Development of lanthanide probes for cellular imaging

Abstract

Luminescent complexes of europium and terbium, incorporating new sensitizing chromophore moieties containing carboxylic acid functional groups, have been synthesised. It has been shown that the new tetraazatriphenylene chromophore leads to highly emissive complexes. A thiaxanthone chromophore, despite sensitizing lanthanide emission, results in complexes with lower quantum yields and is only practically useful for europium. Modification of the azaxanthone chromophore by formation of its N-oxide was investigated as a possibility of extending its longest wavelength absorption maximum beyond 340 nm. Phosphinate pendant arms were introduced into complexes containing the azaxanthone chromophore and resulted in highly emissive complexes Complexes of the new chromophores were investigated, together with numerous further examples, in terms of their susceptibility to quenching by electron rich species (iodide, ascorbate, urate). These experiments enhanced the mechanistic understanding of this process. Complexes using an azaxanthone chromophore with a carboxylic function and phenyl amide arms were used in coupling reactions. The coupling reactions involved isolation of the NHS ester of the complex. Cellular uptake and cytotoxicity experiments were carried out with several of these conjugate complexes. The possibility to observe these complexes using two photon excitation fluorescence microscopy was demonstrated.