β‐Cyclodextrin adducts of Gd(III) chelates: useful models for investigating the structural and dynamic determinants of the relaxivity of gadolinium‐based systems

Gadolinium‐chelates bearing hydrophobic substituents on their surfaces form inclusion complexes with β‐cyclodextrin. When the chelate contains more than one substituent, the observed relaxation enhancement has to be analysed on the basis of the contributions arising from the actual speciation of the resulting inclusion complexes. This analysis allows the assessment of the binding constants for the individual inclusion complexes, as well as their specific relaxation enhancements. The relaxivities obtained of the supramolecular adducts display a good linearity with their molecular weights to outline that, in these systems, the main determinant of the relaxation enhancement is represented by the overall molecular reorientational time.