FORMATION AND STRUCTURE OF INCLUSION COMPLEXES INVOLVING ALPHA-CYCLODEXTRIN AND ALKYL(AQUA)COBALOXIME

A series of inclusion complexes involving alpha-cyclodextrin (alpha-cd ) and alkyl(aqua)cobaloximes has been synthesized for the first time a nd characterized by elemental analysis, one and two-dimensional H-1 NM R spectroscopy. Their formation constants K-a were determined by quant itative H-1 NMR methods. The crystal structures of alpha-cd-[Co(Hdmg)( 2)Pr-n(H2O)] (H(2)dmg = dimethylglyoxime) and its guest molecule [Co(H dmg)(2)Pr-n(H2O)] were determined. According to both NMR and crystal s tructure data, 1:1 inclusion complexes of alpha-cd and alkylcobaloxime s are formed, in which the alkyl groups of the guests are included int o the cavity of alpha-cd. After formation of the inclusion complexes, variations in the bond lengths and angles around the cobalt atom, and conformation changes of the n-propyl(aqua)cobaloxime were observed. It is suggested that these changes in the guest molecule are probably du e to the hydrophobic interaction between the alkyl groups and the alph a-cd cavities, and steric interaction between alpha-cd and Co(Hdmg)(2) . It has also been established that the stability of the inclusion com plexes in aqueous solution is related to the length and the size of th e alkyl groups, the K-a values varying in the order n-C5H11 much great er than Bu(n) > Pr-n > Bu(i).