Jean-Claude Bunzli - A versatile ditopic ligand system for sensitizing the luminescence of bimetallic lanthanide bio-imaging probes

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      Publication Details (including relevant citation   information):

      Chauvin,A.S., Comby,S., Song,B., Vandevyver,C.D.B., Bunzli,J.C.G.   Chemistry-A European Journal 2008  14 (6) 1726-1739

      Abstract: The homoditopic ligand   6,6'-[methylenebis(1-methyl-1H-benzimid-   azole-5.2-diyl)]bis(4-{2-[2-(2-methoxyethoxy)ethoxy]ethoxylpyridine-2-carboxyli c   acid) (H2LC2) 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 (109023) are   close to 25 at physiological pH and under stoichiometric   conditions. The ligand triplet state features adequate energy   (0-phonon transition at approximate to 21900 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 mu m [Eu-2(L-C2)(3)] during 24 h. Bright Eu-III   emission is seen for incubation concentrations above 10 mu 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

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