title: A heterobimetallic ruthenium-gadolinium complex as a potential agent for bimodal imaging.
abstract: Trinuclear heterobimetallic Ln(III)-Ru(II) complexes (Ln = Eu, Gd) based on a 1,10-phenanthroline ligand bearing a diethylenetriaminepentaacetic acid (DTPA) core have been synthesized and fully characterized by a range of experimental techniques. The (17)O NMR and proton nuclear magnetic relaxation dispersion (NMRD) measurements of Gd(III)-Ru(II) show that, in comparison to the parent Gd-DTPA, this complex exhibits improved relaxivity, which is the result of an increase of the rotational correlation time. Relaxometry and ultrafiltration experiments indicate that the 1,10-phenanthroline ligand has a high affinity for noncovalent binding to human serum albumin, which results in a high relaxivity r(1) of 14.3 s(-1) mM(-1) at 20 MHz and 37 °C. Furthermore, the Ln(III)-Ru(II) complexes (Ln = Eu, Gd) show an intense light absorption in the visible spectral region due to metal-to-ligand charge transfer (MLCT) transitions. Upon excitation into the MLCT band at 440 nm, the complexes exhibit a bright-red luminescence centered at 610 nm, with a quantum yield of 4.7%. The luminescence lifetime equals 540 ns and is therefore long enough to exceed the fluorescent background. Monometallic lanthanide complexes have also been synthesized, and the Eu(III) analogue shows a characteristic red luminescence with a quantum yield of 0.8%. Taking into account the relaxometric and luminescent properties, the developed Gd(III)-Ru(II) complex can be considered as a potential in vitro bimodal imaging agent.
authors.affiliation: Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, P.O. Box 2404, B-3001 Heverlee, Belgium.
authors.forename: Geert
authors.initials: G
authors.lastname: Dehaen
authors.forename: Peter
authors.initials: P
authors.lastname: Verwilst
authors.forename: Svetlana V
authors.initials: SV
authors.lastname: Eliseeva
authors.forename: Sophie
authors.initials: S
authors.lastname: Laurent
authors.forename: Luce
authors.initials: L
authors.lastname: Vander Elst
authors.forename: Robert N
authors.initials: RN
authors.lastname: Muller
authors.forename: Wim M
authors.initials: WM
authors.lastname: De Borggraeve
authors.forename: Koen
authors.initials: K
authors.lastname: Binnemans
authors.forename: Tatjana N
authors.initials: TN
authors.lastname: Parac-Vogt
mesh_terms: D000042:Absorption; D005682:Gadolinium / Q000737:chemistry*; D006801:Humans; D008024:Ligands; D008163:Luminescent Measurements; D008958:Models, Molecular; D008968:Molecular Conformation; D057054:Molecular Imaging / Q000379:methods*; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism; D010618:Phenanthrolines / Q000737:chemistry; D012428:Ruthenium / Q000737:chemistry*; D012709:Serum Albumin / Q000378:metabolism
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D010618:Phenanthrolines; D012709:Serum Albumin; D012428:Ruthenium; D005682:Gadolinium; C025205:1,10-phenanthroline