Issue 42, 2015

Kinetico-mechanistic studies of substitution reactions on cross-bridged cyclen CoIII 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.

Graphical abstract: Kinetico-mechanistic studies of substitution reactions on cross-bridged cyclen CoIII complexes with nucleosides and nucleotides

Supplementary files

Article information

Article type
Paper
Submitted
14 May 2015
Accepted
27 Sep 2015
First published
30 Sep 2015

Dalton Trans., 2015,44, 18643-18655

Kinetico-mechanistic studies of substitution reactions on cross-bridged cyclen CoIII complexes with nucleosides and nucleotides

M. Vázquez, M. Font-Bardia and M. Martínez, Dalton Trans., 2015, 44, 18643 DOI: 10.1039/C5DT01816A

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