Category Archives: Biomass Recalcitrance

Studying cellulose hydrolysis

8.7.1 Work to date The questions researchers have tried to answer over the last two decades using molecular mechanics and molecular dynamics have been, what are the structures of cellulose isotypes Ia, Ip, and II, and, can the uncertainties and irregularities in the experimental data be clarified? Many insights have been gained from simulations using multiple force fields, models, and […]

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Cellulase synergism

Synergism is usually only seen in the digestion of substrates that contain crystalline cellulose, probably because there are only a few regions in this substrate that are accessible to each cellulase. It seems likely that synergism occurs only when two cellulases attack different regions of the cellulose molecule and each one creates new sites of attack for the other enzymes […]

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Lime pretreatment

Pretreatment using lime has been studied as a low-cost process that primarily achieves acetyl and lignin solubilization (10,14,18,62,63). Lime pretreatment has been practiced at a wide range of temperatures, from 25°C to about 130°C, with lime loadings of about 10 wt% (on a dry feedstock basis) and solids loadings of 20% or less. At the higher temperatures, the pretreatment times […]

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Molecular associations between wall polymers

The organization of walls can be described as consisting of cellulosic microfibrils and struc­tural proteins inserted into and reinforcing a multicomponent gel matrix, composed of stereo-irregular, non-cellulosic heteropolysaccharides (heteroglucans, heteromannans, het — eroxylans, (1^3,1^4)-p-D-glucans, and pectins). In primary walls these matrix polysac­charides may interact through physical associations with one another and the cellulosic microfibrils and also through covalent associations. In […]

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GDP-$ — L-galactose (GDP-Gal)

GDP-$-L-gluclose gulose (GDP-Gul) GDP-Gal is a major precursor for the synthesis of ascorbic acid in plants, and relatively low amounts of L-Gal are found in plant glycans. A GDP-Man 3′,57 epimerase activity first identified in the Neufeld’s laboratory (493) epimerizes GDP-Man into GDP-Gal. Careful biochemical analyses of the specific activity of recombinant Arabidopsis At5g28840 (494) and rice (497) protein demonstrate […]

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Lignin subunit and lignin structural analyses by NMR spectroscopy

For a period now approximating well over 30 years, NMR spectroscopy has been applied to the study of various lignin isolates (71, 131, 132, 154-177). In this way, it has been possible, together with the study of various dimeric monolignol-derived products, to identify a number of the most abundant substructures in lignins. Many of these were previously shown in Figure […]

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Future outlook: remaining questions in ligninтmacromolecular assembly/configuration, proposed lignin template replication, and overall cell wall formation

The fields of lignin chemistry, biochemistry, molecular biology, and plant cell wall biomechanics/anatomy are of greatly renewed interest as the twenty-first century unfolds. This contrasts with the preliminary studies of the mid-twentieth century on lignin consti­tution, which more or less relegated this important class ofmacromolecules to the scientific curiosity of being randomly assembled. This, in turn, was largely as a […]

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Xylobiose calculations

As a model system for hydrolysis and dehydration of xylo-oligomers and xylan, static quan­tum mechanical calculations were conducted on the decomposition of xylobiose. As with xylose, acid-catalyzed reactions were studied by computing the energy barriers for proto — nated xylobiose in vacuum. Because of the large size of this molecule, highly accurate CBS calculations could not be conducted. Instead DFT […]

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Rumen protozoa

Rumen protozoa are reported to account for up to 50% of the microbial biomass in the rumen, and it has long been suspected that certain species play a significant role in the breakdown of plant material. There has been uncertainty, however, whether protozoa pro­duce their own cellulases and xylanases, or whether the activities that can be measured for the protozoal […]

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