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991.
Cycloaddition reactions between 1,3-butadiene and the C-terminated SiC(1 0 0)-c(2 × 2) surface have been addressed using quantum-chemical methods. The c(2 × 2) structure consists of ---CC--- bridges between underlayer Si atoms which themselves form Si---Si bonds. Of various possible reaction products, the one formed by a [2 + 4] reaction with the ---CC--- bridge (giving a species resembling 1,4-cyclohexadiene) is the lowest in energy. Density functional calculations for the bare c(2 × 2) surface, using a cluster model with mechanical embedding, gave good agreement with structural parameters obtained in previous fully ab initio studies. Similar calculations for the cycloaddition product and for the transition state gave a reaction energy of −50.3 kcal/mol and an activation energy of +6.1 kcal/mol to form a planar ring structure lying normal to the surface. Detailed results for the frequency and infrared polarization behavior of adsorbate vibrational modes have also been obtained. 相似文献
992.
993.
994.
995.
L. Ouali S. Stoll E. Pefferkorn A. Elaissari V. Lanet C. Pichot B. Mandrand 《先进技术聚合物》1995,6(7):541-546
The paper describes a study of the kinetics and mechanism of the coagulation of two types of immunoassays using sensitized latexes. The positive response to the first test is based on the aggregation of the gamma globulin (IgG)-coated polystyrene latexes in the presence of IgM rheumatoid antigen. The second test is relative to the heteroaggregation of two types of sensitized latexes induced by the presence of human chorionic gonadotropin (HCG). In the latter test, two identical polystyrene latexes bearing carboxylic acid surface groups were sensitized by covalent coupling of monoclonal antibodies specific for the αHCG determinant on one type of latex and for the βHCG determinant on the other type. Using the Coulter Counter method, the aggregate size distribution c(n) was determined as a function of the number n of elementary constituents, thus enabling calculation of the number N(t) and weight S(t) average sizes of the aggregates. The temporal variations of the average sizes were compared with typical situtions of reaction-limited aggregation processes in order to characterize the mechanism of aggregation induced by antibody–antigen reactions. 相似文献
996.
New results on elements 111 and 112 总被引:1,自引:0,他引:1
S. Hofmann F.P. Heßberger D. Ackermann G. Münzenberg S. Antalic P. Cagarda B. Kindler J. Kojouharova M. Leino B. Lommel R. Mann A.G. Popeko S. Reshitko S. Śaro J. Uusitalo A.V. Yeremin 《The European Physical Journal A - Hadrons and Nuclei》2002,14(2):147-157
Experiments on the synthesis and identification of the nuclei 272111 and 277112 were performed in order to confirm previous results. Three additional decay chains were measured in the reaction 64Ni + 209Bi →273111*. The study revealed considerably improved data on the decay chain originating from 272111. One additional chain was measured in the reaction 70Zn + 208Pb →278112*. The decay properties of the chain starting at 277112 are in excellent agreement with the second chain of the first experiment down to 265Sg, where the new chain ends by a previously unknown spontaneous-fission branch. A re-analysis of all the data on elements
110, 111, and 112 measured at GSI since 1994 (a total of 34 decay chains was investigated) revealed that for 2 chains (the
second chain of 269110 measured in 1994 and the first chain of 277112 measured in 1996) the results of the new analysis differed from the previous one. In all other cases the earlier data
are exactly reproduced.
Received: 21 December 2001 / Accepted: 15 January 2002 相似文献
997.
Fluorous chiral BINOLs and BINAP were prepared and used as the ligands for an asymmetric addition of Et2Zn to aromatic aldehydes and an asymmetric Heck reaction, respectively. The enantioselectivities were similar in homogeneous system to those of the original non-fluorous reactions. Consecutive reactions were examined by utilizing fluorous–organic biphase and fluorous solid phase extraction techniques. Enantioselectivities in consecutive reactions were close to that attained in the non-fluorous system. The solid phase extraction method also enabled us to perform a simultaneous screening procedure. 相似文献
998.
999.
Y. Mera 《Surface science》2007,601(22):5207-5211
Reversible polymerization and depolymerization reactions of fullerene (C60) molecules are induced by tunnel injection of holes from tips of scanning tunneling microscopes similarly to the reactions induced by tunneling electrons. The bi-directional and bi-polar features of the hole-induced and electron-induced reactions can be interpreted by a unified model considering ionic reactions over symmetry-imposed barriers in the [2+2] cyclo-addition and the reverse reactions. 相似文献
1000.
On the Influence of Chemical Transport on the Habit of Crystals The chemical transport of silicon with silicon tetrachloride as transporting agent leads to crystals with octahedral shape. On the other hand in the presence of adsorbable impurities the transported silicon crystallizes in the shape of long needles. Chemical transport reactions of tellurium are successful with iodine or sulphur. The presence of adsorbable transporting agents has considerable influence on the habit of crystals. 相似文献