פרסומים

The reactive sites on platinum metal catalysts for the hydrogenation of unsatd. hydrocarbons and related reactions were the most coordinatively unsatd. exposed metal atoms. The surface atoms were divided into 3 groups with one, two, or three units of coordinative unsatn. (corresponding to the no. of monodentate ligands which may become attached) and were symbolized by 1M, 2M, and 3M, then, when exposed to H the 1st structures formed were 2MmH2 and 3MH2, which were transformed, in part, to 2MH and 3MH by diffusion of H from the edge to other surface sites or to the interior of the crystallite. The proportions of 3M and 3MH present during a reaction were a function of the metal and the conditions of prepn. and use. These structures bore a formal relation to the structure of the complexes ClRh(PPh3)2 (I) and HRhCO(PPh3)2 (II) which are formed through the dissocn. of ClRh(PPh3)3 and HRh(CO)(PPh3)3, resp. The catalytic functions of both I and II involved the same kinds of elementary processes, but the presence of the hydrido group in II led to recognizably different phenomena (kinetics, stereochem., exchange reactions). Accordingly, the characteristics of hydrogenations catalyzed by platinum metals may be rationalized by considering the elementary processes which may occur at each category of site. [on SciFinder(R)]

Thesis–ha-Universiṭah ha-'Ivrit, 1978. / Added t.p.: Isaac Orobio de Castro and his circle. Hebrew, English and/or Spanish.

Although the aetiological agents responsible for the initiation of rheumatoid arthritis in the human are not known, the possibility that the disease is of bacterial origin has been considered. The bacterial factors involved may be small fragments of undegraded wall components which persist for long periods within macrophages and trigger the active release of lysosomal enzymes which cause tissue destruction. The failure to identify such wall components in diseases tissues may be due to the lack of adequate sensitive techniques to detect minute amounts of these wall components, shown to trigger chronic destructive arthritis in laboratory animals. Two models of arthritis caused by mycobacterial and streptococcal wall components are described and the possible role played by immune responses, to the persisting bacterial factors, in the pathogenesis of human arthritis is discussed.

It is. proved that every continuous value is. diagonal, which in particular implies that every value on a closed reproducing space is diagonaL We deduce als.o that there are noncontinuous values.

Human leukocyte extracts, egg white lysozyme, cationic proteins, polymyxin, colimycin, and phenol are capable of releasing lipoteichoic acids (LTA) from group A streptococci and Strep. mutans. While the extraction of LTA by phenol is optimal at pH 4.7, the release of LTA from streptococci by the other agents is optimal at pH 7.4. LTA released by all agents was found to have the same sensitizing abilities, as determined by passive hemagglutination, and to have a similar chemical composition, as shown by thin-layer chromatography and radioactive scanning. The LTA-releasing capacity of all the agents is strongly inhibited by normal human serum. The possible role played by LTA released by leukocyte factors in the pathogenesis of tissue damage during bacterial infections is discussed.

Hydrogenation of 1,4- (I) and 1,3-di-tert-butylbenzene (II), p-xylene (III), and m-xylene (IV) over a Rh/Al2O3 catalyst at 0.34-150 atm H pressure was examd. With I, the rate of hydrogenation, the amt. of intermediate cyclohexene formed, and the cis-trans ratio of final product all increased, then decreased, with increasing pressure, but with II the rate and amt. of intermediate increased, while the product cis-trans ratio decreased, with increasing pressure. Hydrogenation of III paralleled that of I, except that the cis-trans ratio of dimethylcyclohexane steadily increased with increasing pressure; the same pressure effect on product isomer distribution was obtained with IV, but with IV the rate of hydrogenation increased with pressure throughout the obsd. range. The results are discussed in terms of possible types of reactive sites and their interconversion. [on SciFinder(R)]