On the factors affecting product distribution in laccase-catalyzed oxidation of a lignin model compound vanillyl alcohol: Experimental and computational evaluation

M. Lahtinen (Corresponding Author), P. Heinonen, M. Oivanen, P. Karhunen, Kristiina Kruus, J. Sipilä

Research output: Contribution to journalArticleScientificpeer-review

11 Citations (Scopus)

Abstract

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.
Original languageEnglish
Pages (from-to)5454-5464
Number of pages10
JournalOrganic and Biomolecular Chemistry
Volume11
Issue number33
DOIs
Publication statusPublished - 2013
MoE publication typeA1 Journal article-refereed

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Laccase
lignin
Lignin
alcohols
Oxidation
oxidation
evaluation
products
Dimers
enzymes
Quinones
Deprotonation
dimers
Protonation
Solvation
Enzymes
Hydrogen Bonding
dosage
Thermodynamics
Free energy

Cite this

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title = "On the factors affecting product distribution in laccase-catalyzed oxidation of a lignin model compound vanillyl alcohol: Experimental and computational evaluation",
abstract = "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.",
author = "M. Lahtinen and P. Heinonen and M. Oivanen and P. Karhunen and Kristiina Kruus and J. Sipil{\"a}",
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On the factors affecting product distribution in laccase-catalyzed oxidation of a lignin model compound vanillyl alcohol : Experimental and computational evaluation. / Lahtinen, M. (Corresponding Author); Heinonen, P.; Oivanen, M.; Karhunen, P.; Kruus, Kristiina; Sipilä, J.

In: Organic and Biomolecular Chemistry, Vol. 11, No. 33, 2013, p. 5454-5464.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - On the factors affecting product distribution in laccase-catalyzed oxidation of a lignin model compound vanillyl alcohol

T2 - Experimental and computational evaluation

AU - Lahtinen, M.

AU - Heinonen, P.

AU - Oivanen, M.

AU - Karhunen, P.

AU - Kruus, Kristiina

AU - Sipilä, J.

PY - 2013

Y1 - 2013

N2 - 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.

AB - 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.

U2 - 10.1039/c3ob40783g

DO - 10.1039/c3ob40783g

M3 - Article

VL - 11

SP - 5454

EP - 5464

JO - Organic and Biomolecular Chemistry

JF - Organic and Biomolecular Chemistry

SN - 1477-0520

IS - 33

ER -