Optically active Ru(II) complexes with a chiral Tröger’s base ligand and their interactions with DNA

Three stereoisomers of a Ru(II) complex bearing a chiral bis-phenanthroline Tröger’s base analogue, TBphen2 (1), have been isolated from the reaction of the enantiomerically pure precursor complex Λ- (or Δ-) cis-[Ru(phen)2(py)2]2+ (phen = 1,10-phenanthroline, py = pyridine) with the racemic mixture of 1. Each stereoisomer of [Ru(phen)2TBphen2]2+ (2) has been characterized by 1H NMR and CD spectroscopy. Electrochemical studies revealed that the redox properties of 2 are not influenced by the stereochemistry, however, the electrochemical oxidation of the metallic center is irreversible because of the diazocine bridge of the TBphen2 ligand. Steady-state emission measurements in the presence of calf thymus DNA showed that the DNA binding of [Ru(phen)2TBphen2]2+ depends on the stereoisomer and is mainly controlled by the absolute configuration of the metal center of the complex. The affinity constant for the stereoisomer Δ-S-2 is 102 higher than that for Λ-S-2 and rac-[Ru(phen)3]2+.