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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)