Enhancement of cellulose saccharification kinetics using an ionic liquid pretreatment step

X-ray scattering based scanning tomography for imaging and structural characterization of cellulose in plants

X-ray and neutron scattering have long been used for structural characterization of cellulose in plants. Due to averaging over the illuminated sample volume, these measurements traditionally overlooked the compositional and morphological heterogeneity within the sample. Here, a scanning tomographic imaging method is described, using contrast derived from the X-ray scattering intensity, for virtually sectioning the sample to reveal its internal structure at a resolution of a few micrometres. This method provides a means for retrieving the local scattering signal that corresponds to any voxel within the virtual section, enabling characterization of the local structure using traditional data-analysis methods. This is accomplished through tomographic reconstruction of the spatial distribution of a handful of mathematical components identified by non-negative matrix factorization from the large dataset of X-ray scattering intensity. Joint analysis of multiple datasets, to find similarity between voxels by clustering of the decomposed data, could help elucidate systematic differences between samples, such as those expected from genetic modifications, chemical treatments or fungal decay. The spatial distribution of the microfibril angle can also be analyzed, based on the tomographically reconstructed scattering intensity as a function of the azimuthal angle.

Microwave Encounters Ionic Liquid: Synergistic Mechanism, Synthesis and Emerging Applications

Progress in microwave (MW) energy application technology has stimulated remarkable advances in manufacturing and high-quality applications of ionic liquids (ILs) that are generally used as novel media in chemical engineering. This Review focuses on an emerging technology via the combination of MW energy and the usage of ILs, termed microwave-assisted ionic liquid (MAIL) technology. In comparison to conventional routes that rely on heat transfer through media, the contactless and unique MW heating exploits the electromagnetic wave-ions interactions to deliver energy to IL molecules, accelerating the process of material synthesis, catalytic reactions, and so on. In addition to the inherent advantages of ILs, including outstanding solubility, and well-tuned thermophysical properties, MAIL technology has exhibited great potential in process intensification to meet the requirement of efficient, economic chemical production. Here we start with an introduction to principles of MW heating, highlighting fundamental mechanisms of MW induced process intensification based on ILs. Next, the synergies of MW energy and ILs employed in materials synthesis, as well as their merits, are documented. The emerging applications of MAIL technologies are summarized in the next sections, involving tumor therapy, organic catalysis, separations, and bioconversions. Finally, the current challenges and future opportunities of this emerging technology are discussed.

Green chemical and hybrid enzymatic pretreatments for lignocellulosic biorefineries: Mechanism and challenges

The greener chemical and enzymatic pretreatments for lignocellulosic biomasses are portraying a crucial role owing to their recalcitrant nature. Traditional pretreatments lead to partial degradation of lignin and hemicellulose moieties from the pretreated biomass. But it still restricts the enzyme accessibility for the digestibility towards the celluloses and the interaction of lignin-enzymes, nonproductively. Moreover, incursion of certain special chemical treatments and other lignin sulfonation techniques to the enzymatic pretreatment (hybrid enzymatic pretreatment) enhances the lignin structural modification, solubilization of the hemicelluloses and both saccharification and fermentation processes (SAF). This article concentrates on recent developments in various chemical and hybrid enzymatic pretreatments on biomass materials with their mode of activities. Furthermore, the issues on strategies of the existing pretreatments towards their industrial applications are highlighted, which could lead to innovative ideas to overcome the challenges and give guideline for the researchers towards the lignocellulosic biorefineries.

Challenging DESs and ILs in the valorization of food waste: a case study

In this study, the efficacy of two of the best performing green solvents for the fractionation of lignocellulosic biomass, cholinium arginate (ChArg) as biobased ionic liquid (Bio-IL) and ChCl:lactic acid (ChCl:LA, 1:10) as natural deep eutectic solvent (NADES), was investigated and compared in the pretreatment of an agri-food industry waste, apple fibers (90°C for 1 h). For the sake of comparison, 1-butyl-3-methylimidazolium acetate (BMIM OAc) as one of the best IL able to dissolve cellulose was also used. After the pretreatment, two fractions were obtained in each case. The results gathered through FTIR and TG analyses of the two materials and the subsequent DNS assay performed after enzymatic treatment led to identify ChArg as the best medium to delignify and remove waxes, present on the starting apple fibers, thus producing a material substantially enriched in cellulose (CRM). Conversely, ChCl:LA did not provide satisfactorily results using these mild conditions, while BMIM OAc showed intermediate performance probably on account of the reduced crystallinity of cellulose after the dissolution-regeneration process. To corroborate the obtained data, FTIR and TG analyses were also performed on the residues collected after the enzymatic hydrolysis. At the end of the pretreatment, ChArg was also quantitatively recovered without significant alterations.

