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951.
Yamaguchi Y Kashiwabara T Ogata K Miura Y Nakamura Y Kobayashi K Ito T 《Chemical communications (Cambridge, England)》2004,(19):2160-2161
The reaction of an imidazolium salt with LiBEt(3)H afforded triethylborane adduct of imidazol-2-ylidene, which can act as a carbene precursor for the synthesis of a transition metal complex as well as a main group element complex. 相似文献
952.
Polymer modifications of ultrafine monodispersed colloidal metal oxide particles, smaller than 80 nm in diameter, by the graft-polymerization of styrene to a hydrophilic macromer adsorbed on the surface were investigated. The polymerization in ethanolic silica and titania colloid solution, which had negatively larger ζ-potentials, ?30 and ?42 mV in neutral aqueous solution respectively, gave poly(styrene)–silica or titania composite, being of nonspherical shape. The modifications of colloidal particles, having lower surface energy, such as Al(OH)3 and CeO2–TiO2–SiO2 complex, led to the formation of spherical composites, ranging in size from 500 to 3000 nm, of scattered metal oxide or hydroxide particles. 相似文献
953.
Kazuyoshi Tanaka Tokio Yamabe Kenichi Fukui Hiroshi Kato 《Chemical physics letters》1977,48(1):141-144
A perturbation theory method is developed in the tight-binding LCAO MO treatment of a one-dimensional polymer under local perturbation with the aid of the Wannier function. As the first step, electronic states of an infinite polyene under a few of significant cases of perturbation are formulated in the scheme of the Hückel MO approach, giving the changes in total energies, electron densities, and bond orders of the perturbed systems. 相似文献
954.
Tsutomu Kagiya Isao Maruta Taizo Ichida Shizuo Narisawa Kenichi Fukui 《Journal of polymer science. Part A, Polymer chemistry》1967,5(7):1645-1658
The alternating copolymerization of carbon monoxide and ethylenimine to give poly-β-alanine could be initiated by γ-irradiation but hardly by α,α'-azobisisobutyronitrile (AIBN). It was found that in the case of the addition of olefin, this system could be copolymerized even by AIBN and that, in the γ-ray copolymerization of carbon monoxide and ethylenimine, the addition of olefin brought about an increase in the copolymer yield. No difference was observed between the nature of copolymers obtained by AIBN and those obtained by γ-irradiation, except in the system carbon monoxide–ethylenimine–ethylene. An increase in the amount of reacted olefin gave rise to an increase in copolymer yield. The melting points of the copolymers were in the range 295–335°C. The infrared spectra, x-ray diffraction diagrams, and NMR spectra of the copolymers were almost identical with that of poly-β-alanine obtained by the hydrogen-migration polymerization of acrylamide. Paper chromatographic analysis of the hydrolysis product of the copolymer showed the existence of β-alanine, ethylamine, and δ-aminovaleric acid homolog in the products. From these results, it was concluded that terpolymerization of carbon monoxide, ethylenimine, and olefin took place in the presence of AIBN or γ-irradiation which gave a crystalline solid copolymer containing the units of nylon 3 and nylon 5. A mechanism of this copolymerization was proposed on the basis of these results. 相似文献
955.
Yamashita K Ogura D Yamaguchi Y Miyazaki M Briones MP Nakamura H Maeda H 《Analytical and bioanalytical chemistry》2005,382(7):1477-1483
Microfluidic systems enable superior control of fluidics. We have developed a novel size-separation method utilizing secondary flow within a microchannel. Using confocal fluorescence microscopy and computer simulation, we confirmed that separation occurred as a result of specific molecular localization in the curving part of the microchannel. Maximum separation efficiency was achieved by optimizing microchannel design and flow rate for individual separation targets. In addition, more effective separation was achieved by use of plural microchannel curves. This method was used for sequence-selective DNA sensing. Double-stranded DNA formed by hybridization between target DNA and a complementary probe had different elution profiles from those of the single-stranded non-complementary sequence. Moreover, the response depends on the length of the DNA molecules. This method does not require immobilization of either probe or target DNA, because all reactions occurred in the solution phase. Such features may reduce experimental error and the difference between data from different operators. 相似文献
956.
