title: Kinetico-mechanistic studies of substitution reactions on cross-bridged cyclen Co(III) complexes with nucleosides and nucleotides.
abstract: Kinetico-mechanistic studies on the substitution reactivity of the [Co{(μ-ET)cyclen}(H2O)2](3+) complex cation at pH values within the 6.0-7.0 range with biologically significant ligands have been carried out. The substitution processes have been found to occur exclusively on the mono-hydroxobridged [(Co{(μ-ET)cyclen}(H2O))2(μ-OH)](5+) species formed after equilibration of the cobalt complex in the relevant medium. The studies conducted on the substitution of the aqua/hydroxo ligands of this dinuclear species are indicative of a dominant role of outer-sphere complexation, involving hydrogen-bonding interactions. The values of the outer-sphere complex formation equilibrium constant are in line with the intervention of both the exiting aqua ligands and the NH groups at the encapsulating {(μ-ET)cyclen} ligand. These complexes result in the preferential formation of O- or N-bonded nucleotides depending on the structure of the base moiety of the ligand. Even the entry of the different donor bonded nucleotides is hampered by the hydrogen-bonding interaction with the dangling moiety of an already coordinated ligand. In general the overall substitution processes occur at a faster rate than those published for the fully alkylated encapsulating {(Me)2(μ-ET)cyclen} ligand derivative, as expected for the still available base-catalysing NH groups in the {(μ-ET)cyclen} ligand.
authors.affiliation: Departament de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain. manel.martinez@qi.ub.es.
authors.forename: Marta
authors.initials: M
authors.lastname: Vázquez
authors.forename: Mercè
authors.initials: M
authors.lastname: Font-Bardia
authors.forename: Manuel
authors.initials: M
authors.lastname: Martínez
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D000080027:Cyclams; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008968:Molecular Conformation; D009705:Nucleosides / Q000737:chemistry*; D009711:Nucleotides / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D000080027:Cyclams; D006571:Heterocyclic Compounds; D009705:Nucleosides; D009711:Nucleotides; D003035:Cobalt; C038072:cyclen