Effect of different ionic liquids and organic solvents on the structural and physicochemical properties of cellulose-protein complexes extracted from Se-enriched peanut leaves

Abundant cellulose and insoluble protein were contained in the Se-enriched peanut leaf residue, a by-product from leaf protein extraction. Ionic liquids (ILs) were used to extract the cellulose-protein complexes (CPCs) from Se-enriched peanut leaf residue. The effects of various ILs as extractants and organic solvents as regenerant on the physicochemical properties of CPCs were compared. The results showed that the yield of CPCs and recovery yield of [AMIM]Cl (1-allyl-3-methylimidazole chloride) were better than those of [BMIM]Cl (1-butyl-3-methylimidazolium chloride). Simultaneously, it could be seen from the infrared absorption peaks and secondary structure fitting results that [BMIM]Cl seemed stronger than [AMIM]Cl in destroying the secondary structure of CPCs. Scanning electron microscope (SEM) showed that the CPCs extracted by [BMIM]Cl were lamellate with holes on the surface, and the CPCs extracted by [AMIM]Cl were rough, almost without holes on the surface. Furthermore, the transmittance and tensile strength of the film which contained BA-CPC ([BMIM]Cl as extractant and acetonitrile as regenerant) film were better than those contained AA-CPC ([AMIM]Cl as extractant and acetonitrile as regenerant) film, which might be mainly because the types of ILs and regenerants affect the particle size of CPCs, thereby influencing the mechanical properties of the film.

Co-immobilization of Cellulase and β-Glucosidase into Mesoporous Silica Nanoparticles for the Hydrolysis of Cellulose Extracted from Eriobotrya japonica Leaves

Fungal cellulases generally contain a reduced amount of β-glucosidase (BG), which does not allow for efficient cellulose hydrolysis. To address this issue, we implemented an easy co-immobilization procedure of β-glucosidase and cellulase by adsorption on wrinkled mesoporous silica nanoparticles with radial and hierarchical open pore structures, exhibiting smaller (WSN) and larger (WSN-p) inter-wrinkle distances. The immobilization was carried out separately on different vectors (WSN for BG and WSN-p for cellulase), simultaneously on the same vector (WSN-p), and sequentially on the same vector (WSN-p) in order to optimize the synergy between cellulase and BG. The obtained results pointed out that the best biocatalyst is that prepared through simultaneous immobilization of BG and cellulase on the same vector (WSN-p). In this case, the adsorption resulted in 20% yield of immobilization, corresponding to an enzyme loading of 100 mg/g of support. 82% yield of reaction and 72 μmol/min·g activity were obtained, evaluated for the hydrolysis of cellulose extracted from Eriobotrya japonica leaves. All reactions were carried out at a standard temperature of 50 °C. The biocatalyst retained 83% of the initial yield of reaction after 9 cycles of reuse. Moreover, it had better stability than the free enzyme mixture in a wide range of temperatures, preserving 72% of the initial yield of reaction up to 90 °C.

Preparation, Characterization and Application of Amorphized Cellulose-A Review

This review describes the methods of cellulose amorphization, such as dry grinding, mercerization, treatment with liquid ammonia, swelling in solvents, regeneration from solutions, etc. In addition, the main characteristics and applications of amorphized celluloses are discussed. An optimal method for preparing completely amorphous cellulose (CAC) via the treatment of original cellulose material with a cold NaOH/Urea-solvent at the solvent to cellulose ratio R ≥ 5 is proposed. Structural studies show that amorphous cellulose contains mesomorphous clusters with a size of 1.85 nm and specific gravity of 1.49 g/cm³. Furthermore, each such cluster consists of about five glucopyranose layers with an average interlayer spacing of 0.45 nm. Amorphous cellulose is characterized by increased hydrophilicity, reactivity, and enzymatic digestibility. Due to its amorphous structure, the CAC can be used as a promising substrate for enzymatic hydrolysis to produce glucose, which can be applied in biotechnology for growing various microorganisms. In addition, the application of CAC in agriculture is described. A waste-free method for producing amorphous nanocellulose is considered, and the main applications of nanosized amorphous cellulose are discussed.

