Cyclohexaamylose inclusion complexes

The reaction of cyclohexaamylose with a series of p-carboxyphenyl esters is an example of a decelerating effect which may be clearly attributed to nonproductive binding. Rate effects imposed by cyclohexaamylose on the hydrolyses of three such esters are summarized in Table IX. As the hydrophobicity of the ester function is increased by alkyl substitution, the hydrolysis is inhibited the stability of the inclusion complex, on the other... 

Manifestation of specificity in maximal rate constants rather than in stability constants is illustrated particularly well by the cyclohexaamylose-accelerated release of fluoride ion from Sarin. Although the inclusion complex of (rate acceleration is much larger for the (—)-enantiomer. Specificity is equally dramatic in... 

Regardless of the relative importance of polar and nonpolar interactions in stabilizing the cyclohexaamylose-DFP inclusion complex, the results derived for this system cannot, with any confidence, be extrapolated to the chiral analogs. DFP is peculiar in the sense that the dissociation constant of the cyclohexaamylose-DFP complex exceeds the dissociation constants of related cyclohexaamylose-substrate inclusion complexes by an order of magnitude. This is probably a direct result of the unfavorable entropy change associated with the formation of the DFP complex. Thus, worthwhile speculation about the attractive forces that lead to enantiomeric specificity must await the measurement of thermodynamic parameters for the chiral substrates. 

In analogy to the derivative prepared by Breslow and Overman, the cyclohexaamylose-iV-methylhydroxamic acid displays a pronounced specificity for p-nitrophenyl acetate as opposed to n-nitrophenyl acetate. This specificity is probably again derived from the geometry of the inclusion complex i.e., a more favorable location of the reactive center of the para-isomer relative to the hydroxamate function within the inclusion complex. 

This is part V of the series Topography of Cyclodextrin Inclusion Complexes. Part IV Crystal and Molecular Structure of the Cyclohexaamylose -Propanol-4.8 Hydrate Complex , W. Saenger, R. K. McMullan, J. Fayos, and D. Mootz Acta Crystallogr. B30, 2019 (1974). 

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