Debroye, E., Dehaen, G., Eliseeva, S. V. Laurent, S., Vander Elst, L., Muller, R. N., Binnemans, K., Parac-Vogt, T. N.
Dalton Transactions (2012) 41 (35) 10549-10556 - doi : 10.1039/C2DT30605K
A ditopic DTPA monoamide derivative containing an 8-hydroxyquinoline moiety was synthesized and the corresponding gadolinium(iii) complex ([Gd(H5)(H2O)]-) was prepared. After adding aluminum(iii), the 8-hydroxyquinoline part self-assembled into a heteropolymetallic triscomplex [(Gd5)3Al(H2O)3]3-. The magnetic and optical properties of this metallostar compound were investigated in order to classify it as a potential in vitro bimodal contrast agent. The proton nuclear magnetic relaxation dispersion measurements indicated that the relaxivity r1 of [Gd(H5)(H2O)]- and [(Gd5)3Al(H2O)3]3- at 20 MHz and 310 K equaled 6.17 s-1 mM-1 and 10.9 s-1 mM-1 per Gd(iii) ion respectively. This corresponds to a relaxivity value of 32.7 s-1 mM-1 for the supramolecular complex containing three Gd(iii) ions. The high relaxivity value is prominently caused by an increase of the rotational tumbling time [small tau]R by a factor of 2.7 and 5.5 respectively, in comparison with the commercially used MRI contrast agent Gd(iii)-DTPA (Magnevist[registered sign]). Furthermore, upon UV irradiation, [(Gd5)3Al(H2O)3]3- exposes green broad-band emission with a maximum at 543 nm. Regarding the high relaxivity and the photophysical properties of the [(Gd5)3Al(H2O)3]3- metallostar compound, it can be considered as a lead compound for in vitro bimodal applications.