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A Versatile Ditopic Ligand System for Sensitizing the Luminescence of Bimetallic Lanthanide Bio‐Imaging Probes
Author(s) -
Chauvin AnneSophie,
Comby Steve,
Song Bo,
Vandevyver Caroline D. B.,
Bünzli JeanClaude G.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701357
Subject(s) - lanthanide , bimetallic strip , luminescence , ligand (biochemistry) , luminescent measurements , chemistry , materials science , nanotechnology , combinatorial chemistry , ion , optoelectronics , organic chemistry , biochemistry , receptor , metal
The homoditopic ligand 6,6′‐[methylenebis(1‐methyl‐1 H ‐benzimidazole‐5,2‐diyl)]bis(4‐{2‐[2‐(2‐methoxyethoxy)ethoxy]ethoxy}pyridine‐2‐carboxylic acid) (H 2 L C2 ) has been tailored to self‐assemble with lanthanide ions (Ln III ), which results in the formation of neutral bimetallic helicates with the overall composition [Ln 2 (L C2 ) 3 ] and also provides a versatile platform for further derivatization. The grafting of poly(oxyethylene) groups onto the pyridine units ensures water solubility, while maintaining sizeable thermodynamic stability and adequate antenna effects for the excitation of both visible‐ and NIR‐emitting Ln III ions. The conditional stability constants (log β 23 ) are close to 25 at physiological pH and under stoichiometric conditions. The ligand triplet state features adequate energy (0‐phonon transition at ≈21 900 cm −1 ) to sensitize the luminescence of Eu III ( Q =21 %) and Tb III (11 %) in aerated water at pH 7.4. The emission of several other VIS‐ and NIR‐emitting ions, such as Sm III ( Q =0.38 %) or Yb III (0.15 %), for which in cellulo luminescence is evidenced for the first time, is also sensitized. The Eu III emission spectrum arises from a main species with pseudo‐ D 3 symmetry and without coordinated water. The cell viability of several cancerous cell lines (MCF‐7, HeLa, Jurkat and 5D10) is unaffected if incubated with up to 500 μ M [Eu 2 (L C2 ) 3 ] during 24 h. Bright Eu III emission is seen for incubation concentrations above 10 μ M and after a 15‐minute loading time; similar images are obtained with Tb III and Sm III . The helicates probably permeate into the cytoplasm of HeLa cells by endocytosis. The described luminescent helical stains are robust chemical species which remain undissociated in the cell medium and in presence of other complexing agents, such as edta, dtpa, citrate or L ‐ascorbate. Their derivatization, which would open the way to the sensing of targeted in cellulo phenomena, is currently under investigation.