Enthalpy of formation of aqueous tungstate ion and of crystalline tungstic acid (H2WO4)

Calorimetric measurements of the enthalpy of reaction of WO₃(c) with excess OH^?(aq) have been made at 85°C. Similar measurements have been made with MoO₃(c) at both 85 and 25°C, to permit estimation of ΔH°=?13.4 kcal mol^?1 for the reaction WO₃(c)+2OH^?(aq)=WO^2?₄(aq)+H₂O(liq) at 25°C. Combination of this ΔH° with ΔH°_f for WO₃(c) leads to ΔH°_f=?256.5 kcal mol^?1 for WO^2?₄(aq). We also obtain ΔH°_f=?269.5 kcal mol^?1 for H₂WO₄(c). Both of these values are discussed in relation to several earlier investigations.     

Tailoring pore size and pore size distribution of kidney dialysis hollow fiber membranes via dual-bath coagulation approach

Polyethersulfone (PES) hollow fiber membranes for kidney dialysis application were prepared by the dry-jet wet-spinning method. A dual-coagulation bath technology was first time employed for fabricating the kidney dialysis membranes with a tight inner skin and loose outer supporting layer structure. A weak coagulant isopropanol (IPA) was served as the first external coagulation bath, while water as the second bath. Experiments demonstrate their advantages of better controlling both inner and outer skin morphology. The as-spun fibers have a higher mean effective pore size (μ_p), pure water permeation flux (PWP) and molecular weight cut-off (MWCO) with an increase in N-methyl-2-pyrrolidone (NMP) percentage in bore fluid (i.e., internal coagulant). After being treated in 8000 ppm NaOCl solution for 1 day, fibers show larger pore sizes and porosity in both inner and outer surfaces, and thinner inner and outer layers than their as-spun counterparts. Among them, the bleached fibers spun with 50 wt.% NMP in bore fluid have the MWCO (43 kDa) and PWP (40 × 10⁻⁵ L m⁻² Pa⁻¹ h⁻¹) suitable for kidney dialysis application. Based on SEM observations and solute rejection performance, the further heat treated fibers in an aqueous solution is found to be an effective way to fine tune membranes morphology and MWCO for kidney dialysis application. The solute rejection performance data of the hollow fiber membranes spun with 55 wt.% NMP in bore fluid after heat treated at 90 °C in water for 2 h were found to be very appropriate for the kidney dialysis application.     

Syntheses and evaluation of novel biodegradable amino acid based anhydride polymer resins and composites

A novel synthetic biodegradable oligomer based upon methacrylated aminocaproyl maleamic acid (MACMA), was synthesized and characterized. Injectable and in situ crosslinkable polymer networks were formulated by copolymerization of MACMA with triethyleneglycol dimethacrylate (TEGDMA). In addition, composites composed of MACMA, TEGDMA and beta-tricalcium phosphate (β-TCP) were prepared. The networks and composites were initiated by photo- and redox-polymerization, respectively. The initial compressive (CS) and diametral tensile strengths (DTS) of these materials were determined and used to evaluate the effects of MACMA/TEGDMA ratios on the degradation behavior of the materials. The neat resin networks exhibited initial CS values ranging from 6.7 to 284.2 MPa and the composites demonstrated initial DTS values ranging from 2.8 to 20.8 MPa and CS values ranging from 19.1 to 119.5 MPa. During the course of degradation the polymer neat resins lost 51%, 69% and 61% of their initial CS after 3 weeks for the MACMA/TEGDMA ratios at 25/75, 50/50 and 75/25, respectively. The resin with the MACMA/TEGDMA ratio of 75/25 completely degraded after 6 months. The composite with the MACMA/TEGDMA ratio of 25/75 exhibited a significant increase in CS after an initial decrease for 7 days and then lost 57% of its initial CS after 3 months. The composite composed of poly(MACMA) homopolymer showed a complete degradation after 21 days.     

Study of osmium and ruthenium distillation with radioactive tracers

The distillation characteristics of osmium and ruthenium, which have been studied by using both radioactive tracers and inactive compounds, are reported. The tracer solutions were prepared from hexachloro and hexabromo compounds and from the purified sponges of both metals. A quantitative separation of osmium from ruthenium can be made by distillation from peroxide-sulphuric acid solution at 110 degrees for about 40 min. Slow and incomplete distillations are observed when osmium is present as either the chloro or bromo complex. Optimum conditions for the dissolution of acid-insoluble materials containing osmium and ruthenium are discussed.     

Synthesis of novel furan and thiophene PAH'S related to acephenanthrylene

The total syntheses of furan and thiophene PAH's related to acephenanthrylene are reported. Cyclobutanones which were obtained by [2 + 2] addition of ketenes with 2,3-dihydrofuran or 2,3-dihydrothiophene regioselectively could be converted into angular PAH skeleton molecules by rearrangements with polyphosphoric acid. 2,3-Dichloro-5,6-dicyanobenzoquinone was applied for aromatization to achieve the formation of PAH's.     