Marcus RK Anfone AB Luesaiwong W Hill TA Perahia D Shimizu K 《Analytical and bioanalytical chemistry》2002,373(7):656-663
While the array of analytical methods routinely applied for depth profile analysis was fairly static over the decades of the 1980s and 1990s, there appears to be an emerging technique that has a number of very positive and complementary attributes, and warrants serious consideration by the thin film community. Radio frequency glow discharge optical emission spectroscopy (rf-GD-OES) is a technique that provides depth-resolved elemental composition information on a wide variety of sample types. In a manner very much like most depth profiling methods, the rf-GD plasma utilizes an ion sputtering step to ablate sample material in a layer-by-layer fashion. Different from the more commonly applied methods, the device operates at elevated pressures [2-10 Torr Ar (266-1,330 Pa)] and has the inherent capability of sputtering electrically insulating materials directly, without any auxiliary means of charge compensation. In addition, sputtering rates on the order of 1 micro m/min provide rapid analysis, with depth resolving powers that are comparable to high-vacuum sputtering methods. Three examples of the use of the rf-GD-OES method are presented as examples of its analytical potential: (1) boron-implanted silicon wafer, (2) a barrier-type alumina film, and (3) a porous-type alumina film. It is believed that the method holds a great deal of promise as part of the arsenal of weapons in the thin films laboratory. 相似文献
957.
Sadamoto R Niikura K Sears PS Liu H Wong CH Suksomcheep A Tomita F Monde K Nishimura S 《Journal of the American Chemical Society》2002,124(31):9018-9019
The cell walls of living bacteria were chemically modified by adding cell-wall precursors. As the precursors to be incorporated into the cell wall, UDP-MurNAc pentapeptide, lipid I, and lipid II derivatives were synthesized. The aimed compounds were attached to the amine residue of lysine at the pentapeptide moiety. Fluorescein-attached UDP-MurNAc pentapeptide was efficiently incorporated into both Gram-positive and Gram-negative bacteria. In the case of Gram-negative bacteria, such as Escherichia coli, the permeability of the outer membrane (lipopolysaccharide layer) was enhanced by EDTA treatment before the incorporation. For Gram-positive bacteria, UDP-MurNAc derivatives were incorporated in the cell wall without EDTA treatment due to the lack of the lipopolysaccharide layer. Furthermore, instead of dyes, a ketone group was attached to the UDP-MurNAc pentapeptide. The ketone group was also delivered to the bacterial cell wall of lactic acid bacteria, giving a platform to attach large molecules on the surface. 相似文献
958.
Huda Izzat OmarYuka Odo Yasuhiro ShigemitsuTetsuro Shimo Kenichi Somekawa 《Tetrahedron》2003,59(41):8099-8105
The experimental results of the triplet [2+2] photocycloaddition reactions of substituted 2-cyclohexenone 1 with cycloalkenylesters 2, 3, 4 have showed remarkable change in the regioselectivity of the products. The ht/hh product ratio increases with increment of the cycle-size. The FMO investigations in addition to the transition state analysis were used to rationalize such regioselectivity. The FMO method with their orbital coefficients and energies could not explain the reaction selectivity since these values of 2-4 showed tendency to form the hh adduct mainly. PM3, PM5, CIS/6-31G, and B3LYP/6-31G methods were used to locate the hh and ht transition states of the three reactions. As the potential energy barriers (TS1) on the first TS surface for the major products were lower than that for the minor products in most of the cases, the real ratio can be explained in terms of TS analysis. The recently improved PM5 and the B3LYP methods were more successful in this debate as partitioning the activation energy at the potential energy barriers into reactant deformation and the interaction (or repulsion) energies is easy and effective. The changes in the ht/hh ratio with the enlargement of the alkene ring size may be due to the increment of the repulsion energy and large changes in the deformation energy of the reactants. In the transition state structures the stabilities of the major products are thought to be due to the existence of some repulsion between the enone carbonyl and esters in the alkenylesters, and some hydrogen bonding between the reactants. The FMO and second transition state (TS2) energy on the biradical intermediates are also thought to play some role in controlling the product selectivity by lowering the closure energy of the biradicals according to the possibility of their overlapping. 相似文献
959.
Cerium ammonium nitrate (CAN) removed hydroxyethyl units from 2-hydroxyethyl ethers and 2-hydroxyethyl amines to produce alcohols and amines in good yields. Especially, removal of the 2-hydroxyethyl ethers from C2-symmetric diols, chiral 2,3-butanediol and chiral hydrobenzoin, was very useful for asymmetric syntheses using C2-symmetric diols. The reactions using dual abilities of CAN, i.e., the ability for removal of the 2-hydroxyethyl unit and the ability for acetal hydrolysis by a single electron transfer, were also achieved successfully. The reaction conditions were very mild and efficient, and many functional groups, which can be affected under normal conditions, were unaffected during the reaction. 相似文献
960.
Masaru Sato Shinsuke Tanaka Seiji Ebine Kenichi Morinaga Sadatoshi Akabori 《Journal of organometallic chemistry》1985,282(2):247-253
Of the 1,n-dithia[n]ferrocenophanes prepared from disodium 1,1′-ferrocenedithiolate and polymethylene dibromides, the ferrocenophane with n = 7 showed the largest shift in the electronic and 13C NMR spectra and the largest decrease of the redox potential. This can be interpreted by a new type of stereoelectronic interaction between the sulfur atom and the ferrocene nucleus. 相似文献