Abstract
Scalar coupling patterns contain a wealth of structural information. The determination, especially of small scalar coupling constants, is often prevented by merging the splittings with the signal line width. Here we show that real-time J-upscaling enables the visualization of unresolved coupling constants in the acquisition dimension of one-dimensional (1D) or multidimensional NMR spectra. This technique, which works by introducing additional scalar coupling evolution delays within the recording of the FID (free induction decay), not only stretches the recorded coupling patterns but also actually enhances the resolution of multiplets, by reducing signal broadening by magnetic field inhomogeneities during the interrupted data acquisition. Enlarging scalar couplings also enables their determination in situations where the spectral resolution is limited, such as in the acquisition dimension of heteronuclear broadband decoupled HSQC (heteronuclear single quantum correlation) spectra.
Highlights
Structural information in NMR spectra is obtained mainly from resonance frequencies and scalar coupling patterns
We have presented a method for real-time J-upscaling of NMR spectra by successive interruption of the FID for additional scalar coupling evolution
This approach simplifies the extraction of J-values from the acquisition dimension of NMR experiments and visualizes splittings which are hidden within the line width of regular NMR spectra
Summary
Structural information in NMR spectra is obtained mainly from resonance frequencies and scalar coupling patterns. Real-time J-upscaling expands scalar coupled signals and enhances the resolution of multiplets by lowering the effective transverse relaxation during acquisition interruptions, thereby allowing the direct visualization of small couplings which are hidden in the line shape of a regular spectrum. It allows enhanced J-evolution during short acquisition times, as needed for heteronuclear decoupled experiments, like HSQCs.[18]. This can be described as the FID being sampled only at certain time points, depending on the upscaling factor. J-upscaling enables scalar coupling constants to be determined even with the necessarily short acquisition times
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