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41.
The electronic structure of an icosaedral cluster of 13 nickel atoms is studied using an Extended Hückel method. Near the highest occupied level at ?7.65 eV, h and t orbitals are accidentally degenerate so that the fundamental state possesses a high spin multiplicity (2S + 1 = 9) accounting for the magnetism of the particule. We have considered several geometries for a hydrogen molecule approaching the cluster at a minimum distance of 1.47 Å. In all cases the H-H bond is weakened because of electron transfer from the nickel towards the hydrogen atoms and partial filling of the antibonding orbital of h2. During the increase of the H-H distance the weakening is easier than in the absence of a nickel catalyst leading to the dissociative adsorption of the molecule. The activation mechanism of H2 requires participation of both the s and d orbitals of the metal and leads to a lowering of the spin multiplicity. Finally, we have shown that a dissociative adsorption is obtained when the H2 molecule approaches a triangular face. After breaking of the H-H bond, the more stable system corresponds to atomic H adsorption on two opposite vertices. 相似文献
42.
Marie-France Ludmann-Obier MichÈle Dartiguenave Yves Dartiguenave 《Journal of Molecular Structure》1973,18(1):123-133
Electronic spectra of chloro- and bromoacetates of copper (II) (hydrated and as addition compounds with ethyl acetate) have been obtained in the solid state at 298 °K and 77 °K. The results are discussed and compared with magnetic susceptibility measurements. The band at about 27.5 kK. is present in the monomers and in the dimers and cannot be used to characterize the dimer species. It is assigned to the npπ → dx2?y2 symmetry forbidden transition. 相似文献
43.
Francis F Saguez J Cherqui A Vandermoten S Vincent C Versali MF Dommès J De Pauw E Giordanengo P Haubruge E 《Applied biochemistry and biotechnology》2012,166(5):1291-1300
Hydrolytic enzymes involved in chitin degradation are important to allow moulting during insect development. Chitinases are
interesting targets to disturb growth and develop alternative strategies to control insect pests. In this work, a chitinase
from the aphid Myzus persicae was purified with a 36-fold purification rate in a three step procedure by ammonium sulphate fractionation, anion-exchange
chromatography on a DEAE column and on an affinity Concanavalin A column. The purified chitinase purity assessed by 1D and
2D SDS–PAGE revealed a single band and three spots at 31 kDa, respectively. Chitinases were found to have high homologies
with Concanavalins A and B, two chitinase-related proteins, a fungal endochitinase and an aphid acetylhydrolase by peptide
identification by Maldi-Tof-Tof. The efficiency of two potent chitinase inhibitors, namely allosamidin and psammaplin A, was
tested and showed significant rate of enzymatic inhibition. 相似文献
44.
Elise VilleminBenjamin Elias Raphaël RobietteKoen Robeyns Marie-France HerentJean-Louis Habib-Jiwan Jacqueline Marchand-Brynaert 《Tetrahedron letters》2011,52(40):5140-5144
The synthesis of novel [4+2] cycloadducts by Diels-Alder (DA) reaction between diethyl 1-phosphono-1,3-butadiene and cyclic CC and NN dienophiles, such as maleimide and 1,2,4-triazole-3,5-dione derivatives, is described. These phosphonated bicyclic frameworks feature a cage shape enabling metal chelation. Indeed, stable complexes were formed in solution with M2+ and M3+ metal cations, as evidenced by HRMS in the ESI mode (electrospray ionization). L1:M (one ligand-one metal) and L2:M (two ligands-one metal) complexes were identified depending on the nature of the cation. 相似文献
45.
El Ghachtouli S Wójcik K Copey L Szydlo F Framery E Goux-Henry C Billon L Charlot MF Guillot R Andrioletti B Aukauloo A 《Dalton transactions (Cambridge, England : 2003)》2011,40(36):9090-9093
Herein, we report the manganese complex with a novel trianionic ligand, the pentafluorophenyldipyrrinphenol ligand DPPH(3). The X-ray crystal structure reveals that the Mn(III) complex exists in a dimeric form in the solid state. Electrochemical studies indicate two quasi-reversible one electron oxidation processes. EPR data on the one electron oxidised species in solution support the formation of a monuclear Mn complex with an S = 3/2 spin system. Preliminary studies towards epoxidation reactions were tested in the presence of iodosylbenzene (PhIO) and are in favour of an oxygen-atom-transfer (OAT) reaction catalyzed by the Mn(III) complex. 相似文献
46.
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48.
The synthesis of polyhetarylenes containing exclusively s-tetrazine and another nitrogen heterocycle (pyridine or s-triazine) is described. The key step involved the polymerization of a suitable di- or triamidrazone, leading to a linear or hyperbranched dihydrotetrazine-based assembly, respectively. The triazinylenetetrazinylene material stands as one of the most nitrogenated polymers ever described. 相似文献
49.
Marie-France PouliotLaetitia Angers Jean-Denys HamelJean-François Paquin 《Tetrahedron letters》2012,53(32):4121-4123
The preparation of 2-oxazolines and related N-containing heterocycles from the corresponding hydroxyamides using XtalFluor-E ([Et2NSF2]BF4) as a cyclodehydration agent is described. A wide range of heterocycles are obtained under mild conditions in good to excellent yields. 相似文献
50.
Dhriti Khandal Pierre-Yves Mikus Patrice Dole Christophe Bliard Jérémie Soulestin Marie-France Lacrampe Stéphanie Baumberger Xavier Coqueret 《Radiation Physics and Chemistry》2012,81(8):986-990
The present paper focuses on the effects of electron beam (EB) irradiation on thermoplastic materials based on destructurized starch including glycerol and water as plasticizers to assess the potentiality of cinnamyl alcohol as reactive additive capable of counterbalancing the degradation of the polysaccharide by inducing interchain covalent linkages. The tensile properties at break of test specimens of controlled composition submitted to EB irradiation at doses ranging from 50 to 200 kGy revealed the presence of competitive chain scission and bridging in samples containing cinnamyl alcohol at a relative concentration of 2.5% with regard to dry starch. The occurrence of crosslinking under particular conditions was evidenced by gel fraction measurements. The treatment under radiation was also applied to model blends including maltodextrin as a model for starch and the other ingredients to gain an insight into the radiation induced mechanisms at the molecular level. The presence of cinnamyl alcohol is found to limit degradation. Size exclusion chromatography and gel fraction allowed to monitor the effects and confirmed unambiguously the attachment of UV-absorbing chromophores onto the maltodextrin main chain. The combination of the obtained results demonstrates the possibility of altering in a favorable way the tensile properties of plasticized starch by applying high energy radiation to properly formulated blends including aromatic compounds like cinnamyl alcohol. 相似文献