Non-directional forces drive guest affinity and discrimination in a calix[5]arene-based receptor

In this paper we report the binding behavior of a receptor based on a calix [5]arene possessing two convergent benzoic acids that serve to bind a guest . The receptor recognizes diketopiperazines (DKP) having a variety of alkyl substituents to form a 1:1 host-guest complex. We demonstrate that the rec eptor shows selectivity for the DKPs based on the size of the alkyl substit uent. As a result, the selectivity arises from non-directional forces betwe en the pi-basic aromatic ring of the calixarene and the alkyl group of the guest. (C) 2000 Elsevier Science Ltd. All rights reserved.