Tailoring macrocycles for metal ion binding

Absrract: We have been concerned with the development of alternate strategies for achievinc; metalion recognition. An important aspect of this research has been to investigate meta! ion complexation over a range of related macrocycles, incorporating different macrocyclic rhg sizes, donor atom set combinations and/or degree of ring substitution and to search for stability rrnxima at different points within this range. Assessment of the possible factors influencing any observed metal-ion recognition behaviour is then performed. This is followed by structural modification of particular ligand systems in an attempt to 'tune up' such behaviour. In particular instances it has proved possible to modify a ligand type progressively, using several 'tuning' cycles, such that very considerably enhanced discrimination towards a metal ion of interest has been achieved. In this manner, it has also proved possible to elucidate the subtle factors underlying different discrimination mechanisms. Studies of this type have tended to provide further insight into the factors influencing metal-ion discrimination than is normally possible for investigations involving a more limited ligand range.