MOLECULAR RECOGNITION OF SUGARS WITH MACROCYCLIC HOST COMPOUNDS

Resorcinol cyclic tetramer (calix [4] resorcinarene) binds hydroxylic guest compounds including sugars in apolar organic media. The driving force of this complexation is a combination of hydrogen bonding and CH-pi interaction. The latter interaction gives rise to not only a 1 : 1 host : guest stoichiometry but also a sizable selectivity arizing from the apolar alkyl moiety of the guests. Sugars and related guests can also be bound in water to tetrasulfonate derivatives of the host. The CH-pi interaction again provides the major driving force. It is sensitive to the pi-electron density of the aromatic cavity of the host. Thus, the guest (sugar) binding ability of the host is enhanced either by introduction of additional electron-donating OH groups on the benzene rings or upon deprotonation of the OH groups giving rise to anionic host. The CH-pi interaction may be regarded as a kind of hydrogen bonding between pi-base and sigma-acid.