Lignin-derived polyphenols with enhanced antioxidant activities by chemical demethylation and their structure-activity relationship
International journal of biological macromolecules(2023)
Abstract
Lignin valorization to biobased polyphenols antioxidants is increasingly attractive in the modern industry due to their inherent phenolic structures. Herein, lignin-derived polyphenols with enhanced antioxidant activities were prepared from the most available technical lignin including organosolv lignin (OL), alkali lignin (AL), and enzyme lignin (EL) by iodocyclohexane (ICH) chemical demethylation. The structural evolution of lignin indicated that the C-Ar-OCH3 group and the C-Ar-O-C-alkyl side-chain could be effectively transformed into the C-Ar-OH group, resulting in a significant increase of the phenolic-OH content and a slight decrease of the molecular weight. The 1,1-diphenyl-2-picrylhydrazyl radical (DPPH center dot) scavenging activity was in the order of ICHOL-24 > ICHAL-24 > ICHEL-24 approximate to FA > BHT, and the IC50 value of ICHOL-24 was 0.56 times lower than that of BHT. The structure-activity relationship demonstrated the activities were quasi-linearly related to phenolic-OH contents and could be affected by molecular weights. The H/G/S proportions of lignin could be an indicator for accurate screening of efficient lignin-derived polyphenols antioxidants (LPA). It was preliminarily estimated to have economic feasibility for producing LPA from technical lignin by demethylation compared with synthetic or natural antioxidants. This work will help to develop efficient biobased antioxidants for lignin valorization.
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Key words
Technical lignin,Polyphenols antioxidants,Chemical demethylation
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