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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Downregulation of pectin biosynthesis gene GAUT4 leads to reduced ferulate and lignin-carbohydrate cross-linking in switchgrass

Abstract Knockdown (KD) expression of GAlactUronosylTransferase 4 ( GAUT4 ) in switchgrass improves sugar yield and ethanol production from the biomass. The reduced recalcitrance of GAUT4 -KD transgenic biomass is associated with reduced cell wall pectic homogalacturonan and rhamnogalacturonan II content and cross-linking, and the associated increases in accessibility of cellulose to enzymatic deconstruction. To further probe the molecular basis for the reduced recalcitrance of GAUT4 -KD biomass, potential recalcitrance-related factors including the physicochemical properties of lignin and hemicellulose are investigated. We show that the transgenic switchgrass have a lower abundance of ferulate and lignin-carbohydrate complex cross-linkages, reduced amounts of residual arabinan and xylan in lignin-enriched fractions after enzymatic hydrolysis, and greater coalescence and migration of lignin after hydrothermal pretreatment in comparison to the wild-type switchgrass control. The results reveal the roles of both decreased lignin-polymer and pectin cross-links in the reduction of recalcitrance in PvGAUT4 -KD switchgrass.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

In situ plant materials hyperspectral imaging by multimodal scattering near-field optical microscopy

Plant cells are elaborate three-dimensional polymer nano-constructs with complex chemistry. The bulk response of plants to light, in the far-field, is ultimately encoded by optical scattering from these nano-constructs. Their chemical and physical properties may be acquired through their interaction with a modulated nano-tip using scattering scanning near-field optical microscopy. Here, using this technique, we present 20 nm spatial resolution mechanical, spectral and optical mappings of plant cell walls. We first address the problem of plant polymers tracking through pretreatment and processing. Specifically, cellulose and lignin footprints are traced within a set of delignified specimen, establishing the factors hindering complete removal of lignin, an important industrial polymer. Furthermore, we determine the frequency dependent dielectric function ${\epsilon }(\omega)={(n+ik)}^{2}$ of plant material in the range 28 ≤ ω ≤ 58 THz, and show how the environmental chemical variation is imprinted in the nanoscale variability of n and k . This nanometrology is a promise for further progress in the development of plant-based (meta-)materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electronically transparent graphene replicas of diatoms: a new technique for the investigation of frustule morphology

The morphogenesis of the silica cell walls (called frustules) of unicellular algae known as diatoms is one of the most intriguing mysteries of the diatoms. To study frustule morphogenesis, optical, electron and atomic force microscopy has been extensively used to reveal the frustule morphology. However, since silica frustules are opaque, past observations were limited to outer and fracture surfaces, restricting observations of interior structures. Here we show that opaque silica frustules can be converted into electronically transparent graphene replicas, fabricated using chemical vapor deposition of methane. Chemical vapor deposition creates a continuous graphene coating preserving the frustule’s shape and fine, complicated internal features. Subsequent dissolution of the silica with hydrofluoric acid yields a free-standing replica of the internal and external native frustule morphologies. Electron microscopy renders these graphene replicas highly transparent, revealing previously unobserved, complex, three-dimensional, interior frustule structures, which lend new insights into the investigation of frustule morphogenesis.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Synchrotron-based X-ray fluorescence microscopy enables multiscale spatial visualization of ions involved in fungal lignocellulose deconstruction

