High-relaxivity contrast agents for magnetic resonance imaging based on multisite interactions between a #beta#-cyclodextrin oligomer and suitably functionalized Gd~(III) chelates

摘要

The results reported in this work show that tightly assembled adducts formed by trisubstituted Gd~(III) complexes and a #beta#-CD multimer may represent very interesting candidates for novel MRI applicatios wherein a high number of paramagnetic ions endowed with high relaxivity are necessary.The relaxivities found for the paramagnetic adducts represent a remarkable step forward on the relaxivity xcale.However,a detailed investigaton of the determinants fo the relaxaton enhancemet in these systems shows that their relaxivities are still limited by a nonoptimal #tau#_R and a relatively long exchange lifetime of the coordianted water(s).Moreover,the exchange rate of the water moelcule(s) coordianted tothe Gd~(III) ion further decreases upon binding tothe poly-#beta3-CD.It is suggested that this finding is related to the structural properties of the supramolecule,which brings a high density of hydroxyl groups intothe 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 arrangemet appears responsible for enhanced contribution tot he observed reaxivity arising from water moelcules int he second coordiantion sphere of the metal center.