On the reactivity of the Melanocarpus albomyces laccase and formation of coniferyl alcohol dehydropolymer (DHP) in the presence of ionic liquid 1-allyl-3-methylimidazolium chloride

M. Lahtinen (Corresponding Author), L. Viikari, P. Karhunen, J. Asikkala, Kristiina Kruus, I. Kilpeläinen

Research output: Contribution to journalArticleScientificpeer-review

11 Citations (Scopus)

Abstract

Some ionic liquids are able to dissolve wood, including lignin and lignocellulose, and thus they provide an efficient reaction media for modification of globally abundant wood-based polymers. Lignin can be modified with laccases (EC 1.10.3.2), multicopper oxidases, which selectively catalyze the oxidation of phenolic hydroxyl to the phenoxy radical in lignin by using oxygen as the co-substrate and an electron acceptor. Many enzymes, including laccases, retain their catalytic activity in the presence of ionic liquids. However, the enzyme activity is usually decreased in the presence of ionic liquids, and the most deactivating ionic liquids have been observed to be those dissolving wood most efficiently. In the present study the activity, pH optimum and catalyzed oxidation of coniferyl alcohol by the laccase from the ascomycete Melanocarpus albomyces was investigated in the ionic liquid 1-allyl-3-methyl-imidazolium chloride ([Amim]Cl), known to dissolve wood and expected to affect the laccase activity. Indeed, with an increasing concentration of [Amim]Cl, the activity of M. albomyces laccase decreased, and the pH range of the enzyme activity was narrowed. The pH optimum, using 2,6-dimethoxyphenol as the substrate, was shifted from 6.5 to 6.0 when the amount of [Amim]Cl was increased to 60% (m-%). It was also found that the inhibition of laccase with NaN3 was not as severe in the ionic liquid as in water. The insoluble fraction of the dehydropolymer (DHP) formed in the presence of [Amim]Cl had clearly higher molecular weight compared to the one formed in water. DHPs formed in the absence and presence of [Amim]Cl both contained β-5, β–β, β-O-4, α-CO/β-O-4 and α-O-4/β-O-4 structures. However, in the presence of [Amim]Cl, less β-O-4, slightly less β-5 and more β–β structures were formed.
Original languageEnglish
Pages (from-to)169-177
Number of pages9
JournalJournal of Molecular Catalysis B: Enzymatic
Volume85-86
DOIs
Publication statusPublished - 2013
MoE publication typeA1 Journal article-refereed

Keywords

  • Dehydropolymer (DHP)
  • enzyme
  • ionic liquid
  • lignin
  • two-dimensional nuclear magnetic resonance (2D NMR)

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