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 determination of accurate homonuclear coupling-constant values. Pure absorption lineshapes with tilted cross-peak patterns are obtained by a combination of the active-coupling-pattern tilting (ACT) scheme with J-scaling. Characteristic features include separate heteronuclear echo and antiecho acquisition with a BIRD(y) pulse positioned before or after the t(1) period, respectively, 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) domain is largely under experimental control. The most important advantage of the proposed method is that the I-spin homonuclear coupling evolution occurs simultaneously with the evolution of the heteronuclear zero and double-quantum coherences, which exhibit a slower transverse relaxation than I-spin single-quantum coherences. The effectiveness of the new sequence is demonstrated by a determination of the (3)J(HN,Halpha) couplings in a peptide sample. Additionally, the broadband property of the new sequence is verified with a sucrose sample. Copyright 1999 Academic Press.
Kozminski
W
Department of Chemistry, Warsaw University, Warszawa, ul. Pasteura 1, 02-093, Poland.