Simple hybrid polymeric nanostructures encapsulating macro-cyclic Gd/Eu based complexes: luminescence properties and application as MRI contrast agent.

Lanthanide-based macrocycles are successfully incorporated into hybrid polyionic complexes, formed by adding a mixture of zirconium ions to a solution of a double-hydrophilic block copolymer. The resulting nanoobjects with an average radius of approximately 10-15 nm present good colloidal and chemical stability in physiological media even in the presence of competing ions such as phosphate or calcium ions. The final optical and magnetic properties of these objects benefit from both their colloidal nature and the specific properties of the complexes. Hence these new nanocarriers exhibit enhanced T1 MRI contrast, when administered intravenously to mice.

New polyaminocarboxylate macrocycles containing phenolate binding units: synthesis, luminescent and relaxometric properties of their lanthanide complexes.

The synthesis of two new polyaminocarboxylate macrocycles incorporating one or two intracyclic phenol units (H4L1 and H8L2, respectively) is described. The 12-membered H4L1 macrocycle leads to soluble and stable mononuclear LnIII complexes of [(L1)Ln(H2O)2]- composition (Ln = Eu, Tb and Gd) in aqueous solutions. In Tris buffer (pH 7.4), the [(L1)Tb(H2O)2]- complex displays a suitable efficiency for sensitized emission (ηsens = 48%) and a high luminescence quantum yield (Φ = 22%), which is worthy of note for a bis-hydrated terbium complex. Besides, luminescence experiments show that bidentate endogenous anions (citrate, carbonate, and phosphate) do not displace the two inner-sphere water molecules of this complex. In contrast, the possible presence of LMCT states causes the europium complex to be weakly luminescent. The [(L1)Gd(H2O)2]- complex is characterized by high relaxivity (r = 7.2 s-1 mM-1 at 20 MHz) and a very short water residence time of the coordinated water molecules (τ = 9 ns), promising values for the realisation of macromolecular systems with high relaxivities. Thus, the Tb and Gd complexes of the H4L1 macrocycle exhibit several improvements in terms of luminescent (lower excitation energy, higher brightness) and relaxometric (shorter τM) properties compared to the corresponding LnPCTA complexes, where a phenol moiety substitutes a pyridine ring. On the other hand, the 24-membered H8L2 macrocycle including two phenol units in its structure leads to dinuclear complexes of [(L2)Ln2]2- composition. Its terbium complex shows a long luminescence lifetime (2 ms) and a high quantum yield (43%) in aqueous solutions, making this compound a new promising candidate for time-resolved applications.