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941.
Karunakaran Radhakrishnan Henri Cramail Alain Deffieux Philippe Franois Ardchir Momtaz 《Macromolecular rapid communications》2002,23(14):829-833
A facile nonaqueous synthetic route to methylaluminoxane (MAO) by heating a mixture of benzophenone and trimethylaluminium (TMA) is described. The MAO prepared such reveals to be an efficient activator of metallocenes and late transition metal complexes for ethylene polymerization. The [TMA]/[benzophenone] ratio used for the preparation of MAO is shown to have a dramatic effect on the catalytic activity as well as the molecular weight distribution of the resulting polyethylenes. 相似文献
942.
943.
Alain Walcarius Jérôme Devoy Jacques Bessiere 《Journal of Solid State Electrochemistry》2000,4(6):330-336
Pure silica particles were dispersed within carbon paste and the resulting modified electrode was applied to the selective
voltammetric detection of mercury(II) species after their accumulation at open circuit. The remarkable selectivity observed
between pH 4 and 7 was attributed to the intrinsic adsorption mechanism which involves a condensation reaction between mercury(II)
hydroxide and hydroxyl groups on the silica surface, leading to the formation of an inner-sphere-type surface complex. After
optimization with respect to the electrode composition, the detection medium, and the voltammetric scan mode, a linear response
was obtained in the concentration range between 2 × 10−7 M to 1 × 10−5 M, by applying anodic stripping square wave voltammetry. Various silica samples were used and their sorption behavior was
discussed in relation to their specific surface area and porosity. The effect of chloride and pH on the accumulation of mercury(II)
on silica was also investigated.
Received: 4 September 1999 / Accepted: 5 January 2000 相似文献
944.
Nathalie Sanz Patrice L. Baldeck Jean-Franois Nicoud Yvette Le Fur Alain Ibanez 《Solid State Sciences》2001,3(8):8347
In order to compare the polymorphism of 1-cyano-1-(4-nitrophenyl)-2-(4-methoxyphenyl)ethene CMONS crystallized in solutions to that of CMONS nanocrystals grown in the pores of dense sol-gel matrices, we have first studied the CMONS polymorphism in various solvents which were then used in the nanocrystallization processes. The different polymorphs were characterized by differential scanning calorimetry, X-ray diffraction and absorption as well as luminescence spectroscopies. The differences observed between CMONS powders and CMONS nanocrystals illustrate the role played by the silicate matrices on the polymorphism of CMONS. This matrix effect would be used to stabilize a particular polymorph of an organic phase and thus to adjust the optical properties of the nanocomposite hybrid organic–inorganic material. 相似文献
945.
Emission lines varie in intensity on a nine orders range of magnitude depending on. 相似文献
946.
Alain Cartier David Brown Bernard Maigret Sandrine Boschi-Muller Sophie Rahuel-Clermont Guy Branlant 《Theoretical chemistry accounts》1999,101(1-3):241-245
In the framework of a theoretical approach to the relationship between structure and reactivity of the catalytic centers
of enzymes, glyceraldehyde-3 phosphate dehydrogenase (GAPDH) has been chosen as a model enzyme. In GAPDH, the proximity of
His176 increases the reactivity of Cys149 at neutral pH; however, its presence alone is not sufficient to explain the reactivity of the catalytic Cys. In order to
determine which other interactions play an important role, a study of the geometric and electronic structure of the catalytic
site has been made using a hybrid quantum mechanics/molecular mechanics local self-consistent field method. This allows the
computation of the electronic properties of amino acid residues in subsystems influenced by other parts of the macromolecule.
The quantum subsystem was centered on the Cys149 residue of GAPDH. The structures of GAPDH taken from the crystallographic database did not include hydrogen atoms and these
had to be added taking into account the fact that, in the active site, His176 has three tautomeric forms: δ-His protonated, ε-His protonated and His+. The results presented here suggest that the most stable His…Cys system in GAPDH is a strongly hydrogen-bonded Cys149
−/His176
+ ion pair.
Received: 24 March 1998 / Accepted: 3 September 1998 / Published online: 23 November 1998 相似文献
947.
This paper is concerned with a non-isothermal phase separation model, for instance, describing component separation dynamics
for a class of binary systems (solid-solid systems). Our model is a couple of nonlinear parabolicPDE's which are possibly degenerate and singular at the same time. It will be shown that our model can be reformulated as a nonlinear
evolution equation governed by subdifferential operator in a Hilbert space, and its mathematically basic questions, such as
existence and uniqueness, can be handled in the abstract theory of nonlinear evolution equations in Hilbert spaces.
Entrata in Redazione il 15 luglio 1997 e, in versione riveduta, il 25 ottobre 1997. 相似文献
948.
We associate canonically a cyclic module to any Hopf algebra endowed with a modular pair in involution, consisting of a group-like element and a character. This provides the key construction for allowing the extension of cyclic cohomology to Hopf algebras in the nonunimodular case and, further, to developing a theory of characteristic classes for actions of Hopf algebras compatible not only with traces but also with the modular theory of weights. This applies to both ribbon and coribbon algebras as well as to quantum groups and their duals. 相似文献
949.
So far,the synthesis of chiral framework with achiral organic ligand still faces great challenge.Herein,three new coordinated complexes[Zn(btca)Cl]·DMA·N(CH3)2(1),[Zn(btca)(Ac-)]·N(CH3)2(2)and[Zn(btca)]·H2O(3)(DMA=N,N-dimethylacetamide,btca=benzotriazole-5-carboxylate acid)were synthesized via different methods.Single-crystal X-ray diffraction analysis revealed that compounds 1 and 2 were isostructural and showed achiral layer network with fes topology,and 3 presented a chiral three-dimensional framework with eta topology.The result of this work has demonstrated that urothermal synthesis will be promising means of constructing chiral framework with achiral building block.Compound 3 also displayed an excellent property of iodine uptake. 相似文献