New methods for measuring1H-31P coupling constants in nucleic acids

New pulse sequences for the measurement of 1H–31P coupling constants in the backbone of DNA duplexes are presented. They have a resemblance to HMBC but the constant J dephasing delay is exploited for heteronuclear J modulation so that the peaks in the two-dimensional spectrum appear as doublets with splittings scaled relative to the 31P chemical shifts. The new pulse sequences have been applied to a self-complementary octamer DNA duplex 5′-CGCTAGCG-3′ (CTAG).