Functional Composition and Structural Features of Higher Plant Lignins

Abstract

NMR spectroscopy is one of the effective methods for the study of plant raw materials, which makes it possible to identify differences in the structure and functional composition of lignins of various types of plant biomass. However, there are a number of limitations in the use of this method – in particular, the registration of NMR spectra at some nuclei (13C, 31P, etc.) usually requires considerable amount of time. This article proposes an approach to reduce the recording time of 31P NMR spectra by a factor of 17 without losing the quality of the result. With the help of this method and with the use of optimized experimental parameters, the functional group analysis of lignins of some softwood and hardwood species and herbaceous plants distributed in the European North of the Russian Federation was carried out. The types of structural units and their characteristic interstructural relationships per 100 phenylpropane units were determined by HSQC NMR. Differences in the functional composition and features of the structural organization of lignins were identified depending on the family to which the plant belongs. On the basis of the obtained array of experimental data the strategies of processing of specific types of plant raw materials were proposed. For example, lignins of the Birch and Beech families showed the largest number of β-aryl ether fragments with a free hydroxyl group in the α-position, which indicates the greater reactivity of these lignins. Accordingly, representatives of these families are priority raw materials in the development of lignin processing methods. At the same time, the structure of lignins of representatives of the Beech family proved to be the most resistant to hydrolytic degradation, which is important for lignin-directed bioprocessing concepts. For citation: Sypalova Yu.A., Shestakov S.L., Kozhevnikov A.Yu. Functional Composition and Structural Features of Higher Plant Lignins. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 5, pp. 164–183. (In Russ.). https://doi.org/10.37482/0536-1036-2023-5-164-183