title: Pyridine-N-oxide analogues of DOTA and their gadolinium(III) complexes endowed with a fast water exchange on the square-antiprismatic isomer.
abstract: Two macrocyclic ligands derived from H4dota containing three acetate pendant arms and one 2-methylpyridine-N-oxide coordinating unit were synthesized. The ligand H3do3apy(NO) (H3L1, 10-[(1-oxidopyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) contains an unsubstituted pyridine-N-oxide ring; the ligand H4do3apy(NO-C) (H4L2, 10-[(4-carboxy-1-oxidopyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) is functionalized with a carboxylic group in the 4 position of the pyridine ring to allow attachment to other molecules. The ligands form octadentate (N4O4 environment) Ln(III) complexes, with one water molecule completing the coordination sphere in a capping position. The complexes are present in solution exclusively as square-antiprismatic isomers over the whole lanthanide series. The introduction of the carboxylic group to the pyridine-N-oxide unit in H4L2 has no significant effect on the hydration number (q = 1) and the water exchange rate of the [Gd(H2O)(L2)]- complex compared to the parent [Gd(H2O)(L1)] complex (water residence times: tauM = 39 ns for [Gd(H2O)(L1)] and tauM = 34 ns for [Gd(H2O)(L2)]- at 298 K).
authors.affiliation: Department of Inorganic Chemistry, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic.
authors.forename: Miloslav
authors.initials: M
authors.lastname: Polásek
authors.forename: Miroslava
authors.initials: M
authors.lastname: Sedinová
authors.forename: Jan
authors.initials: J
authors.lastname: Kotek
authors.forename: Luce
authors.initials: L
authors.lastname: Vander Elst
authors.forename: Robert N
authors.initials: RN
authors.lastname: Muller
authors.forename: Petr
authors.initials: P
authors.lastname: Hermann
authors.forename: Ivan
authors.initials: I
authors.lastname: Lukes
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry; D050091:Dendrimers / Q000737:chemistry; D005682:Gadolinium / Q000737:chemistry*; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D007536:Isomerism; D008024:Ligands; D008163:Luminescent Measurements; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D050091:Dendrimers; D006573:Heterocyclic Compounds, 1-Ring; D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D014867:Water; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; C013229:pyridine N-oxide; D005682:Gadolinium