Measurement of (1)H3 '-P-31 dipolar couplings in a DNA oligonucleotide by constant-time NOESY difference spectroscopy

The ratios of cross peak intensities in a selective constant-time NOESY exp eriment, recorded with and without P-31 decoupling, yield values for the su m of the H3'-P scalar and dipolar couplings. The selective refocusing of H3 ' resonances in this experiment results in excellent resolution and sensiti vity, even in the liquid crystalline phase where the H-1 spectrum is broade ned by unresolved homonuclear dipolar couplings. The vicinal H3'-P scalar a nd dipolar couplings in the DNA oligomer d(CGCGAATTCGCG)(2) were measured i n both isotropic solution, and in a liquid crystalline phase. Isotropic val ues are in good agreement with values reported previously. Dipolar coupling s are in excellent agreement with the NMR structure for this dodecamer, and to a somewhat lesser extent with the X-ray structures.