Chemistry Letters, Vol.30, No.6, 560-561, 2001
Control of ion binding by cooperative ion-pair recognition using a flexible heterotopic receptor
Complex of the host, which bears four amide groups and two crown ethers, and Cs+, recognizes chloride and bromide anions much more strongly than the free host, because the host captures one Cs+ ion with the two crown rings in a face-to-face fashion to cyclize the host, and the preorganization of the amide protons farms the good binding site for the anions.