Abstract
The lignin precursors of coniferin and syringin were synthesised, and guaiacyl-type and guaiacyl-syringyl-type oligomeric lignin dehydrogenation polymers (DHP and DHP-GS) were prepared with the bulk method. The carbon-13 nuclear magnetic resonance spectroscopy showed that both DHP-G and DHP-GS contained β-O-4, β-5, β-β, β-1, and 5-5 substructures. Extraction with petroleum ether, ether, ethanol, and acetone resulted in four fractions for each of DHP-G (C11–C14) and DHP-GS (C21–C24). The antibacterial experiments showed that the fractions with lower molecular weight had relatively strong antibacterial activity. The ether-soluble fractions (C12 of DHP-G and C22 of DHP-GS) had strong antibacterial activities against E. coli and S. aureus. The C12 and C22 fractions were further separated by preparative chromatography, and 10 bioactive compounds (G1–G5 and GS1–GS5) were obtained. The overall antibacterial activities of these 10 compounds was stronger against E. coli than S. aureus. Compounds G1, G2, G3, and GS1, which had the most significant antibacterial activities, contained β-5 substructures. Of these, G1 had the best antibacterial activity. Its inhibition zone diameter was 19.81 ± 0.82 mm, and the minimum inhibition concentration was 56.3 ± 6.20 μg/mL. Atmospheric pressure chemical ionisation mass spectrometry (APCI-MS) showed that the antibacterial activity of G1 was attributable to a phenylcoumarin dimer, while the introduction of syringyl units reduced antibacterial activity.
Highlights
Lignin is one of the most abundant natural materials in the world, accounting for about a quarter of wood tissue, and is a promising renewable material [1,2,3]
Domínguez-Robles et al [13] prepared a composite of softwood kraft lignin and polybutylene succinate (PBS) that was resistant to the adhesion of S. aureus, achieving a reduction in bacterial adhesion of approximately 90% compared to PBS
Rocca et al [18] synthesised lignin-doped silver and gold nanoparticles by one-pot thermochemical and photochemical methods, and they found that the nanoparticles had a certain inhibitory effect on E. coli and S. aureus
Summary
Lignin is one of the most abundant natural materials in the world, accounting for about a quarter of wood tissue, and is a promising renewable material [1,2,3]. Kaur et al [14] chemically modified bagasse lignin through acetylation, epoxidation, and hydroxymethylation reactions They found that among the modified lignin samples, epoxy lignin had the most effective antibacterial activity, with minimum inhibitory concentrations (MIC) against Bacillus aryabhattai and Klebsiella of 90 and 200 μg/mL, respectively, demonstrating that lignin has great potential for antibacterial applications. Marulasiddeshwara et al [19] found that lignin capped silver nanoparticles (LCSN) have antioxidant and antibacterial properties, and did not lyse red blood cell (RBC) membrane when assayed hemolytic activity suggested its non-toxic nature. There studies show that lignin has a broad application prospect biological activity
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