Ions play an important role in the growth and development of filamentous fungi, particularly in the fungal decay process of lignocellulose materials. The role of ions in wood degradation, and more broadly fungal metabolism, have implications for diverse research disciplines ranging from plant pathology and forest ecology, to wood protection. Despite the importance of ions in both enzymatic and non-enzymatic fungal decay mechanisms, the spatial distribution of ions in wood and fungal hyphae during decay is not known. Here we employ synchrotron based X-ray fluorescence microscopy (XFM) to map physiologically relevant ions, such as K, Ca, Mn, Fe, and Zn, in wood being decayed by the model brown rot fungus Serpula lacrymans . Two-dimensional XFM maps were obtained to study the ion spatial distributions from mm to submicron length scales in wood and hyphae. Three-dimensional ion volume reconstructions with submicron spatial resolution were also acquired of wood cell walls and fungal hyphae, and an estimation of oxalate concentration at the microscale was made. Results show that the fungus actively transports some ions, such as Fe, into the wood and controls the distribution of ions at both the bulk wood and cellular length scales. Within the fungal hyphae, ion volume reconstructions show inhomogeneous ion distributions at the micron length scale and this localization may be indicative of both physiological status and requirements or in some cases, potentially sites associated with the initiation of metal-catalyzed wood degradation. Finally, these measurements illustrate how synchrotron based XFM is uniquely qualified for probing the role of ions in the growth and metabolic processes of filamentous fungi.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Lignin Valorization: Emerging Approaches

Lignin, an aromatic biopolymer found in plant cell walls, is a key component of lignocellulosic biomass and generally utilized for heat and power. However, lignin's chemical composition makes it an attractive source for biological and catalytic conversion to fuels and chemicals. Bringing together experts from biology, catalysis, engineering, analytical chemistry, and techno-economic/life-cycle analysis, Lignin Valorization presents a comprehensive, interdisciplinary picture of how lignocellulosic biorefineries could potentially employ lignin valorization technologies. Chapters will specifically focus on the production of fuels and chemicals from lignin and topics covered include (i) methods for isolating lignin in the context of the lignocellulosic biorefinery, (ii) thermal, chemo-catalytic, and biological methods for lignin depolymerization, (iii) chemo-catalytic and biological methods for upgrading lignin, (iv) characterization of lignin, and (v) techno-economic and life-cycle analysis of integrated processes to utilize lignin in an integrated biorefinery. The book provides the latest breakthroughs and challenges in upgrading lignin to fuels and chemicals for graduate students and researchers in academia, governmental laboratories, and industry interested in biomass conversion.

09 BIOMASS FUELS↗
DOE OSTI2018

Chapter 1: A Brief Introduction to Lignin Structure

Lignin is an alkyl-aromatic polymer found in the cell walls of terrestrial plants. Lignin provides structure and rigidity to plants, is a natural, highly effective barrier against microbial attack, and enables water and nutrient transport through plant tissues. Depending on the plant species, the constituents of lignin can vary considerably, leading to substantial diversity in lignin chemistry and structure. Despite nearly a century of research and development attempting to convert lignin into valuable products, lignin in most current and planned biorefinery contexts remains underutilized, most often being burned to generate heat and power. However, the drive towards effective lignin valorization processes has witnessed a significant resurgence in the past decade, catalyzed by advances in improved understanding of lignin chemistry, structure, and plasticity in parallel with new catalytic and biological approaches to valorize this important, prevalent biopolymer. As a preface to the subsequent chapters in this book, this chapter briefly highlights the known aspects of lignin structure.

09 BIOMASS FUELS↗
DOE OSTI2014

Why genetic modification of lignin leads to low-recalcitrance biomass

Genetic modification of plants via down-regulation of cinnamyl alcohol dehydrogenase leads to incorporation of aldehyde groups in the lignin polymer. Moreover, the resulting lignocellulosic biomass has increased bioethanol yield. However, a molecular-scale explanation of this finding is currently lacking. We perform molecular dynamics simulation of the copolymer with hemicellulose of wild type and the genetically modified lignin, in aqueous solution. We find that the non-covalent association with hemicellulose of lignin containing aldehyde groups is reduced compared to the wild-type. This phase separation may increase the cell wall porosity in the mutant plants, thus explaining their easier deconstruction to biofuels. The thermodynamic origin of the reduced lignin-hemicellulose association is found to be a more favorable self-interaction energy and less favorable interaction with hemicellulose for the mutant lignin. Furthermore, reduced hydration water density fluctuations are found for the mutant lignin, implying a more hydrophobic lignin surface. Our results provide a detailed description of how aldehyde incorporation makes lignin more hydrophobic and reduces its association with hemicellulose, thus suggesting that increased lignin hydrophobicity may be an optimal characteristic required for improved biofuel production.

