alpha-1, 2-PW10Ti2O39](2)(10-)

The reaction of trivacant precursor Nag [A-PW9O34] . 19H(2)O with Ti(SO4)(2) affords the novel dimeric, di-Ti-IV-substituted tungstophosphate K4Na6[alpha-1,2-PW10Ti2O39](2) . 14H(2)O. The X-ray structural determination shows the dimeric, anhydride structure was formed by two Ti-O-Ti bonds linking two di-titanium-substituted Keggin anion [alpha-1,2-PW10Ti2O40]. It was also characterized by elemental analysis, TGA, FT-IR and U-V-vis spectroscopies.

Crystal form transition during heating of solvent-induced crystalline syndiotactic polystyrene

The phase transition of two kinds of solvent-induced crystalline syndiotactic polystyrene (sPS). gamma-sPS and delta(c)-sPS, has been studied via WAXD and DSC. gamma-sPS transform to a-sPS at 195-225 degrees C before melt during heating, whereas delta(e)-sPS transform to first gamma-sPS and then a-sPS at 100-200 degrees C and 200-215 degrees C, respectively. The transition of delta(e)-gamma and gamma-a occurs for below melting point of sPS indicates they are all solid-solid transition.

Low-temperature oxidation of methane to form formaldehyde: role of Fe and Mo on Fe-Mo/SiO2 catalysts, and their synergistic effects

The partial oxidation of methane with molecular oxygen was performed on Fe-Mo/SiO2 catalysts. Iron was loaded on the Mo/SiO2 catalyst by chemical vapor deposition of Fe-3(CO)(12). The catalyst showed good low-temperature activities at 723-823 K. Formaldehyde was a major condensable liquid product on the prepared catalyst. There were synergistic effects between iron and molybdenum in Fe-Mo/SiO2 catalysts for the production of formaldehyde from the methane partial oxidation. The activation energy of Mo/SiO2 decreased with the addition of iron and approached that of the Fe/SiO2. The concentration of isolated molybdenum species (the peak at 1148 K in TPR experiments) decreased as the ion concentration increased and had a linear relationship with the selectivity of methane to formaldehyde. The role of Fe and Mo in the Fe-Mo/SiO2 catalyst was proposed: Fe is the center for the C-H activation to generate reaction intermediates, and Mo is the one for the transformation of intermediates into formaldehyde. Those phenomena were predominant below 775 K.

Isochiral form II of syndiotactic polypropylene produced by epitaxial crystallization

Epitaxial crystallization of syndiotactic polypropylene (sPP) on 2-quinoxalinol (2-Quin) yields, in the lower part of the crystallization range, the less common and metastable form II based on the packing of isochiral helices, rather than the stable antichiral form I. The contact plane is (110)(II). Form II exits only as a thin layer (< 50 nm) near the substrate surface. During further growth away from the surface, a transition takes place to the disordered form I, observed in "conventional" thin film growth. The epitaxial relationship rests only partly on dimensional matching with the chain axis repeat distance (which would be valid for both forms I and II) and on interchain distances. Whereas a better dimensional match would be achieved with form I, selection of the isochiral form II results from better correspondence of the surface topographies of the deposit (110)(II) sPP and substrate 2-Quin (001) contact faces.