Studies of enzymatic oxidation of TMP-fibers and lignin model compounds by a Laccase–Mediator-System using different 14C and 13C techniques

Abstract

In this work, the results of the enzymatic oxidation of TMP-fibers (thermomechanical pulp) and a well-structured lignin model compound, the dehydropolymer (DHP), were investigated by different 14 C and 13 C methods, caused by a Laccase-Mediator-System (LMS). These methods are the nuclear magnetic resonance spectroscopy ( 13 C-NMR) with DHP (unmarked) and the determination of the 14 CO 2 release of 14 C-marked DHP and TMP-fibers. The 13 C-NMR measurements were chosen to analyze the structural changes of the LMS-treated DHP model compounds and TMP-fibers qualitatively and quantitatively. The data of 14 CO 2 release give an explanation of the demethylation of DHP and TMP-fibers. The effect of the LMS is shown by comparing the results in respect of DHP and TMP-fibers, which were only treated with laccase and of an inactivated LMS as the control. Comparing the results of the 13 C-NMR method, in particular the use of the Mediator during the enzymatical treatment, showed significant changes in the structure of the DHP. Also, the TMP-fibers were materially influenced by the LMS. The analysis of the 14 CO 2 release data of the 14 C-marked DHP and TMP-fibers revealed that the rate of 14 CO 2 increases in the 14 C-2 atom as well as in the O 14 CH 3 group within the first hour of Laccase-Mediator incubation. Therefore, the 14 CO 2 release from the DHP was higher than from the TMP-fibers.

Phenolics as Mediators to Accelerate the Enzymatically Initialized Oxidation of Laccase-Mediator-Systems for the Production of Medium Density Fiberboards

“…However, one disadvantage is the long incubation time for laccase-only bonded MDF in comparison to other oxidative enzymes due to its limited redox potential and large molecular size (Li et al 1999;Euring 2008). To handle this issue, specific phenolic mediators have been added that ensure faster reactions within the first 20 to 30 min, enabling a lower incubation time for more cost-effective industrial applications (Euring 2008;Euring et al 2011Euring et al , 2012Euring et al , 2014Euring et al , 2015Kirsch et al 2015). Mediators, such as caffeic acid (CA), 4-hydroxy benzoic acid (HBA), and vanillic alcohol (VAl) are low-molecular compounds that act as diffusible electron carriers, enhancing the oxidative reaction of laccase (Bourbonnais and Paice 1990;Potthast et al 1995;Potthast 1998).…”

Hot-Air/Hot-Steam Process for the Production of Laccase-Mediator-System Bound Wood Fiber Insulation Boards

“…These renewable resources have increased in importance in recent years due to their manifold application possibilities. For example, the lignin on the surface of thermo-mechanical pulping (TMP) wood fibers can be activated through laccasemediator-system (LMS) (Euring 2008(Euring , 2012. The reaction mechanism involves the laccase-mediator-system activating the surface lignin of the wood fibers through oxidation (Kües et al 2007;Kudanga et al 2008;Widsten and Kandelbauer 2008;Nyanhongo et al 2010).…”

Laccase, an Emerging Tool to Fabricate Green Composites: A Review

“…A mediator is generally a small-size compound, able to generate stable radicals during reaction (Cañas and Camarero 2010;Euring et al 2011). These radicals react with various chemical compounds, including non-phenolics, that laccase alone cannot oxidize (Giardina et al 2010).…”