Molecular and Nano-Structural Optimization of Nanoparticulate Mn 2+ -Hexarhenium Cluster Complexes for Optimal Balance of High T 1 - and T 2 -Weighted Contrast Ability with Low Hemoagglutination and Cytotoxicity.

The present work introduces rational design of nanoparticulate Mn(II)-based contrast agents through both variation of the μ 3 (inner) ligands within a series of hexarhenium cluster complexes [{Re 6 (μ 3 -Q) 8 }(CN) 6 ] 4 - (Re 6 Q 8 , Q = S 2- , Se 2- or Te 2- ) and interfacial decoration of the nanoparticles (NPs) K 4-2x Mn x Re 6 Q 8 ( x = 1.3 - 1.8) by a series of pluronics (F-68, P-123, F-127). The results highlight an impact of the ligand and pluronic for the optimal colloid behavior of the NPs allowing high colloid stability in ambient conditions and efficient phase separation under the centrifugation. It has been revealed that the K 4-2x Mn x Re 6 Se 8 NPs and those decorated by F-127 are optimal from the viewpoint of magnetic relaxivities r 1 and r 2 (8.9 and 10.9 mM -1 s -1 , respectively, at 0.47 T) and low hemoagglutination activity. The insignificant leaching of Mn 2+ ions from the NPs correlates with their insignificant effect on the cell viability of both M-HeLa and Chang Liver cell lines. The T 1 - and T 2 -weighted contrast ability of F-127-K 4-2x Mn x Re 6 Q 8 NPs was demonstrated through the measurements of phantoms at whole body 1.5 T scanner.