Europium complexes for detection of nucleoside polyphosphate anions

A series of novel europium(III) based anion receptors [Eu.1-8] for nucleoside polyphosphate anions have been designed and synthesized. A study of their binding abilities was carried out in buffered aqueous media against a range of biologically relevant anions. It was demonstrated that certain probes could be used in biological applications such as real-time monitoring of enzymatic activity and real-time monitoring of ATP concentrations in living cells. Chapter 2 describes the synthesis of the 8 cationic Eu(III) complexes, each based on a cyclen macrocyclic scaffold and two quinoline arms in a trans relationship, which serve as antennae for the sensitisation of the central Eu(III) ion. Modifications in the structure of the complexes included varying the hydrogen bond donor groups on the quinoline arms (hydrogen, amide or an urea moiety) and the nature of the ligand donor groups to vary the local charge at the Eu(III) metal centre. The photophysical properties of all 8 complexes were characterised and the two urea bearing compounds proved unsuited for anion sensing as they do not possess a coordinated water molecule in the absence of added anion, preventing the displacement of water by an anion. Chapter 3 focuses on the behaviour of the 6 remaining Eu(III) complexes towards numerous biologically relevant anions in buffered water. The probes bearing the hydrogen moieties showed very little selectivity and low affinity towards the target anion ATP. On the other hand, probes bearing the amide moiety proved selective towards polyphosphate anions with high affinities. Additionally, polyphosphate anions when displacing the bound water molecule of such probes induced significant spectral changes and a large increase (up to 14-fold) in the emission intensity. [Continues.]