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961.
962.
963.
Ivano Tavernelli Dr. Marie‐Pierre Gaigeot Prof. Rodolphe Vuilleumier Dr. Carlos Stia Dr. Marie‐Anne Hervé du Penhoat Dr. Marie‐Françoise Politis Dr. 《Chemphyschem》2008,9(14):2099-2103
The early stages of the Coulomb explosion of a doubly ionized water molecule immersed in liquid water are investigated with time‐dependent density functional theory molecular dynamics (TD–DFT MD) simulations. Our aim is to verify that the double ionization of one target water molecule leads to the formation of atomic oxygen as a direct consequence of the Coulomb explosion of the molecule. To that end, we used TD–DFT MD simulations in which effective molecular orbitals are propagated in time. These molecular orbitals are constructed as a unitary transformation of maximally localized Wannier orbitals, and the ionization process was obtained by removing two electrons from the molecular orbitals with symmetry 1B1, 3A1, 1B2 and 2A1 in turn. We show that the doubly charged H2O2+ molecule explodes into its three atomic fragments in less than 4 fs, which leads to the formation of one isolated oxygen atom whatever the ionized molecular orbital. This process is followed by the ultrafast transfer of an electron to the ionized molecule in the first femtosecond. A faster dissociation pattern can be observed when the electrons are removed from the molecular orbitals of the innermost shell. A Bader analysis of the charges carried by the molecules during the dissociation trajectories is also reported. 相似文献
964.
Winne JM De Clercq PJ Milanesio M Pattison P Viterbo D 《Organic & biomolecular chemistry》2008,6(11):1918-1925
Some nonenzymic epoxide-initiated polyolefin cyclization are reported. The presented molecules are partially constrained analogues of (3S)-oxidosqualene, the natural substrate to many important cyclase enzymes. These model compounds feature a preformed C-ring with built-in stereochemical information. The experimental results allow for an instructive comparison with the enzymic processes, particularly those of the cyclases in steroid biosynthesis (i.e. lanosterol synthase). 相似文献
965.
Pichon C Dolbecq A Mialane P Marrot J Rivière E Sécheresse F 《Dalton transactions (Cambridge, England : 2003)》2008,(1):71-76
Two new insoluble transition metal substituted phosphotungstates, (C2N2H10)11[{(B-alpha-PW9O34)Fe3(OH)3}4(PO4)4Fe].38H2O(1) and K4(C2N2H10)12[(alpha-PW10Fe2O39)4].30H2O(2), have been isolated by the hydrothermal reaction of [A-alpha-PW9O34]9-, Fe(III) ions and ethylenediamine. Compound 1 has a tetrahedral symmetry and contains a Fe13 core built from the assembly of four Fe(III) trisubstituted [B-alpha-PW9O34]9- anions around a central disordered iron ion via four phosphato ligands. The anion in 2 can be described as a square of disubstituted [PW10O37]9- anions linked by Fe(III)-O-Fe(III) bridges. Magnetic measurements performed on 1 and 2 have shown the occurrence of antiferromagnetic interactions between the iron ions and have allowed the coupling constants between the magnetic centers to be determined. 相似文献
966.
Paolini J Tomi P Bernardini AF Bradesi P Casanova J Kaloustian J 《Natural product research》2008,22(14):1270-1278
The composition of the essential oil of Cistus albidus (L.) obtained from plants growing wild in Provence (France) has been investigated using GC-RI (RI = retention indices), GC/MS and (13)C-NMR. Eighty-eight components were reported accounting for 81.8% of the essential oil. This essential oil was characterized by a high content of sesquiterpenes with alpha-zingiberene (12.8%), alpha-curcumene (7.7%), (E)-beta-caryophyllene (5.9%), alpha-cadinol (5.4%), alpha-bisabolol (4.1%), caryophyllene oxide (3.8%), allo-aromadendrene (3.4%), delta-cadinene (3.4%), and germacrene D (3.1%) being the main components. 相似文献
967.
Alaerts L Maes M Jacobs PA Denayer JF De Vos DE 《Physical chemistry chemical physics : PCCP》2008,10(20):2979-2985
The capacity and selectivity of the metal-organic framework MIL-47 for liquid phase adsorption are shown to heavily depend on the pretreatment of the material, as illustrated in detail by the particular case of selective xylene adsorption. By totally removing the uncoordinated terephthalic acid from the pores and simultaneously avoiding oxidation to nonporous V(2)O(5), pore volume and uptake of xylenes can be maximized. The presence of uncoordinated terephthalic acid in the pores improves the selectivity between p- and m-xylene. Calcination bed thickness and oven geometry influence the optimal calcination procedure. The physicochemical modifications of MIL-47 during its activation are investigated in detail with XRD, SEM, nitrogen physisorption, TGA and diffuse reflectance UV-Vis spectroscopy. Using optimally pretreated MIL-47 as adsorbent for xylene, ethyltoluene, dichlorobenzene, toluidine or cresol isomers, the para-isomer is in each case preferred over the meta-isomer in pulse chromatographic and batch experiments. The role of stacking in the selective adsorption of these isomers is discussed. In the case of the dichlorobenzenes, the meta- and para-isomers can be separated in a breakthrough experiment with a selectivity of 5.0. 相似文献
968.
Abstraction of hydrogen atoms by pthalimide-N-oxyl radicals is an important step in the N-hydroxyphthalimide catalyzed autoxidation of hydrocarbons. In this contribution, the temperature dependency of this reaction is evaluated by a detailed transition state theory based kinetic analysis for the case of toluene. Tunneling was found to play a very important role, enhancing the rate constant by a factor of 20 at room temperature. As a result, tunneling, in combination with the existence of two distinct rotamers of the transition state, causes a pronounced temperature dependency of the pre-exponential frequency factor, and, as a consequence, marked curvature of the Arrhenius plot. This explains why earlier experimental studies over a limited temperature range around 300 K found formal Arrhenius activation energies and pre-factors that are 4 kcal mol(-1) and three orders of magnitude smaller than the actual energy barrier and the corresponding frequency factor, respectively. Also as a consequence of tunneling, substitution of a deuterium atom for a hydrogen atom causes a large decrease in the rate constant, in agreement with the measured kinetic isotope effects. The present theoretical analysis, complementary to the experimental rate coefficient data, allows for a reliable prediction of the rate coefficient at higher temperatures, relevant for actual autoxidation processes. 相似文献
969.
A series of 2-alkylsulfanyl-4-(4-fluorophenyl)-5-(2-aminopyridin-4-yl)-substituted imidazoles was prepared and interaction possibilities of the 2-thioether moiety with phosphate/ribose binding pockets of p38 MAP kinase were investigated. Introduction of the alkyl/benzyl amino function at the pyridine moiety was carried out via nucleophilic substitution or via palladium catalyzed aryl-C-N-bond formation. 相似文献
970.
An efficient synthesis of new dioxygenated isoquinolines is reported. The novelty of this approach derives from its use of tricyclic-nitril (3) as a building block in a synthetic sequence of seven steps for the preparation of the tetracyclic isoquinoline (14) and its derivatives. The isoquinoline 16 was 10-fold more active against leukemia L1210 than the corresponding tetrahydroisoquinoline 14. 相似文献