Spectroscopic and electrochemical sensing of anions and cations using novel receptor molecules

The aim of the project was to extend the field of molecular recognition of anions and cations of biochemical, medical, chemical and environmental importance. This was achieved by the use of a number of novel receptor molecules that are designed to bind anionic and cationic guests. The binding of the guest anions and cations was probed by various electrochemical, spectrochemical and IH NMR spectroscopy techniques. The receptor molecules studied included (i) ruthenium(II) trisbipyridyl complexes of acyclic, calix[4]arene and cyclic 2,2'-bipyridine ligands, (ii) the macrocycle Nphenylaza- 15-crown-5, and (iii) crown ether derivatives of diquat. These receptor molecules have been shown to sense anions and cations, such as chloride, bromide, dihydrogen phosphate, sodium, lithium and magnesium. Interestingly, one of diquat crown ether derivatives has been shown to complex both anions and cations at the same time. This is an important development, as the simultaneous molecular trapping of anions and cations in such systems is seen as a possible alternative to the use of ion exchange resins. With a view to producing spectrochemical and/or electrochemical sensor systems, work has been completed by the immobilisation of the novel receptor molecules. This has been achieved by the electropolymerisation of vinyl-substituted ruthenium(Il) trisbipyridyl complexes or the immobilisation of receptor molecules in a polyvinylchloride (PVC) matrix. The latter technique has been particularly successful and has led to the construction of a battery-powered fluorescence detector which has been used for anion sensing.