Structural characteristics of different softwood lignins according to 1D and 2D NMR spectroscopy

Abstract

Along with cellulose, lignin is one of the most common polymers of plant origin. Numerous studies show that the complex and irregular structure of lignin is still unknown. First of all, the existing problems are connected with the peculiarities of lignins as a natural chemical compound. In this paper the general regularities of the chemical structure of dioxane lignins isolated from the softwood – larch (Lárix sibírica), pine (Pinus cembra) and juniper (Juníperus commúnis). The studies were carried out using a combination of ¹³C, ³¹P and 2D NMR spectroscopy. According to HSQC spectra it was established that the main structural fragments are the structures of β-aryl ether, followed by phenylcoumarans, with lower amounts of other substructures. Signals belonging to a methyl substituted phenylcoumaron were first identified on the NMR spectra of softwood dioxane lignins. Signals related to the structure of 3′-O-methylated dihydroquercetin were found in the composition of larch dioxane lignin.

Keywords:

• Softwood
• lignin
• ¹³C-NMR
• ³¹P-NMR
• 2D-NMR
• Py-GC/MS

Additional information

Funding

This work was performed using the instrumentation of Core Facility Center “Arktika” of Northern (Arctic) Federal University under support of the Ministry of education and science of the Arkhangelsk region (project number 04-2019-03A).