Metal-bipyridine complexes in DNA backbones and effects on thermal stability.

Modified oligonucleotides are showing potential for multiple applications, including drug design, nanoscale building blocks, and biosensors. In an effort to expand the functionality available to DNA, we have placed chelating ligands directly into the backbone of DNA. Between one and three nucleosides were replaced with 2,2'-bipyridine phosphates in 23-mer duplexes of DNA. An array of metal ions were added (Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), and Pt(2+)) and the influences on duplex stability were examined by melting temperature studies. Titrations and UV-vis absorption spectroscopy were used to provide insights into the nature of the metal complexes formed. We found that Ni(2+) binding to 2,2'-bipyridine typically provided the greatest increase in duplex stability relative to the other metal ions examined. For example, addition of Ni(2+) to one 2,2'-bipyridine-DNA duplex increased the melting temperature by 13 degrees C, from 65.0 +/- 0.3 to 78.4 +/- 0.9 degrees C. These studies show that metal ions and backbone ligands can be used to regulate DNA structure and stability.