1985 Volume 58 Issue 6 Pages 1658-1662
The alkaline hydrolysis of p-nitrophenyl acetate (p-NPA) in 1.0mol dm−3 NaOH at 25 °C was almost completely retarded by the addition of a binuclear Cu(II) complex with α-cyclodextrin (Cu2α-CD). The dissociation constant for an inclusion complex of Cu2α-CD with p-NPA was determined to be 0.059 mmol dm−3, which is about one 200th that for an inclusion complex of α-CD with p-NPA. The alkaline hydrolysis of o- and m-nitrophenyl acetates was also retarded by Cu2α-CD, though the extent of retardation was much less than that for p-NPA. A binuclear Cu(II) complex with β-cyclodextrin (Cu2β-CD) also caused a stereoselective deceleration of the alkaline hydrolysis of the esters. However, the stereoselectivity of Cu2β-CD was not so remarkable as that of Cu2α-CD. Dissociation constants for inclusion complexes of Cu2α2-CD with several alcohols and other organic substrates were determined by the kinetic examination of the competitive inhibition effect of the substrates on the association of Cu2α-CD with p-NPA. Cu2α-CD formed stable inclusion complexes with such disk-like molecules as cyclohexanol, cycloheptanol, and p-nitrobenzyl alcohol. The geometry of a Cu2α-CD-p-NPA inclusion complex was presumed on the basis of these results.
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