NMR-SPECTROSCOPY OF CYCLODEXTRIN-INORGANIC ANION SYSTEMS

The addition of alkali salts of chaotropic anions such as Br-, I-, SCN -, N-3(-), ClO4-, and NO3- to an alpha r-cyclodextrin (alpha-CD) solut ion in D2O caused marked downfield shifts in the H-1 NMR signal of the C(5)-H located in the interior of the alpha-CD cavity, whereas the si gnal showed no or only small upheld shifts upon the addition of alkali salts of antichaotropic anions such as F-, HCO3-, H2PO4-, HPO42-, and SO42-. The effects of the inorganic salts on the chemical shifts (del ta) for the other protons of alpha-CD were significant but smaller tha n that on delta for C(5)-H. These facts indicate that the chaotropic a nions are included within the alpha-CD cavity and held in the vicinity of C(5)-H. Similar, but smaller, effects of the inorganic salts were observed for beta- and gamma-CD. The binding constants and thermodynam ic parameters determined for complexation of CD's with some chaotropic anions suggest that hydrophobic and van der Waals interactions, as we ll as a conformational change of CD macrocycles and the desolvation of CD's and/or the anions upon complexation, play important roles in com plex stabilization. The effect of inorganic salts on the spin-lattice relaxation times of alpha-CD protons also supports the above conclusio n.