th  - 1987 - 51st ENC Conference

WK8
ISOTROPIC MIXING IN DNA
Peter F. FIynn', Agustin Kintanar, Gary P. Drobny
and Brian R. Reid
Department o] Chemistry, Uniuersity of Washington
Seattle, WA 98195
We have investigated homonuclear coherence transfer in synthetic DNA oligonu-
cleotides using two-dimensional isotropic mixing experiments. These experiments
employ broadband homonuclear decoupling techniques (MLEV-16) during the mix-
ing period to induce isotropic coupling within a spin system resulting in net trans-
fer of coherence. The length of the mixing time determines the extent of coherence
transfer; brief mixing periods lead to COSY-like spectra and at longer mixing times,
relayed coherence transfer effects are introduced.
This method was used to determine the scalar connectivities of sugar protons
in canonical B-form, bent, and hairpin DNA structures. Cross-peaks were assigned
unequivocally without recourse to structural assumptions, since coherence is trans-
ferred only through bonds. Assignments derived from these experiments were used
to simpli~" and confirm NOESY spectrum assignments.
Isotropic mixing techniques as applied to oligonucleotides differs from conven-
tional relayed coherence transfer techniques in that one can simultaneously observe
shor~ and long range coherence transfer within a spin system using the former
method. In addition, long range coherence transfer is more easily observed using
isotropic mixing.