Structural characterization of the lignin from Saxifraga (Saxifraga oppositifolia L.) stems.

As a renewable source of unique aromatic compounds, lignin attracts the attention of many researchers. However, for its successful application, it is necessary to have a clear and accurate idea of its chemical structure. Therefore, it is necessary to expand knowledge about the structure of lignins of various nature using the informative analytical methods. The aim of this study was to characterize the dioxane lignin of the Saxifraga oppositifolia L. - the northernmost angiosperm. The lignin of plants growing in the Arctic zone may differ significantly from other plants, both due to species differences and peculiarities of growing conditions. Studies were conducted on an isolated lignin preparation obtained by the Pepper's method. Analysis of Py-GC/MS data and NMR spectroscopy showed that saxifrage lignin belongs to GH-type. This is evidenced by a significant proportion of p-hydroxyphenyl units (40%), while the content of syringyl units is about 14%. The major substructures of the studied lignin were β-aryl ether, phenylcoumaran, and resinol. It was found that the γ‑carbon of the lignin side chains are partly acetylated, and forms ester bonds with the p-hydroxybenzoate structure. In addition, the NMR spectrum showed a signal of the phenylglycoside evidenced the presence of the lignin-carbohydrate complex.