Brightly Luminescent and Kinetically Inert Lanthanide Bioprobes Based on Linear and Preorganized Chelators

Abstract

The synthesis, photophysical properties and kinetic stability of a series of water-soluble, highly emissive Tb(III) and Eu(III) complexes featuring triethylenetetraamine hexaacetic acid (TTHA) and cyclohexyl triethylenetetraamine hexaacetic acid (cyTTHA) chelator scaffolds and carbostyril sensitizers are reported. The unique and modular design of the chelators gives rise to striking quantum yields of emission in aqueous solutions (up to 54%) as well as the characteristic lanthanides’ photophysical properties (long excited state lifetimes, large effective Stokes shifts, and narrow emission peaks). Furthermore, the pre-organized chelators (L3, L4 and L6) bind metal within minutes at ambient temperature yet exhibit substantial resistance to transchelation in the presence of a challenge solution (EDTA, 1 mM). Moreover, the Eu(III) complex of L4 remains stably luminescent in HeLa cells over hours, demonstrating the suitability of these compounds for live cell imaging applications. Representative chelators suitable for derivatization and protein bioconjugation were also prepared that were functionalized with clickable azide and alkyne moieties, biotin and trimethoprim (TMP). With exceptional long-wavelength brightness, enhanced kinetic inertness, and an adaptable synthetic route, the reported lanthanide complexes are promising probes and labels for time-gated bioanalysis, biosensing and optical microscopy.

Lanthanide-based tools for the investigation of cellular environments

“…For cell-impermeable lanthanides, techniques, such as micro-injection, 27,44 reversible plasma membrane permeabilization, 45 and osmotic lysis of pinocytic vesicles, 29,45 have been used. Co-incubation with compounds that increase cell permeability such as DMSO, 30,46,47 saponin, 34 or TMPyP 48 has also been described.…”

Highly luminescent lanthanide complexes sensitised by tertiary amide-linked carbostyril antennae

“…There are also a few examples of core N-substitutions (alkylations). 34 The effects of exocyclic N-alkylations on Ln sensitization have not been studied in detail, presumably because changes were expected to be small. We hypothesised that the removal of the N-H bond may have a measurable effect on the Ln emission quantum yield, at least for the more sensitive Eu complexes.…”

Efficient route to pre-organized and linear polyaminopolycarboxylates: Cy-TTHA, Cy-DTPA and mono/di- reactive, tert -butyl protected TTHA/Cy-TTHA

“…20 We also demonstrated that Cy-TTHA analogues were substantially more kinetically inert than their linear counterparts, as evidenced by an EDTA challenge assay. In order to prepare brightly emissive complexes, we needed an efficient synthetic approach that permitted selective mono-substitution of chromophoric sensitizer moieties at designated pendant positions.…”

“…1–3 Due to their ability to provide high denticities via a hard base binding core (carboxylate ions and tertiary amines), their corresponding lanthanide complexes have been heavily studied. 4–20 While linear polyaminopolycarboxylates form thermodynamically stable complexes, their relative kinetic instability with respect to many metals such as Gd(III) can limit their utility in biological or clinical environments. 21–25 In contrast, the widely used macrocyclic polyaminocarboxylates DOTA and TETA (Fig.…”