The telomeric DNA oligomers, d(TTAGGG)_n, where n=1, 2, 4, could self-associate into the multi-stranded structures in appropriate condition and exhibited a different CD spectra. The present of Na⁺ was more advantage to facilitate the formation of anti-parallel conformation, but the present of K⁺ enhanced their thermal stability. Spectroscopic analysis of 3, 3´-diethyloxadicarbocyanine (DODC) showed the formation of hairpin quadruplex structures for d(TTAGGG)₂ and d(TTAGGG)₄, but d(TTAGGG) could not. The four-stranded tetraplexes and branched nanowire formed in the present of K⁺ or Na⁺ alone were observed by atomic force microscopy (AFM). The ability to self-assemble of d(TTAGGG)_n, into four-stranded tetraplexes and nanowires depends strongly on the number of repeating units and ionic environment. A model to explain how these structures formed is proposed.

Key words: telomeric DNA, nanowire structure; quadruplex, monovalent cations, circular dichroism, atomic force microscopy.