DNA interaction with a coordination Co(II) compound containing phenanthroline ligands in a 5mM NaCl solution is studied. Spectral studies have shown that complex forms under experimental conditions. The phenanthroline ligands of the compound take part in binding to DNA. The hypochromic effect in the absorption spectrum upon the formation of these complexes is observed. It may indicate the formation of phenanthroline dimers or even stack structures upon binding. Such binding reaches saturation at r > 0.4 (r is the ratio of the molar concentrations C of the compound and DNA (in moles of base pairs for DNA)). At the same time, it seems that the phenanthroline ligand is intercalated into the DNA double helix, as follows from the viscosimetry data - the viscosity of the DNA solutions increases by approximately 20%. This binding reaches saturation at r > 0.2, and at r > 0.4 the formation of another complexes begins, which causes a decrease of the DNA solutions viscosity. This decrease is not associated with a decrease of the DNA stiffness as a result of the breakdown of the secondary structure of DNA upon binding, because its stabilization in the complex is observed, as follows from the study of DNA melting. We can assume that cobalt is able to form a coordination bond with the DNA molecule. In this case, one of the phenanthroline ligands, which received a great mobility upon binding (one bond with cobalt was destroyed as a result of coordination binding of cobalt to the DNA base), and which has a great affinity for the DNA bases, will tend to intercalate into a double helix. The remaining phenanthroline ligand can interact with similar phenanthroline ligands of another cobalt bound to DNA or with free phenanthroline, which can be in solution because of transformation of the cobalt compound upon binding to DNA. All these interactions can influence the change of the measured parameters.
DNA, Co(II) compound, phenenthroline, complexformation, intercalation
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