Reflectance and ellipsometric study of anodic film on platinum electrode

The anodic films on platinum electrode in 0.05 M sulfuric acid solution were examined by means of ellipsometry. By measuring the relative phase retardation (Δ), relative amplitude reduction (tanψ) and also the intensity of the reflected polarized light, the optical constants of the films (n, k) and thickness (τ) at various potentials were obtained. The results showed that the optical properties of the film remain nearly constant (n = 2.8, k = 1.7) while the thickness increases from 2 Å to 5 Å with anodic potential. From this evidence, it is concluded that the film is made of an oxide of platinum forming a definite phase.     

Exchange labeling of proteins:99mTc labeled transferrin

^99mTc-labeled transferrin was prepared by reduction of^99mTcO ₄ ⁻ ; with stannous DTPA or stannous citrate followed by equilibration of the technetium chelate with human transferrin. The rate of transfer of^99mTc to transferrin in the presence of 0.015M citrate buffer was dependent on pH in the order pH 2.1> pH 7.2> pH 4.1> pH 5.9. The incorporation rate was inversely proportional to the concentration of DTPA and citrate buffer. The replacement of citrate buffer by acetate buffer or oxalate buffer reduced drastically the formation of^99mTc-labeled transferrin at pH 4.1. The formation of^99mTc-labeled transferrin prepared from the reduction of^99mTcO ₄ ⁻ with stannous citrate was faster than that from the reduction with stannous DTPA in the presence of 0.015M citrate buffer and pH 2.5. Equilibration of transferrin with^99mTc-labeled pyrophosphate did not produce^99mTc-labeled transferrin at pH 4.5. The ligand exchange labeling of^99mTc to transferrin in 0.015M citrate did not cause appreciable denaturation of the protein at all pH values. This method also enabled labeling of the protein in a low concentration (2.6·10⁻⁴ M) via tin reduction. Sequential external imaging of the^99mTc-labeled transferrin in Sprague-Dawley rats bearing Walker-256 carcinosarcoma showed optimal tumor localization occurred at 3 hr after injection. In spite of this,^99mTc-labeled transferrin does not appear to be a suitable imaging agent because of the low tumor to blood ratio of^99mTc (0.50±0.17) at 3 hr post injection. This is similar to that of^{6 7}Ga-citrate (0.43±0.15%).     

Nonaqueous synthesis of TiO2 nanocrystals using TiF4 to engineer morphology, oxygen vacancy concentration, and photocatalytic activity

Control over faceting in nanocrystals (NCs) is pivotal for many applications, but most notably when investigating catalytic reactions which occur on the surfaces of nanostructures. Anatase titanium dioxide (TiO(2)) is one of the most studied photocatalysts, but the shape dependence of its activity has not yet been satisfactorily investigated and many questions still remain unanswered. We report the nonaqueous surfactant-assisted synthesis of highly uniform anatase TiO(2) NCs with tailorable morphology in the 10-100 nm size regime, prepared through a seeded growth technique. Introduction of titanium(IV) fluoride (TiF(4)) preferentially exposes the {001} facet of anatase through in situ release of hydrofluoric acid (HF), allowing for the formation of uniform anatase NCs based on the truncated tetragonal bipyramidal geometry. A method is described to engineer the percentage of {001} and {101} facets through the choice of cosurfactant and titanium precursor. X-ray diffraction studies are performed in conjunction with simulation to determine an average NC dimension which correlates with results obtained using electron microscopy. In addition to altering the particle shape, the introduction of TiF(4) into the synthesis results in TiO(2) NCs that are blue in color and display a broad visible/NIR absorbance which peaks in the infrared (λ(max) ≈ 3400 nm). The blue color results from oxygen vacancies formed in the presence of fluorine, as indicated by electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) studies. The surfactants on the surface of the NCs are removed through a simple ligand exchange procedure, allowing the shape dependence of photocatalytic hydrogen evolution to be studied using monodisperse TiO(2) NCs. Preliminary experiments on the photoreforming of methanol, employed as a model sacrificial agent, on platinized samples resulted in high volumes of evolved hydrogen (up to 2.1 mmol h(-1) g(-1)) under simulated solar illumination. Remarkably, the data suggest that, under our experimental conditions, the {101} facets of anatase are more active than the {001}.     

