Cycloamyloses as catalysts

The Chemisorption of Benzene R. B. Moves and P. B. Wells The Electronic Theory of Photocatalytic Reactions on Semiconductors Th. Wolkenstein Cycloamyloses as Catalysts David W. Griffiths and Myron L. Bender... 

The reactions of the cycloamyloses may also be useful in achieving stereoselective organic synthesis or they may serve as models for hydrophobic interactions in aqueous solution. As the scope of cycloamylose catalysis is extended to include other reaction types and other cycloamylose derivatives, additional applications will undoubtedly be revealed for the cycloamyloses as catalysts. 

Cycloamyloses as Catalysts David W. Griffiths and Myron L. Bender... 

Griffiths DW, Bender ML. (1973). Cycloamyloses as catalysts. Advances in Catalysis 23 209-261. 

As noted in an earlier section of this article, the utility of the cycloamyloses as covalent catalysts is limited by the low reactivity of the catalytically active hydroxyl groups at neutral pH s and by the relatively slow rates of deacylation of the covalent intermediates. In an effort to achieve effective catalysis, several investigators have attempted to selectively modify the cycloamyloses by either (1) introducing an internal catalyst to facilitate deacylation or (2) introducing a more reactive nucleophile to speed acylation and/or deacylation. 

OrganometaUic compounds, of transition metals as catalysts for polymerization of vinyl monomers and olefins, 23 263-325 OrganometaUic transformation, molecular analogs, 38 288, 290-291 Organophosphorus substrates, hydrolysis of, effect of cycloamyloses on, 23 235 Organosilicon compounds, hexacoordinated, 34 155... 

Hydrolysis of 4-nitrophenyl ferrocinnamate in the presence of cyclohepta-amylose is accelerated approximately 50 000-fold compared with hydrolysis of the ester by buffer alone.It is suggested that cycloamylose-based catalysts have the potential to act as artificial enzymes, providing accelerations of enzymatic magnitudes. 

As noted previously, rate accelerations imposed by the cycloamyloses may be competitively inhibited by the addition of inert reagents to the reaction medium. The inhibitor, by competing with the substrate for the cycloamylose cavity, effectively removes a fraction of the catalyst from the reaction coordinate. This observation lends additional force to the mechanism illustrated in scheme I. 

The acylation of the cyclohepta-amylose anion in 60% DMSO 40% water by the 4-nitrophenyl ester of ferrocinnamic acid (1) is accelerated over 50 000-foId compared with the hydrolysis by buffer alone. The actual rate achieved is similar to that for the acylation of -chymotrypsin by 4-nitrophenyl acetate. This is the greatest acceleration observed for cycloamylose catalysis, but at the same time highlights one of the difficulties of using this class of compounds as general catalysts. The optimum substrate structure has to be found for the catalyst. According to molecular models, (1) fits snugly into the preformed cavity. 

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