NMR analysis of duplex d(CGCGATCGCG)(2) modified by Lambda- and Delta-[Ru(bpy)(2)(m-GHK)]Cl-2 and DNA photocleavage study
The interaction of the diastereomeric complexes Lambda-[Ru(bpy)(2)(m-GHK)]Cl-2 and Lambda-[Ru(bpy)(2)(m-GHK)]Cl-2 (bpy is 2,2'-bipyridine, GHK is glycine-L-histidine-L-lysine) with the deoxynucleotide duplex d(5'-CGCGATCGCG)(2) was studied by means of H-1 NMR spectroscopy. At a Delta-isomer to DNA ratio of 1:1, significant shifts for the metal complex are observed, whereas there is negligible effect on the oligonucleotide protons and only one intermolecular nuclear Overhauser effect (NOE) is present at the 2D nuclear Overhauser enhancement spectroscopy spectrum. The H-1 NMR spectrum at ratio 2:1 is characterized by a slight shift for the Delta-isomer's bpy aromatic protons as well as significant shifts for the decanucleotide G(4) H1' and H '', A(5) H2, G(10) H1', T-6 NH and G(2) NH protons. Furthermore, at ratio 2:1, 11 intermolecular NOEs are observed. The majority of the NOEs involve the sugar H2' and H '' protons sited in the major groove of the decanucleotide. Increasing the Delta-isomer to d(CGCGATCGCG)(2) ratio to 5:1 results in noteworthy spectral changes. The Delta-isomer's proton shifts are reduced, whereas significant shifts are observed for the decanucleotide protons, especially the sugar protons, as well as for the exchangeable protons. Interaction is characterized by the presence of only one intermolecular NOE. Furthermore, there is significant broadening of the imino proton signals as the ratio of the Delta-isomer to DNA increases, which is attributed to the opening of the two strands of the duplex. The Delta-isomer, on the other hand, approaches the minor groove of the oligonucleotide and interacts only weakly, possibly by electrostatic interactions. Photocleavage studies were also conducted with the plasmid pUC19 and a 158-bp restriction fragment, showing that both diastereomers cleave DNA with similar efficiency, attacking mainly the guanines of the sequence probably by generating active oxygen species.