Spatially encoded polarization transfer for improving the quantitative aspect of 1H–13C HSQC

Abstract

Peak overlap hampers quantification in one-dimensional (1D) 1H NMR. 2D 1H -13C HSQC spectrum provides resolution superior to 1D 1H NMR. However, quantifying the components in a complex mixture with HSQC is not straightforward as in 1D 1H NMR. Quantification using HSQC could open up new avenues for studying metabolism. The variations in 1H–13C scalar couplings, T1, T2, and pulse imperfections contribute to this problem. Although T1 and T2 can be suitably chosen to minimize their deleterious effects, the differential polarization transfer for different resonances owing to large variations in 1H -13C couplings does not allow the cross-peak intensities to be directly correlated to the quantity of metabolites. Existing approaches are time-consuming. We show that spatial encoding of the polarization transfer delays in HSQC using sweep frequency pulses in the presence of a magnetic field gradient allows one to have a transfer of polarization from 1H to 13C insensitive to variations in 1H -13C couplings improving the quantitative aspect of HSQC. Comparisons to other QHSQC and perfected HSQC variants are also provided.