Influence of dimensionality and charge on anion binding in amide-based macrocyclic receptors

The influence of dimensionality and charge on anion binding and structure is explored for a selected series of amide-based macrocyclic receptors. Monocyclic, bicyclic and tricyclic hosts are described in terms of affinities towards simple oxo anions (including acetate) and halides. Binding propensities tend to vary, although some selectivity patterns emerge for similar ligand frameworks. Some anions also exert a template influence the cyclization reactions during the synthesis of host precursors. Structurally sandwich complexes are often formed in the monocycles, while bicycles tend to encapsulate their guests. Multiple anions plus water molecules are often found in the larger bicycles. Added charge via quaternization or protonation tends to enhance binding by one or two orders of magnitude while maintaining the same selectivity patterns. (c) 2006 Elsevier B.V. All rights reserved.