Jean-Claude Bunzli - Effect of the length of polyoxyethylene substituents on luminescent bimetallic lanthanide bioprobes

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  Deiters,E., Song,B., Chauvin,A.S., Vandevyver,C.D.B.,   Bunzli,J.C.G. New Journal of Chemistry  2008 32 (7) 1140-1152

  Abstract: The new homoditopic ligand H2LC2'   self-assembles with lanthanide ions (Ln(III)) to yield neutral   bimetallic helicates of overall composition [Ln(2)(L-C2')3]; it   is fitted with two hexakis(oxyethylene) chains to test their   effects on the thermodynamic, photophysical and biochemical   properties of these complexes, with particular emphasis on their   uptake by living cells. At physiological pH and under   stoichiometric conditions, the conditional stability constants   log beta(23) are around 28 resulting in the speciation of the   Eu-III helicate being > 92% for a total ligand concentration   of 1 mM. The ligand triplet state features adequate energy   (0-phonon transition at approximate to 21 800 cm(-1)) for   sensitising the luminescence of Eu-III (Q = 19%) and Tb-III (Q =   10%) in aerated water at pH 7.4. The Eu(D-5(0)) emission spectrum   and lifetime (2.43 ms) are characteristic of a species with   pseudo-D-3 symmetry and without bound water in the inner   coordination sphere. The viability of HeLa cancerous cells is   unaffected when incubated with up to 500 mu M [Eu-2(L-C2')(3)]   during 24 h. The Eu-III helicate permeates into the cytoplasm of   these cells by endocytosis and remains essentially undissociated,   despite a low intracellular concentration of 0.28 mu M. In   addition, the leakage of the Eu-III helicate out of HeLa cells is   very minimal over long periods of time. With respect to similar   complexes with ligands bearing shorter tris( oxyethylene) chains,   no substantial changes are observed, which opens the way for   targeting experiments. This study also demonstrates that the   [Ln(2)(L-CX)(3)] helicates are fairly robust entities since their   core is unaffected by the substitution in the pyridine 4-position

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