Crown ethers conformational characteristics

Calixarenes were developed later than crown ethers and cyclodextrins but have stillbeen extensively researched. Macrocycles of calix[n]arenes are constructed by linking a number of phenol residues via methylene moieties (Fig. 2.16). Like crown ethers, the name calixarene reflects the structures of these molecules, since a calix is a chalice. Calixarenes with various cavity sizes have been designed, each of which has conformation isomers, and their phenolic hydroxyl groups are often modified. These structural characteristics allow us to create calixarene derivatives with various structural modifications. 

Likewise, the strucmre of subtilisin (pH 3.0) suspended in varying ratios of acetonitrile and water demonstrated a-helical content similar to that in the lyophilized powder (Griebenow and Klibanov, 1996). Furthermore, the rate of transesteriflcation reactions of subtilisin (pH 7.8) suspended in DMSO/acetonitrile, formamide/acetonitrile or formamide/dioxane were increased approximately 100-fold over aqueous conditions (Almarsson and Klibanov, 1996). Similar results were obtained for subtilisin (pH 7.8) in a tetrahydrofuran/1-propanol mixture (Affleck et al., 1992). These results can be attributed to the increased structural rigidity of the active conformation of the protein in the solid, and the denaturing characteristics of the solvent at the solvent-particulate interface. Preservation of this molecular memory or molecular imprint of the protein can also be used to stabilize structure and activity (Mishra et al., 1996 Rich and Dordick, 1997 Santos et al., 2001). Subtilisin was lyophilized from crown ethers, resulting in more native like structure, by FTIR, and increased enzyme activity in THF, acetonitrile and dioxane (Santos et al.,2001). 

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