3626-48-0Relevant academic research and scientific papers
On the factors affecting product distribution in laccase-catalyzed oxidation of a lignin model compound vanillyl alcohol: Experimental and computational evaluation
Lahtinen, Maarit,Heinonen, Petri,Oivanen, Mikko,Karhunen, Pirkko,Kruus, Kristiina,Sipil?, Jussi
, p. 5454 - 5464 (2013/09/02)
Laccases (EC 1.10.3.2) are multicopper oxidases, which can oxidize phenolic substrates by the concomitant reduction of oxygen to water. The phenolic substructures of lignin are also oxidized by laccases, resulting mainly in various polymerized products. Several model compound studies indicate that variations in the reaction media, such as the pH and the enzyme dosage used, have an impact on the observed product distribution of laccase promoted oxidation, but no detailed study has been reported to explain these results. In the present study, a monomeric lignin model compound, vanillyl alcohol, was oxidized in laccase-catalyzed reactions by varying the pH, enzyme dosage and temperature. The energies of all the observed products and potential intermediates were calculated by applying density functional theory (DFT) and the polarizable continuum solvation model (PCM). The observed predominant product at pH 4.5 to 7.5 was clearly the 5-5′ dimer, although the thermodynamic product according to the calculated free energies was vanillin, the difference being 5.6 kcal mol-1. The hydrogen bonding is shown to give an additional stabilizing effect on the transition state leading to the 5-5′ dimer, but also a kinetic barrier reduces the formation of vanillin. Based on the calculated pKa-values of the proposed intermediates we suggest that the rearomatization reactions of the quinones formed in the radical reactions under mildly acidic and neutral conditions would preferentially occur through deprotonation rather than through protonation. The Royal Society of Chemistry.
On the reactions of two fungal laceases differing in their redox potential with lignin model compounds: products and their rate of formation
Maarit, Lahtinen,Kristiina, Kruus,Petri, Heinonen,Jussi, Sipilae
experimental part, p. 8357 - 8365 (2010/08/19)
Laceases (EC 1.10.3.2) are multicopper oxidases able to oxidize phenolic compounds such as lignin-related polyphenols. Since the discovery that so-called mediators effectively extend the family of lacease substrates, direct interactions between lignin-like materials and lacease have gained much less attention. In this work, the aim was to characterize oxidation products formed in direct laccase-catalyzed oxidation of different guaiacylic and syringylic lignin model compounds with two different laceases: a low redox potential Melanocarpus alborneces lacease and a high redox potential Trametes hirsuta lacease. By following the formation of different, mainly biphenylic (5-5) and benzylic oxidation products, it was found that although both of these enzymes generated practically the same pattern of products with particular types of syringyl and guaiacyl compounds, in some cases a clear difference in the rates of their formation was observed. The results also confirm further to the suggestions that syringylic compounds are able to act as mediators in their own oxidation reactions and also that in some instances acetylation of phenolic material may produce altered, unexpected structures.
