Cell-penetrating metal complex optical probes: targeted and responsive systems based on lanthanide luminescence.

To understand better the structure and function of biological systems, cell biologists and biochemists would like to have methods that minimally perturb living systems. The development of emissive optical probes is essential for improving our observation of intracellular signaling and recognition processes. Following excitation of the probe, photons emitted from the probe may be observed by spectroscopy or microscopy and encode information about their environments in their energy, lifetime, and polarization.

Enantioselective regulation of a metal complex in reversible binding to serum albumin: dynamic helicity inversion signalled by circularly polarised luminescence.

The helicity of the (SSS)-Delta enantiomer of a terbium and europium(III) complex is inverted on reversible binding to 'drug site II' of serum albumin, signalled by a switch in its circularly polarised emission; no such behaviour occurs with the (RRR)-Lambda complexes, thereby defining a unique chiroptical probe of albumin binding.

Effective and efficient sensitisation of terbium luminescence at 355 nm with cell permeable pyrazoyl-1-azaxanthone macrocyclic complexes.

Emissive terbium complexes, suitable for protein conjugation, incorporating a pyrazoyl-1-aza-xanthone chromophore have been prepared; they exhibit cellular uptake and possess a much lower sensitivity to excited state quenching.

A mechanistic study of the dynamic quenching of the excited state of europium(III) and terbium(III) macrocyclic complexes by charge- or electron transfer.

Dynamic quenching of the metal-based excited state of Eu(III) and Tb(III) complexes of sixteen different macrocyclic ligands has been studied. Quenching by urate, ascorbate and selected catechols is most effective for Tb(III) systems, and involves intermediate formation of an excited state complex (exciplex) between the electron-poor heterocyclic sensitising moiety incorporated into the ligand (tetraazatriphenylene, azaxanthone or a pyrazoyl-azaxanthone) and the electron-rich reductant. The process is sensitive to steric inhibition created by the local ligand environment; quenching is reduced as temperature increases as exciplex formation is entropically disfavoured.

Identification of emissive lanthanide complexes suitable for cellular imaging that resist quenching by endogenous anti-oxidants.

Excited state quenching by urate and ascorbate of selected europium and terbium(III) macrocyclic complexes has been assessed and related to the ease of complex visualisation by optical microscopy inside various living cells, e.g. CHO, COS and NIH 3T3.