09 BIOMASS FUELS↗
DOE OSTI2017

Lignocellulose fermentation and residual solids characterization for senescent switchgrass fermentation by Clostridium thermocellum in the presence and absence of continuous in situ ball-milling

Milling during lignocellulosic fermentation, henceforth referred to as cotreatment, is investigated as an alternative to thermochemical pretreatment as a means of enhancing biological solubilization of lignocellulose. We investigate the impact of milling on soluble substrate fermentation by Clostridium thermocellum with comparison to yeast, document solubilization for fermentation of senescent switchgrass with and without ball milling, and characterize residual solids. Soluble substrate fermentation by C. thermocellum proceeded readily in the presence of continuous ball milling but was completely arrested for yeast. Total fractional carbohydrate solubilization achieved after fermentation of senescent switchgrass by C. thermocellum for 5 days was 0.45 without cotreatment or pretreatment, 0.81 with hydrothermal pretreatment (200 degrees C, 15 minutes, severity 4.2), and 0.88 with cotreatment. Acetate and ethanol were the main fermentation products, and were produced at similar ratios with and without cotreatment. Analysis of solid residues was undertaken using molecular beam mass spectrometry (PyMBMS) and solid-state nuclear magnetic resonance spectroscopy (NMR) in order to provide insight into changes in plant cell walls during processing via various modes. The structure of lignin present in residual solids remaining after fermentation with cotreatment appeared to change little, with substantially greater changes observed for hydrothermal pretreatment - particularly with respect to formation of C-C bonds. The observation of high solubilization with little apparent modification of the residue is consistent with cotreatment enhancing solubilization primarily by increasing the access of saccharolytic enzymes to the feedstock, and C. thermocellum being able to attack all the major linkages in cellulosic biomass provided that these linkages are accessible.

09 BIOMASS FUELS↗
DOE OSTI2017

Effects of organosolv and ammonia pretreatments on lignin properties and its inhibition for enzymatic hydrolysis

Lignin offers structural support and protection for plant cell walls; but, it also contributes to biomass recalcitrance and the costs of biofuel production via the biological pathway. Organosolv and ammonia pretreatments have been developed to reduce biomass recalcitrance and improve sugar release performance during enzymatic hydrolysis. It is believed that lignin properties are related to its inhibition on enzymatic hydrolysis; therefore, understanding the characteristics of lignin is a key for effective biomass conversion to biofuels. In this study, an organosolv pretreatment using 60% ethanol with 1.25% H 2 SO 4 significantly deconstructed poplar lignin and reduced its molecular weights due to the cleavage of lignin inter-unit linkages. The organosolv pretreatment increased the contents of phenolic OH units and the lignin residue showed a high cellulase maximum adsorption capacity. Ammonia pretreatment with 5% ammonium hydroxide was not as effective as organosolv pretreatment on lignin deconstruction. Organosolv lignin residue had lower lignin S/G ratio than the untreated one. Furthermore, when compared to the organosolv lignin residue and untreated lignin, ammonia lignin residue had a higher cellulase adsorption affinity. In addition, the effects of lignin on cellulose hydrolysis was investigated and the results suggested that the presence of lignin with cellulose substrates reduced cellulose hydrolysis, and its inhibitory effect was primarily determined by the lignin properties after each pretreatment. The organosolv pretreatment resulted in a slightly lower cellulase binding strength (249.7 mL g -1 ) on poplar lignin than that on untreated samples (261.1 mL g -1 ), while ammonia lignin residue showed a higher cellulase binding strength (402.8 mL g -1 ) and had more significant inhibition effect on cellulose hydrolysis. Our results demonstrated that the binding strength significantly affected the lignin-derived inhibition on enzymatic hydrolysis of cellulose in the cellulose-lignin mixtures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Temperature-dependent phase behaviour of tetrahydrofuran–water alters solubilization of xylan to improve co-production of furfurals from lignocellulosic biomass

