Lignin Biosynthesis and Degradation — a Major Challenge for Computational Chemistry. In: Palma JMLM, Sousa AA, Dongarra J, Hernández V, editors. High Performance Computing for Computational Science — VECPAR 2002. Berlin: Springer Berlin Heidelberg; 2003. pp. 137-65. [DOI: 10.1007/3-540-36569-9_10]

In vitro cell composition identification of wood decay fungi by Fourier transform infrared spectroscopy

Decay pathogens follow dissimilar metabolic mechanisms to cause irreversible damage to woody tissues. The objective of this study is to perform inter- and intra-species microbial cell structural comparison using attenuated total reflectance Fourier transform infrared spectroscopy. Representative fungi species, causing brown rot and white rot, namely, Postia placenta and Trametes versicolor, respectively, were cultured in laboratory conditions. In vitro spectral measurements were performed at periodic two week intervals of fungal growth. The study shows structural differences for both species of fungi. The prominent presence of protein amide, carbohydrate and carboxyl bands was of interest. Spectral deconvolution of the infrared broadband around approximately 3300 cm-1 produced peaks at four different wavenumbers. The hydrogen bond energy obtained at the four wavenumbers, from deconvolution, varied from approximately 41 kJ mol-1 to approximately 7 kJ mol-1, indicating the presence of strong and weak forces in microbial cell structure. The hydrogen bond distance, obtained at the deconvoluted wavenumbers, varied between 2.7 Å-2.8 Å, indicating the presence of short and long-distance forces within microbial cells. Microscopic observation showed mycelium colonization, hyphal tip and lateral branching.

Molecular Insight into the Cosolvent Effect on Lignin-Cellulose Adhesion

Understanding and controlling the physical adsorption of lignin compounds on cellulose pulp are key parameters in the successful optimization of organosolv processes. The effect of binary organic-aqueous solvents on the coordination of lignin to cellulose was studied with molecular dynamics simulations, considering ethanol and acetonitrile to be organic cosolvents in aqueous solutions in comparison to their monocomponent counterparts. The structures of the solvation shells around cellulose and lignin and the energetics of lignin-cellulose adhesion indicate a more effective disruption of lignin-cellulose binding by binary solvents. The synergic effect between solvent components is explained by their preferential interactions with lignin-cellulose complexes. In the presence of pure water, long-lasting H-bonds in the lignin-cellulose complex are observed, promoted by the nonfavorable interactions of lignin with water. Ethanol and acetonitrile compete with water and lignin for cellulose oxygen binding sites, causing a nonlinear decrease in the lignin-cellulose interactions with the amount of the organic component. This effect is modulated by the water exclusion from the cellulose solvation shell by the organic solvent component. The amount and rate of water exclusion depend on the type of organic cosolvent and its concentration.

Modeling lignin polymerization. I. Simulation model of dehydrogenation polymers

Lignin is a heteropolymer that is thought to form in the cell wall by combinatorial radical coupling of monolignols. Here, we present a simulation model of in vitro lignin polymerization, based on the combinatorial coupling theory, which allows us to predict the reaction conditions controlling the primary structure of lignin polymers. Our model predicts two controlling factors for the beta-O-4 content of syringyl-guaiacyl lignins: the supply rate of monolignols and the relative amount of supplied sinapyl alcohol monomers. We have analyzed the in silico degradability of the resulting lignin polymers by cutting the resulting lignin polymers at beta-O-4 bonds. These are cleaved in analytical methods used to study lignin composition, namely thioacidolysis and derivatization followed by reductive cleavage, under pulping conditions, and in some lignocellulosic biomass pretreatments.