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71.
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73.
Benjamin D. A. Shennan Peter W. Smith Yusuke Ogura Darren J. Dixon 《Chemical science》2020,11(38):10354
An efficient three-step sequence to afford a valuable class of spirocyclic pyrrolidines is reported. A reductive cleavage/Horner–Wadsworth–Emmons cascade facilitates the spirocyclisation of a range of isoxazolines bearing a distal β-ketophosphonate. The spirocyclisation precursors are elaborated in a facile and modular fashion, via a [3 + 2]-cycloaddition followed by the condensation of a phosphonate ester, introducing multiple points of divergence. The synthetic utility of this protocol has been demonstrated in the synthesis of a broad family of 1-azaspiro[4,4]nonanes and in a concise formal synthesis of the natural product (±)-cephalotaxine.A three-step, modular and divergent sequence accessing challenging spirocyclic pyrrolidines has been developed, featuring a novel reductive spirocyclization cascade. 相似文献
74.
The steady-shear viscosity, dynamic viscoelasticity, and stress relaxation behavior were measured for suspensions of silica nanoparticles dispersed in aqueous solutions of poly(ethylene oxide) (PEO). The suspensions of silica with diameters of 8-25 nm show striking shear-thickening profiles in steady shear and highly elastic responses under large strains in oscillatory shear. Since the silica particles are much smaller than the polymer coils, one molecule can extend through several particles by intrachain bridging. Each polymer coil may remain isolated as a floc unit and the silica particles hardly connect two flocs. Therefore, the flow of suspensions is Newtonian with low viscosity at low shear rates. When the polymer coils containing several nanoparticles are subjected to high shear fields, three-dimensional network is developed over the system. The shear-thickening flow may arise from the elastic forces of extended bridges. But, the polymer chain is easily detached from particle surface by thermal energy because of large curvature of particles. As a result, the network structures are reversibly broken down in a quiescent state and the suspensions behaves as viscoelastic fluids with the zero-shear viscosity. 相似文献
75.
The reaction of (1E,3E)-1-(methylthio)-3-tosylhexa-1,3-dien-5-ynes (3) with iodine to form iodine-substituted benzenes (4) is reported. The reaction of 3 with iodine proceeded very slowly, but UV irradiation accelerates the reaction to give 4 in high-to-excellent yields. Irradiation induces the cis-trans isomerization of the C1-C2 double bond, leading to the (1Z,3E)-geometric isomer (3'), which easily reacts with iodine to afford 4. This reaction is applicable to 3-(methoxycarbonyl)-1-(methylthio)-6-phenylhexa-1,3-dien-5-yne (11), which is synthesized as a geometric mixture. Interestingly, this mixture can be used as the starting material. Irradiation of the mixture (the geometric isomer ratio = 50:28:5:17) with iodine resulted in the formation of methyl 3-iodo-4-phenylbenzoate (12) in 80% yield. 相似文献
76.
Associating polymers are hydrophilic long-chain molecules containing a small amount of hydrophobic groups. The aqueous solutions
show viscoelastic responses above some critical concentrations because a three-dimensional structure is formed by association
of hydrophobic groups. When the associating polymers are added to silica suspensions at low concentrations, the flocculation
is induced by bridging mechanisms, and the flow of suspensions become shear-thinning. For suspensions prepared with polymer
solutions in which the associating network is developed, the viscosity decreases, shows a minimum, and then increases with
increasing particle concentration. The viscosity decrease may arise from the breakdown of associating network due to adsorption
of polymer chains onto the silica surfaces. As the particle concentration is increased, the polymer concentration in solution
is decreased, and finally, all polymer chains are adsorbed on the surfaces. Beyond this point, the partial coverage of particle
surfaces takes place and strong interactions are generated between particles by polymer bridging. Since the stable suspensions
are converted to highly flocculated systems, the viscosity is increased and the flow becomes shear-thinning. The concentration
effect of silica particles on the viscosity behavior of suspensions can be explained by a combination of viscosity decrease
in solution due to polymer adsorption and viscosity increase due to flocculation. 相似文献
77.
