Accelerated Light-Induced Aging of Α-, Β-, and Γ-13C-Enriched Cell Wall-Dehydrogenation Polymers Studied With Solid State 13C NMR spectroscopy
J Parkas, David L. VanderHart, U Westermark
Light-induced aging of lignocellulosic materials has been studied with a new technique involving selectively alpha-, beta-, and gamma-13C-enriched cell wall-dehydrogenation polymers (CW-DHP:s) and solid state 13C NMR spectroscopy. The results from cross-polarization magic angle spinning (CP/MAS) 13C NMR experiments of unirradiated and irradiated CW-DHP have revealed mainly a decrease in the amount of end-groups of both coniferaldehyde and coniferyl alcohol type. The results suggest that these end-groups become saturated and that the terminal functionalities, i.e., gamma-aldehyde and gamma-hydroxymethyl groups, at least to some extent, are retained. The results indicate further that no detectable cleavage of the beta-O-4 bonds occurs in the examined lignocellulosic model. In terms of proposed mechanisms of yellowing, there is marginal evidence that up to 2% ofthe alpha-labeled sites are converted by irradiation to alpha-carbonyls (aldehyde or ketones); moreover, we cannot dismiss the possibility that the precursor structures giving rise to these few a-carbonyls are beta-O-4 structures.The 13C-enriched CW-DHP was formed directly on spruce (Picea abies) wood tissue (differentiating xylem) by administering selectively 13C-labeled coniferin at pH 6.0 in the presence of glucose oxidase and beta-glucosidase, i.e., no phenol-oxidizing enzyme was added and the wood cells own enzymes polymerized the precursor.
, VanderHart, D.
and Westermark, U.
Accelerated Light-Induced Aging of Α-, Β-, and Γ-<sup>13</sup>C-Enriched Cell Wall-Dehydrogenation Polymers Studied With Solid State <sup>13</sup>C NMR spectroscopy, Journal of Wood Chemistry and Technology
(Accessed February 22, 2024)