Meso-tetraaryl cofacial bisporphyrins delivered by Suzuki cross-coupling

The Suzuki cross-coupling methodology provides a facile synthetic approach for the modular preparation of meso-tetraaryl cofacial bisporphyrins anchored by xanthene and dibenzofuran. This synthetic method furnishes cofacial bisporphyrin templates with enhanced steric and electronic protection from mu-oxo formation and oxidative degradation. The ability of these platforms to support multielectron oxidation chemistry mediated by proton-coupled electron transfer (PCET) is demonstrated by their reactivity for the catalytic disproportionation of hydrogen peroxide to oxygen and water.     

Dosage de l'azote dans l'uranium : Définition d'un échantillon de référence

Traces of nitrogen can be determined in uranium by reductive fusion in vacuum or in a current of helium. The two methods gave similar results, and these were confirmed by the Kjeldahl method. The excellent agreement between the values obtained made it possible to establish a reference standard.     

Gaussian molecular orbital calculations of the barrier to internal rotation in the ethyl cation

Extended Gaussian orbital basis set calculations have been carried out on an assumed staggered and eclipsed classical geometrical configuration of C₂H. The best total energies obtained for these geometries were ?78.170692 a.u. and ?78.170674 a.u. respectively, corresponding to a barrier to internal rotation of 1.8 × 10^?5 a.u. or 11 kcal/mole. An analysis of the charge density matrix indicates that charge is distributed in these molecules in a manner consistent with the concept of hyperconjugation.     

Theoretical considerations in the zone melting of organic substances Analysis of the diffusion gradient

Further evidence is gathered in the theory of the zone melting of organic compounds under ideal equilibrium conditions by a kinetic study of the diffusion gradient in the melt zone. A mathematical analysis is developed for the concentration distribution of impurities in the moving molten zone, which yields an expression for the concentration gradient at the liquid-solid recrystallisation interface. These expressions describe the transport process and a measure of the rate of segregation of impurity at the recrystallisation interface. In addition, these equations have been programmed on a computer and concentration profiles for two zone velocities have been graphed. It has been found that the concentration gradient is independent of the length of the zone under ideal equilibrium conditions for pure diffusion.     

Neutron activation analysis of microgram amounts of thorium in uranium ores and process liquors by means of thorium-233

A method is described for neutron activation analysis of thorium by employing thorium-233. Decontamination steps include anion exchange in 12.5 N HCL, precipitation of fluoride, extraction with mesityl oxide and thorium oxalate precipitation. The time spent is less than 1 h; spurious activities in counting samples amount only to 2% and can easily be corrected for. The sensitivity of the method is ca. 0.02 μg of thorium in a neutron flux of 10¹²n/cm²/sec with an irradiation time of 5 min.     

Inorganic complexes in volumetric analysis. Part III. Use of ferric fluoride complex in the estimation of iodide

Summary The method for estimation of iodide formulated in the earlier publications of the series bas been modified by the use of sodium fluoride as the complexing agent in the place of oxalate or phosphoric acid. The results obtained are in excellent agreement with the calculated ones and the method has been successfully applied for the estimation of iodide in iodized salt.     

Determination of aluminium in bulk coal samples by neutron activation analysis

The determination of Al₂O₃, in bulk coal samples to an accuracy of about 0.2% Al₂O₃ has been achieved by means of a thermal-neutron activation technique based on the reaction ²⁷Al(n,γ)²⁸Al. In the analysed samples, which had widely different compositions, the Al₂O₃ concentrations ranged from 1 to 11% and the ash contents from 7 to 40%. Al₂O₃ concentrations measured by x-ray fluorescence showed a linear relationship with both the 1.78-MeV γ-ray count following the decay of ²⁸Al and the thermal-neutron count near the samples during irradiation. The linear relationship, which was obtained by regression analysis of the experimental data, determined the Al₂O₃concentrations with a standard deviation of 0.24% Al₂O₃. The particle sizes in the samples ranged from —0.5 to —40 mm, the moisture contents ranged from 1 to 6%, and the sample weights ranged from 8 to 11 kg. However, inclusion of these parameters in the regression analysis did not significantly improve the results for Al₂O₃.     

S-4-methylphenyl-o,o-bis[1-benzotriazolyl] phosphorothioate: a versatile phosphorylating agent

The phosphorylating agent obtained by treatment of S-4-methylphenyl phosphorodichloridothioate with 1-hydroxybenzotriazole can not only be applied for the introduction of polyphosphate functions at the terminal ends of nucleic acids, but also for the formation of 3′-5′-phosphotriester linkages.     

Trace element geochemistry of magmatic rock series of converging and diverging plate boundaries

The new results and developments of trace element geochemistry of magmatic processes are discussed. The interest and limits of neutron activation analysis for studies of trace element distributions in magnetic rocks are shown.     

The iodates of scandium

A dihydrate, a monohydrate, and three polymorphs of the anhydride Sc(IO₃)₃ have been prepared and studied. Sc(IO₃)₃·2H₂O was prepared by gel growth and by precipitation and evaporation at room temperature. The γ-anhydride can be crystallized from boiling water or nitric acid solution. The other compounds are formed on heating the dihydrate, which also dehydrates very slowly at room temperature. The α-anhydride is amorphous. The β-anhydride generates second harmonics, with about twice the efficiency of quartz. In addition differential thermal analysis (DTA), thermogravimetric analysis (TGA), infrared absorption, and powder X-ray diffraction results are presented.