Triple helix formation by alpha-oligodeoxynucleotides: a vibrational spectroscopy and molecular modeling study.

The structures of triple helices αdT 6 .βdA n .βdT n , αdT 12 .βdA n .βdT n , αdC 12 + .βdG n .βdCn and αdC 12 + .βrG n .βrC n have been studied by Fourier transform infrared spectroscopy, Raman spectroscopy, and molecular mechanics calculations. The sugar conformations in these triplexes have been determined by vibrational spectroscopy. Our results show the existence of only S-type sugars in the αdT 12 .βdA n .βdT n triple helix. Both S- and N-type sugar infrared and Raman markers have been detected in the spectra of αdC 12 + .βdG n .βdC n