Enantioselective interactions of inversion‐labile trigonal iron(II) complexes upon binding to DNA

We studied the interactions of the substitution‐inert inversion‐labile complexes Fe(bipy) and Fe(phen) [and the inversion‐stable complex Ru(bipy) ] with DNA. The association of these complexes to DNA is mainly electrostatic, and Fe(phen) shows a more effective binding to DNA than the two bipyridyl complexes, possibly owing to a different binding mode. The interactions are enantioselective, leading to a Pfeiffer shift in the diastereomeric inversion equilibria and an excess of the Δ‐enantiomer of Fe(phen) and Fe(bipy) , which is directly monitorable through CD. The partition constants for the inversion equilibrium range from 1.3 to 2.0 for Fe(bipy) and Fe(phen) , depending on ionic conditions. From flow LD information about the orientation of the complexes on DNA was obtained: it is consistent with a fit of the Δ‐enantiomer in the major groove of the right‐handed DNA helix. The mechanisms of interaction are discussed against equilibrium, spectroscopic, and kinetic data.