Spectral Aliasing

A time-efficient NMR strategy that involves the interleaved acquisition of two 2D HSQC spectra having different spectral widths in the indirect ¹³C dimension is presented. We show how the two equivalent coherence transfer pathways involved in sensitivity-enhanced HSQC experiments are managed selectively and detected separately in different FID periods within the same scan. The feasibility of this new SADA-HSQC (Spectral Aliasing in Dually Acquired HSQC ) technique is demonstrated by recording simultaneously two complementary datasets, conventional and highly-resolved spectral-aliased 2D HSQC spectra, in a single NMR experiment. Combining the information from both datasets, accurate chemical shift determination and excellent signal dispersion is achieved in a unique measurement using only few t₁ increments.

The combination of spectral aliasing and pure shift HSQC experiments represents an excellent routine tool for NMR enantiodifferentiation studies, yielding simultaneous ¹H and ¹³C enantiodifferentiated data (ΔΔδ(¹H) and ΔΔδ(¹³C)) in short times and with high digital resolution and signal dispersion for both ¹H and¹³C nuclei. Its use increases significantly the probability to detect an enantiodifferentiated nucleus since more signals are observed (¹H and ¹³C nuclei), overlapping problems of common 1D ¹H experiments are overcome, and poor enantiodifferentiation in 1D experiments can now be detected, allowing the study of cases abandoned in the past for reasons of poor enantioresolution and/or long experimental times. Alternatively, aliased long-range heteronuclear correlation experiments can be used to measure accurately such ΔΔδ values for quaternary carbons. The method is compatible with other heteronuclei and with the use of other chiral auxiliaries, and it can be of special interest for chiral metabonomic studies, where chiral molecules in complex mixtures are enantiodifferentiated and small chemical shifts need to be resolved in overcrowded spectra.