Lanthanide Complexes as Chiral Probes Exploiting Circularly Polarized Luminescence

Abstract

A series of studies has been undertaken to facilitate the identification and development of chiral lanthanide complexes that are able to report on changes in their local environment through modulation of the circular polarization of their emission. Reports of such systems remain relatively rare in the literature, notwithstanding the prevalence and importance of chirality in biological systems.

The work described herein is separated into five chapters, the first of which comprises a discussion of relevant background information, along with a comprehensive review of responsive lanthanide-based CPL probes reported to date. A classification of these probes is built up, which informs the content of the following three chapters.

Chapter 2 describes work undertaken in the pursuit of a novel lanthanide-based system for use as a CPL probe for the detection of proteins. The synthesis of an enantiopure lanthanide complex was undertaken and characterisation of this system carried out with reference to a structurally related racemic complex. A series of comparative investigations designed to probe the relative protein binding capability of these complexes was subsequently performed, which revealed that the observation of induced CPL from racemic lanthanide systems may be brought about by a change in complex constitution. This is the first example of such an effect from a well-defined racemic lanthanide complex in solution. Chapter 3 goes on to detail studies undertaken to demonstrate the utility of this racemic lanthanide system as a probe for chiral detection.

Chapter 4 describes investigations carried out in an attempt to identify new systems exhibiting chiral quenching effects in solution. Initially, two pairs of enantiomeric electron-rich quenching species were assessed for their ability to quench the emission from an enantiopure DOTA-derived lanthanide complex differentially. Subsequently, investigations were focussed on examining the quenching of emission from novel enantiopure lanthanide complexes based on a 1,4,7-triazacyclononane framework, using cobalt complexes as the quenching species.

Finally, Chapter 5 contains experimental procedures for each compound synthesised, as well as general experimental procedures.