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Issue 7, 2000
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Conjugates of cyclodextrins with charged and neutral macrocyclic europium, terbium and gadolinium complexes: sensitised luminescence and relaxometric investigations and an example of supramolecular relaxivity enhancement

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Abstract

The synthesis and characterisation of lanthanide complexes of mono- and tetra-amide β-cyclodextrin derivatives of 1,4,7,10-tetraazacyclododecane tetraacetate (DOTA) are reported. Luminescence and relaxivity measurements confirm that the Eu, Tb and Gd complexes of the eight-coordinate mono-amide ligand possess one bound water molecule while the tetra-amide complexes are rare examples of q = 0 systems in aqueous solution. The relaxivity of the host β-CD Gd complex (8.50 mM−1 s−1, 20 MHz, 298 K) is enhanced when non-covalently bound to a second gadolinium complex bearing two phenyl moieties with an enhancement that is limited by the slowness of the water exchange rate (τm = 0.6 μs, 298 K). Sensitisation of the terbium luminescence in the mono-amide β-CD complex occurs in the absence of oxygen using various substituted naphthalene derivatives (e.g. naphthalene, K = 1.04 × 104 M−1, 293 K) and methyl p-tert-butylbenzoate. The slowness of the intra-complex energy transfer step severely limits the efficiency of this process and restricts the scope of ‘non-covalently triggered luminescence’ to a narrow range of guest substrates, as deduced by variable temperature time-resolved luminescence and flash-photolysis studies.

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Article information


Submitted
20 Mar 2000
Accepted
17 Apr 2000
First published
05 Jun 2000

J. Chem. Soc., Perkin Trans. 2, 2000, 1329-1338
Article type
Paper

Conjugates of cyclodextrins with charged and neutral macrocyclic europium, terbium and gadolinium complexes: sensitised luminescence and relaxometric investigations and an example of supramolecular relaxivity enhancement

P. J. Skinner, A. Beeby, R. S. Dickins, D. Parker, S. Aime and M. Botta, J. Chem. Soc., Perkin Trans. 2, 2000, 1329
DOI: 10.1039/B002207L

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