Metal ion complexation by acyclic and cyclic multidentate ligands

The objective of this work is to evaluate the different factors that dictate the binding ability of multidentate polyether ligands towards alkali metal and some heavy metal cations with special emphasis on crown ether compounds. The evaluation will involve the use of different analytical techniques, such as solvent extraction, ion-selective electrodes and fluorometry.

A primary objective is to investigate the influence of structural variations within a crown ether compound upon the selectivity and efficiency of alkali metal cation extraction. The research will involve a series of new crown ethers with different ring sizes containing multiple benzo or cyclohexano groups in the polyether ring. The conventional picrate extraction method will be used and the results will be compared with those from other more sophisticated extraction methods.

Other factors (solvent and anion effects) that influence the complexing ability of crown ethers in solvent extraction will be probed. Assessment of anion and solvent effects on the extraction efficiency and selectivity by a series of crown ether compounds with varying ring sizes will be conducted.

The complexing ability of crown ethers will also be evaluated in solvent polymeric membrane electrodes. Crown ethers will be incorporated as active components in PVC-matrix type membrane electrodes and their selective binding towards alkali metal cations will be tested. Special attention will be paid to Na selective ligands due to the importance of this cation in the field of medicine.

Solvent extraction will be performed with lipophilic pseudocyclic polyether dicarboxylic acids. In solvent extraction, these ligands do not require concomitant transfer of the aqueous phase anion into the organic phase. The ligands are known to have good binding ability towards Pb(n) which is an environmentally hazardous metal cation. A supplementary study will be performed to evaluate the stoichiometrics of Pb(II) and Cu(II) complexes formed with these ligands.

The final part of this work will be contribution to the growing field of chemosensors. A new calixarene-based fluorogenic reagent for selective Hg(II) recognition will be tested as a prospective chemosensor.