Dissolution pretreatment of cellulose by using levulinic acid-based protic ionic liquids towards enhanced enzymatic hydrolysis

In this study, an economically competitive and sustainable levulinic acid-based protic ionic liquids were identified to be good solvents for the dissolution pretreatment of cellulose towards enhanced enzymatic hydrolysis. The influences of protic ionic liquids species, dissolution pretreatment time, and pretreatment temperature on the physico-chemical structures of cellulose were systematically investigated by various analytical techniques. The findings indicate that the pretreatment efficiency was correlated to the basicity of the organic bases, and the presence of ketone group in the levulinate anion with particular hydrogen bonding forming ability via keto-enol tautomerism. The DBN derived protic ionic liquids exhibited best performance at 100 °C in 1 h, as evidenced by a 94% glucose yield. This solvent system was also suitable for the dissolution pretreatment of corn stover-based lignocellulosic biomass for sugars production, although a higher temperature and longer pretreatment time was required. Furthermore, the solvent system could be recycled and reused.

Ionic liquid pretreatment of stinging nettle stems and giant miscanthus for bioethanol production

Production of ethanol from lignocellulosic biomass is considered the most promising proposition for developing a sustainable and carbon-neutral energy system. The use of renewable raw materials and variability of lignocellulosic feedstock generating hexose and pentose sugars also brings advantages of the most abundant, sustainable and non-food competitive biomass. Great attention is now paid to agricultural wastes and overgrowing plants as an alternative to fast-growing energetic crops. The presented study explores the use of stinging nettle stems, which have not been treated as a source of bioethanol. Apart from being considered a weed, stinging nettle is used in pharmacy or cosmetics, yet its stems are always a non-edible waste. Therefore, the aim was to evaluate the effectiveness of pretreatment using imidazolium- and ammonium-based ionic liquids, enzymatic hydrolysis, fermentation of stinging nettle stems, and comparison of such a process with giant miscanthus. Raw and ionic liquid-pretreated feedstocks of stinging nettle and miscanthus were subjected to compositional analysis and scanning electron microscopy to determine the pretreatment effect. Next, the same conditions of enzymatic hydrolysis and fermentation were applied to both crops to explore the stinging nettle stems potential in the area of bioethanol production. The study showed that the pretreatment of both stinging nettle and miscanthus with imidazolium acetates allowed for increased availability of the critical lignocellulosic fraction. The use of 1-butyl-3-methylimidazolium acetate in the pretreatment of stinging nettle allowed to obtain very high ethanol concentrations of 7.3 g L^-1, with 7.0 g L^-1 achieved for miscanthus. Results similar for both plants were obtained for 1-ethyl-3-buthylimidazolium acetate. Moreover, in the case of ammonium ionic liquids, even though they have comparable potential to dissolve cellulose, it was impossible to depolymerize lignocellulose and extract lignin. Furthermore, they did not improve the efficiency of the hydrolysis process, which in turn led to low alcohol concentration. Overall, from the presented results, it can be assumed that the stinging nettle stems are a very promising bioenergy crop.

Cellulose-deconstruction potential of nano-biocatalytic systems: A strategic drive from designing to sustainable applications of immobilized cellulases

