Large Relaxivity Enhancement of Paramagnetic Lipid Nanoparticles by Restricting the Local Motions of the Gd(III) Chelates

A Gd(III)-DOTA-like complex bearing two aliphatic chains on adjacent acetic arms was designed, synthesized, and compared with its analogous monofunctionalized complex. A 1/T(1) NMR relaxometric study of the two amphiphilic complexes incorporated into micelles and liposomes showed an unprecedented relaxivity enhancement for the complex with two lipophilic side arms. This remarkable result, which is attributed to a favorable water exchange rate and increased rigidity of the system resulting from limiting of the local motion of the gadolinium center, represents an important advance in the development of highly efficient nanosystems for MRI applications.