title: AMPED: a new platform for picolinate based luminescent lanthanide chelates.
abstract: The synthesis of a new nonacoordinating ligand based on an AMPED (6-amino-6-methylperhydro-1,4-diazepine) scaffold functionalized by three picolinate (6-carboxy-2-methylpyridine) arms is described. Coordination of lanthanide cations (Ln = Eu and Tb) was investigated by spectrophotometric titrations monitored by UV-Vis absorption and steady-state emission spectroscopy, showing the formation of [LnL] complexes in aqueous solutions. The corresponding Eu and Tb complexes were isolated and characterized, and their spectroscopic properties (luminescence quantum yields, excited state lifetimes) were determined in buffered water (TRIS/HCl, pH 7.4) and compared to the data reported in the literature for related systems. DFT modelling of the complexes showed the picolinate arms to be perfectly wrapped around the Ln(3+) cations, affording an excellent shielding of the metal as confirmed by the determination of the hydration number of q = 0 for both complexes. The high resolution emission spectrum was used to determine the radiative lifetime of Eu in the complex (τrad = 3.05 ms) and the metal-centred luminescence quantum yield (0.20). The modest 0.10 overall luminescence quantum yield of the Eu complex is a consequence of an energy transfer with medium efficiency (0.50) and a low metal centred luminescence efficiency attributed in part to the presence of numerous NH and CH bonds in close proximity to the metal centre.
authors: Dipartimento di Scienze del Farmaco, Università del Piemonte Orientale "A. Avogadro", Largo Donegani 2/3, 28100 Novara, Italy. giovenzana@pharm.unipmn.it.
authors: Claudia
authors: C
authors: Guanci
authors: Giovanni
authors: G
authors: Giovenzana
authors: Luciano
authors: L
authors: Lattuada
authors: Carlos
authors: C
authors: Platas-Iglesias
authors: Loïc J
authors: LJ
authors: Charbonnière
mesh_terms: D001381:Azepines / Q000737:chemistry*; D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008024:Ligands; D010848:Picolinic Acids / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: C511496:6-amino-6-methylperhydro-1,4-diazepine; D001381:Azepines; D002614:Chelating Agents; D028581:Lanthanoid Series Elements; D008024:Ligands; D010848:Picolinic Acids; C030614:picolinic acid