Nanostructured materials along with an added value of polymers-based support carriers have gained high interest and considered ideal for enzyme immobilization. The recently emerged nanoscience interface in the form of nanostructured materials combined with immobilized-enzyme-based bio-catalysis has now become research and development frontiers in advance and applied bio-catalysis engineering. With the involvement of nanoscience, various polymers have been thoroughly developed and exploited to nanostructured engineer constructs as ideal support carriers/matrices. Such nanotechnologically engineered support carriers/matrix possesses unique structural, physicochemical, and functional attributes which equilibrate principal factors and strengthen the biocatalysts efficacy for multipurpose applications. In addition, nano-supported catalysts are potential alternatives that can outstrip several limitations of conventional biocatalysts, such as reduced catalytic efficacy and turnover, low mass transfer efficiency, instability during the reaction, and most importantly, partial, or complete inhibition/deactivation. In this context, engineering robust and highly efficient biocatalysts is an industrially relevant prerequisite. This review comprehensively covered various biopolymers and nanostructured materials, including silica, hybrid nanoflower, nanotubes or nanofibers, nanomembranes, graphene oxide nanoparticles, metal-oxide frameworks, and magnetic nanoparticles as robust matrices for cellulase immobilization. The work is further enriched by spotlighting applied and industrially relevant considerations of nano-immobilized cellulases. For instance, owing to the cellulose-deconstruction features of nano-immobilized cellulases, the applications like lignocellulosic biomass conversion into industrially useful products or biofuels, improved paper sheet density and pulp beat in paper and pulp industry, fruit juice clarification in food industry are evident examples of cellulases, thereof are discussed in this work.

Optimization of biogas yield from lignocellulosic materials with different pretreatment methods: a review

Population increase and industrialization has resulted in high energy demand and consumptions, and presently, fossil fuels are the major source of staple energy, supplying 80% of the entire consumption. This has contributed immensely to the greenhouse gas emission and leading to global warming, and as a result of this, there is a tremendous urgency to investigate and improve fresh and renewable energy sources worldwide. One of such renewable energy sources is biogas that is generated by anaerobic fermentation that uses different wastes such as agricultural residues, animal manure, and other organic wastes. During anaerobic digestion, hydrolysis of substrates is regarded as the most crucial stage in the process of biogas generation. However, this process is not always efficient because of the domineering stableness of substrates to enzymatic or bacteria assaults, but substrates' pretreatment before biogas production will enhance biogas production. The principal objective of pretreatments is to ease the accessibility of the enzymes to the lignin, cellulose, and hemicellulose which leads to degradation of the substrates. Hence, the use of pretreatment for catalysis of lignocellulose substrates is beneficial for the production of cost-efficient and eco-friendly process. In this review, we discussed different pretreatment technologies of hydrolysis and their restrictions. The review has shown that different pretreatments have varying effects on lignin, cellulose, and hemicellulose degradation and biogas yield of different substrate and the choice of pretreatment technique will devolve on the intending final products of the process.

Increased mixing intensity is not necessary for more efficient cellulose hydrolysis at high solid loading

To enhance the cellulose hydrolysis at high solid loadings, an increased mixing intensity is generally required for the high solid loading hydrolysis, while it leads to higher energy consumption. In this study, the impact of mixing intensity on cellulose conversion during hydrolysis at different solid loadings were systematically studied. It was found that the increased mixing intensity is not necessary for more efficient cellulose hydrolysis. For cellulose hydrolysis at higher solid loadings, a lower mixing intensity is needed for a higher cellulose conversion. Although the increased mixing intensity promoted enzyme adsorption, it strengthened product inhibition and caused severer enzyme deactivation. Besides, mixing at the initial stage of cellulose hydrolysis was more crucial, while continuous mixing throughout the hydrolysis was not required for more efficient cellulose hydrolysis. Based on the mechanism study, a combined mixing strategy was developed to achieve efficient cellulose hydrolysis with about two-third reduction in energy consumption.

Treatment and characterization of biomass of soybean and rice hulls using ionic liquids for the liberation of fermentable sugars

We investigated the changes in the physical structure of cellulose recovered from soybean and rice hulls treated with the ionic liquids 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) and 1-butyl-3-methylimidazolium acetate ([bmim][Ac]). The characterization was carried out by a combination of thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Regenerated cellulose from soybean hull showed loss of crystallinity and high structural disruption caused by both ionic liquid treatments as compared to the untreated material. In contrast, rice hull presented only a small structural disruption when treated with [bmim][Ac] and was practically unaffected by [bmim][Cl], showing that this biomass residue is recalcitrance towards physico-chemical treatments, possibly as a consequence of its high composition content in silica. These results suggest the use of soybean hull as a substrate to be treated with ionic liquids in the preparation of lignocellulosic hydrolysates to be used in second-generation ethanol production, whereas other methods should be considered to treat rice hull biomass.

