Acquiring and processing ultrafast biomolecular 2D NMR experiments using a referenced-based correction

Thanks to their special spatiotemporal encoding/decoding scheme, ultrafast (UF) NMR sequences can deliver arbitrary 2D spectra following a single excitation. Regardless of their nature, these sequences have in common their tracing of a path in the F1–t2 plane, that will deliver the spectrum being sought after a 1D Fourier transformation versus t2. This need to simultaneously digitize two domains, tends to impose bandwidth limitations along all spectral axes. Along the t2/F2 dimension this problem is exacerbated by the fact that odd and even time points are not equispaced, and by additional artifacts such as time shifts between time points sampled while under the action of positive and negative decoding gradients. As a result, odd and even t2 points are typically Fourier transformed separately, halving the potential spectral width along this dimension. While this halving of the F2 span can be overcome by an interlaced Fourier transform, this post-processing is seldom used because of its sensitivity to hardware inaccuracies requiring even finer corrections of the even/odd t2 data points. These corrections have so far been done manually, but are challenging to implement when dealing with low signal-to-noise ratio signals like those associated with biomolecular NMR experiments. This study introduces an algorithm for an automatic correction of all even/odd ultrafast NMR inconsistencies, based on the acquisition of a reference scan on the solvent. This algorithm was verified experimentally using an 1H-13C UF-HSQC variant on ubiquitin at 600 MHz. Features of this method as well as of the interlaced Fourier transformation in general, are discussed.