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Method to Regioselectively Iodine-Tag Free-Phenolic Aromatic End-Groups in Lignin for 1H–13 C-HSQC NMR Analysis

Journal Article · · ACS Sustainable Chemistry & Engineering
 [1];  [2]
  1. Univ. of Wisconsin, Madison, WI (United States); University of Wisconsin-Madison Department of Biochemistry
  2. Univ. of Wisconsin, Madison, WI (United States)
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Phenolic end-groups on lignin molecules are vital sites for continued lignification, their influence over lignin molecular properties, their ability to enhance lignin degradation, and their potential for derivatization to produce lignin materials. Here we use iodination to regioselectively tag, and HSQC-NMR to monitor, guaiacyl phenolic aromatic end-groups in lignins. Using dimeric lignin models, iodination at the 5-position of the phenolic ring was shown to be clean, and almost quantitative. Additionally, the 6-position C/H correlation peak shifted downfield in both carbon and proton dimensions in HSQC spectra. As phenolic aromatic rings could be selectively iodinated, and as their C6/H6 aromatic signals appear in a clear region of HSQC NMR spectra (different from the original position), we would have a new method for tagging and analyzing such phenolic aromatic rings in lignins if the method could be applied to the polymer. The new tagging approach was therefore applied to a synthetic guaiacyl lignin polymer (DHP) and a milled wood lignin (MWL) isolated from Japanese cedar (Cryptomeria japonica). The derivatization proceeded directly in the NMR tube, without needing isolation or purification, from which HSQC-NMR revealed that the diagnostic C6/H6 correlations matched one from the dimeric model compound. This phenolic unit tagging method adds a useful method to the lignin structural analysis toolbox, helping to gain a better understanding of lignin’s phenolic end-units.

Research Organization:
Univ. of Wisconsin, Madison, WI (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Grant/Contract Number:
SC0018409
OSTI ID:
1600722
Journal Information:
ACS Sustainable Chemistry & Engineering, Journal Name: ACS Sustainable Chemistry & Engineering Journal Issue: 22 Vol. 7; ISSN 2168-0485
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

Figures / Tables (8)

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Guaiacyl lignin
Iodination
Japanese cedar
Lignin end-units
Lignin model compound
Phenolic hydroxyl group
Synthetic lignin