Pure Shift NMR: Application of 1D PSYCHE and 1D TOCSY-PSYCHE Techniques for Directly Analyzing the Mixtures from Biomass-Derived Platform Compound Hydrogenation/Hydrogenolysis
Pure shift, a novel nuclear magnetic resonance (NMR) spectroscopy technique is here applied to analyze the hydrogenation/hydrogenolysis products of the biomass-derived platform compounds. The complex and very overlapped 1H NMR signals of the model mixtures from several biomass hydrogenation/hydrogenolysis reactions, such as glucose hydrogenation, sorbitol hydrogenolysis, levulinic acid (LA) formation, tetrahydrofurfuryl alcohol hydrogenolysis, and a real reaction system, were successfully analyzed and assigned by suppressing homonuclear couplings. Thus, we can clearly achieve component analysis and distinguish most signals according to one-dimensional (1D) pure shift obtained by chirp excitation (PSYCHE) spectra. For sophisticated mixtures, e.g., α-d-glucose, sorbitol, and mannitol, or LA, γ-valerolactone, and 2-methyltetrahydrofuran, and finally the real reaction mixture, the 1D total correlation spectroscopy (TOCSY)-PSYCHE approach was used as a supplementary tool to obtain full signals in one component. This allowed us to further resolve the signals where the PSYCHE technique failed to distinguish the signals sufficiently. The results demonstrated that the combined use of 1D PSYCHE and 1D TOCSY-PSYCHE techniques successfully analyzed various catalytic hydrogenation/hydrogenolysis mixtures and enabled us to provide precise signal assignments. Therefore, the pure shift NMR tool (a combination of 1D PSYCHE and 1D TOCSY-PSYCHE) can significantly simplify and successfully be used to assign the NMR spectra of the biomass-derived complex mixture, such as hydrogenation/hydrogenolysis reaction mixtures.
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