LARGE RING AND HELICAL COMPLEXING AGENTS FOR METAL IONS

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The objective of the proposed research is to develop new types of organic molecules that can bind metal ions, forming complexes that are soluble in organic solvents and membranes. In these new molecules, pyridine and other heterocycles are oriented toward the metal-binding cavity, cleft or channel by fusion of rings, forming the most highly preorganized ligands known. Eight large-ring or helical complexing agents are proposed for study. Six are torands in which a large ring is formed by complete fusion of rings. Four of these torands have already been synthesized. Studies of the first torand will be extended to include complexes with metals throughout the periodic table. Particular emphasis will be placed on complexes of heavy metals and lanthanides do may result in applications, such as metal sensors, luminescent markers and NMR imaging agents. A new torand synthesis will be applied to formation of "tubular" discotic mesophases (liquid crystals). Two new "expanded" or "mixed-heterocycle" torands are proposed and their complexation of large metal ions and transition metal clusters will be examined. Two helical ligands of different sizes are proposed for study and their binding of alkali metals will be examined. These helical ligands and the tubular liquid crystals are potential approaches to synthetic ion channels that could be used to model biomembrane channels or to produce permselective membranes. Double-helical or even triple-helical polynuclear complexes may be formed by these novel ligands. Analogues of these complexes might be developed to interact specifically with helical biomolecules, such as proteins and nucleotides. All complexes will be studied spectroscopically and crystallographically to improve fundamental understanding of the interactions of metals with biomolecules. The new complexing agents will be tested as ionophores in ion-selective electrodes for analysis of metals in biological fluids. The polynuclear transition metal complexes formed by expanded torands may be useful as metalloenzyme models and as polyfunctional or multiple-electron catalysts.