Paramagnetic Clusters of Mn3(O2CCH3)6(Bpy)2 in Polyacrylamide Nanobeads as a New Design Approach to T1-T2 Multi-Modal MRI Contrast Agent

There is an increasing need for gadolinium-free MRI contrast agents, particularly for patients suffering from chronic kidney disease. Using a cluster-nanocarrier combination, we have identified a novel approach to the design of biomedical nanomaterials and report here the criteria for the cluster and the nanocarrier and the advantages of this combination. We have investigated the relaxivity of the following manganese oxo clusters: the parent cluster Mn3(O2CCH3)6(Bpy)2 (1) where Bpy = 2,2’-Bipyridine, and two new analogs, Mn3(O2CC6H4CH=CH2)6(Bpy)2 (2), and Mn3(O2CC(CH3) =CH2)6(Bpy)2 (3), and Mn3O(O2CCH3)6(Pyr)2 (4) where Pyr = pyridine. The parent cluster, Mn3(O2CCH3)6(Bpy)2 (1), had impressive relaxivity (r1 = 12.4 mM-1s-1, r2 = 145 mM-1s-1) and was found to be the most amenable for the synthesis of cluster-nanocarrier nanobeads. Using the inverse miniemulsion polymerization technique, (1) in combination with the hydrophilic monomer acrylamide, we synthesized nanobeads (~125 nm diameter) with homogeneousl...