Analysis of the functional group composition of the spruce and birch phloem lignin

In this article, the functional group composition of the spruce (Picea dbies) and birch (Benda pendula) phloem lignin is described. The features of the chemical structure were studied by analyzing dioxane lignin using the elemental analysis, UV-Vis, FT-IR. and ID NMR spectroscopy. For comparison, samples of xylem dioxane lignin isolated from the corresponding wood species were also analyzed. FT-IR spectroscopy data suggest that the lignins of birch phloem and xylem are similar in chemical structure. However, there are differences in absorption bands in the spectra of spruce dioxane lignin, which indicate the opposite. Quantitative analysis of the functional group composition was performed using C-13 and -P-31 NMR data. It was found that free phenolic hydroxyl groups of catechol and p-hydroxyphenyl types are dominated in the composition of spruce phloem lignin. Birch phloem lignin has a qualitative and quantitative composition of functional groups characteristic of hardwood lignins. However, the content of G-units is greater than S-units, in contrast to the birch xylem lignin, where S-units predominate. The revealed differences are relevant from the point of view of plant physiology. The practical significance of the study is connected with understanding the reactivity of lignins when considering the chemical processing of tree bark. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This study describes the functional group composition of spruce and birch phloem lignin, showing similarities and differences in their chemical structures. Spruce phloem lignin is dominated by free phenolic hydroxyl groups of catechol and p-hydroxyphenyl types, while birch phloem lignin has a composition closer to typical hardwood lignins. The findings are important for understanding lignin reactivity in chemical processing of tree bark.