10-25: Characterization of monolignols' coupling mechanism through in vitro, various peroxidases-catalyzed dehydrogenative polymerization

In this study dehydrogenative polymers (DHPs) were synthesized in vitro with various feeding ratios of sinapyl and coniferyl alcohol (10:0, 8:2, 6:4, 2:8, 0:10) using horseradish peroxidase (HRP), Coprinus cinereus peroxidase (CiP) and soybean peroxidase (SBP) with H₂O₂ via “Zutrophverfahren”. The DHPs were subjected to chemical analyses, such as GPC, DFRC analysis and analytical pyrolysis- GC/MS.

The turnover capacity of the peroxidases revealed that coniferyl alcohol was more favorable substrate than sinapyl alcohol. Coniferyl alcohol was easily oxidized in the order of CiP > SBP > HRP. As for sinapyl alcohol SBP and CiP showed similar oxidative capacity, but HRP was relative low. The yields of DHPs prepared by HRP (H-DHP) and CiP (C-DHP) amounted to 7 – 70 % and 9 – 72 %, respectively. The average molecular weights of both DHPs were determined to 4,000 – 5,000. With increasing the ratio of coniferyl alcohol/sinapyl alcohol, yields of DHPs and the average molecular weights gradually increased. When the DHPs were prepared with only sinapyl alcohol the frequency of β-O-4 bond determined by DFRC method was ca. 940 - 1,000 mmol/g. However, the frequencies of β-O-4 bonds in DHPs were obviously lowered with addition of coniferyl alcohol. The frequency of β-O-4 bonds in H-DHP prepared with only coniferyl alcohol was determined to ca. 93 mmol/g. However, the frequency of β-O-4 bonds in C-DHP prepared with only coniferyl alcohol was estimated to ca. 400 mmol/g. This observation demonstrates that peroxidases in vivo could be involved to radical-radical coupling during dehydrogenative polymerization.