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91.
A new strategy for carotenoid butenolides has been developed that is based in part in halogen-selective Stille cross-coupling of dihalogenated ylidenebutenolide segment 2 and highly functionalized alkenylstannanes. [reaction: see text] 相似文献
92.
Esteves PM Araújo CL Horta BA Alvarez LJ Zicovich-Wilson CM Ramírez-Solís A 《The journal of physical chemistry. B》2005,109(26):12946-12955
Details on the mechanism of HF catalyzed isobutylene-isobutane alkylation were investigated. On the basis of available experimental data and high-level quantum chemical calculations, a detailed reaction mechanism is proposed taking into account solvation effects of the medium. On the basis of our computational results, we explain why the density of the liquid media and stirring rates are the most important parameters to achieve maximum yield of alkylate, in agreement with experimental findings. The ab initio Car-Parrinello molecular dynamics calculations show that isobutylene is irreversibly protonated in the liquid HF medium at higher densities, leading to the ion pair formation, which is shown to be a minimum on the potential energy surface after optimization using periodic boundary conditions. The HF medium solvates preferentially the fluoride anion, which is found as solvated [FHF](-) or solvated F(-.)(HF)(3). On the other hand, the tert-butyl cation is weakly solvated, where the closest HF molecules appear at a distance of about 2.9 Angstrom with the fluorine termination of an HF chain. 相似文献
93.
We investigate mixing in a viscoelastic and shear-thinning fluid-a very common combination in polymers and suspensions. We find that competition between elastic and viscous forces generates self-similar mixing, lobe transport, and other characteristics of chaos. The mechanism by which chaos is produced is evaluated both in experiments and in a simple model. We find that chaotic flow is generated by spontaneous oscillations, the magnitude and frequency of which govern the extent of chaos and mixing. 相似文献
94.
Domínguez M Alvarez R Martras S Farrés J Parés X de Lera AR 《Organic & biomolecular chemistry》2004,2(22):3368-3373
Ring-oxidized retinoids have been synthesized stereoselectively using the Stille cross-coupling reaction. Kinetic constants of mouse class I alcohol dehydrogenase (ADH1) with these retinoids were determined. 相似文献
95.
Gologan B Takáts Z Alvarez J Wiseman JM Talaty N Ouyang Z Cooks RG 《Journal of the American Society for Mass Spectrometry》2004,15(12):1874-1884
Protein ions, after mass spectrometric separation, can be soft-landed into liquid surfaces with preservation of their native structures. Retention of biological activity is strongly favored in glycerol-based surfaces but not in self-assembled monolayer solid surfaces. Soft-landing efficiency for multiply-charged hexokinase ions was found to be some four times higher for a glycerol/fructose liquid surface than for a fluorinated self-assembled monolayer surface. Soft-landing into liquid surfaces is also shown to allow (1) protein purification, (2) on-surface identification of the soft-landed material using MALDI, and (3) protein identification by in-surface tryptic digestion. Pure lysozyme was successfully isolated from different mixtures including an oxidized, partially decomposed batch of the protein and a partial tryptic digest. Liquid glycerol/carbohydrate mixtures could be used directly to record MALDI spectra on the soft-landed compounds provided they were fortified in advance with traditional MALDI matrices such as p-nitroaniline and alpha-cyano-4-hydroxycinnamic acid. Various proteins were soft-landed and detected on-target using these types of liquid surface. Soft-landing of multiply-charged lysozyme ions onto fluorinated self-assembled monolayer surfaces was found to occur with a limited amount of neutralization, and trapped multiply-charged ions could be desorbed from the surface by laser desorption. Initial data is shown for a new approach to protein identification that combines top-down and bottom-up approaches by utilizing protein ion soft-landing from a protein mixture, followed by tryptic digestion of the landed material and detection of characteristic tryptic fragments by MALDI. 相似文献
96.
A security analysis of a recently proposed secure communication scheme based on the phase synchronization of chaotic systems is presented. It is shown that the system parameters directly determine the cipher text waveform, hence it can be readily broken by system parameter estimation from the cipher text signal. 相似文献
97.
The superconducting properties of carbon nanotube ropes are studied using a new computational framework that incorporates the renormalization of intratube interactions and the effect of intertube Coulomb screening. This method allows one to study both the limits of thin and thick ropes ranging from purely one-dimensional physics to the setting of 3D Cooper-pair coherence, providing good estimates of the critical temperature as a function of the rope physical parameters. We discuss the connection of our results with recent experiments. 相似文献
98.
Rodríguez-Fortea A Alemany P Alvarez S Ruiz E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(3):627-637
A computational study of the exchange coupling is presented for a selected sample of carboxylato-bridged dinuclear copper(II) compounds. Model calculations have been used to examine the influence of several factors on the coupling constants: a) the electron-withdrawing power of the bridging ligands; b) the nature of the axial ligands; c) the number of bridging carboxylato groups; d) some structural distortions frequently found in this family of compounds; and e) the coordination mode of the carboxylato bridge. Coupling constants calculated for some complete structures, as determined by X-ray diffraction, are in excellent agreement with experimental data, confirming the ability of the computational strategy used in this work to predict the coupling constant for compounds for which experimental data are not yet available. 相似文献
99.
The sesquiterpenoid fractions from the chloroform extracts of roots and aerial parts of the weed Cyrtocymura cincta (Griseb.) H. Robinson (Compositae) were tested to observe the effects on seed germination and growth of three dicot and four monocot species. Promotion and inhibition effects were observed according to the examined compound, specific seed or cultivar, and concentration. 相似文献
100.
A. Gillibert A. Obertelli N. Alamanos M. Alvarez F. Auger R. Dayras A. Drouart G. de France B. Jurado N. Keeley V. Lapoux W. Mittig X. Mougeot L. Nalpas A. Pakou N. Patronis E. Pollacco F. Rejmund M. Rejmund P. Roussel-Chomaz H. Savajols F. Skaza Ch. Theisen 《The European physical journal. Special topics》2007,150(1):161-163
27Ne has been investigated through the one neutron transfer reaction 26Ne(d,p)27Ne in inverse
kinematics at 9.7 MeV/nucleon. The results support the existence of a low lying negative parity state
in 27Ne which is a signature of a reduced sd-fp shell gap in the N = 16 neutron rich region, at variance
with stable nuclei. 相似文献