Effect of Salts on Laccase‐Catalyzed Polymerization of Lignosulfonate

• Published in: ChemSusChem 2024-07, Vol.17 (14), p.e202301134-n/a
• Main Authors: Mayr, Sebastian A., Rennhofer, Harald, Gille, Lars, Schwaiger, Nikolaus, Nyanhongo, Gibson S., Weiss, Renate, Guebitz, Georg M.
• Format: Article
• Language: English
• Subjects: anions; Binding sites; Biocatalysis; Degree of polymerization; Dicarboxylic acids; Electron paramagnetic resonance; green chemistry; Laccase; Laccase - chemistry; Laccase - metabolism; Lignin - analogs & derivatives; Lignin - chemistry; Lignosulfonates; Low concentrations; oxidation; Polymerization; radical reactions; Resonance scattering; Saline solutions; Salts - chemistry; Substrates; Surface charge; Viscometry; Zeta potential
• ISSN: 1864-5631; 1864-564X; 1864-564X
• DOI: 10.1002/cssc.202301134

Enzymatic polymerization of lignosulfonate (LS) has a high potential for various applications ranging from coatings to adhesives. Here, the effect of different ions in low concentrations on enzymatic polymerization of LS was investigated, including salt solutions consisting of mono‐ and dicarboxylic acids, sulfate, phosphate and chloride with sodium as counter ion. LS polymerization was followed by viscometry and size exclusion (SEC) chromatography. Interestingly, there was only a small effect of ions on the activity of the laccase on standard substrate ABTS, while the effect on polymerization of LS was substantially different. The presence of acetate led to a 39 % higher degree of polymerization (DP) for LS. Small angle X‐ray scattering (SAXS) revealed that the structure of the enzyme was largely unaffected by the ions, while the determination of the zeta potential showed that those ions conveying higher negative surface charges onto LS particles showed lower DPs, than those not affecting the surface charge. Further, electron paramagnetic resonance (EPR) spectroscopy showed 5‐times higher intensity in phenoxyl radicals for the monovalent ions compared to the divalent ones. It was concluded that the DPs of LS could be tuned in the presence of certain ions, by facilitating the interaction between the laccase substrate‐binding site and the LS molecules. In this study, it was found that the presence of diverse ions at low concentrations could tune the rate of laccase‐catalyzed lignosulfonate polymerization, which helps in further optimizing the process.