Preparation of diverse metal binding sites along the helical structure of duplex DNA.

DNA duplexes containing 4-N-carboxymethylcytosine (1) were synthesized: duplex-I (5'-GTGACCA1TGCAG TG-3':3'-CACTGGT1ACGTCAC-5'), duplex-II (5'-GC CCA1TCCA1TGCG-3':3'-CG GGT1AGGT1ACGC-5'), and duplex-III (5'-GCTCCA11TGCACCG-3':3'-CGAG GT11ACGTGGC-5'). In the presence of Cu(II) or Ni(II) ions, duplex-I and duplex-II, which contain isolated 1-1 pair(s), were stabilized. In contrast, duplex-III, which contained consecutive 1-1 pairs, was stabilized significantly in the presence of Cu(II) ions, while the addition of Ni(II) ions had no notable effect on its thermal denaturation profile.