Abstract

At pD 6·80 in D₂O containing 0·10 mol dm^-3 phosphate buffer, the association constants of the complexes of Naproxen and Ibuprofen with 6^A-amino-6^A-deoxy-β-cyclodextrin are 810±200 and 8900±2100 mol^-1 dm³ , respectively, while those of the corresponding complexes with β-cyclodextrin are 940±170 and 8800±1800 mol^-1 dm³ , respectively. A 2D-ROESY experiment shows that Naproxen includes lengthwise in the substituted cyclodextrin, with the reverse orientation to that of the complex with β-cyclodextrin. The orientation in the host{guest complex of the substituted cyclodextrin results in the alignment of the host amino substituent and the guest carboxy group, which at this pD are predominantly protonated and deprotonated, respectively. The similarity in the association constants of the complexes of Naproxen indicates that any stabilization provided by interactions between the ionic groups in the complex of the substituted cyclodextrin is offset by other factors, such as the extent of desolvation of the host and guest.