Pseudomultidimensional NMR by spin-state selective off-resonance decoupling

An alternate technique for accurately monitoring the chemical shift in multidimensional NMR experiments using spin-state selective off-resonance decoupling is presented here. By applying off-resonance decoupling on spin S during acquisition of spin I, we scaled the scalar coupling J(I,S) between the spins, and the residual scalar coupling turns out to be a function of the chemical shift of spin S. Thus, the chemical shift information of spin S is indirectly retained, without an additional evolution period and the accompanying polarization transfer elements. The detection of the components of the doublet using spin-state selection enables an accurate measurement of the residual scalar coupling and a precise value for the chemical shift, concomitantly. The spin-state selection further yields two subspectra comprising either one of the two components of the doublet and thereby avoiding the overlap problems that arise from off-resonance decoupling. In general, spin-state selective off-resonance decoupling can be incorporated into any pulse sequence. Here, the concept of spin-state selective off-resonance decoupling is applied to 3D C-13 or N-15-resolved [H-1,H-1]-NOESY experiments, adding the chemical shift of the heavy atom attached to the hydrogen (C-13 or N-15 nuclei) with high resolution resulting in a pseudo-4D. These pseudo-4D heavy-atom resolved [H-1,H-1]-NOESY experiments contain chemical shift information comparable to that of 4D C-13 or N-15-resolved [H-1,H-1]-NOESY, but with an increase in chemical shift resolution by 1-2 orders of magnitude.