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961.
962.
963.
Friedel-Crafts alkylation of indoles with epoxides to afford 3-alkyl indole derivatives at room temperature with moderate to good yields and high regioselectivity using nanocrystalline titanium(IV) oxide catalyst is described. 相似文献
964.
A. Borgschulte R. Gremaud S. de Man R.J. Westerwaal J.H. Rector B. Dam R. Griessen 《Applied Surface Science》2006,253(3):1417-1423
The optical properties, the switching kinetics and the lifetime of hydrogen switchable mirrors based on Mg-Ni alloys are determined with particular regard to the composition of the optically active metal-hydride layer in combination with the thickness of the catalytic capping layer. For this, a high-throughput experiment is introduced. The switching kinetics and the reversibility of switchable mirrors are strongly thickness dependent, though the details hinge on the fine structure of the clustered capping layer. Therefore, the kinetics is correlated with the surface structures of Pd on MgyNi1−y as investigated by scanning tunneling microscopy. The results are explained by the so-called strong metal-support interaction (SMSI) state, characterized by a complete encapsulation of the capping layer clusters by oxidized species originating from the support. The SMSI-effect is less important with increasing Pd-layer thickness, and is suppressed by a good wetting of the Pd-clusters on the optically active film. This explains the critical thickness for the catalyzed hydrogen uptake observed in many switchable mirror systems. Moreover, the degradation of the kinetics during cycling is found to depend on the Pd-layer thickness and on the gas environment. Only films, covered with at least 15 nm Pd, show small degradation caused by the SMSI-effect. The SMSI-effect is partly reversible: after changing the gas environment from hydrogen to oxygen, the oxide on the Pd-clusters can be partly removed. 相似文献
965.
The low-temperature reaction of magnesium with fluorobenzene has been investigated. Joint condensation of magnesium and fluorobenzene vapours at low temperatures quantitatively gave phenylmagnesium fluoride in one stage. 相似文献
966.
A new probabilistic cellular automaton model is introduced to simulate cluster and interface growth in two dimensions. The dynamics of this model is an extension to higher dimensions of the compact directed percolation studied by Essam. Numerical results indicate that the two-dimensional cluster coarsening and growth can be described only approximately by the conventional cluster size scaling due to a crossover in the growth mode. The spreading of the initially flat interface follows a purely diffusional,t
1/2, law. 相似文献
967.
968.
Determination of some hydroxycholesterols in human serum samples 总被引:4,自引:0,他引:4
B J Koopman J C van der Molen B G Wolthers J B Vanderpas 《Journal of chromatography. A》1987,416(1):1-13
The simultaneous determination of some hydroxycholesterols in human serum samples is described. The procedure is based on hydrolysis and extraction of these compounds in serum samples, followed by removal of especially cholesterol (making use of reversed-phase high-performance liquid chromatography) and derivatization of the purified compounds to their trimethylsilyl ethers and subsequent gas chromatography using flame ionization detection. Serum levels of 7 alpha-hydroxycholesterol, 7 beta-hydroxycholesterol and 26-hydroxycholesterol were determined in several groups of patients: normals, untreated patients suffering from cerebrotendinous xanthomatosis, patients suffering from cerebrotendinous xanthomatosis and treated with either chenodeoxycholic acid or cholic acid in an effective dose, patients suffering from cerebro-hepato-renal syndrome, patients suffering from hypercholesterolemia and treated with cholestyramine for prolonged periods and one patient presumed to be suffering from an inborn error of metabolism in bile acid synthesis. It can be concluded that the 7 alpha-hydroxycholesterol concentration in serum is a good parameter for establishing disorders involving the metabolic conversion of 7 alpha-hydroxycholesterol towards bile acids. In addition, 26-hydroxycholesterol levels in patients suffering from cerebrotendinous xanthomatosis are beyond detectable limits, even during treatment with bile acids in an effective dose, whereas in all other conditions this compound is substantially present. 相似文献
969.
Starting from cyclohexanecarboxylic acid, a combination of an Ireland ester Claisen rearrangement and RCM reactions was exploited for an efficient construction of spiro[5.5]undecanes containing a quaternary carbon atom adjacent to the spirocentre and the methodology was extended to complete total syntheses of three chamigrenes. 相似文献
970.
Ion synthesis and laser annealing of Cu nanoparticles in Al2O3 总被引:1,自引:0,他引:1
A.L. Stepanov V.N. Popok D.E. Hole I.B. Khaibullin 《Applied Physics A: Materials Science & Processing》2002,74(3):441-446
Al2O3 samples with Cu nanoparticles, synthesised by ion implantation at 40 keV with a dose of 1×1017 ion/cm2 and a current density from 2.5 to 12.5 μA/cm2, were annealed using ten pulses from a KrF excimer laser with a single pulse fluence of 0.3 J/cm2. The copper depth distribution, formation and modification of metal nanoparticles under the ion implantation and laser treatment
were studied by Rutherford backscattering (RBS), energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM) and
optical spectroscopy. It was found that laser annealing leads to a reduction in the nanoparticle size without diffusion of
metal atoms into the bulk. The change in particle size and the possibility for oxidation of the copper particles are examined
in the framework of Mie theory. Calculations presented show that under excimer laser treatment, Cu nanoparticles are more
likely to be reduced in size than to undergo oxidation.
Received: 19 April 2001 / Accepted: 7 November 2001 / Published online: 23 January 2002 相似文献