Xylose, Xylan, Hemicellulose, CELF, THF, Co-solvent, Pretreatment, Biomass ABSTRACT: Xylan is an important polysaccharide found in the hemicellulose fraction of lignocellulosic biomass that can be hydrolysed to xylose and further dehydrated to the furfural, an important renewable platform fuel precursor. Here, pairing molecular simulation and experimental evidences, we reveal how the unique temperature-dependent phase behaviour of water-tetrahydrofuran (THF) co-solvent can delay xylan solubilization to synergistically improve catalytic co-processing of biomass to furfural and 5-HMF. Our results indicate, based on polymer correlations between polymer conformational behaviour and solvent quality, that both co-solvent and aqueous environments serve as ‘good’ solvents for xylan. Interestingly, the simulations also revealed that unlike other cell-wall components (i.e., lignin and cellulose), the make-up of the solvation shell of xylan in THF-water is dependent on the temperature-phase behaviour. At temperatures between 333K and 418K, THF and water become immiscible, and THF is evacuated from the solvation shell of xylan, while above and below this temperature range, THF and water are both present in the polysaccharide’s solvation shell. This suggested that the solubilization of xylan in THF-water may be similar to aqueous-only solutions at temperatures between 333K and 418K and different outside this range. Experimental reactions on beachwood xylan corroborate this hypothesis by demonstrating 2-fold reduction of xylan solubilization in THF-water within a miscible temperature regime (445K) and unchanged solubilization within an immiscible regime (400K). Translating this phase-dependent behaviour to processing of maple wood chips, we demonstrate how the weaker xylan solvation in THF-water under miscible conditions can delay furfural production from xylose, allowing 5-HMF production from cellulose to “catch-up” such that their high yield production from biomass can be synergized in a single pot reaction.

09 BIOMASS FUELS↗
DOE OSTI2018

Impact of hydration and temperature history on the structure and dynamics of lignin

The full utilization of plant biomass for the production of energy and novel materials often involves high temperature treatment. Examples include melt spinning of lignin for manufacturing low-cost carbon fiber and the relocalization of lignin to increase the accessibility of cellulose for production of biofuels. These temperature-induced effects arise from poorly understood changes in lignin flexibility. Here, we combine molecular dynamics simulations with neutron scattering and dielectric spectroscopy experiments to probe the dependence of lignin dynamics on hydration and thermal history. We find a dynamical and structural hysteresis: at a given temperature, the lignin molecules are more expanded and their dynamics faster when the lignin is cooled than when heated. The structural hysteresis is more pronounced for dry lignin. The difference in dynamics, however, follows a different trend, it is found to be more significant at high temperatures and high hydration levels. The simulations also reveal syringyl units to be more dynamic than guiacyl. The results provide an atomic-detailed description of lignin dynamics, important for understanding lignin role in plant cell wall mechanics and for rationally improving lignin processing. The lignin glass transition, at which the polymer softens, is lower when lignin is cooled than when heated, therefore extending the cooling phase of processing and shortening the heating phase may offer ways to lower processing costs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Dynamics of the lignin glass transition

The dynamics of lignin, a complex and heterogeneous major plant cell-wall macromolecule, is of both fundamental and practical importance. Lignin is typically heated to temperatures above its glass transition to facilitate its industrial processing. Here, we performed molecular dynamics simulations to investigate the segmental (α) relaxation of lignin, the dynamical process that gives rise to the glass transition. It is found that lignin dynamics involves mainly internal motions below T g , while segmental inter-molecular motions are activated above T g . The segments whose mobility is enhanced above T g consist of 3–5 lignin monomeric units. The temperature dependence of the lignin segmental relaxation time changes from Arrhenius below T g to Vogel–Fulcher–Tamman above T g . This change in temperature dependence is determined by the underlying energy landscape being restricted below T g but exhibiting multiple minima above T g . The Q-dependence of the relaxation time is found to obey a power-law up to Q max , indicative of sub-diffusive motion of lignin above T g . Temperature and hydration affect the segmental relaxation similarly. Increasing hydration or temperature leads to: (1) the α process starting earlier, i.e. the beta process becomes shortened, (2) Q max decreasing, i.e. the lengthscale above which subdiffusion is observed increases, and (3) the number of monomers constituting a segment increasing, i.e. the motions that lead to the glass transition become more collective. The above findings provide molecular-level understanding of the technologically important segmental motions of lignin and demonstrate that, despite the heterogeneous and complex structure of lignin, its segmental dynamics can be described by concepts developed for chemically homogeneous polymers.

