New developments in the spatial encoding of spin interactions for single‐scan 2D NMR

Abstract

Single-scan 2D NMR relies on a spatial axis for encoding the indirect-domain internal spin interactions. Various strategies have been demonstrated for fulfilling the needs underlying this procedure. All such schemes use gradient-echoed sequences that leave at their conclusion solely the effects of the internal interactions along the indirect domain; they also include a real-time scheme that though simple, yields in general mixed-phase line shapes. The present paper introduces two new proposals geared up for easing the spatial encoding underlying single-scan 2D NMR methodologies. One of these is capable of delivering dispersive-free peaks along the indirect domain, and thereby purely-absorptive 2D line shapes, in amplitude-encoded experiments. The other demonstrates for the first time, the possibility to obtain single-scan 2D spectra without echoing the effects of the encoding gradient-simply by applying a single-pulse frequency sweep to encode the interactions. Both of these modes are compatible with homo- and heteronuclear correlations, and exhibit a number of complementary features vis-à-vis encoding alternatives that have so far been presented. The overall principles underlying these new spatially encoding protocols are derived, and their performance demonstrated with single-scan 2D NMR TOCSY and HSQC experiments on model compounds.

Fast access to residual dipolar couplings by single‐scan 2D NMR in oriented media

“…Further resolution improvements are expected by using more performing hardware and/or by alternative strategies such as the non-uniform sampling of UF data in the conventional dimension. [63] Although UF methods were investigated here with a focus on small organic molecules in organic solvents, they should be applicable to other classes of compounds and particularly in the biomolecular context, a field where the efficiency of UF 2D NMR has already been highlighted. [64,65] UF 2D NMR also offers the possibility to perform real-time measurement of RDCs on unstable compounds or on those undergoing chemical or biological reactions.…”

Fast hybrid multi‐dimensional NMR methods based on ultrafast 2D NMR

“…Monitoring very fast dynamic processes is therefore not possible. However, the hybrid UF techniques mentioned in this paper could be accelerated by combining them with some other fast sampling strategies, such as the reduction of the indirect spectral width by peak aliasing, [37] the shortening of the recovery delay through pulse sequence modifications, [51] the switching of the indirect domain sampling to a projection-reconstruction scheme, [52] or the sparse sampling of the indirect dimensions, including nonuniform sampling [23] and Hadamard [19] approaches.…”

“…It is actually mentioned in numerous publications on UF NMR, and in many cases, a few scans were accumulated to reach the sensitivity needed by the targeted application while keeping an acquisition duration between a few tens of seconds and 1-2 min. [21][22][23][24] In several other applications, the sensitivity was not an issue, but a few scans (typically two or four) were accumulated for phase cycling purposes, when the gradient-based coherence selection was not sufficient. [8,[25][26][27] In the reported applications, it was typically the case when a strong signal needed to be suppressed, such as the solvent signal in 1 H NMR or the signal from 1 H bound to 12 C in heteronuclear NMR.…”

Single-scan 2D NMR spectroscopy on a 25 T bitter magnet

“…The I(Ω 1 ) spectrum encoded by such spatial pattern is then repeatedly read out by oscillating an acquisition gradient G a during each Δt 2 ; the gradient echoes arising during each such dwell time can then be Fourier transformed as a function of the direct-domain acquisition time t 2 , to provide the 2D I(Ω 1 , Ω 2 ) NMR spectrum being sought. A variety of spatial encoding modes discussed in the literature were assayed over the course of this study, including discrete and continuous excitations as well as real-time and constant time alternatives [17][18][19][20]. Only those modes that displayed the best experimental performance are hereby presented.…”