ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
O15. Lanthanide Metallacrowns as Anion Receptors and Potential MRI
Contrast Agents
M. Tegoni a , M. Remelli b , F. Dallavalle a , L. Marchiò a
a
Department of General and Inorganic Chemistry, University of Parma, Viale G.P. Usberti 17A, 43100, Parma,
Italy
e-mail: matteo.tegoni@unipr.it
b
Department of Chemistry, University of Ferrara, Via L. Borsari 46, 44100, Ferrara, Italy
Metallacrowns (MCs) are a class of metallamacrocycles structurally related to crown ethers with extraordinary
capabilities of encapsulating various metal ions into the central cavity of a self-assembled supramolecule. [1]
Peripheral divalent cations and bridging ligands form the metallacycle, while examples of core ions are Cu(II) in
12-MC-4 and Ln(III) in 15-MC-5. Known since a decade, the 15-MC-5 complexes are capable to encapsulate
selectively Ln(III) in presence of Ca(II) or uranyl, and to coordinate anions to the peripheral and core ions on
both faces of the metallamacrocycle. [2]
The capability of 15-MC-5 to bind the hydroxide ion arise from the high acidity of coordinated water molecules,
one of which deprotonates at pH 4. These results obtained by thermodynamic studies in aqueous solution
allowed also to establish that the 15-MC-5 formation is a real self-assembly and that the 15-MC-5 species are the
only stable Ln(III) complexes up to pH 7.
The remarkable ability of 15-MC-5 to coordinate carboxylates was studied by means of fluorescence and PGSE
– NMR in water. The results demonstrate on a thermodynamic basis the observation that 15-MC-5 complexes of
phenylalaninehydroxamate coordinate preferentially aromatic than aliphatic carboxylates in their hydrophobic
pocket.
The stability of Gd(III) 15-MC-5 with potential applications as MRI contrast agents in presence of competing
ligands and endogenous metals has also been interpreted on the basis of thermodynamic data.
References:
[1] G. Mezei, C.M. Zaleski, V.L. Pecoraro, Chem. Rev., 107(11), 2007, 4933-5003.
[2] C.S. Lim, A. Cutland Van Noord, J.W. Kampf, V.L. Pecoraro, Eur. J. Inorg. Chem., 10, 2007, 1347-1350.
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