Combination of Homonuclear Decoupling and Spectral Aliasing to Increase the Resolution in the 1H Dimension of 2D NMR Experiments

Abstract

Broadband homonuclear decoupling (BBHD) in the indirect 1 H dimension of 2D experiments can be obtained using a modified Zangger and Sterk combination of a selective pulse with a pulsed-field gradient. The coupling structure of signals is reduced to a singlet along the F1 dimension at the cost of a sensitivity loss. With the classical sampling in F1, the full resolving power of BBHD-experiments requires very long acquisition times. Spectral aliasing can reduce the number of time increments accessing the top resolution of homodecoupled spectra of small molecules by two orders of magnitude. The TOCSY spectra of androst-4-ene-3,17-dione are shown as an example.

Homonuclear decoupling in the 13C indirect dimension of HSQC experiments for 13C‐enriched compounds

“…Second‐order effects are known to cause problems to both ZS and PSYCHE decoupling applied to 1 H . The same is expected in the case of 13 C, except that their severity may be scaled down thanks to the greater signal dispersion.…”

“…Such a design of the non‐equidistant modulation averages out the possible recoupling artifacts within these 50 ppm ranges . An additional advantage of this solution using a set of blocks is that it requires, in the case of the 5 + 1 scheme, only 20% more power for the modulated selective pulse (we mean here exclusively the cost of ensuring the homogeneous coverage) instead of a factor 2 with the two single‐block approach presented earlier for 1 H decoupling . It should be noted, however, that in the unlikely case of two coupled spins distant by an integer number of times the distance between the blocks (here 50, 100, 150, or 200 ppm), doublets are expected for the two coupling partners because they will be active in the same sample slices.…”

1D NMR Homodecoupled 1H Spectra with Scalar Coupling Constants from 2D NemoZS‐DIAG Experiments

“…Signal assignment was clearly facilitated by the availability of the coupling constants.K nowing that all couplings above 9Hzare geminal (12)(13)(14)(15)(16)(17)(18)(19)(20) Hz in the case of androsten) or trans diaxial (9)(10)(11)(12)(13)(14)(15), the visual inspection of the couplings …”

“…The nemoZS sequence element can be applied to 2D-TOCSY [16] and other NMR experiments and the DIAGapproach used with other decoupling scheme. The nemoZS sequence element can be applied to 2D-TOCSY [16] and other NMR experiments and the DIAGapproach used with other decoupling scheme.…”

Multiplicity‐edited 1H‐1H TOCSY experiment

“…An F1‐homodecoupled TOCSY version, known as PSYCHE‐TOCSY and here referred to as HD‐TOCSY, has been proposed to improve signal resolution by several orders of magnitude . In this experiment, a PSYCHE element is applied together with a hard 180° pulse to achieve broadband homodecoupling along F1, in a similar way that proposed early in a region selective version referred to as BASHD‐TOCSY experiment . Thus, signals with similar 1 H chemical shift can be discerned and therefore the corresponding relayed cross‐peaks can be differentiated and unambiguously assigned.…”