78.
S. A. Khubezhov I. V. Silaev Z. S. Demeev A. V. Ramonova A. G. Kaloeva I. V. Tvauri G. S. Grigorkina D. D. Kibizov O. G. Ashkhotov S. Ogura D. Sekiba K. Fukutani T. T. Magkoev 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(7):1489-1492
The distribution of NO molecules desorbed from a Pt(111) surface due to valence electron excitation over rotational energy levels N(J) is analyzed using a simple impulse-induced model. A linear dependence is found between lnN(J) and (Er)1/2, where Er is the rotational energy of the desorbed molecules. The lifetime of the excited state and the critical time of residence in the excited state estimated using this dependence are found to be close to one another (~10?15 s). The frequency and amplitude of the tilting vibrations of the adsorbed molecules in the excited state are estimated. 相似文献
79.
Usui S Fujieda H Suzuki T Yoshida N Nakagawa H Ogura M Makishima M Miyata N 《Chemical & pharmaceutical bulletin》2007,55(7):1053-1059
To find novel PPAR ligands, we prepared several 3-{3 or 4-[2-(nonylpyridin-2-ylamino)ethoxy]phenyl}propanoic acid derivatives which were designed based on the structure of our previous PPARgamma ligand 1. In PPAR binding affinity assays, compound 4, which had an ethoxy group at the C-2 position of the propanoic acid of 1, showed selective binding affinity for PPARgamma. Compound 3, with an ethyl group at the C-2 position, was found to be a PPARalpha/gamma dual ligand. Compound 6, the meta isomer of 1, has been shown to be a PPARalpha ligand. The introduction of methyl (7) and ethyl (8) groups to the C-2 position of the propanoic acid of 6 further improved PPARalpha-binding potency. In cell-based transactivation assay, compounds 3 and 4 showed dual-agonist activity toward PPARalpha and PPARgamma. Compound 6 was found to be a triple agonist and compound 8 proved to be a selective PPARalpha agonist. In the human hypodermic preadipocyte differentiation test, it was demonstrated that the maximal activity of compounds 3 and 4 was higher than that of rosiglitazone. 相似文献
80.
Hongyuan Wang Toshinari Ugomori Yong Wang Kazuhiro Tanaka Hidetoshi Kita Ken‐Ichi Okamoto Yasunori Suma 《Journal of Polymer Science.Polymer Physics》2000,38(13):1800-1811
Poly(ethylene oxide imide) segmented copolymer (PEO‐PI) membranes were crosslinked by the chemical reaction between ethylene glycol diglycidyl ether and benzylalcohol groups of diamine moieties in polyimide segments at high temperatures. Sorption and diffusion of penetrants took place in poly(ethylene oxide) segment microdomains. Sorption and desorption behavior of pure vapors such as benzene (Bz), cyclohexane (Cx) and n‐hexane (Hx) was classified as the Fickian diffusion. Sorption isotherms of binary liquid mixtures could be represented by the Flory–Rehner model, but the model overpredicted the sorption amounts of Cx and Hx, leading to small predictions of sorption selectivity αS for Bz/Cx and Bz/Hx systems. UNIFAC‐FV model fairly well predicted the sorption amounts of aromatic hydrocarbons, but significantly overestimated those of nonaromatic ones, leading to too small predictions of αS. Pervaporation (PV) behavior of PEO‐PI membranes was governed by sorption behavior followed by membrane swelling. Diffusion coefficient weakly depended on the minimum cross section of a penetrant. The diffusivity selectivity αD hardly depended on the feed composition and was about 1.4 and 0.75 for Bz/Cx and Bz/Hx, respectively. PV selectivity αPV was larger for Bz/Hx than for Bz/Cx because of larger αS. PEO‐PI membranes displayed high specific permeation flux Ql and reasonably high αPV for aromatic/nonaromatic hydrocarbons; for example, Ql = 60 Kg μm/(m2 h) and αPV = 8 for a feed mixture containing Bz, Tol, Hx, n‐Ot and i‐Ot of 20 wt % at 353 K. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1800–1811, 2000 相似文献