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171.
Fibrin, the biopolymer produced in the final step of the coagulation cascade, is involved in the resistance of arterial thrombi to fragmentation under shear flow. However, the nature and strength of specific interactions between fibrin monomers are unknown. Thus, the shear-induced detachment of spherical monodispersed fibrin-coated latex particles in adhesive contact with a plane fibrin-coated glass surface has been experimentally studied, using an especially designed shear stress flow chamber. A complete series of experiments for measuring the shear stress necessary to release individual particles under various conditions (various number of fibrin layers involved in the adhesive contact, absence or presence of plasmin, the main physiological fibrinolytic enzyme) has been performed. The nonspecific DLVO interactions have been shown to be negligible compared to the interactions between fibrin monomers. A simple adhesion model based on the balance of forces and torque on particles, assuming an elastic behavior of the fibrin polymer bonds, to analyze the experimental data in terms of elastic force at rupture of an elementary intermonomeric fibrin bond has been used. The results suggested that this force (of order 400 pN) is an intrinsic quantity, independent of the number of fibrin layers involved in the adhesive contact. Copyright 2001 Academic Press. 相似文献
172.
A variety of double collision experiments, whereby fast species undergo collisional interactions in two distinct regions of a mass spectrometer, are described. These include two-stage charge reversal of negative ions, two-stage double electron transfer from targets to cations, neutralization-reionization experiments as well as delayed analysis of organic cations formed in a one-step charge reversal of anions. Experiments have been performed on a number of systems of current interest in gas-phase ion chemistry. It is concluded that autoelectron detachment of benzyl anions leads to benzyl radicals, whereas the collisionally induced electron detachment produces a mixture of benzyl and tropyl radicals. By contrast, electron detachment from [H3CNH]? is not a metastable process and occurs only after excitation to produce H3CNH˙ radicals, which do not rearrange into the thermodynamically more stable H2CNH2˙. It is shown that in the double electron transfer reactions H+ + Xe→H˙ + Xe+˙ and H˙ + Xe→H? + Xe+˙, excited states are produced. From double collision experiments on methyl formate ions, it is concluded that the non-decomposing ions have undergone rearrangement on the time-scale of 10 μs into the distonic isomer, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H} - \mathop {\rm C}\limits^ + ({\rm OH}){\rm O}\mathop {\rm C}\limits^. {\rm H}_2 $\end{document}. Finally, it is shown that short-lived (<0.2 μs) [H2, C, N]+ ions generated by charge-reversal of [H2CN]? have the [H2CN]+ structure, whereas most of the long-lived (10 μs) ions have the [HCNH]+ structure. 相似文献
173.
Sylvie Guerre 《Israel Journal of Mathematics》1986,56(3):361-380
Let 1≦q<p<2. We construct a bounded sequence (X n ) n∈N inL q which defines a typeσ onL q , such that:
- (X n ) n∈N is equivalent to the unit vector basis ofl p .
- The l-conic classK 1(σ) generated byσ is not relatively compact for the topology of uniform convergence on bounded sets ofL q .
- (X n ) n∈N has no almost exchangeable subsequence after any change of density.
174.
Jérôme F Monnier F Lawicka H Dérien S Dixneuf PH 《Chemical communications (Cambridge, England)》2003,(6):696-697
Catalytic hydrophosphination of propargyl alcohols by ruthenium complexes RuCl(cod)(C5Me5) and RuCl(PPh3)2(C5Me5) leads to the formation of functionalized vinylphosphines, with linkage of the phosphorus atom to the terminal alkyne carbon, via a ruthenium vinylidene intermediate. 相似文献
175.
Schinzer D Bourguet E Ducki S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(13):3217-3224
The total synthesis of furano-epothilone D by a convergent route is reported. The key fragments are available on a large scale to provide sufficient material for biological evaluation. The approach involves a palladium-catalyzed coupling that generates a highly functionalized aldehyde which is connected in a stereoselective aldol reaction to yield the framework of furano-epothilone D. Finally, a macrolactonization provides furano-epothilone D. 相似文献
176.