Chemoselective synthesis of 1-alkyl-4-(4-amino-2,6-dichlorophenoxy)-5-halopyridazin-6-ones

Some 1-alkyl-4-(4-amino-2,6-dichlorophenoxy)-5-halopyridazin-6-ones were synthesized chemoselectively from 1-alkyl-4,5-dihalopyridazin-6-ones and 4-amino-2,6-dichlorophenol via a fluoride ion-assisted reaction.     

Crystal Structure of [Co2(μ-dmg)2(μ-dmg H)(dmg H)(Pø3)] 1/2 dmg H2 · 1/2 CH3OH: A Crystal Containing Various Forms of dmg Ligand

The crystal structure of [Co₂(μ-dmg)₂(μ-dmg H)(dmg H)(Pø₃)] · 1/2 dmg H₂ · 1/2 CH₃OH has been determined by single crystal X-ray diffraction. The title complex crystallizes in triclinic space group P&1bar; with a=10.859(3), b=13.299(3), c=15.247(3)Å, α=98.52(2), β=99.26(2), γ=97.80(2)° and Z=2. The agreement indices are R(F)=0.062 and R_w(F)=0.085 for 5231 observations and 515 variables. Both cobalt atoms have an oxidation state of 3+ and are both six-coordinated; one Co(III) atom is bonded to a phosphorous atom of triphenylphosphine, four nitrogen atoms of two planar ligands, dmg^2? and dmgH^?, and one oxygen atom of another dmg^2? ligand. The other Co(III) atom is coordinated by four nitrogen atoms of two cis nonplanar ligands, dmg^2?, dmgH^?, and two oxygen atoms of the other dmg^2? and dmgH^? ligands. There are three N-O bridged ligands namely two dmg^2? and one dmgH^? between two Co(III) atoms. A free molecule of dmgH₂ and a molecule of CH₃OH are also found in the crystal lattice. The structure interestingly demonstrates the possible various forms of dmg, not only on their charge but also in different conformations upon coordination.     

High sensitivity of positron annihilation lifetime to time and pressure effects in gas-exposed polymers

Positron annihilation lifetime (PAL) experiments are performed in polycarbonate (PC) exposed to CO₂ and He gases as a function of time and pressure. In PC/CO₂ systems, hole size and fraction reduced from PAL data increase as a function of CO₂ pressure and exposure time. Significant hysteresis in positron lifetime data is observed during CO₂ abasorption/desorption. In PC/He systems, no variation is observed. Hole size distribution in the CO₂-exposed polymers is found to be significantly broader than in unexposed samples. The high sensitivity of PAL results to CO₂ exposure of PC is thought to relate to the microstructural changes in the polymer matrix, such as penetrant plasticization, gas hydrostatic pressure effect, and molecular filling and creation of holes.     

Synthesis and Catalytic Applications of Dendrimer-Templated Bimetallic Nanoparticles

Dendrimers, well-defined hyper-branched macromolecules with characteristic globular structure, have emerged as an attractive material in the field of catalysis and have been considered as a new type of host for the accommodation of guest molecules by virtue of their three-dimensional structure having interior void space. In line with the prospect of dendrimer as a nanoreactor, various metal nanoparticles have been successfully prepared via encapsulation in or formation of particles surrounded by dendrimer branches. However, it is worth noting that most of the previous studies have been confined to the monometallic nanoparticles, and bimetallic nanoparticles have been scarcely exploited yet. In this article, we present the synthesis and characterization of dendrimer-templated bimetallic nanoparticles and their application to catalysis.     

Electrochemical dimerization of 2-(2'-thienyl)pyridine adsorbed on Au(111) observed by in situ fluorescence

The study of heterodentate molecules adsorbed on metal electrodes provides an opportunity to expand the functionality of modified surfaces while offering insights into the surface and intramolecular electronic interactions of organic adsorbates. The adsorption of 2-(2'-thienyl)pyridine, a molecule containing both pyridine and thiophene moieties, on a Au(111) electrode is reported. Adsorption was characterized by electrochemistry in neutral and basic aqueous electrolyte and was compared to that of pyridine. The aqueous electrochemistry of thiophene on Au(111) was also characterized for comparison purposes. At negative potentials, in the presence of 2-(2'-thienyl)pyridine, a diffuse, pi-bonded monolayer was formed, and a phase transition to a close-packed N- and/or S-bonded configuration was observed near -0.4 V in a 1 mM solution of adsorbate, similar to that seen in pyridine on Au(111). The thiophene-like oxidative dimerization of the molecule was confirmed at positive potentials using in situ fluorescence microscopy by comparison with the spectrum of the chemically synthesized dimer.