Enzymatic Modification of Cellulose To Unlock Its Exploitation in Advanced Materials

Nowadays natural biopolymers have a wide variety of uses in various industrial applications, such as food, adhesives and composite materials. Among them, cellulose has attracted the interest of researchers due to its properties: high strength and flexibility, biocompatibility and nontoxicity. Despite that, in many cases its practical use is limited because of poor solubility and/or an unsuitable hydrophilic/hydrophobic balance. In this context, enzymatic modification appears as a powerful strategy to overcome these problems through selective, green and environmentally friendly processes. This minireview discusses the different methods developed for the enzymatic modification of cellulose, emphasizing the type of reaction, the enzymes used (laccases, esterases, lipases, hexokinases, etc.), and the properties and applications of the cellulose derivatives obtained. Considering that cellulose is the most abundant natural polymer on Earth and can be derived from residual lignocellulosic biomass, the impact of its use in bio-based process following the logic of the circular economy is relevant.

Lignocellulosic hydrogel from recycled old corrugated container resources using ionic liquid as a green solvent

Lignocellulosic hydrogels are valuable bio-products that have been considered widely in recent investigations. Also, application of low value recycled fibers for high value added products can be of much interest. In this respect, current research has focused on producing hydrogel from recycled old corrugated container (OCC) resources, using 1-butyl-3-methyl-imidazolium chloride ionic liquid (IL) as a green solvent. The results indicated that the IL successfully dissolved OCC fibers, allowing the production of lignocellulosic hydrogel. Considering total water absorption amount as a main criterion for evaluation of hydrogels, the fabricated hydrogel showed promising results (up to 4700% water absorption). X-ray diffraction analysis confirmed obvious reduction in cellulose material crystallinity and crystallite size as a result of the process. Field emission scanning electron microscopy also demonstrated the microstructure of the hydrogel, pore size and shape in the hydrogel, which well supported the laboratory research results. Furthermore, the effect of processing parameters showed that specimens washed with distilled water as the anti-solvent resulted in the highest water absorption. Infrared spectroscopy can be used to suggest the presence of more lignin content in the hydrogel washed with ethanol. Moreover, the best water re-absorption results were observed for the hydrogel washed with distilled water.

Anti-staphylococcal hydrogels based on bacterial cellulose and the antimicrobial biopolyester poly(3-hydroxy-acetylthioalkanoate-co-3-hydroxyalkanoate)

Polymeric hydrogels from bacterial cellulose (BC) have been widely used for the development of wound dressings due to its water holding capacity, its high tensile strength and flexibility, its permeability to gases and liquids, but lacks antibacterial activity. In this work, we have developed novel antimicrobial hydrogels composed of BC and the antimicrobial poly(3-hydroxy-acetylthioalkanoate-co-3-hydroxyalkanoate) (PHACOS). Hydrogels based on different PHACOS contents (20 and 50 wt%) were generated and analysed through different techniques (IR, DSC, TGA, rheology, SEM and EDX) and their bactericidal activity was studied against Staphylococcus aureus. PHACOS20 (BC 80%-PHACOS 20%) hydrogel shows mechanical and thermal properties in the range of human skin and anti-staphylococcal activity (kills 1.8 logs) demonstrating a huge potential for wound healing applications. Furthermore, the cytotoxicity assay using fibroblast cells showed that it keeps cell viability over 85% in all the cases after seven days.

Immobilization of Cellulolytic Enzymes in Mesostructured Silica Materials

Mesostructured silica nanoparticles offer a unique opportunity in the field of biocatalysis thanks to their outstanding properties. The tunable pore size in the range of mesopores allows for immobilizing bulky enzyme molecules. The large surface area improves the catalytic efficiency by increasing enzyme loading and finely dispersing the biocatalyst molecules. The easily tunable pore morphology allows for creating a proper environment to host an enzyme. The confining effect of mesopores can improve the enzyme stability and its resistance to extreme pH and temperatures. Benefits also arise from other peculiarities of nanoparticles such as Brownian motion and easy dispersion. Fossil fuel depletion and environmental pollution have led to the need for alternative sustainable and renewable energy sources such as biofuels. In this context, lignocellulosic biomass has been considered as a strategic fuel source. Cellulases are a class of hydrolytic enzymes that convert cellulose into fermentable sugars. This review is intended to survey the immobilization of cellulolytic enzymes (cellulases and β-glucosidase) onto mesoporous silica nanoparticles and their catalytic performance, with the aim to give a contribution to the urgent action required against climate change and its impacts, by biorefineries’ development.

