Affiliation: | aInstitut Català d’Investigació Química, Avinguda dels Països Catalans 16, E-43007 Tarragona, Spain bDepartament de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain cCátedra de Química Inorgánica, Facultad de Química, Universidad de la República, Avenida General Flores 2124, 11800 Montevideo, Uruguay |
Abstract: | The use of classical Werner-type cis-[Co(Cl)2(tetraamine)]+ (tetraamine = cyclen or tren) complexes for their complexation study of biologically relevant ligands has been pursued. These chlorocomplexes are found to be in the chloroaqua/chlorohydroxo forms under the physiological conditions used, their chloride substitution reactivity being dominated by conjugate base pathways, specially when tetraamine = cyclen. Further studies with nucleotides indicate that the substitution processes on cis-[Co(H2O)2(tetraamine)]3+, up to neutral pH, correspond to a simple reaction producing final stable phosphato bound mononucleotide complexes. These complexes are found to be an equilibrium mixture between monodentate O-phosphato and chelate O-phosphato-N-nucleotide forms. No evidence has been found for hydrolytic cleavage of the phosphato-nucleoside bond, as found in other systems with activated phosphates or higher pH values. A full kinetic profile of the process is proposed for the systems in the 2–7 pH range which is the same for chloride, nucleoside and nucleotide substitutions. The results are indicative of an important degree of outer-sphere hydrogen bonding between the cobaltocomplex and the entering biologically relevant ligands, as expected for these processes. |