Jean-Claude Bunzli - Remarkable tuning of the photophysical properties of bifunctional lanthanide tris(dipicolinates) and its consequence on the design of bioprobes

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      Gassner,A.L., Duhot,C., Bunzli,J.C.G., Chauvin,A.S. Inorganic   Chemistry 2008 47 (17) 7802-1

      Abstract: Derivatives of dipicolinic acid with a   polyoxyethylene pendant arm at the pyridine 4-position have been   functionalized for potential grafting with biological material.   Four ligands with different terminal functions (alcohol, methoxy,   phtalimide and amine) have been synthesized, which react with   trivalent lanthanide ions Ln(III) to yield triple helical   [Ln(L)(3)](3-) complexes, as shown by NMR and UV-vis titrations.   The tris chelates display large thermodynamic stability with 109   beta 13 approximate to 19-20 for all Eu(III) complexes for   instance. Photophysical measurements reveal adequate   sensitization of the metal-centered luminescence in the europium   (eta(sens) = 33-72%) and terbium complexes, which is modulated by   the nature of the terminal function. The lifetimes of the   metal-centered excited states are long, up to 1.4 ms for   [Eu(L)(3)](3-) and 1.6 ms for [Tb(L)(3)](3-) at room temperature,   in line with hydration numbers essentially equal to zero. Quantum   yields are as high as 29% for the (Eu(L(NH2))(3)](3-) and 18% for   the [Tb(L(OH))(3)](3-) tris chelates in water at physiological   pH. These series of complexes demonstrate the extent of   fine-tuning achievable for lanthanide luminescent probes and are   simple models for investigating the effect of binding to   biological molecules on the metal-centered luminescent properties

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