Cyclodextrins carbonic anhydrase model

Artificial Enzymes, p. 76 Carbonic Anhydrase Models, p. 178 Catalytic Antibodies, p. 193 Cyclodextrins, p. 398... 

Carbohydrates, Recognition of, p. 169 Carbonic Anhydrase Models, p. 178 Carcerands and Hernicarcerands. p. 189 Cation-n Interactions, p. 214 Cavitands, p. 219 Chiral Guest Recognition, p. 236 Classical Descriptions of Inclusion Compounds, p. 253 Classification and Nomenclature of Supramolecular Compounds, p. 261 Clathrate Hydrates, p. 274 Conzplexation of Fullerenes, p. 302 Concepts in Ciystal Engineering, p. 319 Crown Ethers, p. 326 Cryptands, p. 334 Cryptophanes, p. 340 Cyclodextrins, p. 398... 

On treatment with potassium iodide, the capped disulfonate j8-cyclo-dextrin discussed above could easily be converted to the corresponding diiodide jS-cyclodextrin. With appropriate nucleophiles (imidazole, histamine) a new route to bis(iV-imidazolyl)-j8-cyclodextrin and bis(iV-histamino)-j8-cyclodextrin was developed by Tabushi s team (182). In the presence of Zn(II) ion, both regiospecifically bifunctionalized cyclodextrins hydrate CO2 and are the first successful carbonic anhydrase models. The Zn(II) ion binds to the imidazole rings located in the edge of the cyclodextrin pocket and the presence of an additional basic group, as with bis(histamino)-cyclodextrin-Zn(II), enhances the activity. Therefore, the present models show that all three factors, Zn(II)-imidazole, hydrophobic environment, and a base seem to help to generate the carbonic anhydrase activity (182). The chemistry of this enzyme is further discussed in Section 6.2, p. 331. 

I. Tabushi, Y. Kuroda, and A. Mochizuki (1980), The first successful carbonic anhydrase model prepared through a new route to regiospecifically bifunction-alized cyclodextrin. /. Amer. Chem. Soc. 102, 1152-1153. 

Several model systems related to metalloenzymes such as carboxypeptidase and carbonic anhydrase have been reviewed. Breslow contributed a great deal to this field. He showed how to design precise geometries of bis- or trisimidazole derivatives as in natural enzymes. He was able to synthesize a modified cyclodextrin having both a catalytic metal ion moiety and a substrate binding cavity (26). Murakami prepared a novel macrocyclic bisimidazole compound which has also a substrate binding cavity and imidazole ligands for metal ion complexation. Yet the catalytic activities of these model systems are by no means enzymic. 

Another interesting enzyme model obtained by use of difunctionalized cyclodextrin having two imidazole groupings also afforded carbonic an-hydrase models as reported by the authors (69). Carbonic anhydrase has Zn2 + surrounded by three imidazoles in the active site and COz is bound to the active site is close proximity to Zn2+ with the assistance of hydrophobic... 

Over the last two decades, a thousand structural and functional models for carbonic anhydrase were reported to address the features of the active site and the mechanism of the catalytic reaction. One of the earliest functional models is the supramolecular composite of the Z /5(histamino)cyclodextrin-Zn-imidazole complex 3 that accelerates CO2 hydration at pH 7.0. although the catalytic activity is not good compared with the native... 

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