Host–Guest Complexation of Mono[6-(1-pyridinio)-6-deoxy]-α-cyclodextrin with Several Inorganic Anions

Abstract

Abstract Mono[6-(1-pyridinio)-6-deoxy]-α-cyclodextrin (1) formed 1:1 charge-transfer complexes with such inorganic anions as I−, SCN−, and Br− in an aqueous solution to afford characteristic UV absorption bands. The binding constant (Ka) for a I− complex with 1 was ca. 45 times as large as that with a nonmacrocyclic analog of 1, ca. 10 times that with native α-cyclodextrin, and 4.4 times that with a β-cyclodextrin analog. The I− ion was bound to a dipyridinio analog of 1 more strongly than to 1 by a factor of 10. The Ka values decreased with an increase in the ionic strength of the medium. The complexation was competitively inhibited by ClO4−. Hydrophobic, van der Waals, electrostatic, and charge-transfer interactions were supposed to take part in the complexation co-operatively.