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High‐Relaxivity Contrast Agents for Magnetic Resonance Imaging Based on Multisite Interactions between a β ‐Cyclodextrin Oligomer and Suitably Functionalized Gd III Chelates
Author(s) -
Aime Silvio,
Botta Mauro,
Fedeli Franco,
Gianolio Eliana,
Terreno Enzo,
Anelli Pierlucio
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20011217)7:24<5261::aid-chem5261>3.0.co;2-d
Subject(s) - paramagnetism , molecule , adduct , hydrogen bond , chemistry , chelation , relaxation (psychology) , ion , gadolinium , crystallography , oligomer , coordination sphere , metal ions in aqueous solution , polymer chemistry , inorganic chemistry , organic chemistry , social psychology , psychology , physics , quantum mechanics
The results reported in this work show that tightly assembled adducts formed by trisubstituted Gd III complexes and a β ‐CD multimer (Poly‐ β ‐CD, d.p. ca. 12) may represent very interesting candidates for novel MRI applications wherein a high number of paramagnetic ions endowed with high relaxivity (per Gd III ion) are necessary. The relaxivities found for the paramagnetic adducts represent a remarkable step forward on the relaxivity scale. However, a detailed investigation of the determinants of the relaxation enhancement in these systems shows that their relaxivities are still limited by a nonoptimal τ R and a relatively long exchange lifetime of the coordinated water(s). Moreover, the exchange rate of the water molecule(s) coordinated to the Gd III ion further decreases upon binding to the Poly‐ β ‐CD. It is suggested that this finding is related to the structural properties of the supramolecule, which brings a high density of hydroxyl groups into the proximity of the “guest” complexes, and this yields an overall reinforcement of the hydrogen‐bonding network involving the coordinated water(s). On the other hand, such a tight arrangement appears responsible for an enhanced contribution to the observed relaxivity arising from water molecules in the second coordination sphere of the metal center.