A pure-phase homonuclear J-modulated HMQC experiment with tilted cross-peak patterns for an accurate determination of homonuclear coupling constants

A new HMQC-based experiment is presented which allows for an efficient dete rmination of accurate homonuclear coupling-constant values. Pure absorption lineshapes with tilted cross-peak patterns are obtained by a combination o f the active-coupling-pattern tilting (ACT) scheme with J-scaling. Characte ristic features include separate heteronuclear echo and antiecho acquisitio n with a BIRDy pulse positioned before or after the t(1) period, respective ly, to refocus I-spin homonuclear coupling evolution, Additionally, due to the incorporation of J-scaling the relative spacing of the S-spin chemical- shift differences and I-spin homonuclear coupling splittings in the F-1 dom ain is largely under experimental control. The most important advantage of the proposed method is that the I-spin homonuclear coupling evolution occur s simultaneously with the evolution of the heteronuclear zero and double-qu antum coherences, which exhibit a slower transverse relaxation than I-spin single-quantum coherences. The effectiveness of the new sequence is demonst rated by a determination of the (3)J(HN,H alpha) couplings in a peptide sam ple. Additionally, the broadband property of the new sequence is verified w ith a sucrose sample. (C) 1999 Academic Press.