Understanding Laccase-Ionic Liquid Interactions toward Biocatalytic Lignin Conversion in Aqueous Ionic Liquids

Joseph C. Stevens, Lalitendu Das, Justin K. Mobley, Shardrack O. Asare, Bert C. Lynn, David W. Rodgers, Jian Shi

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

Abstract

Lignin is a crucial component of plant matter; however, it is also largely responsible for the recalcitrance of lignocellulosic biomass when subjected to pretreatment processes. Lignin is generated in large volumes as a waste product from paper and pulping industry as well as cellulosic biorefineries. As a result, lignin valorization is critical to the successful implementation of cellulosic biofuels. To this end, we investigated interactions between three ionic liquids (ILs) and the lignolytic enzyme laccase toward biocatalytic lignin conversion to aromatic monomers. Laccase exhibited minimal loss of activity in 10% diethylamine hydrogensulfate ([DEA][HSO4]). Changes in Vmax and Km of laccase with respect to IL concentration indicate that [DEA][HSO4] is a noncompetitive inhibitor, whereas cholinium lysinate ([Ch][Lys]) and [C2C1Im][OAc] are mixed inhibitors. Docking simulations suggested that [Ch][Lys] and [C2C1Im][OAc] disrupt residues leading to the active site. Experiments with a β-O-4′ linked model dimer revealed that laccase in [C2C1Im][OAc] and [Ch][Lys] requires the presence of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to oxidize the β-O-4′ linkage, leading to polymerization of the model dimer. Alkaline lignin treated with laccase, ABTS, and the aqueous ILs (AILs) showed few structural changes, although the lignin was partially solubilized and converted to degradation products. The major products obtained from alkaline lignin were vanillin, acetosyringone, syringaldehyde, and acetovanillone. The results of this study provide, for the first time, an in-depth explanation of the interactions between laccase and AILs for the purpose of lignin valorization.

Original languageEnglish
Pages (from-to)15928-15938
Number of pages11
JournalACS Sustainable Chemistry and Engineering
Volume7
Issue number19
DOIs
StatePublished - Oct 7 2019

Bibliographical note

Funding Information:
The authors acknowledge the National Science Foundation under Cooperative Agreement nos. 1355438 and 1632854. This is a publication of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. This work is also supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch-Multistate project under accession number 1003563.

Keywords

  • biocatalysis
  • docking
  • ionic liquid
  • laccase
  • lignin

ASJC Scopus subject areas

  • Chemistry (all)
  • Environmental Chemistry
  • Chemical Engineering (all)
  • Renewable Energy, Sustainability and the Environment

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