The effect of coumaryl alcohol incorporation on the structure and composition of lignin dehydrogenation polymers

Understanding the structure and composition of the lignin polymer in biomass is essential for the development of deconstructive technologies that convert biomass to fuels and chemicals. Density functional theory calculations have predicted certain linkages in lignin to be more or less favorable amongst the three monomers (sinapyl, coniferyl, and coumaryl alcohol. For example, calculations show that the coumaryl monomer has favorable self- and cross-coupling reactions within the polymeric framework, yet certain linkages with this monomer could inhibit polymeric elongation.¹ The hypothesis is that the incorporation of the coumaryl monomer could result in changes in the types of linkages present in lignin and result in lower molecular weight polymers. The goal of our study was to experimentally validate/invalidate the predictions made for the structure of lignin polymers that incorporate coumaryl alcohol. Lignin dehydrogenation polymers were synthesized using the three monomers in the presence of horseradish peroxidase and peroxide in order to study the effect of coumaryl alcohol on lignin polymerization. The amount of coumaryl alcohol was varied 0 to 20% (molar) and the polymers were characterized using GPC for determination of molecular weight and polydispersity. The polymers structure and composition were also characterized using NMR, thioacidolysis and pyrolysis-MBMS. This is the first report of the characterization of lignin dehydrogenation polymers synthesized using varying amounts of coumaryl alcohol.

¹Sangha, A. K.; Davison, B. H.; Standaert, R. F.; Davis, M. F.; Smith, J. C.; Parks, J. M., Chemical Factors that Control Lignin Polymerization. The Journal of Physical Chemistry B 2014, 118 (1), 164-170.