Gadolinium DTPA-monoamide complexes incorporated into mixed micelles as possible MRI contrast agents

Four monoamide derivatives of Gd-DTPA with alkyl chains consisting of 12, 14, 16, or 18 carbon atoms were synthesized. The gadolinium(iii) complexes with chain lengths of 14, 16 or 18 carbon atoms were efficiently incorporated into mixed micelles whereas the complex with a chain length of 12 carbon atoms was not incorporated into a micellar structure. The size distribution of the micelles was measured by photon correlation spectroscopy. The mean sizes of the micelles for all the complexes lay within a narrow range, typically between 11 and 20 nm. The NMRD curves of the gadolinium(iii) DTPA-monoamide complexes incorporated into mixed micelles display higher relaxivity values than the commercially available Gd-DTPA contrast agent. Moreover, micelles with gadolinium DTPA-monoamide complexes showed higher relaxivities than micelles containing the corresponding gadolinium DTPA-bis(amide) complexes, most likely because of a more efficient exchange of the coordinated water molecule. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)