All-Cellulose Composites: A Review of Recent Studies on Structure, Properties and Applications

Nowadays, there is greater demand for greener materials in societies due to environmental consciousness, depleting fossil fuels and growing ecological concerns. Within the foreseeable future, industries and suppliers will be required to be more aware of challenges faced due to the availability of resources and use more sustainable and renewable raw materials. In this context, cellulose can be expected to become a vital resource for materials owing to its abundance, versatility as a biopolymer, several different forms and potential applications. Thus, all-cellulose composites (ACCs) have gained significant research interest in recent years. ACC is a class of biocomposites in which the matrix is a dissolved and regenerated cellulose, while the reinforcement is undissolved or partly dissolved cellulose. This review paper is intended to provide a brief outline of works that cover recent progress in the manufacturing and processing techniques for ACCs, various cellulose sources, solvents and antisolvents, as well as their properties.

Supercritical Fluids: A Promising Technique for Biomass Pretreatment and Fractionation

Lignocellulosic biomasses are primarily composed of cellulose, hemicelluloses and lignin and these biopolymers are bonded together in a heterogeneous matrix that is highly recalcitrant to chemical or biological conversion processes. Thus, an efficient pretreatment technique must be selected and applied to this type of biomass in order to facilitate its utilization in biorefineries. Classical pretreatment methods tend to operate under severe conditions, leading to sugar losses by dehydration and to the release of inhibitory compounds such as furfural (2-furaldehyde), 5-hydroxy-2-methylfurfural (5-HMF), and organic acids. By contrast, supercritical fluids can pretreat lignocellulosic materials under relatively mild pretreatment conditions, resulting in high sugar yields, low production of fermentation inhibitors and high susceptibilities to enzymatic hydrolysis while reducing the consumption of chemicals, including solvents, reagents, and catalysts. This work presents a review of biomass pretreatment technologies, aiming to deliver a state-of-art compilation of methods and results with emphasis on supercritical processes.

Fast and Efficient Method to Evaluate the Potential of Eutectic Solvents to Dissolve Lignocellulosic Components

The application of eutectic solvents (ESs) in lignocellulosic biomass fractionation has been demonstrated as a promising approach to accomplish efficient and environmentally friendly biomass valorization. In general, ESs are a combination of two components, a hydrogen-bonding donor and a hydrogen-bonding acceptor, in which the melting point of the mixture is lower than that of the individual components. However, there are plenty of possible combinations to form ESs with the potential to apply in biomass processing. Therefore, the development of fast and effective screening methods to find combinations capable to dissolve the main biomass components—namely cellulose, hemicelluloses, and lignin—is highly required. An accurate and simple technique based on optical microscopy with or without polarized lenses was used in this study to quickly screen and monitor the dissolution of cellulose, xylose (a monomer of hemicelluloses), and lignin in several ESs. The dissolution of these solutes were investigated in different choline-chloride-based ESs (ChCl:UREA, ChCl:PROP, ChCl:EtGLY, ChCl:OXA, ChCl:GLY, ChCl:LAC). Small amounts of solute and solvent with temperature control were applied and the dissolution process was monitored in real time. The results obtained in this study showed that cellulose was insoluble in these ESs, while lignin and xylose were progressively dissolved.

