The inhibition of p-hydroxyphenyl hydroxyl group in residual lignin on enzymatic hydrolysis of cellulose and its underlying mechanism

• Phenolic OH was the main inhibitors in lignin for enzymatic hydrolysis. • Phenolic OH of lignin inhibits enzymatic hydrolysis by non-productive adsorption. • The p -hydroxyphenyl OH showed the highest inhibition and non-productive adsorption. • The electrophilicity and steric hindrance of phenolic OH affect its enzyme affinity. • H-bonds and π-π stacking between lignin and enzyme were responsible for inhibition. The controlling factors of the inhibition on enzymatic hydrolysis caused by residual lignin were identified with molecular level understanding of the mechanism. Residual lignin samples with different properties were isolated, characterized and added into the enzymatic hydrolysis of Avicel. It was found that the phenolic hydroxyl group (OH) was the main inhibitor in residual lignin, and the p -hydroxyphenyl OH was the crucial sub-structure that exhibited the highest inhibition and non-productive adsorption, ascribing to its higher electrophilicity and lower steric hindrance. The H-bond interaction and π-π stacking between phenolic OH of lignin and phenolic OH of tyrosine on the planar face of carbohydrate binding module of cellulase were probably responsible for the non-productive adsorption. The binding sites of H-bonds may be the H in phenolic OH of lignin and the O in phenolic OH of tyrosine, respectively, and that of the π-π stacking may be the benzene rings of them.