New polyaminocarboxylate macrocycles containing phenolate binding units: synthesis, luminescent and relaxometric properties of their lanthanide complexes. Issue 14 (22nd March 2017) - Enel, Morgane
Abstract : The relaxometric and (or) luminescent properties in aqueous solutions of new Ln III macrocyclic complexes derived from PCTA are reported. Abstract : The synthesis of two new polyaminocarboxylate macrocycles incorporating one or two intracyclic phenol units (H4 L 1 and H8 L 2, respectively) is described. The 12-membered H4 L 1 macrocycle leads to soluble and stable mononuclear Ln III complexes of [(L 1 )Ln(H2 O)2 ] − composition (Ln = Eu, Tb and Gd) in aqueous solutions. In Tris buffer (pH 7.4), the [(L 1 )Tb(H2 O)2 ] − complex displays a suitable efficiency for sensitized emission ( η sens = 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 [(L 1 )Gd(H2 O)2 ] − complex is characterized by high relaxivity ( r 298 K1 = 7.2 s −1 mM −1 at 20 MHz) and a very short water residence time of the coordinated water molecules ( τ 298 KM = 9 ns), promising values for the realisation of macromolecular systems with high relaxivities. Thus, the Tb and Gd complexes of the H4 L 1 macrocycle exhibit several improvements in terms of luminescent (lower excitation energy, higher brightness) and relaxometric (shorter τ M ) properties compared to the corresponding LnPCTA complexes, where a phenol moiety substitutes a pyridine ring. On the other hand, the 24-membered H8 L 2 macrocycle including two phenol units in its structure leads to dinuclear complexes of [(L 2 )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.