title: Investigating the Complexation of the Pb(2+)/Bi(3+) Pair with Dipicolinate Cyclen Ligands.
abstract: The complexation properties toward Pb(2+) and Bi(3+) of the macrocyclic ligands 6,6'-((1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(methylene))dipicolinic acid (H2do2pa) and 6,6'-((4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(methylene))dipicolinic acid (H2Me-do2pa) have been investigated. A new three-step synthesis of H2do2pa following the bisaminal methodology has also been developed. The X-ray structures of [Pb(Me-do2pa)]·6H2O and [Bi(Me-do2pa)](NO3)·H2O show that the two metal ions are eight-coordinated by the ligand. The two complexes exist as the racemic Δ(δδδδ)/Λ(λλλλ) mixture both in the solid state and in solution, as indicated by NMR and DFT studies. The stability constants of the lead(II) and bismuth(III) complexes of the two ligands were determined in 0.5 M KCl using potentiometric and spectrophotometric techniques. The stability constants determined for the complexes of Pb(2+) are relatively high (log KML = 16.44 and 18.44 for H2do2pa and H2Me-do2pa, respectively) and exceptionally high for the complexes of Bi(3+) (log KML = 32.0 and 34.2 for H2do2pa and H2Me-do2pa, respectively). The [Pb(Me-do2pa)] complex presents rather fast formation and very good kinetic inertness toward transchelation. Additionally, the [Bi(Me-do2pa)](+) complex was found to present a remarkably fast complexation rate (full complexation in ∼2 min at pH 5.0, acetate buffer) and a very good kinetic inertness with respect to metal ion dissociation (half-life of 23.9 min in 1 M HCl), showing promise for potential applications in α-radioimmunotherapy.
authors.affiliation: †Université de Bretagne Occidentale, UMR-CNRS 6521, UFR des Sciences et Techniques, 6 avenue Victor le Gorgeu, C.S. 93837, 29238 BREST Cedex 3, France.|‡Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal.
authors.forename: Luís M P
authors.initials: LM
authors.lastname: Lima
authors.affiliation: †Université de Bretagne Occidentale, UMR-CNRS 6521, UFR des Sciences et Techniques, 6 avenue Victor le Gorgeu, C.S. 93837, 29238 BREST Cedex 3, France.
authors.forename: Maryline
authors.initials: M
authors.lastname: Beyler
authors.affiliation: ‡Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal.
authors.forename: Rita
authors.initials: R
authors.lastname: Delgado
authors.affiliation: §Departamento de Química Fundamental, Facultade de Ciencias, Universidade da Coruña, Campus da Zapateira-Rúa da Fraga 10, 15008 A Coruña, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Platas-Iglesias
authors.affiliation: †Université de Bretagne Occidentale, UMR-CNRS 6521, UFR des Sciences et Techniques, 6 avenue Victor le Gorgeu, C.S. 93837, 29238 BREST Cedex 3, France.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Tripier
mesh_terms: D001729:Bismuth / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D000080027:Cyclams; D006571:Heterocyclic Compounds / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D010848:Picolinic Acids / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D000080027:Cyclams; D006571:Heterocyclic Compounds; D008024:Ligands; D010848:Picolinic Acids; D007854:Lead; C038072:cyclen; D001729:Bismuth; C004860:dipicolinic acid