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411.
Mpoh GE Tapsoba E Nébié RC Bonzi-Coulibaly YL Sié FS 《Rapid communications in mass spectrometry : RCM》2002,16(21):2040-2043
Electron impact mass spectra of 1,3,5-triarylpentane-1,5-diones are reported. All compounds studied show a tendency to eliminate a water molecule and also the elements of [H3O] before fragmentation to smaller ions. The [H3O] loss proceeds via loss of water to form a pyran ion, which subsequently eliminates a hydrogen atom to form the stable pyrillium cation. 相似文献
412.
Lilly Sanathanan Elizabeth Danaher Ki-Hwan Kim Yvonne Martin 《Journal of computational chemistry》1987,8(8):1075-1083
The computer program PRODIS is used to find low energy conformations of flexible molecules by searching the potential energy surface(s) of one or more torsion angles via rigid rotation. The n-dimensional grid of energy versus torsion angles is then converted to a Boltzman probability distribution, with the probability being represented not as a function of torsion angle, but rather a distance between two atoms. These atoms are chosen by comparison with a known, active analogue in which certain atoms have previously been determined as requirements for drug activity. PRODIS produces a list of low energy conformations, their corresponding interatomic distances and the Boltzman probability for each distance ±0.125, as well as the total probability for each conformation. The user also specifies a target interatomic distance and range (usually derived from a more rigid analogue) for which PRODIS lists all conformations and their Boltzman probability that meet this distance. 相似文献
413.
G. Benz H. Lüers P. Bohrisch M. Tortelli R. Ruggeri W. Otte E. Kröger W. Lühr H. Schmalfuß H. Werner R. Strohecker J. Großfeld A. Beckel H. Thaler K. Täufel K. Richter H. Damm E. Ruppol H. A. A. Aitken R. Delaby Yvonne Breugnot S. F. Juschkewitsch N. M. Ssokolow P. Arup und J. T. Minster 《Fresenius' Journal of Analytical Chemistry》1933,94(7-8):286-295
Ohne Zusammenfassung 相似文献
414.
Yvonne Choquet-Bruhat James Isenberg Daniel Pollack 《Journal of Fixed Point Theory and Applications》2007,1(1):31-46
The Einstein-scalar field theory can be used to model gravitational physics with scalar field sources. We discuss the initial
value formulation of this field theory, and show that the ideas of Leray can be used to show that the Einstein-scalar field
system of partial differential equations is well-posed as an evolutionary system. We also show that one can generate solutions
of the Einstein-scalar field constraint equations using conformal methods.
Dedicated to the memory of Jean Leray 相似文献
415.
Yvonne Kavanagh 《Tetrahedron》2009,65(39):8259-8268
An approach towards the construction of bicyclic analogues of monoterpene alkaloids belonging to the kinabalurine, incarvilline and skytanthine families of natural products is reported. These syntheses rely on a stereoselective intramolecular Pauson-Khand cyclisation of a chiral pool-derived enyne in order to prepare the bicyclic core. Stereoselective further elaboration generates diastereomeric analogues of the naturally occurring alkaloids. 相似文献
416.
We prove the global existence and uniqueness of wave maps onexpanding universes of dimension three or four, that is Robertson–Walkerspacetimes whose inverse radius is integrable with respect to the cosmictime. A result is obtained for small initial data by using the first andsecond energy estimates. 相似文献
417.
418.
TEM,XRD and AFM study of poly(<Emphasis Type="Italic">o</Emphasis>-ethoxyaniline) films: new evidence for the formation of conducting islands 总被引:1,自引:0,他引:1
Fabio L. Leite William F. Alves Mirta Mir Yvonne P. Mascarenhas Paulo S. P. Herrmann Luiz H. C. Mattoso Osvaldo N. OliveiraJr. 《Applied Physics A: Materials Science & Processing》2008,93(2):537-542
The existence of conducting islands in polyaniline films has long been proposed in the literature, which would be consistent with conducting mechanisms based on hopping. Obtaining direct evidence of conducting islands, however, is not straightforward. In this paper, conducting islands were visualized in poly(o-ethoxyaniline) (POEA) films prepared at low pH, using Transmission Electron Microscopy (TEM) and atomic force spectroscopy (AFS). The size of the islands varied between 67 and 470 Å for a pH=3.0, with a larger average being obtained with AFS, probably due to the finite size effect of the atomic force microscopy tip. In AFS, the conducting islands were denoted by regions with repulsive forces due to the double-layer forces. On the basis of X-ray diffraction (XRD) patterns for POEA in the powder form, we infer that the conducting islands are crystalline, and therefore a POEA film is believed to consist of conducting islands dispersed in an insulating, amorphous matrix. From conductivity measurements we inferred the charge transport to be governed by a typical quasi-one dimensional variable range hopping (VRH) mechanism. 相似文献
419.
420.
The synthesis and isolation of 12 alpha-aryl, beta, beta'-disilyl-substituted vinyl cations 1b-l, 7, and 8 with the tetrakis(pentafluorophenyl)borate counteranion is reported. The vinyl cations are characterized by NMR spectroscopy and are identified by their specific NMR chemical shifts (delta13C(C(+)) = 178.1-194.5; delta13C (Cbeta) = 83.3-89.9; delta13C (Cipso)) = 113.6-115.2; delta (29)Si = 25.0-12.0), supported by density functional calculations at the B3LYP/6-311G(2d,p)//B3LYP/6-31G(d) level. All cations are found to be stable at room temperature in solution and in the solid state. The NMR chemical shifts as well as J-coupling data indicate for vinyl cations, 1b-l, 7, and 8, the occurrence of substantial stabilization through pi-resonance via the aryl substituents and through sigma-delocalization via the beta-silyl groups. For vinyl cation 8, the free enthalpy of stabilization via pi-resonance by the alpha-ferrocenyl substituent is determined by temperature-dependent (29)Si NMR spectroscopy to be DeltaG++ = (48.9 +/- 4.2) kJ mol(-1). A Hammett-type analysis, which relates the (1)J(SiC(beta)) coupling constant and the low-field shift of the (29)Si NMR signal upon ionization, Deltadelta (29)Si, with the electron-donating ability of the aryl group, indicates an inverse relation between the extent of Si-C hyperconjugation and pi-donation. The computed structures (at B3LYP/6-31G(d)) of the vinyl cations 1a-l, 7, and 8 reveal the consequences of Si-C hyperconjugation and of pi-resonance interactions with the aryl groups. The structures, however, fail to express the interplay between sigma-delocalization and pi-conjugation in that the calculated Si-C bond lengths and the C+-C(ipso) bond lengths do not vary as a function of the substituent. 相似文献