Double-quantum filtering in magic-angle-spinning NMR spectroscopy applied to DNA oligomers
Double quantum filtering in magic-angle-spinning (MAS) NMR experiments is used to correlate pairs of 18C nuclei in synthetically labelled DNA oligomers. A new pulse sequence is introduced for this purpose, DQ-DRAWS. This sequence is a modification of the DRAMA sequence (R. Tycko and G. Dabbagh, 1990, Chem. Phys. Lett., 173, 461). DQ-DRAWS is compared with earlier sequences and found to be more generally applicable to 18C nuclei with a large range of chemical shift anisotropies and offsets. Experimental results are presented for several small model compounds and for the DNA sequences [d(CGCGAA*T*TCGCG)]2 and [d(CGAGGT*T*TAAACCTCG)]2. The DNA molecules contain 18C labels on adjacent 2'-deoxythymidine bases. Applications of these techniques to the study of DNA-protein interactions and structure are discussed.