09 BIOMASS FUELS↗
DOE OSTI2019

A critical review on the analysis of lignin carbohydrate bonds

Replacing fossil-based resources with renewable alternatives is generally acknowledged as a critical component to address several of today's environmental concerns. In this context, lignocellulosic biomass is an attractive, sustainable resource. Yet, the constitutional biopolymers of interest are locked in the structural complexity of the plant cell walls, which defines their properties and contributes to fractionation recalcitrance. One of the key elements restricting fractionation of the biopolymers in high yield is the presence of lignin–carbohydrate bonds forming a matrix referred to as lignin–carbohydrate complex (LCC). Nonetheless, covalent bonds between lignin and carbohydrates, remain one of the most controversial topics in lignocellulose chemistry. This challenge can be attributed to the slow progress made in their research, which also forms the basis for this review. Herein, we will critically discuss the literature with a particular focus on the latest characterization and analytical techniques. Discussions on existing techniques and, importantly the drawbacks with them should be compelling to researchers in the area, especially at this time when crucial issues surrounding the realization of biorefineries need to be addressed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Cellulolytic enzyme-aided extraction of hemicellulose from switchgrass and its characteristics

The isolation of biomass components with their intact structure is integral for understanding the characteristics of biomass. Compared to other major biomass components such as cellulose and lignin, hemicellulose remains a challenging component to be isolated from the plant cell wall without significant depolymerization and modification. Here, a novel cellulolytic enzyme-aided hemicellulose (CEH) isolation method was developed to isolate hemicellulose with a near-native branched structure from switchgrass. The structural characteristics of CEH were investigated and compared with hemicelluloses isolated by conventional alkaline extracted hemicellulose (AEH) and DMSO extracted hemicellulose (DMSOH) methods. Gel permeation chromatography (GPC) analysis indicated that CEH had a weight-average molecular weight of 44 kDa, which was comparable to that of AEH (43 kDa) but higher than that of DMSOH (37 kDa). The chemical composition analysis revealed that CEH retained a higher proportion of glucuronic acid compared to AEH and DMSOH. The 2D 13 C– 1 H heteronuclear single quantum coherence (HSQC) NMR spectra containing the β-(1,4)-linked-D-xylan backbone, non-reducing-end peaks and both α- and β-reducing-end peaks in CEH were comparable to the spectra of the commercial beechwood xylan. CEH showed a highly branched hemicellulose structure, which retained methoxyl groups, O -acetyl groups, and 4- O -methyl-glucuronic acid attached to the xylan backbone.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Tunable, Bacterio-Instructive Scaffolds Made from Functional Graphenic Materials

The balance of bacterial populations in the human body is critical for human health. Researchers have aimed to control bacterial populations using antibiotic substrates. However, antibiotic materials that non-selectively kill bacteria can compromise health by eliminating beneficial bacteria, which leaves the body vulnerable to colonization by harmful pathogens. Due to their chemical tunablity and unique surface properties, graphene oxide (GO)-based materials – termed “functional graphenic materials” (FGMs) – have been previously designed to be antibacterial but have the capacity to actively adhere and instruct probiotics to maintain human health. Numerous studies have demonstrated that negatively and positively charged surfaces influence bacterial adhesion through electrostatic interactions with the negatively charged bacterial surface. We found that tuning the surface charge of FGMs provides an avenue to control bacterial attachment without compromising vitality. Using E. coli as a model organism for gram-negative bacteria, we demonstrate that negatively charged Claisen graphene (CG), a reduced and carboxylated FGM, is bacterio-repellent through electrostatic repulsion with the bacterial surface. Though positively charged poly-L-lysine (PLL) is antibacterial when free in solution by inserting into the bacterial cell wall, here, we found that covalent conjugation of PLL to CG (giving PLLn-G) masks the antimicrobial activity of PLL by restricting polypeptide mobility. This allows the immobilized positive charge of the PLLn-Gs to be leveraged for E. coli adhesion through electrostatic attraction. We identified the magnitude of positive charge of the PLLn-G conjugates, which is modulated by the length of the PLL peptide, as an important parameter to tune the balance between the opposing forces of bacterial adhesion and proliferation. We also tested adhesion of gram-positive B. subtilis to these FGMs and found that the effect of FGM charge is less pronounced. B. subtilis adheres nondiscriminatory to all FGMs, regardless of charge, but adhesion is scarce and localized. Overall, this work demonstrates that FGMs can be tuned to selectively control bacterial response, paving the way for future development of FGM-based biomaterials as bacterio-instructive scaffolds through careful design of FGM surface chemistry.

