Impact of steam explosion on the wheat straw lignin structure studied by solution-state nuclear magnetic resonance and density functional methods

Harri Heikkinen (Corresponding Author), T. Elder, Hannu Maaheimo, Stella Rovio, Jenni Rahikainen, Kristiina Kruus, Tarja Tamminen

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28 Citations (Scopus)

Abstract

Chemical changes of lignin induced by the steam explosion (SE) process were elucidated. Wheat straw was studied as the raw material, and lignins were isolated by the enzymatic mild acidolysis lignin (EMAL) procedure before and after the SE treatment for analyses mainly by two-dimensional (2D) [heteronuclear single-quantum coherence (HSQC) and heteronuclear multiple-bond correlation (HMBC)] and 31P nuclear magnetic resonance (NMR). The β-O-4 structures were found to be homolytically cleaved, followed by recoupling to β-5 linkages. The homolytic cleavage/recoupling reactions were also studied by computational methods, which verified their thermodynamic feasibility. The presence of the tricin bound to wheat straw lignin was confirmed, and it was shown to participate in lignin reactions during the SE treatment. The preferred homolytic β-O-4 cleavage reaction was calculated to follow bond dissociation energies: G–O–G (guaiacyl) (69.7 kcal/mol) > G–O–S (syringyl) (68.4 kcal/mol) > G–O–T (tricin) (67.0 kcal/mol).
Original languageEnglish
Pages (from-to)10437-10444
JournalJournal of Agricultural and Food Chemistry
Volume62
Issue number43
DOIs
Publication statusPublished - 2014
MoE publication typeA1 Journal article-refereed

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Keywords

  • lignin
  • wheat straws
  • steam explosion
  • tricin
  • density-functional methods

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