Origin of free radicals produced from the syringyl end groups in lignins
1998
Oniki, Takayuki
Enzyme lignin was prepared from reed; it was acid-hydrolyzed and reduced with NaBH₄. Spin concentrations of radicals produced by oxidation of the lignins with K₃[Fe(CN)₆] or H₂O₂ were determined from electron spin resonance spectra. The radicals were observed by the oxidation of sinapyl alcohol. It was found that the two radicals observed by the oxidation of dioxane lignins were deprotonated 2,6-dimethoxyp-benzosemiquinone and 6-hydroxy-2-methoxy-p-benzosemiquinone, and that they were produced from syringyl end groups. The production rate of radicals from syringyl end groups possessing anα-carbonyl group was greater than that possessing anα-hydroxyl group. It was suggested that stilbene-type syringyl end groups were produced from phenylcoumaran moieties in lignins by acidolysis. The radicals produced from guaiacyl end groups were not observed by the oxidation process.
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