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1.
Beyond Stereoselectivity,Switchable Catalysis: Some of the Last Frontier Challenges in Ring‐Opening Polymerization of Cyclic Esters
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Dr. Sophie M. Guillaume Dr. Evgueni Kirillov Dr. Yann Sarazin Prof. Dr. Jean‐François Carpentier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):7988-8003
Metal‐based catalysts and initiators have played a pivotal role in the ring‐opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis. This Review is not intended to comprehensively cover all of these aspects. Rather, it provides a personal overview of the very recent progress achieved in some selected, important aspects of ROP catalysis—stereocontrol and switchable catalysis. Hence, the first part addresses the development of new metal‐based catalysts for the isoselective ROP of racemic lactide towards stereoblock copolymers, and the use of syndioselective ROP metal catalysts to control the monomer sequence in copolymers. A second part covers the development of ROP catalysts—primarily metal‐based catalysts, but also organocatalysts—that can be externally regulated by the use of chemical or photo stimuli to switch them between two states with different catalytic abilities. Current challenges and opportunities are highlighted. 相似文献
2.
We show that every plane graph of diameter 2r in which all inner faces are triangles and all inner vertices have degree larger than 5 can be covered with two balls of radius r. © 2003 Wiley Periodicals, Inc. J Graph Theory 44: 65–80, 2003 相似文献
3.
Yann Bugeaud 《Comptes Rendus Mathematique》2002,335(2):117-120
We prove that there exist Liouville numbers which are normal, as well as Liouville numbers which are non-normal to any base. To cite this article: Y. Bugeaud, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 117–120. 相似文献
4.
Caruntu D Remond Y Chou NH Jun MJ Caruntu G He J Goloverda G O'Connor C Kolesnichenko V 《Inorganic chemistry》2002,41(23):6137-6146
Study of the reactivity of 3d transition metal cations in diethylene glycol solutions revealed several key features that made it possible to develop a new method for synthesis of the nanocrystalline transition metal ferrites. The 3-7 nm particles of [MFe2O4]n[O2CR]m, where M = Mn, Fe, Co, Ni, and Zn, ligated on their surface with long-chain carboxylate anions, have been obtained in an isolated yield of 75-90%. The key features are the following. Complexation of the first-row transition metal cations with diethylene glycol at a presence of alkaline hydroxide is sufficient to enable control over the rate of their hydrolysis. The reaction of hydrolysis leads to the formation of metal oxide nanocrystals in colloidal solution. The nanoparticles growth is terminated by an added long-chain carboxylic acid, which binds to their surface and acts as a capping ligand. The isolated nanocrystalline powders are stable against agglomeration and highly soluble in nonpolar organic solvents. 相似文献
5.
Bretonnière Y Mazzanti M Pécaut J Olmstead MM 《Journal of the American Chemical Society》2002,124(31):9012-9013
The simple asymmetric tetradentate ligand 2,2':6',2' '-terpyridine-6-carboxylic acid leads to the self-assembly of the first europium nanowheel containing europium ions in two different coordination environments. Moreover the self-assembly of bis(terpyridinecarboxylate) europium species to form a hexameric wheel capable of strongly binding LnIII cations is controlled by the ligand/cation ratio. 相似文献
6.
Euzenat L Horhant D Ribourdouille Y Duriez C Alcaraz G Vaultier M 《Chemical communications (Cambridge, England)》2003,(18):2280-2281
Thermal decomposition of hindered amine-borane adducts leads in high yields to monomeric (dialkylamino)boranes R1R2N-BH2 (R1 and R2 = alkyl) that are new and efficient boron-sources in the Pd0 catalyzed borylation reaction affording monomeric aryl(dialkylamino)boranes R1R2N-BHR3 (R3 = aryl). 相似文献
7.
We describe a concise and convergent synthesis of (rac)-5-methoxy-6-azatricyclco[7.3.1.0(2,7)]trideca-2(7),3,5,11-tetraen-13-ol, which has the basic ring system of huperzine A, a potent inhibitor of acetylcholinesterase. We also describe the synthesis of the novel system 5-methoxy-6-azatricyclo[7.2.2.0(2,7)]trideca-2(7),3,5-trien-10-one and a series of related systems. 相似文献
8.
Poriel C Ferrand Y le Maux P Raul-Berthelot J Simonneaux G 《Chemical communications (Cambridge, England)》2003,(9):1104-1105
Anodic oxidation of tetraspirobifluorene-manganese porphyrin lead to the coating of the working electrode by insoluble electroactive poly(9,9'-spirobifluorene-manganese porphyrin) films for which electrochemical behaviour and physicochemical properties are described; these polymeric materials are able to catalyze the heterogeneous epoxidation of styrene with iodobenzene diacetate and iodosylbenzene. 相似文献
9.
Capillary isoelectric focusing (CIEF) separations are usually performed with neutral coated fused-silica capillaries in aqueous anticonvective media. Glycerol, a very viscous solvent (eta = 945 mPa x s at 25 degrees C), known to help stabilize any kind of proteins and solubilize hydrophobic ones, was tested as an alternative to using commercial gels. Viscosity and electroosmotic mobility were measured as a function of gel or glycerol content in water, and a 30:70 v/v glycerol-water medium appeared as a good compromise for performing CIEF in a bare fused-silica capillary without imposing too high a viscosity. To demonstrate the feasibility of this new CIEF system, a standard mixture of nine model proteins was separated according to their pI with a good agreement between experimental and literature aqueous pIs. Moreover, better resolution was achieved with this system than with the conventional aqueous CIEF system, as two of the model proteins could not be separated in the latter system. Glycerol-water CIEF in bare silica capillary was next applied to the separation of horse radish peroxidase, a complex mixture of protein isoforms. The good concordance with the separation obtained by the conventional CIEF system indicated the adequacy of this new system. Finally, as anticipated from the results obtained for the separation of bacteriorhodopsin, a membrane protein, glycerol-water CIEF performed in bare silica capillary appears to be a promising alternative to conventional aqueous CIEF for hydrophobic protein characterization, under their native form. 相似文献
10.
[structure: see text] The first total synthesis of anachelin H is reported. Starting from L-Ser, a stereodivergent synthesis of the polyketide fragment resulting in all possible diastereoisomers is described. The alkaloid peptide fragment is prepared via a tellurium-mediated oxidative aza annulation as the key step. Coupling of the fragments gave synthetic anachelin H, which was found to be identical to a sample of the natural product, thus confirming the configuration by total synthesis. 相似文献