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101.
Aziz Ghoufi Pierre Archirel Jean-Pierre Morel Nicole Morel-Desrosiers Anne Boutin Patrice Malfreyt 《Chemphyschem》2007,8(11):1648-1656
We report potential of mean force (PMF) calculations on the interaction between the p-sulfonatocalix[4]arene and a monovalent cation (Cs(+)). It has been recently shown from microcalorimetry and (133)Cs NMR experiments that the association with Cs(+) is governed by favourable cation-pi interactions and is characterized by the insertion of the cation into the cavity of the macrocycle. We show that the PMF calculation based upon a classical model is not able to reproduce both the thermodynamic properties of association and the insertion of the cation. In order to take into account the different contributions of the cation-pi interactions, we develop a new methodology consisting of changing the standard PMF by an additional contribution resulting from quantum calculations. The calculated thermodynamic properties of association are thus in line with the microcalorimetry and (133)Cs NMR experiments and the structure of the complex at the Gibbs free-energy minimum shows the insertion of the cation into the cavity of the calixarene. 相似文献
102.
The symmetric and unsymmetric phenylchlorohydrodigermanes can be isolated or characterized via partial halogenation of the Ge? H bonds of the symmetrical phenylhydrodigermanes Ph2(H)GeGe(H)2Ph, Ph(H)2GeGe(H)2Ph by chloromethyl methyl ether and carbontetrachloride. Some of these phenylchlorohydrodigermanes are formed by insertion of phenylchlorogermylene (PhGeCl) on the Ge? H or Ge? Cl bonds of the phenylchlorohydrogermanes. The hydrolysis of the monochloro phenylhydrodigermanes Ph2(Cl)GeGe(H)2 and Ph(Cl)(H)GeGe(H)2Ph leads to the phenyl phenylhydrogermyl digermoxanes [Ph2(H)GeGePh2]2O and [Ph(H)2GeGe(H)Ph]2O. Treatment of these oxides with the concentrated aqueous solutions of hydracides leads to the monofluorinated, brominated and iodinated phenylhydrodigermanes Ph2(H)GeGe(X)Ph2 and Ph(H)2GeGe(H)(X)Ph (X) = F, Br, I). Phenylchlorohydrodigermanes decompose thermally by α-elimination on one germanium atom with formation of germylene and phenylchlorohydrogermane. The physico-chemical IR. and NMR. study of these phenylhalogenohydrodigermanes indicates that, if the vGe? H frequency variations are mostly linked to the inductive effects of the substituents on the same germanium, the variations of the chemical shifts of the Ge? H protons seem to be due to many factors and especially to the inductive effect of the substituents on the germanium and the magnetic anisotropy of the Ge? X bonds. 相似文献
103.
Rosu F Gabelica V Houssier C Colson P Pauw ED 《Rapid communications in mass spectrometry : RCM》2002,16(18):1729-1736
DNA triplex and quadruplex structures have been successfully detected by electrospray ionization mass spectrometry (ESI-MS). Circular dichroism and UV-melting experiments show that these structures are stable in 150 mM ammonium acetate at pH 7 for the quadruplexes and pH 5.5 for the triplexes. The studied quadruplexes were the tetramer [d(TGGGGT)](4), the dimer [d(GGGGTTTTGGGG)](2), and the intramolecular folded strand dGGG(TTAGGG)(3), which is an analog of the human telomeric sequence. The absence of sodium contamination allowed demonstration of the specific inclusion of n - 1 ammonium cations in the quadruplex structures, where n is the number of consecutive G-tetrads. We also detected the complexes between the quadruplexes and the quadruplex-specific drug mesoporphyrin IX. MS/MS spectra of [d(TGGGGT)](4) and the complex with the drug are also reported. As the drug does not displace the ammonium cations, one can conclude that the drug binds at the exterior of the tetrads, and not between them. For the triplex structure the ESI-MS spectra show the detection of the specific triplex, at m/z values typically higher than those typically observed for duplex species. Upon MS/MS the antigene strand, which is bound into the major groove of the duplex, separates from the triplex. This is the same dissociation pathway as in solution. To our knowledge this is the first report of a triplex DNA structure by electrospray mass spectrometry. 相似文献
104.
105.
Pierre A. Vuillermot 《Communications in Mathematical Physics》1980,76(1):1-26
For any initial spin configuration we prove the existence, unicity and regularity properties of the solution of Hamilton's equations for the infinite classical Heisenberg model with stable interactions, along with the essential selfadjointness of the associated Liouville operator. We also prove new properties of SU (2)-coherent states which, together with the concept of Trotter approximations for one-parameter (semi-) groups, are used to show that this dynamics is nothing but the classical limit of the time evolution generated by the infinite quantum (suitably normalized) Heisenberg Hamiltonian. The classical limit emerges when the spin magnitude S goes to infinity while Plank's constant goes to zero, their product S remaining fixed. The main results are stated in the form of intertwining relations between the classical and the quantum unitary group.Work supported in part by the Swiss National Science Foundation under Grant 820-436-76 and in part by the U.S. Department of Energy under contract EG-77-C-03-1538. 相似文献
106.
