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81.
[reaction: see text] Alkoxycarbenium ions having no substituents on the cationic carbon have been accumulated as "cation pools" by the introduction of an ether group in an appropriate position. Intramolecular participation of the ether oxygen is suggested to be responsible for stabilization of the alkoxycarbenium ions. 相似文献
82.
83.
An acid-stable hydride complex [Cp*IrIII(bpy)H]+ {1, Cp* = eta5-C5Me5, bpy = 2,2'-bipyridine} serves as the active catalyst for the highly chemoselective synthesis of alpha-amino acids by reductive amination of alpha-keto acids with aqueous NH3 and HCOO- in water at pH 5-8. pH-dependent catalytic 15N- and 2H-double-labeling has also been accomplished by using 15NH3 and DCOONa, which are ideal amine and hydride ion sources, respectively. 相似文献
84.
Nakagawa S Nihei KT Myer LR Majer EL 《The Journal of the Acoustical Society of America》2003,113(6):3012-3023
Elastic wave scattering off a layer containing a single set of vertical periodic fractures is examined using a numerical technique based on the work of Hennion et al. [J. Acoust. Soc. Am. 87, 1861-1870 (1990)]. This technique combines the finite element method and plane wave method to simulate three-dimensional scattering off a two-dimensional fractured layer structure. Each fracture is modeled explicitly, so that the model can simulate both discrete arrivals of scattered waves from individual fractures and multiply scattered waves between the fractures. Using this technique, we examine changes in scattering characteristics of plane elastic waves as a function of wave frequency, angle of incidence, and fracture properties such as fracture stiffness, height, and regular and irregular spacing. 相似文献
85.
Highly selective Friedel-Crafts monoalkylation of aromatic compounds with N-acyliminium ions has been achieved by efficient 1:1 mixing using a multilamination-type micromixer. 相似文献
86.
Hatano T Takeuchi M Ikeda A Shinkai S 《Chemical communications (Cambridge, England)》2003,(3):342-343
It was found that [60]fullerene encapsulated in anionic calix[8]arenes can be readily deposited by electrochemical oxidative polymerization of ethylenedioxythiophene: the resultant electrode generates a photocurrent wave (ca. 100 nA cm(-2)) in response to visible light irradiation. 相似文献
87.
88.
Kerckhoffs JM Ishi-i T Paraschiv V Timmerman P Crego-Calama M Shinkai S Reinhoudt DN 《Organic & biomolecular chemistry》2003,1(14):2596-2603
This article describes the complexation of phenol derivatives by hydrogen-bonded receptors. These phenol receptors are formed by self-assembly of calix[4]arene dimelamine or tetramelamine derivatives with 5,5-diethylbarbiturate (DEB) or cyanurate derivatives (CYA). The double rosette assemblies 3(3).(DEB)6/(CYA)6 have their phenol-binding functionalities (ureido groups) at the top and at the bottom of the double rosette (exo-receptors). The tetrarosette assemblies 4(3).(DEB)12/(CYA)12 form a cavity with binding sites between the two double rosettes for guest encapsulation (endo-receptors). An intrinsic binding constant Ka of 202 M-1 and 286 M-1 for the binding of 4-nitrophenol to the ureido functionalized exo- and endo-receptors, respectively, was observed. For the exo-receptor a 1:6 stoichiometry was observed while for the endo-receptor 1:4 binding stoichiometry was determined by Job plot and MALDI-TOF MS. The important role that the hydroxy group's acidity plays in the complexation of 4-nitrophenol is clarified by binding studies with different phenol derivatives. The hydrogen-bonded receptors showed a much smaller response towards less acidic phenol derivatives. 相似文献
89.
Sugiyasu K Fujita N Takeuchi M Yamada S Shinkai S 《Organic & biomolecular chemistry》2003,1(5):895-899
A 1,10-phenanthroline-appended cholesterol-based gelator (1) and its nongelling reference compound (2) were synthesized. Among 19 solvents tested herein, gelator 1 could gelate 11 solvents including alcohols, dipolar aprotic solvents, organic acids and a base (triethylamine), indicating that 1 acts as a versatile gelator. The TEM observation gave a visual image showing that fibrillar aggregates are entangled in the three-dimensional network structure. In the fluorescence measurements, most gels afforded an emission maximum at 394 nm (purple emission), whereas only the acetic acid gel afforded an emission maximum at 522 nm (yellow emission). Thus, the influence of protonation of the 1,10-phenanthroline nitrogens (by trifluoroacetic acid) on the fluorescence properties in the gel phase was investigated in detail. The results have established that the fluorescence intensity of 1 x H+ becomes particularly strong in the gel phase, presumably because of the energy transfer from neutral 1* to protonated 1 x H+ and the restriction of the 1 x H+ molecular motion. The finding suggests the possibility that the gel system would be useful not only as a new proton-sensitive fluorescence system but also as a new medium for designing efficient energy transfer systems. 相似文献
90.