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  1. ABSTRACT Improving access to the carbohydrate content of lignocellulose is key to reducing recalcitrance for microbial deconstruction and conversion to fuels and chemicals. Caldicellulosiruptor bescii completely solubilizes naked microcrystalline cellulose, yet this transformation is impeded within the context of the plant cell wall by a network of lignin and hemicellulose. Here, the bioavailability of carbohydrates toC. bescii at 70°C was examined for reduced lignin transgenic switchgrass lines COMT3(+) and MYB Trans, their corresponding parental lines (cultivar Alamo) COMT3(–) and MYB wild type (WT), and the natural variant cultivar Cave-in-Rock (CR). Transgenic modification improved carbohydrate solubilization by C. bescii to 15%more » (2.3-fold) for MYB and to 36% (1.5-fold) for COMT, comparable to the levels achieved for the natural variant, CR (36%). Carbohydrate solubilization was nearly doubled after two consecutive microbial fermentations compared to one microbial step, but it never exceeded 50% overall. Hydrothermal treatment (180°C) prior to microbial steps improved solubilization 3.7-fold for the most recalcitrant line (MYB WT) and increased carbohydrate recovery to nearly 50% for the least recalcitrant lines [COMT3(+) and CR]. Alternating microbial and hydrothermal steps (T→M→T→M) further increased bioavailability, achieving carbohydrate solubilization ranging from 50% for MYB WT to above 70% for COMT3(+) and CR. Incomplete carbohydrate solubilization suggests that cellulose in the highly lignified residue was inaccessible; indeed, residue from the T→M→T→M treatment was primarily glucan and inert materials (lignin and ash). While C. bescii could significantly solubilize the transgenic switchgrass lines and natural variant tested here, additional or alternative strategies (physical, chemical, enzymatic, and/or genetic) are needed to eliminate recalcitrance.« less
  2. The identification of chemical impurities is crucial in elucidating the structures of biorefinery products using nuclear magnetic resonance (NMR) spectroscopic analysis. In the current biorefinery platform, contaminants derived from pretreatment solvents and decomposition byproducts may lead to misassignment of the NMR spectra of biorefinery products (e.g, lignin and bio-oils). Therefore, we investigated in this paper 54 commonly reported compounds including alcohols, carbohydrates, organic acids, aromatics, aldehydes, and ionic liquids associated with biomass pretreatment using 31P NMR. The chemical shifts of these chemicals after derivatizing with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane (TMDP) were provided. Finally, the 31P NMR signals of these derivatives could serve asmore » valuable and informative spectral data in characterizing lignocellulose-based compounds.« less
  3. Hydrothermal pretreatment using liquid hot water (LHW) is capable of substantially reducing the cell wall recalcitrance of lignocellulosic biomass. It enhances the saccharification of polysaccharides, particularly cellulose, into glucose with relatively low capital required. Due to the close association with biomass recalcitrance, the structural change of the components of lignocellulosic materials during the pretreatment is crucial to understand pretreatment chemistry and advance the bio-economy. Although the LHW pretreatment has been extensively applied and studied, the molecular structural alteration during pretreatment and its significance to reduced recalcitrance have not been well understood.
  4. Because cellulosic ethanol production remains cost-prohibitive„ advances in consolidated bioprocessing (CBP) have been directed towards lifting this restriction. CBP reduces the need for added enzymes and can potentially slash ethanol production costs through process integration. Clostridium thermocellum, a CBP microorganism, organizes its enzymes in a multi-enzyme complex - a stark contrast to fungal enzymes. Nonetheless, recalcitrance may limit the extent of biomass deconstruction. Here in this study, six Populus were treated with C. thermocellum (ATCC 27405) and characterized to determine structural changes that resulted from CBP. The 2D HSQC NMR spectra of lignin-enriched residues revealed that higher S/G ratio (2.6)more » and fewer carbon-carbon interunit linkages (generally 2–5%) were present in the top performing poplar. Furthermore, cellulose degree of polymerization data suggests that C. thermocellum likely circumvents long chain cellulose, while cellulose crystallinity and hemicellulose molecular weight data do not provide a direct indication of features connected to recalcitrance. Hence, C. thermocellum is similarly impacted by the proposed lignin properties that negatively impact biomass deconstruction using fungal enzymes.« less
  5. Acid chlorite delignification is frequently used to obtain a mixture of cellulose and hemicellulose known as holocellulose from biomass. While a majority of lignin is removed after holocellulose pulping, there appears to be a minor fraction of lignin that is more resistant to acid chlorite treatment and remains in the holocellulose even after repeated delignification treatment. This type of lignin, defined as hololignin, has not been characterized, is likely to contribute to biomass recalcitrance and is clearly of fundamental interest to understand its structural characteristics. In this study, hololignin isolated from poplar holocellulose was characterized with a wide array ofmore » techniques including GPC, quantitative 13C, DEPT-135, HSQC, and 31P NMR. The results were then compared to those from milled wood lignin (MWL), the representative native lignin isolated from poplar. NMR analysis demonstrated a depletion of cinnamyl aldehyde, acetyl group, and decrease of p-hydroxybenzoate structural units in hololignin. An enrichment of condensed structures in hololignin was observed. Hololignin also had a significantly lower molecular weight than MWL. Finally, hololignin is relatively enriched in guaiacyl units and has a lower S/G ratio, lower β-O-4 ether linkages, fewer aliphatic and phenolic hydroxyl groups, and more carboxylic acid groups than MWL.« less