Non-aqueous capillary electrophoresis of the positional isomers of a sulfated monosaccharide 总被引:2,自引:0,他引:2
Descroix S Varenne A Goasdoue N Abian J Carrascal M Daniel R Gareil P 《Journal of chromatography. A》2003,987(1-2):467-476
A non-aqueous capillary electrophoresis (NACE) method coupled to indirect absorbance detection has been developed for the separation of the three positional isomers of monosulfated fucose. The optimized electrolyte was composed of 12 mM ethanolamine, 2 mM trimesic acid buffer in a methanol-ethanol (1:1, v/v) mixture. As the retained electrolyte entails no separating agent other than the pH buffer, the NACE separation of the positional isomers has been ascribed mainly to selective ion-pairing with the electrolyte counter-ion and the possibility of a selective solvation effect in the alcohol mixture. In the absence of pure isomeric standards, peak identification was completed by MS and NMR spectroscopy and selective enzymatic desulfation. This method should be of interest for the structure elucidation of monosulfated fucose-based polysaccharides and for the screening of sulfoesterase of unknown activity. 相似文献
107.
Claude Villiers Pierre Thury Michel Ephritikhine 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(6):m243-m245
In the title compound, (1,4,7,10,13,16‐hexaoxacyclooctadecane‐1κ6O)‐μ‐oxo‐1:2κ2O:O‐hexakis(tetrahydroborato)‐1κ3H;2κ2H;2κ2H;2κ3H;2κ3H;2κ3H‐diuranium(IV), [U2(BH4)6O(C12H24O6)], one of the U atoms (U1), located at the centre of the crown ether moiety, is bound to the six ether O atoms, and also to a tridentate tetrahydroborate group and a μ‐oxo atom in axial positions. The other U atom (U2) is bound to the same oxo group and to five tetrahydroborate moieties, three of them tridentate and the other two bidentate. The two metal centres are bridged by the μ‐oxo atom in an asymmetric fashion, thus giving the species (18‐crown‐6)(κ3‐BH4)U=(μ‐O)—U(κ3‐BH4)3(κ2‐BH4)2, in which the U1=O and U2—O bond lengths to the μ‐O atom [1.979 (5) and 2.187 (5) Å, respectively] are indicative of the presence of positive and negative partial charges on U1 and U2, respectively. 相似文献
108.
Linear trigermoxanes, R1 RGeOGe(R3)2OGeRR1, a new series of organogermanium compounds, were synthesized by reaction of a lithium organogermanolate with a suitable organogermanium dihalide. With alkyl or phenyl substituents, these trigermoxanes are structurally unstable viscous oils, due to redistribution reactions. When R3 substituents are bulky groups, such as mesityl, trigermoxanes are thermally and structurally stable oils; depending on the R1 and R2 substituents their viscosities lie in the range 240 to more than 1500 cPo (mPa s) at 20°C. When both terminal germanium atoms are substituted with two mesityl groups, trigermoxanes are stable glassy solids. 相似文献
109.
The preparation of 5,6-bis((E)-chlorommethylidene)bicyclo[2.2.2]oct-2-ene ( 13 ), 2,3-bis((E)-chloromethyl idene)-5exo,6exo- and -5endo,6endo-epoxybicyclo[2.2.2] octane ( 14 and 15 ), 5,6-bis((E)-chloromethylidene)-2exo- and -2endo-bicyclo[2.2.2] octanol ( 16 and 17 ) and 5,6-bis((E)-chloromethylidene)-2-bicyclo[2.2.2]octanone ( 18 ) are described. The face selectivity (endo-face vs. exo-face attack onto the exo-cyclic diene) of their cycloadditions to tetracyanoethylene has been determined in benzene at 20°. It is 78/22, 80/20, 60/40, 68/32, 3/97 and 30/70 for 13 , 14 , 15 , 16 , 17 and 18 , respectively. 相似文献
110.
Jacques Dubac Pierre Mazerolles Pierre Fagoaga 《Journal of organometallic chemistry》1977,139(3):271-277
The reaction of organomagnesium organolithium compounds (alkyl, aryl, allyl and benzyl derivatives) with 1,2-dimethyl-1-alkoxy-l-silacyclobutanes proceeds with retention of configuration at the silicon atom. Stereochemical results are discussed in terms of the SN2Si mechanism. The proposed configurations are supported by 1H and 13C NMR data. 相似文献