Mixed ligand ruthenium(II) complexes containing an amino acid (AA) and 1,10-phenanthroline (phen), i.e. [Ru(AA)(phen)(2)](n+) (n = 1, 2, AA = glycine (gly), L-alanine (L-ala), L-arginine (L-arg)) have been synthesized. The interactions of these complexes and [Ru(phen)(3)](2+) with DNA have been examined by absorption, luminescence, and circular dichroism spectroscopic methods. Absorption spectral properties revealed that [Ru(AA)(phen)(2)](+) (AA = gly, L-ala) interacted with CT-DNA by the electrostatic binding mode. [Ru(L-arg)(phen)(2)](2+) exhibited the greatest hypochromicity, red shift, and binding constant, indicating that this complex may partially intercalate into the base-pairs of DNA. These results were also suggested by luminescence spectroscopy. CD spectral properties have been examined to understand the detailed interactions of the ruthenium(II) complexes with artificial DNA. In the case of Delta-[Ru(L-arg)(phen)(2)](2+), the solution on adding [poly(dG-dC)](2) exhibited two well-defined positive peaks, which the shorter and longer wavelength peaks were assigned as originating from the major and the minor groove binding modes, respectively. Then, the solution on adding [poly(dA-dT)](2) exhibited only one positive peak, which was assigned as a peak corresponding to the minor groove binding mode. (C) 2004 Elsevier B.V. All rights reserved.