Mössbauer study of sediment alteration produced by heat treatment

Pincenvent (France) cooking-place silt-like sediments have been studied by using Mössbauer spectroscopy and characterized by using X-ray diffraction (XRD). The sediments were treated at 400, 600, 800 and 1000°C under oxidizing conditions. We discuss the results and we suggest a Mössbauer thermometer to be used to recognize the temperatures and atmosphere ancient people used in their cooking-places.Fellow of CONICET, Argentina, on leave, Laboratoire d'Ethnologie Prehistorique, 44 Rue de L'Almiral Mouchez, 75014 Paris, France.     

Biphenol-based phosphoramidite ligands for the enantioselective copper-catalyzed conjugate addition of diethylzinc

Phosphoramidite ligands, based on ortho-substituted biphenols and a chiral amine, induce high enantioselectivities (ee's up to 99%) in the copper-catalyzed conjugate addition of dialkylzinc reagents to a variety of Michael acceptors. Particularly, the best reported ee's were obtained for acyclic nitroolefins.     

Propane Aromatization over Mo/HZSM-5 Catalysts

Impregnation, mechanical mixing and hydrothermal treatment methods were used to introduce molybdenum species into the HZSM-5 zeolite. The structure and surface acidity of the catalysts were studied by means of XRD, FT-IR, NH3-TPD, TPR and XPS. The effects of Mo content and reaction time on stream on the aromatization of propane were investigated. It was found that the performance of the Mo/HZSM-5 catalyst prepared by the hydrothermal treatment method was much better than that of the other two catalysts. For example, under the reaction conditions of 823 K and 600 h-1, propane conversion and aromatics selectivity over the catalyst prepared by hydrothermal pretreatment could reach 89.17% and 78.56%, respectively. XRD and XPS results showed that the Mo species in the catalysts prepared by hydrothermal treatment were highly dispersed on the surface of the HZSM-5, and larger amounts of them could penetrate into the HZSM-5 channel, as compared with the other two kinds of catalysts. These factors may be responsi     

On the theory of the low-temperature electrical resistivity of potassium

Expressing the residual resistivity ?₀ as a force-force correlation, a first-principles basis is afforded for the low temperature expansion of the electrical resistivity ? as

(I)$\text{? = ?}{}_0\text{[1 +}\text{λ1}\text{λ}\text{+ … ]}$

where λ = const T^-2 is the non-resistive mean free path arising from electron-electron scattering. λ¹ is found to reflect directly long-range correlations in the electronic motions via the off-diagonal behaviour of the local density of states at the Fermi energy.     

Nonlocal energy density functionals: Models plus some exact general results

Holas and March (Phys Rev 1995 A51, 2040) gave a formally exact expression for the force ??V_xc( r )/? r associated with the exchange‐correlation potential V_xc( r ) of density functional theory. This forged a precise link between first‐ and second‐order density matrices and V_xc( r ). Here models are presented in which these low‐order matrices can be related to the ground‐state electron density. This allows nonlocal energy density functionals to be constructed within the framework of such models. Finally, results emerging from these models have led to the derivation of some exact “nuclear cusp” relations for exchange and correlation energy densities in molecules, clusters, and condensed phases. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Non-local relation between kinetic and exchange energy densities in Hartree–Fock theory

A non-local generalization K( r, r' ) of the kinetic energy t( r ) such that t( r ) = ∫K( r, r' ) dr' is defined using the idempotency property of the Hartree–Fock first-order density matrix. This is, in turn, related by means of an explicit differential equation to the non-local exchange energy density X( r, r' ). The relationship is illustrated for a couple of examples: with the Fermi-hole in a uniform electron gas, of importance in the local density version of density functional theory, and with inhomogeneous electron systems.     

Kinetic fluorimetric determination of cerium with 1,5-diphenyl-3-(2-stiryl)-Δ2-pyrazoline

A kinetic fluorimetric method for the determination of cerium(IV) (0.04–0.2 ppm) is described. The fluorescent species obtained results from oxidative transformation of the reagent. The reaction are described and the experimental variables and interferences in the determination are reported.     

A kinetic template effect in the metal ion-catalysed formation of arylphosphonium salts

Tertiary phosphines react with $\text{o}$-halobenzaldimines and $\text{o}$-bromodiarylazo compounds, under mild conditions in the presence of a metal ion catalyst, with displacement of the halogen to form the related arylphosphonium salts. The corresponding $\text{o}$-haloaryl compounds do not undergo these reactions.     

Reactions between technetium(VII) and some hydrazones and the spectrofluorimetric determination of technetium(VII) with 2,2′-dipyridylketone hydrazone

The reactions between pertechnetate and five hydrazones are described. Of these, the technetium(VII)/2,2′-dipyridylketone hydrazone system was found to be most sensitive, and is studied in detail. Spectrofluorimetric procedures for the determination of technetium(VII) over the range 0.01–12 mg l^?1 are reported. The reaction proceeds most favourably under acidic conditions (1.4 M hydrochloric acid). For 1 mg l^?1 technetium(VII), 100 mg l^?1 levels of U(VI), Re(VII), Mo(VI) or W(VI) do not interfere when the reaction proceeds at room temperature. Sensitivity improves at higher temperatures.     

The reactions of 4-hydroxy-2-pyrones with 2-hydroxybenzaldehydes. A note of warning

The reaction between 2-hydroxybenzaldehyde and 4-hydroxy-6-methyl-2-pyrone (triacetic acid lactone) affords 3-acetoacetyl-2-chromenone, 7 , instead of 3-(2-hydroxybenzylidene)-6-methyl-3,4-dihydro-2H-pyran-2,4-dione, 6 . The structures previously reported in the literature for the products formed in the reactions of 4-hydroxy-2-chromenone with 2-hydroxybenzaldehydes in a molar ratio 1:1 are considered erroneous. Thus, the previously reported 3-(2-hydroxybenzylidene)chroman-2,4-dione, 10 , should be formulated as 3-(2-hydroxybenzoyl)-2-chromenone, 11 .