Diastereomeric oligopyridine-ruthenium(II)-amino acid conjugated complexes of the general formulas Lambda- and Delta-[Ru(bpy)(2)(4,4'(CO(2)Y)(2)-bpy)](2+), where Y = L-AlaCONH(2), L-LysCONH(2), L-HisCONH(2), L-TyrCONH(2)), were synthesized and characterized. Their binding properties with ct-DNA and the oligonucleotide duplex d(5'CGCGCG-3')(2), by means of circular dichroism (CD), NMR spectroscopy and DNA thermal denaturation (T(m)) curves were studied. CD and T(m) data indicate that all diastereomeric complexes bind to the DNA major groove, Delta-diastereomers in a similar manner, while Lambda-diastereomers in dependence of the nature of the amino acid. NMR studies of d(5'CGCGCG-3')(2), and the complexes Delta-1, Delta-2, Lambda-1 and Lambda-2 indicate that Delta-1 and Delta-2 were bound having the ancillary bpy ligands towards the DNA groove, while the corresponding Lambda-1 and Lambda-2 were orientated in a similar way, facing the ligand 4,4'(CO(2)Y)(2)bpy towards the DNA major groove. Photoinduced DNA cleavage was observed in all cases studied, which take place through singlet oxygen production. Delta-4 and Lambda-4 show the lower photoinduced cleavage yield, probably because the singlet oxygen ((1)O(2)) oxidizes not only the DNA phosporodiesteric bonds but the tyrosine's phenolic OH bond as well.