HIGHLY EMISSIVE CHIRAL LANTHANIDE(III) COMPLEXES FOR LABELLING AND IMAGING

Abstract

Sensitised lanthanide complexes based on macrocyclic chelating ligands have been used extensively to study biological function at a cellular level, due to their very bright and long-lived emission, sharp emission bands and high stability to photo-degradation. These photophysical properties, in addition to their excellent chiroptical behaviour, also make these complexes promising candidates for security labelling and as anti-counterfeiting tools.

Novel highly emissive chiral europium(III) complexes based on macrocyclic ligands have been synthesised and their photophysical properties studied. They possess high molar extinction coefficients and are amenable to excitation using commonly available light sources. These complexes have been resolved by chiral HPLC and the circularly polarised luminescence (CPL) spectra of their enantiomers recorded. They exhibit strong circularly polarised emission in response to excitation using near ultra-violet light, and are stable to thermally-activated racemisation.

A simple off-the-shelf camera set up has been developed which is capable of discriminating ‘real’ europium(III) emission from emission from a ‘fake’ marking, based on emission lifetime and wavelength. Additionally, chiroptical discrimination has been achieved using a custom built microscope incorporating a quarter-wave plate and linear polariser.

The solvent dependent emission behaviour of a series of C3-symmetric lanthanide(III) complexes has been studied, demonstrating that the form of the total emission and CPL is extremely sensitive to minor changes in the outer solvation sphere of the complex.

Finally, macropinocytosis has been identified as the mechanism of cell uptake of this family of complexes in NIH-3T3 cells, and the internalisation and subsequent sub-cellular localisation has been shown to be dependent on complex chirality.