We introduce a radio frequency (rf) pulse sequence for efficient homonuclear double-quantum dipolar recoupling under magic-angle spinning NMR. The sequence is optimized for two-dimensional double-quantum 13C−13C chemical shift correlation spectroscopy in multiple spin systems, such as the U-13C-labeled antibiotic erythromycin A. Spin systems such as this display a wide range of isotropic and anisotropic chemical shifts and, therefore, require a broadband dipolar recoupling sequence that minimizes the errors arising from the interaction of chemical shifts and rf inhomogeneity. The sequence should also preserve the theoretical efficiency over the powder average (∼73%) provided by the C7 experiment of Levitt and co-workers (Lee, Y. K.; Kurur, N. D.; Helmle, M.; Johannessen, O. G.; Nielsen, N. C.; Levitt, M. H. Chem. Phys. Lett. 1995, 242, 304−309). We satisfy these criteria by combining the standard C7 (2πφ−2πφ +180) elements with π-pulse permuted elements (πφ−2πφ +180−πφ, in analogy to the MLEV decoupling scheme) to remove error terms over a ±10% range of rf amplitude. The new sequence, which we refer to as CMR7 (combined MLEV refocusing and C7), yields for two-spin systems broadband double-quantum filtering efficiencies greater than 70%. For multispin systems, the improved polarization transfer efficiency results in greater cross-peak intensities, facilitating assignment of U-13C-labeled molecules in the solid state.

The backbone conformation of DNA plays an important role in the indirect readout mechanisms for protein-DNA recognition events. Thus, investigating the backbone dynamics of each step in DNA binding sequences provides useful information necessary for the characterization of these interactions. Here we use 31 P Dynamic NMR to characterize the backbone conformation and dynamics in the Dickerson Dodecamer, a sequence containing the EcoRI binding site, and confirm solid-state 2 H-NMR results showing that the C3pG4 and C9pG10 steps experience unique dynamics and that these dynamics are quenched upon cytosine methylation. In addition, we show that cytosine methylation affects the conformation and dynamics of neighboring nucleotide steps but this effect is localized to only near neighbors and base pairing partners. Lastly, we have been able to characterize the %BII in each backbone step and illustrate that the C3pG4 and C9pG10 favor the non-canonical BII conformation, even at low temperatures. Our results demonstrate that 31 P Dynamic NMR provides a robust and efficient method for characterizing the backbone dynamics in DNA. This allows simple, rapid determination of sequence-dependent dynamical information, providing a useful method for studying trends in protein-DNA recognition events.