Protected ester,nitrile, carbinol and carbinyl amine cyclopropanone hydrates

Methyl diazoacetate reacted with the ketene acetal I in the presence of dirhodium tetraacetate yielding the metastable cyclopropanone ketal ester II, which was converted to the primary and tertiary cyclopropyl carbinols III and IV by treatment with lithium aluminum hydride and methyl lithium, respectively. Diazoacetonitrile yielded a stable crystalline cyclopropanone ketal nitrile X following reaction with the ketene acetal I.     

Post‐Synthetic Reversible Incorporation of Organic Linkers into Porous Metal–Organic Frameworks through Single‐Crystal‐to‐Single‐Crystal Transformations and Modification of Gas‐Sorption Properties

The porous metal–organic framework (MOF) {[Zn₂(TCPBDA)(H₂O)₂]?30 DMF?6 H₂O}_n ( SNU‐30 ; DMF=N,N‐dimethylformamide) has been prepared by the solvothermal reaction of N,N,N′,N′‐tetrakis(4‐carboxyphenyl)biphenyl‐4,4′‐diamine (H₄TCPBDA) and Zn(NO₃)₂?6 H₂O in DMF/tBuOH. The post‐synthetic modification of SNU‐30 by the insertion of 3,6‐di(4‐pyridyl)‐1,2,4,5‐tetrazine (bpta) affords single‐crystalline {[Zn₂(TCPBDA)(bpta)]?23 DMF?4 H₂O}_n ( SNU‐31 SC ), in which channels are divided by the bpta linkers. Interestingly, unlike its pristine form, the bridging bpta ligand in the MOF is bent due to steric constraints. SNU‐31 can be also prepared through a one‐pot solvothermal synthesis from Zn^II, TCPBDA^4?, and bpta. The bpta linker can be liberated from this MOF by immersion in N,N‐diethylformamide (DEF) to afford the single‐crystalline SNU‐30 SC , which is structurally similar to SNU‐30 . This phenomenon of reversible insertion and removal of the bridging ligand while preserving the single crystallinity is unprecedented in MOFs. Desolvated solid SNU‐30′ adsorbs N₂, O₂, H₂, CO₂, and CH₄ gases, whereas desolvated SNU‐31′ exhibits selective adsorption of CO₂ over N₂, O₂, H₂, and CH₄, thus demonstrating that the gas adsorption properties of MOF can be modified by post‐synthetic insertion/removal of a bridging ligand.     

Three-component velocity field measurements of propeller wake using a stereoscopic PIV technique

A stereoscopic PIV (Particle Image Velocimetry) technique was used to measure the three-dimensional flow structure of the turbulent wake behind a marine propeller with five blades. The out-of-plane velocity component was determined using two CCD cameras with an angular displacement configuration. Four hundred instantaneous velocity fields were measured for each of four different blade phases, and ensemble averaged in order to find the spatial evolution of the propeller wake in the region from the trailing edge up to one propeller diameter (D) downstream. The influence of propeller loading conditions on the wake structure was also investigated by measuring the velocity fields at three advance ratios (J=0.59, 0.72 and 0.88). The phase-averaged velocity fields revealed that a viscous wake formed by the boundary layers developed along the blade surfaces. Tip vortices were generated periodically and the slipstream contracted in the near-wake region. The out-of-plane velocity component and strain rate had large values at the locations of the tip and trailing vortices. As the flow moved downstream, the turbulence intensity, the strength of the tip vortices, and the magnitude of the out-of-plane velocity component at trailing vortices all decreased due to effects such as viscous dissipation, turbulence diffusion, and blade-to-blade interaction.     

A biogentic-type synthesis of dendrolasin

Dendrolasin¹ was synthesized from farnesol via biogenetic-type intermediates.     

Enhanced isosteric heat of H2 adsorption by inclusion of crown ethers in a porous metal-organic framework

Inclusion of 18-crown-6 or 15-crown-5 in a porous MOF increased the isosteric heats of H(2) adsorption significantly, which are comparable to MOFs containing open metal sites.