HECADE: HMQC- and HSQC-Based 2D NMR Experiments for Accurate and Sensitive Determination of Heteronuclear Coupling Constants from E.COSY-Type Cross Peaks
✍ Scribed by Wiktor Koźmiński; Daniel Nanz
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 209 KB
- Volume
- 124
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
Two-dimensional pulse sequences for the determination of hetpeak patterns is also available in two-spin systems. No addieronuclear long-range coupling constants are presented. The setional passive spin is required. Purely absorptive phase in quences are based on the HMQC/HMBC or HSQC technique with both dimensions and broadband homonuclear I-spin decousubsequent optional homonuclear I-spin transfer. However, they pling in the F 1 domain are achieved. The F 1 domain encodes yield tilted cross-peak patterns displaying antiphase heteronuclear arbitrarily scaled shift and coupling information (ASSCI), coupling constants in the projections of both dimensions, which namely S-spin chemical-shift differences and heteronuclear allow accurate determination of the couplings even in cases where coupling splittings that can be scaled to optimize signal disthe linewidth is of comparable magnitude. Two characteristic persion and resolution. Sequences that allow a long-range pulse-sequence elements were implemented to shape the F 1 do-(I r S) transfer are also presented. The new pulse sequence main: the first element allows an arbitrary scaling of the heterofamily is called HECADE (heteronuclear couplings from nuclear coupling splittings relative to S-spin chemical-shift differences, whereas the second element achieves homonuclear broad-aSSCI-domain Experiments with e.COSY-type cross peaks). band decoupling among the I spins in the HMQC/HMBC
The starting point for this work was the intention to imexperiments and thus allows purely absorptive representations of prove the (v 1 ) X-half-filtered TOCSY family of pulse sesuch spectra. In comparison with established (v 1 ) X-half-filtered quences (HETLOC) for the determination of heteronuclear TOCSY spectra, the signal dispersion in F 1 is significantly imcoupling constants (8, 9). The corresponding spectra display proved and largely under experimental control. Furthermore, het-E.COSY-type cross-peak patterns but also have the followeronuclear couplings of (I 1 , S) pairs where S is either quaternary ing disadvantages: (i) Signal overlap due to homonuclear or carries one or more I spins that do not belong to the same Icoupling evolution in two dimensions which also produces coupling network as I 1 can also be measured. The implementation mixed phases that can be purged only with concomitant of pulsed field gradients results in good suppression of spectral reduction in signal intensity. For nongeminal couplings this artifacts. ᭧ 1997 Academic Press problem might be solved by placing a BIRD y pulse in the center of t 1 (10,11). (ii) Signal overlap caused by the inherent small chemical-shift range of the I-spin when I is a