Abstract
Over decades multidimensional NMR spectroscopy has become an indispensable tool for structure elucidation of natural products, peptides and medium sized to large proteins. Heteronuclear single quantum coherence (HSQC) spectroscopy is one of the work horses in that field often used to map structural connectivity between protons and carbons or other hetero nuclei. In overcrowded HSQC spectra, proton multiplet structures of cross peaks set a limit to the power of resolution and make a straightforward assignment difficult. In this work, we provide a solution to improve these penalties by completely removing the proton spin multiplet structure of HSQC cross peaks. Previously reported sideband artefacts are diminished leading to HSQC spectra with singlet responses for all types of proton multiplicities. For sideband suppression, the idea of restricted random delay (RRD) in chunk interrupted data acquisition is introduced and exemplified. The problem of irreducible residual doublet splitting of diastereotopic CH2 groups is simply solved by using a phase sensitive JRES approach in conjunction with echo processing and real time broadband homodecoupling (BBHD) HSQC, applied as a 3D experiment. Advantages and limitations of the method is presented and discussed.
Highlights
Over decades multidimensional NMR spectroscopy has become an indispensable tool for structure elucidation of natural products, peptides and medium sized to large proteins
One of the main difficulties in obtaining real time broadband homodecoupling (BBHD) Heteronuclear single quantum coherence (HSQC) spectra is the problem of sideband artefacts in the ω2 dimension, which are the result of alternating repeatedly between RF blocks and chunk data acquisition
In case of homonuclear Zangger and Sterk (ZS) experiments, theoretical investigations were published to remove these artefacts by computational approaches and to obtain a reconstructed 1D sideband free pure shift spectrum[34]
Summary
Over decades multidimensional NMR spectroscopy has become an indispensable tool for structure elucidation of natural products, peptides and medium sized to large proteins. Zangger and Sterk (ZS) first proposed an experiment, where a selective refocusing RF pulse in combination with a weak gradient pulse was applied to create the proton spin subset enabling a decoupling during the chemical shift detection in a direct or indirect d imension[11,25]. A combination of the JRES technique with conventional HSQC executed as a 3D experiment is conceivable to deliver phase sensitive fully homodecoupled spectra.
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