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Origin of free radicals produced from the syringyl end groups in lignins


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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Correspondence to Takayuki Oniki.

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Oniki, T. Origin of free radicals produced from the syringyl end groups in lignins. J Wood Sci 44, 314–319 (1998).

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Key words

  • ESR
  • Lignin
  • Acidolysis
  • Reduction
  • Syringyl end group