Copper(II) forms a 2: 1 complex with cyclodextrin in an alkaline solution. The complexes with α- and β-cyclodextrins were isolated from solutions by the addition of ethanol. They are labile, and, upon heating, the Cu(II) is reduced to Cu(0). The role of the hydroxide ion was examined by means of potentiometrie and conductometric titrations; it was found that the reaction of 1 mol of α-cyclodextrin with 2 mol of Cu(OH)2consumes 2 mol of the hydroxide ion, whereas 3 mol of the hydroxide ion are consumed for the reaction of β-cyclodextrin. Polarimetric measurements showed that the optical rotation of cyclodextrin changes from dextrorotatory to levorotatory upon the formation of the Cu(II)-cyclodextrin complex. It was suggested, with a molecular model, that the two pairs of C2 and C3′ secondary hydroxyl groups of contiguous glucose units are cross-linked by the Cu(OH−)2Cu ion bridge in the α-cyclodextrin complex and by Cu(OH−)(O2−)Cu ion bridge in the β-cyclodextrin complex. Furthermore, the circular ring of cyclodextrin may be distorted to the ellipsoidal form by the complex formation, causing a pronounced change in the optical rotation.

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The apparent dissociation constant (Kapp) of a complex between β-cyclodextrin and an azo dye, sodium p-(4-hydroxy-1-naphthylazo)benzenesulfonate, was determined by spectrophotometry in a phosphate buffer solution (pH 5.91) in the absence and in the presence of various inorganic salts at 25 °C. The cyclodextrin and the azo dye formed a 1 : 1 complex with the Kapp value of 2.44×10−3 M in a 0.1 M phosphate buffer. Kapp decreased with an increase in the concentration of the phosphate buffer and with the addition of some inorganic salts, such as Li2SO4, Na2SO4, K2SO4, LiIO3, NaIO3, KIO3, and KF. These results were explained mainly in terms of the decrease in the activity of water, which takes part in the dissociation reaction of the inclusion complex, with an increase in the concentration of the inorganic salts. On the other hand, Kapp increased with the addition of such salts as KCl, KBr, KI, KNO3, KSCN, and KClO4. These results were attributed mainly to the formation of the inclusion complexes of the cyclodextrin with the anions of these salts, competing with the azo dye for the cyclodextrin-binding site.

Cyclodextrin accelerates the phenol release from organic phosphates such as dialkyl 4-nitrophenyl phosphates, but it decelerates the reactions of the corresponding monothiophosphates in alkaline solutions. Each reaction proceeds via the prior formation of a cyclodextrin–substrate inclusion complex, followed by the nucleophilic attack of the cyclodextrin alkoxide ion or the hydroxide ion on the reaction site of the included substrate. The equilibrium and kinetic parameters involved in the reaction processes were determined and discussed in connection with the geometry of a cyclodextrin–substrate complex.