Biocompatible supramolecular dendrimers bearing a gadolinium-substituted polyanionic core for MRI contrast agents

Two cationic dendrons bearing terminal groups of triethylene glycol monomethyl ether in different generations were used to encapsulate a paramagnetic polyoxometalate cluster K₁₃[Gd(β₂-SiW₁₁O₃₉)₂], in which the Gd³⁺ ion was sandwiched by the coordination of two lacunary [β₂-SiW₁₁O₃₉]^8- sub-clusters, through electrostatic interaction. Benefiting from the surface covering of cationic dendrons and ionic complexation, both inorganic polyanionic core and the complexes formed maintained chemical stability in a physiological environment. In addition, the formed charge-neutralized supramolecular complex dendrimers with biocompatible periphery had low cytotoxicity but high relaxivity for in vitro and in vivo magnetic resonance imaging (MRI) in the self-assembled state. Because of the branched structure of organic components on the cluster surface and the disordered packing of complexes in aggregations, a reasonable communication of cluster core with the bulk environment was concluded. Importantly, due to the assembled particle size and molecular weight, the complex dendrimers were a suitable model for liver-specific MRI contrast agents. The results obtained showed that the dendritic supramolecular hybrid complexes represent potential MRI contrast agents in the development of new biomedical materials.