A two-dimensional liquid-state NMR experiment cleanly separating chemical shifts and scalar couplings information is introduced. This DIAG experiment takes advantage of a drastic reduction of the spectral window in the indirect dimension to be quickly recorded and of a new non-equidistant modulation of the selective pulse to improve the sensitivity of the broadband homodecoupling Zangger-Sterk sequence element by one order of magnitude. A simple automatic analysis results in 1D spectra displaying singlets and lists of the scalar couplings for first-order multiplets. This facilitates the analysis of 1D spectra by resolving multiplets based on their differences in chemical shifts and coupling structures.

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.

A two-dimensional liquid-state NMR experiment cleanly separating chemical shifts and scalar couplings information is introduced. This DIAG experiment takes advantage of a drastic reduction of the spectral window in the indirect dimension to be quickly recorded and of a new non-equidistant modulation of the selective pulse to improve the sensitivity of the broadband homodecoupling Zangger-Sterk sequence element by one order of magnitude. A simple automatic analysis results in 1D spectra displaying singlets and lists of the scalar couplings for first-order multiplets. This facilitates the analysis of 1D spectra by resolving multiplets based on their differences in chemical shifts and coupling structures. The complexity of 1D1 H spectra is a long-standing problem in many liquid-state NMR applications. This is mostly because of the presence of scalar coupling making it difficult to identify the individual resonances because the multiplet structure causes serious signal overlap (see Figure 1 a).Ideally, these complex multiplets should be separated in an additional dimension. If the classic J-resolved experiment was close to this goal, [1] problems with the signal lineshape and the complexity of the multiplet structures in the presence of second-order effects found partial solutions [2] but not satisfactory enough to become generally applicable. One solution consists in taking advantage of the large chemical shift dispersion of 13 C and use decoupled HSQC [3] or more recent variants [4] of this experiment to resolve signals and facilitate the determination of coupling constants.We developed an approach based on a 2D homonuclear sequence (see Figure 2) producing spectra where multiplets that are overlapping in 1D spectra (Figure 1 a) are spread along the indirect dimension (Figure 1 b). We called this experiment "DIAG" because it generates signals only along the diagonal (dashed line in Figure 1 b). Parallels could be drawn with earlier attempts to exploit the diagonal of COSY spectra.[5] But our approach, which is based on in-phase magnetization, avoids the difficulties of dealing with the numerous anti-phase magnetizations and the risk of signal cancellation because of the presence of positive and negative peaks. In order to simplify the structure of signals, the indirect F1 dimension is decoupled using the Zangger-Sterk sequence element (ZS) [6] because the constant-time incrementation used in many NMR pulse sequences cannot be applied to high-resolution homonuclear 1 H experiments. The first part of the nemoZS-DIAG sequence (see Figure 2) is quite similar to the pure shift experiment.[7] But instead of using the ZS element to generate series of spin echos, it is used to decouple only the indirect dimension of a 2D spectrum. In this manner, the precious scalar coupling information is retained in the detected dimension. The dresolved [8] experiment developed by Giraud et al. was aiming at the same goal, but it is based on version of the ZS sequence using more than one selective pulse which is detrimental. T...

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