Ionic Liquid Tolerance of Yeasts in Family Dipodascaceae and Genus Wickerhamomyces

In previous studies of ionic liquid (IL) tolerance of numerous species of ascomycetous yeasts, two strains of Wickerhamomyces ciferrii and Galactomyces candidus had unusually high tolerance in media containing up to 5% (w/v) of the 1-ethyl-3-methylimidazolium acetate ([C₂C₁Im][OAc]). The study aimed at investigating whether additional strains of these species, and additional species in the Dipodascaceae family, also possess IL tolerance, and to compare sensitivity to the acetate and chloride versions of the ionic liquid. Fifty five yeast strains in the family Dipodascaceae, which encompasses genera Galactomyces, Geotrichum, and Dipodascus, and seven yeast strains of species Wickerhamomyces ciferrii were tested for ability to grow in laboratory medium containing no IL, 242 mM [C₂C₁Im][OAc], or 242 mM [C₂C₁Im]Cl, and in IL-pretreated switchgrass hydrolysate. Many yeasts exhibited tolerance of one or both ILs, with higher tolerance of the chloride anion than of the acetate anion. Different strains of the same species exhibited varying degrees of IL tolerance. Galactomyces candidus, UCDFSTs 52-260, and 50-64, had exceptionally robust growth in [C₂C₁Im][OAc], and also grew well in the switchgrass hydrolysate. Identification of IL tolerant and IL resistant yeast strains will facilitate studies of the mechanism of IL tolerance, which could include superior efflux, metabolism or exclusion.

Zwitterionic Polypeptides: Chemoenzymatic Synthesis and Loosening Function for Cellulose Crystals

A polypeptide with a GlyHisGly repeating sequence containing zwitterionic structures that effectively interact with cellulose was synthesized for dissociation of cellulose crystals. Polypeptide with the GlyHisGly sequence was synthesized by chemoenzymatic polymerization and postfunctionalization of the His residues was performed to afford imidazolium butyrate on the side chains. The resulting zwitterionic polypeptide effectively dissociated bundles of tunicate cellulose nanocrystals, even when the conditions were mild and the concentration of the polypeptide was as low as 1-2 mg mL^-1. Polypeptide treatment also affected the morphology of the cell walls in cultured plant cells, and the cellulose microfibril networks and amorphous polysaccharide layer were dissociated according to atomic force microscopy (AFM). The zwitterionic polypeptide treatment did not change the crystal structure of the cellulose nanocrystals. Analysis of the mechanical properties of the cellulose nanocrystals by force curve measurements using AFM revealed that the elastic modulus of the cellulose nanocrystals increased after treatment with the zwitterionic polypeptide, indicating that the amorphous part of the cellulose nanocrystals was removed by interactions with the polypeptide. At a concentration of the polypeptide that enabled the dissociation of the cellulose network, the zwitterionic polypeptide showed negligible cytotoxicity to the plant cells. The mild and noncytotoxic technique for loosening cellulose microfibrils/nanocrystals that was developed in this study has tremendous significance for the modification of cellulose in terms of polymer chemistry, material science, and plant biotechnology.

Structure and dynamics of ionic liquid tolerant hyperthermophilic endoglucanase Cel12A from Rhodothermus marinus

Economic deconstruction of lignocellulose remains a challenge due to the complex architecture of cellulose, hemicellulose, and lignin. Advancements in pretreatment processes have introduced ionic liquids (ILs) as promising non-derivatizing solvents for reducing biomass recalcitrance and for promoting enzymatic hydrolysis. However, available commercial cellulases are destabilized or inactivated even in low concentration of residual ILs. Thus, a molecular understanding of IL-enzyme interactions is crucial for developing IL-tolerant enzymes with high catalytic activity. In this study, molecular insight behind the IL tolerance of hyperthermophilic endoglucanase Cel12A from Rhodothermus marinus (RmCel12A) has been investigated in 20%, 40%, and 60% 1-ethyl-3-methylimidazolium acetate (EmimAc) through molecular dynamic simulations at 368 K. Though the enzyme retained its stability in all EmimAc concentrations, the activity was affected due to the loss of essential dynamic motions. A protein structure network was constructed using the snapshots of protein structures from the simulation trajectories and the hub properties of residues R20, Y59, W68, W197, E203, and F220 were found to be lost in 60% EmimAc. Emim cations were observed to intrude the active site tunnel and interact with more number of catalytic residues with higher cumulative fractional occupancy in 60% EmimAc than in 20% or 40% EmimAc. Some non-catalytic residues have also been identified at the active site, which can be probable mutation targets for improving the IL tolerance. Our findings reveal the molecular understanding behind the origin of activity loss of RmCel12A and proposed insights for the further improvement of IL sensitivity.

