Coherence transfer in deoxyribose sugars produced by isotropic mixing: an improved intraresidue assignment strategy for the two-dimensional NMR spectra of DNA.

Two-dimensional isotropic mixing spectroscopy has been used to confirm assignments of the deoxyribose sugar protons in the H NMR spectrum of the DNA oligonucleotides d(CGCGTTTTCGCG) and [d(GCCGTGGCCACGGC)]2. The broad-band decoupling sequence MLEV-16 was applied during the mixing period to induce isotropic coupling within the spin systems, resulting in net transfer of coherence throughout the coupled spin networks. Nearly all 1', 2', 2'', 3', and 4' protons of a given nucleotide could be identified on the basis of through-bond scalar connectivities. In addition, in the hairpin, a number of connectivities to 5'/5'' protons were found. The dependence of cross-peak intensity on the length of radio-frequency irradiation for several different coherence transfer orders is presented, and implications for optimization are discussed.