Conformation of double‐stranded polydeoxynucleotides in solution by proton two‐dimensional nuclear overhauser enhancement spectroscopy

Proton 2D‐NOE spectroscopy has been used to investigate the three‐dimensional conformations of several sonicated polydeoxynucleotides in solution. The observed pattern of cross peaks indicate that poly(dA‐dT) · poly(dA‐dT) in all salt concentrations studied (up to 6.6M CsF), and poly(dG‐m⁵dC) · poly(dG‐m⁵dC) in low salt (0.1M NaCl) are righthanded B‐structures. Poly(dG‐m⁵dC) · poly(dG‐m⁵dC) in Mg²⁺ (3 mM) solution exhibits a pattern characteristic of the left‐handed Z‐form. These results for poly(dA‐dT) · poly(dA‐dT) are in contrast to suggestions that this copolymer exists as a left‐handed form, either in low or high salt. We present pure absorption‐mode 2D‐NOE spectra that enable us to compare several distances and define the conformations of these polydeoxynucleotides in solution.