title: Terpyridine-based heteroditopic ligand for Ru(II)Ln3(III) metallostar architectures (Ln = Gd, Eu, Nd, Yb) with MRI/optical or dual-optical responses.
abstract: A new ditopic ligand (L) based on a 2,2':5',4″-terpyridine unit substituted in the 2″,6″ positions with iminodiacetate arms has been designed and synthesized for the construction of Ru(II)L3Ln3(III) supramolecular architectures. The two components of this system, a 2,2'-bipyridine unit for Ru(II) coordination and a pyridine-bis(iminodiacetate) core for Ln(III) coordination, are tightly connected via a covalent Carom(py)-Carom(py) bond. The paramagnetic and photophysical properties of the corresponding tetrametallic Ru(II)L3Gd3(III) complex have been evaluated, highlighting the potential of this metallostar structure to act as a bimodal MRI/optical imaging agent. Variable-temperature (17)O NMR and proton nuclear magnetic relaxation dispersion (NMRD) measurements showed that this complex exhibits (i) a remarkable relaxivity per metallostar molecule, particularly at clinical and high magnetic fields (r1(310K) = 51.0 and 36.0 mM(-1) s(-1) at 20 and 300 MHz, respectively) and (ii) a near-optimal residence lifetime of Gd(III) coordinated water molecule (τM(310K) = 77.5 ns). This is the result of the presence of two inner-sphere water molecules in the Gd(III) components of the metallostar and a slow tumbling rate of the molecule (τR(310K) = 252 ps). Upon excitation in the visible domain (λexc = 472 nm), the Ru(II) component of the complex exhibits a bright-red luminescence centered at 660 nm with a quantum yield of 2.6% in aqueous solutions at pH 7.4. Moreover, this Ru(II)L3Gd3(III) assembly is also characterized by a high kinetic inertness in biological media (PBS and human serum solutions) and a high photostability (photobleaching). Finally, preliminary photophysical studies on RuL3Nd3 and RuL3Yb3 assemblies revealed that the Ru(II) center acts as an effective sensitizer for Ln(III)-based luminescence in the near-IR region. The Nd(III) species was found to be the most effective at quenching the (3)MLCT luminescence of the Ru center.
authors.affiliation: CNRS, Laboratoire de Synthèse et Physico-Chimie de Molécules d'Intérêt Biologique, SPCMIB, UMR-5068 , 118 Route de Narbonne, F-31062 Toulouse cedex 9, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Boulay
authors.forename: Céline
authors.initials: C
authors.lastname: Deraeve
authors.forename: Luce
authors.initials: L
authors.lastname: Vander Elst
authors.forename: Nadine
authors.initials: N
authors.lastname: Leygue
authors.forename: Olivier
authors.initials: O
authors.lastname: Maury
authors.forename: Sophie
authors.initials: S
authors.lastname: Laurent
authors.forename: Robert N
authors.initials: RN
authors.lastname: Muller
authors.forename: Béatrice
authors.initials: B
authors.lastname: Mestre-Voegtlé
authors.forename: Claude
authors.initials: C
authors.lastname: Picard
mesh_terms: D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008024:Ligands; D008279:Magnetic Resonance Imaging; D015394:Molecular Structure; D055620:Optical Phenomena; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D028581:Lanthanoid Series Elements; D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D012428:Ruthenium