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

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.