Vibrational structure of selected compounds derived from biomass: lignin dimers, selected aldopentoses and aldohexoses

The production of chemicals from biomass is a very challenging process due to its diverse chemical composition. Lignin, cellulose and hemicellulose are the three main biopolymers of wood biomass, with cell walls of plant origin. Lignin has been chosen for the present studies due to its range of different linkages and structures. The present work involved a computational study of the most dominant lignin dimers and their vibrational structures, based on the Density Functional Theory method. Full geometry optimization of the compartments used the StoBe code with cluster model and non-local functional (RPBE) approach. The calculations of the vibrational frequencies were performed with harmonic approximations as well as an anharmonicity fit in the Morse potential function, as implemented in the StoBe code. In the case of lignin, the calculations included three different precursors based on: coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. To represent the cellulose and hemicellulose derivatives, selected aldopentoses and aldohexoses (arabinose, xylose, glucose, galactose, and mannose) were considered. Presented here are the theoretical investigations for a variety of biomass derived compounds, to give the possibility of obtaining a theoretical VBD (Vibrations Basis Database) for experimental spectra interpretation. Such a database could be further used in the preliminary composition assessment of biomass derived substrates, which will be discussed here in more detail.