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摘要
A Multimeric systems assembled by linking Gd-III complexes to a central scaffold can be Magnetic Resonance Imaging (MRI) contrast agents of improved efficiency at high magnetic fields. Two novel mononuclear GdDO3A-derivatives (DO3A = 1,4,7,10-tetraazacyclododecane-N, N', N ''-triacetic acid) featuring a flexible (hexanoic acid, GdL1) or rigid (methyl benzoic acid, GdL2) pendant arm were synthesized and conjugated to a central 1,4,7-triazacyclononane unit through amide coupling to form two novel trinuclear systems (Gd(3)L3 and Gd(3)L4). A variable temperature and frequency H-1 and O-17 NMR relaxometric study on the mononuclear complexes indicated that GdL2 exhibits two water molecules in the inner coordination sphere, as does the parent [Gd(DO3A)(H2O)(2)] complex (q = 2). However, the flexibility of the alkyl chain of GdL1 allows its folding and coordination to the Gd3+ ion with displacement of one water molecule (q = 1) around neutral pH. In Gd(3)L4, the linker rigidity results in a compact and rather rigid trinuclear system from the point of view of rotational dynamics, with each Gd-III center having q = 2. This favors a considerable degree of coupling between local and overall tumbling motions and hence high relaxivity values (r(1) = 13.8 mM(-1) s(-1); 60 MHz and 298 K). On the other hand, the flexibility of the alkyl chain significantly affects the properties of Gd(3)L3. The relaxation data suggest the easy folding of one of the chelates with coordination of Gd by an amide group of the central macrocyclic unit (q = 1). The other two complexes (q = 2) exhibit a high degree of rotational mobility around the linker that results in a significant limit on the relaxivity (r(1) = 9.8 mM(-1) s(-1); 60 MHz and 298 K).
- 出版日期2018-5-21
