Honorary Staff: Len Lindoy, FAA

Emeritus Professor Address: School of Chemistry, Building F11 The University of Sydney, NSW, 2006, Australia Email address: L.Lindoy@chem.usyd.edu.au Telephone: +61-2-9351 4400 Fax: +61-2-9351 3329

Career Profile:

PhD (1968), DSc(1985) University of NSW
Postdoctoral Fellow, Ohio State University, 1968-1970
Bye-Fellow, Robinson College, Cambridge
Personal Chair, James Cook University
Appointed at the University of Sydney in 1997

Areas of interest:

• Metal ion and small molecule recognition
  

• Selfassembly in chemistry
  

• Supramolecular chemistry
  

• Macrocyclic ligand chemistry
  

• Ligand design
  

• Reagents for solvent extraction and membrane transport

Research:

Reagents for Metal-Ion Recognition: A major research area of the group has been the design and synthesis of macrocyclic systems for the recognition of heavy metal ions and their application to a number of areas such as metal-ion transport through liquid membranes and macrocyclic immobilisation on solid substrates.

As part of the investigations, original and deliberate strategies for obtaining heavy metal-ion recognition have been developed. Thus, a major aim of the project has been to produce ligands which are specific for particular heavy metal ions and to understand the reasons for such specificity when it does occur. Such studies are of considerable fundamental importance since the entire area of metal-ion recognition by organic substrates is quite poorly understood - even though it is central to the role of metal ions in a wide range of chemical and biochemical systems.

An aspect of the work has been to use macrocyclic ligand hole size as one means of 'tuning' a cyclic ligand system for a particular metal ion. Two mechanisms for achieving ring-size discrimination have been investigated. One of these, 'dislocation discrimination', was first recognised and systematically investigated by our group.

In parallel studies (in association with Dr. K. R. Adam and Dr. I. M. Atkinson of James Cook University) considerable effort has been expended on developing satisfactory computational procedures for modelling the respective metal-containing species. The studies have led to the observation of a variety of discrimination phenomena within the respective (industrially important) series Co(II)/Ni(II)/Cu(II), Zn(II)/Cd(II) and Pb(II)/Ag(I) with, in some instances, spectacular discrimination having been achieved.

Apart from the production of reagents of potential practical utility, collectively the work has contributed towards the general understanding of heavy metal-ion recognition by organic substrates.

As an extension of the studies just outlined, much current research activity is concerned with the application of selective reagents to systems to the practical separation and/or sensing of particular metal ions. New developments include extensive studies of the use of such reagents immobilised on solid supports (such as silica gel). An extensive series of studies involving heavy metal ion discrimination via solvent extraction and transport across hydrophobic membranes has been performed; much of it in association with Professor P. A. Tasker of the University of Edinburgh. New metal ion sensors based on the above systems have also been developed.

The Assembly Effect - a New Effect in Coordiation Chemistry: In a project that spands the areas of classical metal coordination chemistry and supramolecular chemistry, we have investigated the self assemply of simple host-guest adducts between ligands that may correspond to a 'coordination shell' for coordination of a metal ion of interest. Our initial studies, carried out in association with Professor P. A. Tasker (University of Edinburgh) involved host-guest formation between long-chain carboxylic acid moieties and amine-containing macrocycles. The nature of these adducts and the factors influencing the observed stoichiometries of individual adducts has been of especial interest. As well as adding to the lipophilicity of individual systems, particular host-guest species of this type act as 'organised assemblies' for use in metal-ion solvent extraction and membrane transport studies. Mutual ligand assembly such as this has potentially important implications for enhanced efficiency of metal-ion binding - the study of which continues to be an important focus of our continuing investigations.

The use of the 'assembly effect' in the design of particular assemblies for use as ionophores in (selective) solvent extraction and bulk membrane transport experiments involving transition and post-transition ions is another facet of the project.

Molecular Architecture: New Molecular Receptors: The efficient 'step-wise' syntheses for a range of new supramolecular receptors incorporating macrocycles as structural elements has recently been developed in association with Associate Professor G.V.Meehan at James Cook University.
Examples include families of new 'super' cages, as well as a range of new 'linked' macrocyclic species incorporating mixed donor atom sets. The cages are capable of incorporating a range of smaller molecules and ions in their central cavities while the 'chain like' and dendritic molecules are able to bind a heavy metal at each macrocyclic node. Heavy metal-containing species of this latter type show potential for acting as nanoscale 'catalytic surfaces'. The prospect of adsorption of these large flat molecules onto solid supports for use in catalytic or electrochemical (including sensor) processes is especially appealing.

In ongoing studies, systems incorporating both S2N2-donor rings as well as N4-donor rings in a number of molecular architectures are continuing - these include both simple linked systems as well as higher order moieties containing up to nine macrocyclic rings. The synthesis of such large macrocyclic systems capable of binding heavy metals represents access to an unusual and interesting class of metal-containing materials whose properties at this time are not able to be fully predicted.