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81.
Taking pyridine as a prototypal example of biologically important nitrogen bases involved in proton-coupled electron transfers, it is shown with the example of the photochemically triggered oxidation of phenol by Ru(III)(bpy)(3) that this proton acceptor partakes in a concerted pathway whose kinetic characteristics can be extracted from the overall kinetic response. The treatment of these data, implemented by the results of a parallel study carried out in heavy water, allowed the determination of the intrinsic kinetic characteristics of this proton acceptor. Comparison of the reorganization energies and of the pre-exponential factors previously derived for hydrogen phosphate and water (in water) as proton acceptors suggests that, in the case of pyridine, the proton charge is delocalized over a primary shell of water molecules firmly bound to the pyridinium cation. 相似文献
82.
Chen P El Ojaimi M Gros CP Richard P Barbe JM Guilard R Shen J Kadish KM 《Inorganic chemistry》2011,50(8):3479-3489
A series of homobimetallic manganese cofacial porphyrin-corrole dyads were synthesized and investigated as to their electrochemistry, spectroelectrochemistry, and ligand binding properties in nonaqueous media. Four dyads were investigated, each of which contained a Mn(III) corrole linked in a face-to-face arrangement with a Mn(III) porphyrin. The main difference between compounds in the series is the type of spacer, 9,9-dimethylxanthene, anthracene, dibenzofuran, or diphenylether, which determines the distance and interaction between the metallomacrocycles. Each redox process of the porphyrin-corrole dyads was assigned on the basis of spectroscopic and electrochemical data and by comparison with reactions and properties of the monocorrole and the monoporphyrin which were examined under the same solution conditions. The Mn(III) porphyrin part of the dyad undergoes two major one-electron reductions in pyridine and benzonitrile, the first of which involves a Mn(III)/Mn(II) process and the second the addition of an electron to the conjugated π-ring system of the macrocycle. The Mn(III) corrole part of the dyads also exhibits two major redox processes, one involving Mn(III)/Mn(II) and the other Mn(III) to Mn(IV) under the same solution conditions. The potentials and reversibility of each electron transfer reaction were shown to depend upon the solvent, type of spacer separating the two macrocycles, and the presence or absence of axial ligation, the latter of which was investigated in detail for the case of acetate ion which was found to bind within the cavity of the dyad to both manganese centers, both before and after the stepwise electroreduction to the Mn(II) forms of the two macrocycles. An intramolecular chloride ion exchange between the porphyrin part of the dyads which contain Mn(III)Cl and the singly oxidized corrole in the dyad is observed after the Mn(III)/Mn(IV) reaction of the corrole, suggesting that chloride is coordinated inside the cavity in the neutral compound. 相似文献
83.
The synthesis of polyacetylene in a new class of solvents - liquid crystals - will be reported. The effect of the solvent molecules orientation in the polymer's structure and its properties will be discussed. 相似文献
84.
Jean-Michel NavarreDominique Guianvarc'h Audrey Farese-Di GiorgioRoger Condom Rachid Benhida 《Tetrahedron letters》2003,44(10):2199-2202
A short route to novel α-(2-aminothiazolyl)-C-nucleosides has been developed. The key step was the high diastereoselective reduction of the hemiacetal intermediates using L-Selectride, which afforded the corresponding R-diols in quantitative yields. These diols were converted, after C4-C1 ring closure and protecting groups cleavage, to their corresponding free α-C-nucleosides. 相似文献
85.
The structure and absolute configuration of natural 8-epi-9-deoxygoniopypyrone have been confirmed by an efficient and highly diastereoselective synthesis in 15 steps from (S)-mandelic acid with an overall yield of 43%. 相似文献
86.
Claudia Lederman Jean-Michel Roquejoffre Noemi Wolanski 《Comptes Rendus Mathematique》2002,334(7):569-574
This Note is devoted to the justification of an asymptotic model for quasisteady three-dimensional spherical flames proposed by G. Joulin [7]. The paper [7] derives, by means of a three-scale matched asymptotic expansion, starting from the classical thermo-diffusive model with high activation energies, an integro-differential equation for the flame radius. In the derivation, it is essential for the Lewis number – i.e., the ratio between thermal and molecular diffusion – to be strictly less than unity. In this Note, we give the main ideas of a rigorous proof of the validity of this model, under the additional restriction that the Lewis number is close to 1. To cite this article: C. Lederman et al., C. R. Acad. Sci. Paris, Ser. I 334 (2002) 569–574. 相似文献
87.
This paper surveys problems related to achieving agreement in distributed systems. Various agreement problems can be specified as a variant of the basic consensus problem. Unfortunately, this fundamental problem cannot be solved in asynchronous systems if crash failures can occur. In order to overcome this impossibility result, Chandra and Toueg have augmented the asynchronous system model with the notion of failure detectors. A failure detector is associated with each process of the distributed computation and is responsible for detecting external failures. Suspicions are essentially implemented using time-out mechanisms, which means that (1) the detection of a real failure is usually delayed and (2) a failure detector can make mistakes by incorrectly suspecting a process to have crashed. In this paper, various classes of failure detectors are presented. All are specified by a completeness property and an accuracy property. A completeness property puts a condition on the detection of crashed processes, while an accuracy property restricts the possible mistakes made by a failure detector. After reviewing the hierarchy of failure detector classes, two particular solutions to the consensus problem are examined. In each case, a different class of failure detectors is used. The proposed solutions have liveness properties and deliver their expected results provided that a minimal set of well-defined conditions is satisfied. After a detailed presentation of the consensus problem, various agreement problems are reviewed and their relationship with the consensus problem are underlined. Finally, for each agreement problem, we indicate under which minimum assumptions a solution can be found. 相似文献
88.
89.
Jean-Michel Bismut 《Comptes Rendus Mathematique》2002,335(3):243-247
In this Note, we announce the vanishing of the holomorphic torsion forms of the relative de Rham complex of an equivariant fibration. To cite this article: J.-M. Bismut, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 243–247. 相似文献
90.
Hans Fritz Jean-Michel Henlin Thophile Tschamber Jacques Streith Andreas Riesen Margareta Zehnder 《Helvetica chimica acta》1988,71(4):822-834
Azeitidinodiazepines 4b and 4c react with acylnitroso dienophiles 5a–c , specifically from their convexe α-side, but in a non-regiospecific way, leading thereby stereospecifically to the expected adducts 6a–d and 7a–d . The three-dimensional structures of 6a and 7a were determined by X-ray analyses which corroborated their NMR data. OsO4 cis-glycolization occurred in good yield with the inverse adducts 7a and 7e and led to the rearranged products 10 . These latter ones result from an intramolecular N- to O-transbenzoylation of the short-lived intermediates 9 followed by fragmentation of the animal function. X-Ray analysis of 7a showed the N(10) atom to be pyramidal, a result which demonstrates that it does not have any pronounced benzamide character; otherwise no such N- to O-transbenzoylation would have taken place. Structure and relative configuration of 10a were ascertained by X-ray analysis which confirmed its NMR data as well as the stereochemical outcome of its formation. 相似文献