Comparative study of chemical and topological structure of macromolecules of lignins of birch (Betula verrucosa) and apple (Malus domestica) wood.

Recent advances in investigations of chemical structure of lignin give rise to questions about relationship between chemical structure and topology of the macromolecules. In this paper, we made a comparison of results of the studies of chemical and topological structures of lignins. The features of topological structure of lignins of birch and apple wood were identified on the basis of the study of dilute solutions of the lignins by the sedimentation-diffusion analysis and viscometry. The number of branches of macromolecules in the birch and apple lignins was calculated by the Zimm-Kilb equation. Quantitative characteristics of chemical structure of the lignins were obtained by 2D NMR spectroscopy and nitrobenzene oxidation. The structural analysis and the calculations based on the hydrodynamic data gave estimation of the degree of branching of macromolecules, which fit well in the theory on the role of dibenzodioxocin and 4'-O-5 structures in branching of lignin macromolecules.