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Issue 8, 2015
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Structural characterization of 13C-enriched humins and alkali-treated 13C humins by 2D solid-state NMR

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Abstract

Humin by-products are formed during the acid-catalyzed dehydration of carbohydrates to bio-based platform molecules, such as hydroxymethylfurfural and levulinic acid. The molecular structure of these humins has not yet been unequivocally established. 1D 13C solid-state NMR data reported have, for example, provided considerable insight, but do not allow for the unambiguous assignment of key structural motifs. Complementary (2D) techniques are needed to gain additional insight into the molecular structure of humins. Here, the preparation of 13C-enriched humins is reported, together with the reactive solubilization of these labeled humins and their characterization with complementary 1D and 2D solid-state NMR techniques. 1D cross polarization (CP) and direct excitation (DE) 13C solid-state NMR spectra, 2D 13C-detected double-quantum single-quantum (DQSQ) as well as 2D 1H-detected heteronuclear correlation (HETCOR) were recorded with different excitation schemes. These experiments unambiguously established that the original humins have a furan-rich structure with aliphatic linkers and allowed for a refinement of the molecular structure proposed previously. Solid-state NMR data of alkali-treated 13C-labeled humins showed that an arene-rich structure is formed at the expense of the furanic network during alkaline pretreatment.

Graphical abstract: Structural characterization of 13C-enriched humins and alkali-treated 13C humins by 2D solid-state NMR

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Publication details

The article was received on 10 Feb 2015, accepted on 29 Jun 2015 and first published on 09 Jul 2015


Article type: Paper
DOI: 10.1039/C5GC00327J
Citation: Green Chem., 2015,17, 4383-4392
  • Open access: Creative Commons BY-NC license
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    Structural characterization of 13C-enriched humins and alkali-treated 13C humins by 2D solid-state NMR

    I. van Zandvoort, E. J. Koers, M. Weingarth, P. C. A. Bruijnincx, M. Baldus and B. M. Weckhuysen, Green Chem., 2015, 17, 4383
    DOI: 10.1039/C5GC00327J

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