Eckhart, Karoline E.↗
DOE OSTI2020

Natural deep eutectic solvent mediated extrusion for continuous high-solid pretreatment of lignocellulosic biomass

Several deep eutectic solvents (DESs) have been demonstrated to be highly effective for lignocellulosic biomass pretreatment, combining the advantages of simple synthesis, relatively low chemical cost and better biocompatibility. However, low biomass loading that is usually involved with DES pretreatment hinders its practical use. Here, a twin-screw extruder was used for pretreating biomass sorghum bagasse at solid loadings up to 50%, mediated by a neutral-pH DES, choline chloride : glycerol (ChCl : Gly). This continuous extrusion process led to high glucose and xylose yields of >85% from enzymatic saccharification of the pretreated sorghum. A combination of microscopic, spectroscopic, and X-ray diffraction analyses demonstrate a high degree of defibration and disruption of the biomass cell wall structures; however, little or no change in chemical compositions. Further results from gel permeation chromatographic (GPC) and nuclear magnetic resonance (NMR) spectroscopic analyses indicate that ChCl : Gly-mediated extrusion preserved the basic lignin structural characteristics with no significant differences between extruded biomass at a solid loading of 30% and 50%. This study demonstrates the potential of DES-mediated extrusion as a highly effective continuous high-solid biomass pretreatment technology for industrially relevant applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Enhancing the multi-functional properties of renewable lignin carbon fibers via defining the structure–property relationship using different biomass feedstocks

Lignin has been explored extensively as a renewable precursor for carbon materials, considering its abundance as a major component of plant cell walls and its sustainability as a byproduct of both lignocellulosic biorefinery and the paper-making industry. Despite the extensive efforts to define the process–property relationship, it remains largely unknown how lignin biosynthesis and its chemistry would impact the resultant carbon fiber properties, for both mechanical and electroconductive performances. Such inadequate understanding fundamentally limits feedstock design and selection to improve carbon fiber properties toward broader commercial applications. Using lignin from a broad range of biomass feedstocks for carbon fiber manufacturing, we have fundamentally explored the structure–function relationship between lignin chemistry and carbon fiber performance. Specifically, lignin extracted from hardwood (sugar maple), softwood (loblolly pine and red cedar), and herbaceous plants (corn stover and switchgrass) was used for carbon fiber manufacturing, considering the very different lignin structures from these feedstocks. Linear regression models were established to define the relationship between carbon fiber mechanical properties and lignin structural characteristics. The results highlighted that the content of β-O-4 linkages correlates significantly with the tensile strength and elastic modulus of lignin carbon fibers, indicating that more linear β-O-4 linkages would promote the carbon fiber mechanical performance. Moreover, electroconductive properties are essential for broader energy device application of lignin-based carbon fibers, yet the mechanisms controlling their electroconductivity are largely unknown. Furthermore, we hereby demonstrated that a higher β-O-4 content also promotes the electroconductivity of lignin carbon fibers. Microstructure analysis further revealed that the crystallite size and content of the pre-graphitic turbostratic carbon structure in lignin-based carbon fibers were enhanced as the β-O-4 linkages increased. The content of β-O-4 linkages has shown a strong correlation with the crystallite content in a linear regression model. This study thus revealed the underlying mechanisms regarding how the lignin structure in planta defines the resultant carbon fiber properties. Moreover, the study also highlighted the correlation between the mechanical and electroconductive properties of lignin-based carbon fibers, both of which were defined by the lignin structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