  6. Bio-char is a by-product from thermochemical treatment of biomass and has been identified as an energy condensed product with a comparable heating value as commercial coal. However, the combustion of such solid product as an energy resource is only a preliminary application. It is highly possible to convert bio-char, which always has a condensed aromatic and porous structure to various high-value products. The investigations of the structures and formation pathways for the bio-char are very important to any future applications. In this study, six different biomass components, including cellulose, lignin, and tannin, and three whole biomasses—pine wood, pine residue, andmore » pine bark—have been used to produce bio-char at 400, 500, and 600 °C. Solid-state NMR and FT-IR have been employed in this study to characterize the structures for the bio-chars. The results indicated that the bio-chars produced from lignin contained some methoxyl groups, and the bio-chars produced from tannin contained significantly higher amount of phenolic hydroxyl groups. Compared to the bio-chars produced from pine wood and residue, the bio-chars produced from pine bark contained more aromatic C–O bonds, and aliphatic C–O and C–C bonds, which may be due to the significantly higher amount of lignin and tannin in the pine bark. Furthermore, the elevated amounts of aromatic C–O and aliphatic C–O and C–C bonds in the bio-chars from pine bark appeared to be completely decomposed at 600 °C.« less
  7. Lignocellulosic biomass was decomposed to produce crude bio-oil in water and ethanol using hydrated cerium (III) chloride as a catalyst. Use of the catalyst affected not only the yield of crude bio-oil but also the composition of bio-crude for both water and ethanol. The catalyst had a detrimental effect on the crude bio-oil yields obtained from water processing for all runs. However, in ethanol, use of the catalyst improved the crude bio-oil yields in all tested runs. The solid residue yields decreased with the catalyst use in the runs with water but increased in all studies with ethanol, except thosemore » with the shortest tested residence time of 10 min. The highest crude bio-oil yield of 48.2 wt% was obtained at 300 °C using 5 mmol of hydrated cerium (III) chloride at a residence time of 90 min in ethanol. The heating values of the crude bio-oils increased with the catalyst use for both water and ethanol processing. In conclusion, the highest heating value of 33.3 MJ kg –1 was obtained with hydrated cerium (III) chloride at 300 °C and a residence time of 120 min.« less
  8. Biomass deuteration is an effective engineering method that can be used to provide key insights into understanding of biomass recalcitrance and the complex biomass conversion process. In this study, production of deuterated switchgrass was accomplished by growing the plants in 50% D 2O under hydroponic conditions in a perfusion chamber. Cellulolytic enzyme lignin was isolated from deuterated switchgrass, characterized by Fourier transform infrared (FTIR), gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) and compared with its protiated control sample to determine the effect of in vivo deuteration on the chemical structure of lignin. FTIR results showed that D 2Omore » can be taken up by the roots and transported to the leaves, and deuterium was subsequently incorporated into hydroxyl and alkyl groups in the plant and its lignin through photosynthesis. According to GPC results, deuterated lignin had slightly higher molecular weight, presumably due to isotope effects. 31P and heteronuclear single quantum coherence (HSQC) NMR results revealed that lignin in the deuterated biomass preserved its native physicochemical characteristics. Finally, the conserved characteristics of the deuterated lignin show its great potential applications for structural and dynamic studies of lignocellulose by techniques such as neutron scattering.« less
  9. This study aims to reveal the structural features and reaction pathways for solid–liquid products from hydrothermal carbonization of Loblolly pine, where the solid products can be used as catalysts, adsorbents and electrode materials while liquid products can be treated yielding fuels and platform chemicals. Results revealed when treated at 240 °C, cellulose and hemicellulose were degraded, in part, to 5-hydroxy-methyl furfural and furfural which were further transformed to aromatic structures via ring opening and Diels Alder reactions. Lignin degradation and formation of carbon–carbon bonds, forming aromatic motifs in the presence of furanic compounds connected via aliphatic bridges, ether or condensationmore » reactions. After hydrothermal treatment, condensed aromatic carbon materials with methoxy groups were recovered with high fixed carbon content and HHV. As a result, the recovered liquid products are lignin-like value-added chemicals consisting of furfural and polyaromatic structure with alkanes and carboxyl, their total hydroxyl group content decreased when increasing reaction time.« less
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