The methods of flow birefringence, low shear viscometry, and circular dichroism were used to investigate the DNA conformation in solution during the interaction with coordination compounds [Co(NH3)6]Cl3 and [Co(NO2)6]Na3. It has been shown that the compound [Co(NO2)6]Na3, which dissociates in an aqueous solution to produce a negative complex ion [Co(NO2)6]3-, binds to a DNA molecule, causing considerable changes in its parameters. For the binding to occur, the complex ion must undergo a transition to its aqueous form. Even a low cobalt content is shown to produce DNA shrinkage. It is attended by an increased DNA optical anisotropy. This effect was observed for both compounds used. The comparison of these data with earlier results on DNA−Fe3+ interaction has revealed some features common to the DNA binding to trivalent metal ions. We have suggested that the mutual orientation of DNA statistical segments is changed because of the formation of intramolecular linkages between trivalent ions and remote DNA chain segments.

A comparative study of DNA interaction with different counterions in solution has been conducted by the following methods: flow birefringence (FB), low‐gradient viscometry, circular dichroism (CD), and UV‐spectroscopy. The influence of counterions on the persistence length and polyelectrolyte swelling of DNA has been investigated. The process of DNA packing during the interaction with trivalent ions in solution has been studied, as well as the influence of Mn2+ on the binding of trivalent ions with DNA.

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