Density Functional Theory Calculations and Infrared Spectral Analysis of Lignin

Lignin is one of the building blocks of plant cell walls, and the study of the spectral characterization of its cleavage process can help to monitor the production and reuse of straw after decay. In this paper, four theoretical model structures of lignin formed by lignin G monomers and connected by β-O-4 bonding type were optimized and calculated based on the density functional theory using the B3LYP/3-21g and B3LYP/6-311g basis sets. The results showed that the theoretical infrared spectra of lignin increased sequentially in the absorption peaks of 1500 cm^-1 blue shift and 2932 cm^-1 and 1200 cm^-1 red shift, while the latter three theoretical models showed new infrared absorption peaks of 716 cm^-1 and 823 cm^-1 due to the presence of the β-O-4 structure, which is of great value for the theoretical spectral study of organic macromolecules and also provides data support for the spectral change in lignin in the degradation of graminaceous plants.