Differentiating sites

There had been two major problems to overcome for the development of MRNi with high EDA. One was the possibility of the presence of two kinds of differentiating sites on the surface of MRNi. That is, even though the same modifying reagent was used, MRNi often produced an opposite direction of EDA when modifying conditions were varied. The other problem was the possibility of the presence of unmodified surface area on the catalyst. 

The former problem was overcome by finding conditions for the treatment of RNi with hydroxy acid under acidic condition. Uniform differentiating sites were prepared by this treatment 47). 

The above findings indicate that two kinds of surface structures exist even on the surface of HNi and one kind can be removed by pretreatment with hydroxy acid. On the surface of RNi, aluminum does not directly participate in the formation of the differentiating site, but must participate in the formation of the surface structure of nickel which is removed by the pretreatment with hydroxy acid. 

The rate of hydrogenation of acetone over TA MRNi was higher than over TA NaBr-MRNi (47). Thus, the NaBr inhibits partially the hydrogenation activity of TA-MRNi, and the increase in EDA of TA- MRNi with NaBr can be ascribed to the inhibition of hydrogenation at the unmodified surface of TA-MRNi. In other words, most of the hydrogenation with TA NaBr MRNi must be performed at the enantio-differentiating site. 

When the rates of the enantio-differentiating hydrogenation ( ) and non-enantio-differentiating hydrogenation (N) are postuated to be equal, and the EDA at the enantio-differentiating site is defined as 100%, the following equation is derived ... 

The second approximation to the F vs. b plot is shown in Figure 2,a as well as F3 vs. 6, obtained by repeating the above procedure. In the present example F i vs. b was taken to be in the terminal approximation (also shown in Figure 1,6) and, by means of Equation 4, the integral site energy distribution F(Q) was obtained. The corresponding differential site energy distribution is shown in... 

It has been demonstrated that there are two types of sites on nickel surface [5]. (1) The site with affinity for TA where e.d. hydrogenation takes place (e.d. site). This site would locate on the surface of the crystallite nickel. (2) The site without affinity for TA where racemic products are produced (non-enantio-differentiating site (non-e.d. site)). This site would locate on the surface of aluminum derivatives or the amorphous nickel. The e.d. ability of the catalyst was represented by both the intrinsic e.d. ability of the modification reagent and the ratio of the optically active compounds produced on the e.d. site to the racemates produced on the non-e.d. site. Therefore, one of the effective strategies for raising the e.d. ability of the catalyst is to investigate the various catalyst preparation conditions in order to remove the non-e.d. site from the catalyst surface. 

Larger animals, including rats, cats, and monkeys, are studied in a sleep laboratory. In these studies, electrophysiologic and electroencephalographic measurements are obtained and often are helpful in gaining information about the site of action of CNS depressants as well as about induced sleep patterns. Drug discrimination studies also have been useful in differentiating sites of action of CNS depressants. 

The authors made two important observations. Enantio-differentiating sites contain adsorbed tartaric acid and are constituted by pure nickel domains. In contrast, non-enantio-differentiating sites contain aluminum compounds. Sonication of the heterogeneous catalysts prepared by regular procedures allows eliminating the aluminum-containing domains, and highly enantioselective... 

The described protein matrix-assisted inorganic synthesis provides an interesting pathway for the formation of novel hetero metal containing clusters. A particular interestet in this field arises from the possibility of forming new biocataiysts with unexpected properties. Also the introduction of a differentiated site into a cubane-type structure with intrinsic properties enables to explore magnetism in vaience - deiocalized /locaiized systems as well as the simplification of the spectral analysis. Synthesis of reievant modei compounds via the formation of hetero metal cubane-type... 

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