MOLECULAR RECOGNITION OF DIHYDROXY-AROMATICS WITH BIS-O-XYLYLENEGLYCOLURIL HOSTS

A variety of 'molecular clip' host molecules based on glycoluril have been synthesised and their binding to resorcinol and catechol guests i n chloroform investigated by NMR, JR and phase transfer. The glycoluri l unit provides two convergent hydrogen-bond accepters, and two xylyle ne 'walls' complete a cleft which further binds the guest by aryl stac king; 1:1 binding constants of up to 2500 M(-1) are obtained. Modellin g suggests that the systems have moderate conformational flexibility, allowing for an induced fit to the guest. Placing pi-electron-donating substituents on the walls enhances binding, despite the presence of s uch substituents on the target guests: this has been explained in term s of the interactions of pi-poor and pi-rich atoms at the points of co ntact of the host and guest. The host molecules catalyse the transport of resorcinol from water into chloroform.