Ferlay S Holakovsky R Hosseini MW Planeix JM Kyritsakas N 《Chemical communications (Cambridge, England)》2003,(11):1224-1225
The co-crystallisation of [Fe(CN)5NO]2- and cyclic achiral 1(2+) and chiral 2(2+) or 3(2+) bisamidinium tectons leads in the crystalline phase to the formation of 1-D H-bonded achiral and chiral molecular networks respectively. In all cases, the network is formed by mutual bridging of the anionic and cationic units through a chelate mode of H-bonding. 相似文献
177.
This review reports the contribution of the catalyst precursor RuCl(COD)C5Me5, and of the Rennes team, for the selective transformation of alkynes to generate high value chemicals with atom economy reactions. Ruthenium activation processes are discussed. Are successively presented (i) the cross-oxidative coupling of alkyne and allyl alcohol to generate γ,δ-unsaturated aldehydes, (ii) the head-to-head dimerisation of alkynes in the presence of carboxylic acids, via a mixed Fischer-Schrock type biscarbene-ruthenium complex, to give functional dienes, and that of propargyl alcohols, via cyclobutadienyl-ruthenium intermediate, to produce cyclobutene derivatives, (iii) the addition of diazoalkanes to alkynes leading to functional dienes via double carbene addition and (iv) the reaction of diazoalkanes to enynes leading to new bicyclo[3.1.0]hexane compounds. Most of the above catalytic reactions involve carbene-ruthenium catalytic species of type Cp*(Cl)Ru(biscarbene) or Cp*(Cl)RuCHR. 相似文献
178.
Sylvie le Stang Frédéric Paul Claude Lapinte 《Chemistry of Heterocyclic Compounds》1999,35(9):1063-1074
The functionalized complexes [(dppe)Cp*Fe(CC)]2-(Py) (Py=2,6-C5H3N and 3,5-C5H3N (dppe=1,2-bis(diphenylphosphino)ethane) were isolated in good yields from reaction of the chloro complex (dppe)Cp*FeCl with the protected bis-acetylenic heterocyclic precursor. These electron-rich pyridyl ligands constitute interesting examples of organometallic heterocycles bearing redox-active substituents. Attempts to find an alternative route starting from the alkynyl complex [(dppe)Cp*Fe(CCH)] and the corresponding dibromopyridines using a Sonogashira cross-coupling reaction are also described. By this route, the monofunctionalized products [(dppe)Cp*Fe(CC)]-2,6-Py-Br and [(dppe)Cp*Fe(CC)]-3,5-Py-Br could be cleanly isolated. These compounds open the way to the generation of heteroaromatics featuring nonequivalent alkyne substituents such as [(dppe)Cp*Fe(CC)]-2,6-Py-[(CC)SiMe3] or [(dppe)Cp*Fe(CC)]-3,5-Py-[(CC)SiMe3] by further coupling.In commemoriation of the centenary of Academician A. N. Nesmeyanov.UMR CNRS 6509 Organométalliques et catalyse: Chimie et Electrochimie Moléculaires, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1207–1218, September, 1999. 相似文献
179.
Hourdin S Longchamp S Gallet O Nigretto JM 《Journal of colloid and interface science》2001,236(1):132-140
The occurrence of a thermally induced first-order transition affecting the amidolytic activity of plasmin adsorbed onto bare and protein-modified graphite and glassy carbon was demonstrated in the 10-45 degrees C temperature range in the presence of a chromogenic substrate. Modification of the surfaces was achieved upon spontaneous adsorption of plasmin to surfaces bearing a coating of fibrinogen, whether electrochemically oxidized or not. The amount of fibrinogen adsorbed at graphite was determined by ELISA. The kinetics of the transition was characterized by its starting temperature (T(c)), which was between 14 and 19 degrees C, the first-order rate constant, and the activation energy E(a) deduced from Arrhenius plots. Results showed the absence of a correlation between T(c), E(a), and contact angle variations. It is therefore likely that these variables address separate steps in a complex pathway of reactions undergone by plasmin under mild thermal constraints. Copyright 2001 Academic Press. 相似文献
180.