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31.
Cantat T Jaroschik F Nief F Ricard L Mézailles N Le Floch P 《Chemical communications (Cambridge, England)》2005,(41):5178-5180
New samarium carbene complexes have been synthesized and characterized by X-ray diffraction analysis; the carbenic nature was assessed by reactivity studies. 相似文献
32.
The initial stages of the heterogeneous photoreduction of quinone species by self-assembled porphyrin ion pairs at the water|1,2-dichloroethane (DCE) interface have been studied by ultrafast time-resolved spectroscopy and dynamic photoelectrochemical measurements. Photoexcitation of the water-soluble ion pair formed by zinc meso-tetrakis(p-sulfonatophenyl)porphyrin (ZnTPPS(4)(-)) and zinc meso-tetrakis(N-methylpyridyl)porphyrin (ZnTMPyP(4+)) leads to a charge-separated state of the form ZnTPPS(3)(-)-ZnTMPyP(3+) within 40 ps. This charge-separated state is involved in the heterogeneous electron injection to acceptors in the organic phase in the microsecond time scale. The heterogeneous electron transfer manifests itself as photocurrent responses under potentiostatic conditions. In the case of electron acceptors such as 1,4-benzoquinone (BQ), 2,6-dichloro-1,4-benzoquinone (DCBQ), and tetrachloro-1,4-benzoquinone (TCBQ), the photocurrent responses exhibit a strong decay due to back electron transfer to the oxidized porphyrin ion pair. Interfacial protonation of the radical semiquinone also contributes to the photocurrent relaxation in the millisecond time scale. The photocurrent responses are modeled by a series of linear elementary steps, allowing estimations of the flux of heterogeneous electron injection to the acceptor species. The rate of electron transfer was studied as a function of the thermodynamic driving force, confirming that the activation energy is controlled by the solvent reorganization energy. This analysis also suggests that the effective redox potential of BQ at the liquid|liquid boundary is shifted by 0.6 V toward positive potentials with respect to the value in bulk DCE. The change of the redox potential of BQ is associated with the formation of hydrogen bonds at the liquid|liquid boundary. The relevance of this approach toward modeling the initial processes in natural photosynthetic reaction centers is briefly discussed. 相似文献
33.
Brahim Lakhrissi Mohamed Massoui El Mokhtar Essassi Vincent Lequart Nicolas Joly Patrick Martin Grard Goethals 《Journal of heterocyclic chemistry》2004,41(6):1011-1014
Reaction of 1,5‐benzodiazepin‐2,4‐dione with 3‐O‐substituted‐5,6‐anhydro‐1,2‐isopropylidene‐α‐D‐glucofuranose gave the unexpected N,N'‐di‐glucofuranosyl benzimidazol‐2‐one by a novel rearrangement and ring closure reaction. A mechanism is proposed. 相似文献
34.
Peptide-based reversible and irreversible cysteine proteases inhibitors are well reported in the literature. Many of these compounds have an electrophilic carbonyl group as a cysteine trap in the place of a scissile amide moiety of the natural substrate. As a common mechanism strategy, we have designed a probe library of a cysteine trap for rapid optimization of P1-P1' pockets of different cysteine proteases. The synthesis of this library using a straightforward methodology based on polymer-supported reagents and scavengers to avoid tedious purification steps has been achieved. For the selective monobromination of diazo ketones, preparation of a new supported reagent, piperidinoaminomethylpolystyrene hydrobromide, is also described. 相似文献
35.
M. Nicolas 《Journal of Electroanalytical Chemistry》1985,185(2):365-378
Hydrogen adsorption on plantinum polycrystalline films in methanolic medium has been studied between 293 and 163 K by cyclic voltammetry. At the same time, the electrooxidation of the solvent was followed down to the solidification point of the electrolyte. The oxidation reactions of the residues coming from methanol adsorption on platinum are thermally activated phenomena which are controlled by diffusion at very low temperature, whereas the mechanism of hydrogen adsorption does not seem to be thermally activated. The adsorption of hydrogen on Pt in methanolic medium is not all “blocked” below T = 243 K. Moreover, at low temperature, it seems to be stronger than that at room temperature. 相似文献
36.
P Leroy A Nicolas C Gavriloff M Matt P Netter B Bannwarth B Hercelin M Mazza 《Journal of chromatography. A》1991,564(1):258-265
A simple and fast high-performance liquid chromatographic method was developed for the simultaneous measurement of 2-mercaptopropionylglycine (Tiopronine) and its metabolite (2-mercaptopropionic acid) in human plasma after the administration of a pharmaceutical dosage form (Acadione). The sample treatment before high-performance liquid chromatographic analysis consisted of the reduction of the corresponding disulphides by tri-n-butylphosphine and protein precipitation with ethanol. Separation was achieved by ion-pair high-performance liquid chromatography on a reversed-phase column (LiChrospher RP 18e) with cetrimonium bromide as counter ion and detection by fluorimetry after post-column derivatization with a selective thiol reagent, i.e. pyrenemaleimide. The high frequency of the analyzed samples and validation results make the method suitable for pharmacokinetic studies, and this was demonstrated by the first results obtained after the administration of an oral dose of 500 mg of Tiopronine to two healthy subjects. 相似文献
37.
The Ramanujan Journal - Let $$\sigma (n)=\sum _{d\mid n}d$$ be the sum of divisors function and $$\gamma =0.577\ldots $$ the Euler constant. In 1984, Robin proved that, under the Riemann... 相似文献
38.
We consider a model of spinless fermions on a lattice, interacting through a nearest neighbor repulsion. In the half-filled band case and for dimensionsd 2, we rigorously prove that there is long-range order in some domain of the parameters=(k
B
T)–1 andt/U, wheret is the hopping amplitude of the particles,U the strength of their repulsion, and the inverse temperature. Our technique is based on the usual Peierls argument of classical statistical mechanics but fails for the groundstate. We discuss the specific difficulties introduced by the Fermi statistics.Work supported in part by U.S. NSF grant PHY 90-19433-A02. 相似文献
39.
Chevallier Nicolas 《Potential Analysis》1993,2(2):187-194
LetP be a positive contraction ofL 1, we say that a sequence (Q n ) n of positive operators is subordinated toP if $$Q_0 = Id, \forall n \in \mathbb{N} Q_n P \geqslant Q_{n + 1} .$$ Let (Q n,k ) be a double sequence of operators such that for each integerk the sequence (Q n,k ) n is subordinated toP. We prove a result of almost everywhere convergence for the quotientsW k f/W k g, whereW k f=∑ n=0 ∞ Q n,k f. 相似文献
40.
[reaction: see text] A zirconocene-mediated ring contraction of 4-vinylfuranosides generated either from d-arabinose or d-glucose is followed by sequential oxidation to the ketone and alkynyl Grignard addition. The resulting cis-cyclobutanediols are subjected in turn to thermal rearrangement and intramolecular oxymercuration-demercuration. The regiochemistry of the final ring closure is controlled by the nature of R. 相似文献