Jean-Claude Bunzli - Lanthanide podates with programmed intermolecular interactions: Luminescence enhancement through association with cyclodextrins and unusually large relaxivity of the gadolinium self-aggregates

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      Fatin-Rouge,N., Toth,E., Perret,D., Backer,R.H., Merbach,A.E.,   Bunzli,J.C.G. Journal of the American Chemical Society  2000 122 (44) 10810-10820

      Abstract: The synthesis of the phenyl anchored   podand H4L1 fitted with four 3-carboxylate pyrazole arms and   programmed for intermolecular interactions is reported, and its   protonation constants are determined. interaction with Ln(3+)   ions (Ln = La, Eu, Lu) in dilute aqueous solutions leads to   complexes with 1:I and 1:2 metal-ligand stoichiometry. The   stability constants are in the range log beta (110) = 12.7-13.5   and log beta (120) = 22.5-23.8 (pLn values in the range 9-10).   The podates display a fair sensitization of the metal-centered   luminescence with an absolute quantum yield of 5% in case of   Tb-III. The average numbers of water molecules coordinated to the   Ln(III) ion amount to 3.8 and 4.9 for the 1:1 Eu and Tb podates,   respectively, as determined by lifetime measurements. The   addition of beta- and gamma -cyclodextrins to the 1:1 podates   results in a strong association with the host, mainly through the   phenyl anchor (Ln = Tb, log K-11 = 5-6 depending on the   cyclodextrin) and, for the Tb complex, to a large increase in   luminescence intensity at physiological pH. Self-aggregation of   the podates occurs at concentration larger than 3 x 10(-5) M.   This process is characterized by luminescence, using a pyrene   probe, light-scattering measurements, and transmission electron   microscopy. The novelty of the reported systems is their ability   to self-aggregate into nanometric, rigid, and spherical particles   in a controlled way (mean diameter: 10, 60, and similar to 300   nm), opening large perspectives for various applications. In   particular, a record-high relaxivity (r(1) = 53 mM(-1) s(-1) at   20 MHz, T = 25 degreesC) is observed for the aggregates of 1:2 Gd   pedate, which is not modified upon addition of an equimolar   quantity of Zn-II

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