A ruthenium-based metallostar: synthesis, sensitized luminescence and 1H relaxivity

Ru-based metallostars Na4{Ru[Ln2bpy-DTTA2(H2O)4]3} (Ln = Y, Gd, and Eu) have been self-assembled in aqueous solution and their relaxivity and optical properties unravelled. The synthesis and the purification of the new, highly stable heptametallic entities have been optimized for the diamagnetic Y3+ complex and followed by 1H NMR. The europium(III) ruthenium-based metallostar {Ru[Eu2bpy-DTTA2(H2O)4]3}4− displays sensitized 5D0→7FJ luminescence upon excitation of the tris(2,2′-bipyridyl)ruthenium(II) unit in the ultraviolet around 293 nm, as well as in the visible around 450 nm (1MLCT state). NMRD profiles at two temperatures (25 °C and 37 °C) were performed on {Ru[Gd2bpy-DTTA2(H2O)4]3}4−. NMRD profiles of the ruthenium-based {Ru[Gd2bpy-DTTA2(H2O)4]3}4− and the iron-based {Fe[Gd2bpy-DTTA2(H2O)4]3}4− metallostars were fitted with SBM theory coupled to the model-free Lipary-Szabo method for internal motion as well as with the modified Florence approach. Comparison of both fitting methods shows that the Florence approach is able to fit NMRD profiles up to 100 MHz, fails however at higher frequencies because it does not account for internal motion. Overall, the results detailed point to the heptametallic self-assembled edifices being potential relaxivity and luminescence bimodal bioprobes for use in animal models.