Understanding the behavior of ionic liquid tolerant hyperthermophilic endoglucanase Cel12A from Rhodothermus marinus in different concentrations of EmimAc.

Reversible covalent chemistry of carbon dioxide unlocks the recalcitrance of cellulose for its enzymatic saccharification

To overcoming the natural recalcitrance of cellulose for glucose production via enzymatic hydrolysis, a new strategy of destroying hydrogen bond donor to reconstruct cellulose's hydrogen bonding network was developed via a mild reversible reaction of cellulose with CO₂ catalyzed by organic bases. The reaction dynamics of cellulose with CO₂ in the presence of organic bases was studied by using in situ IR. Investigation also included how the organic bases in pretreatment media and pretreatment parameters including CO₂ pressure, pretreatment temperature and time affected the physical-chemical structure of cellulose by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Atomic force microscopy (AFM) and subsequent enzymatic scarification of cellulose. The findings showed that dissolution activation efficiency significantly correlated to various parameters, that can be optimized to be the tetramethyl guanidine (TMG)/CO₂/DMSO solvent system at 50 °C, 2 MPa of CO₂ for 2 h, by which a complete transformation the cellulose crystalline structure from I to II, and 100% glucose yield were achieved. The recyclability and usability are also investigated.

Pretreatment and fermentation of lignocellulosic biomass: reaction mechanisms and process engineering

At a time of rapid depletion of oil resources, global food shortages and solid waste problems, it is imperative to encourage research into the use of appropriate pre-treatment techniques using regenerative raw materials such as lignocellulosic biomass.

Moderate halophilic bacteria, but not extreme halophilic archaea can alleviate the toxicity of short-alkyl side chain imidazolium-based ionic liquids

Imidazolium-based ionic liquids (IL) with short-alkyl side chain such as 1-ethyl-3-methyl-imidazolium chloride ([Emim]Cl) and 1-butyl-3-methyl-imidazolium chloride ([Bmim]Cl) has immense application potential including in lignocellulosic bioenergy production. But they are toxic to most microorganisms, and those isolated from different environments as IL-tolerant have salt tolerance capabilities. This study evaluates the relationship between salt and [Emim]Cl tolerance of microorganisms using different salinity sediments (2-19%) and brines (35%) of India's largest inland hypersaline lake, Sambhar in Rajasthan as the model system. While samples with 2% and 35% salinities do not yield any [Emim]Cl (100 mM) tolerant colonies, others have 6-50% colonies tolerant to the IL. Similar trend was observed with 50 mM [Bmim]Cl. Moderate halophilic isolates of genera Halomonas and Bacillus (growth in 0.7-3.0 M NaCl) isolated from the sediments could grow in as high as 375 mM [Emim]Cl, or 125 mM [Bmim]Cl facilitated by higher synthesis, and uptake of organic osmolytes; and up to 1.7-fold increased activity of active efflux pumps. [Bmim]Cl was more toxic than [Emim]Cl in all performed experiments. [Emim]Cl-adapted cells could trounce IL-induced stress. Interestingly, enrichment with 100 mM [Emim]Cl resulted in increase of IL-tolerant colonies in all sediments including the one with 2% salinity. However, the salt saturated brines (35%) do not yield any such colony even after repeated incubations. Extreme halophilic archaea, Natronomonas (growth in 3.0-4.0 M NaCl) isolated from such brines, were exceedingly sensitive to even 5 mM [Emim]Cl, or 1 mM [Bmim]Cl. Two additional extremophilic archaea, namely Haloferax and Haladaptatus were also sensitive to the tested ILs. Archaeal sensitivity is possibly due to the competitive interaction of [Emim]⁺ with their acidic proteome (15.4-17.5% aspartic and glutamic acids, against 10.7-12.9% in bacteria) that they maintain to stabilize the high amount of K⁺ ion accumulated by salt-in strategy. Thus, general salt adaptation strategies of moderate halophilic bacteria help them to restrain toxicity of these ILs, but extremophilic archaea are highly sensitive and demands meticulous use of these solvents to prevent environmental contamination.

Partially Acetylated Cellulose Dissolved in Aqueous Solution: Physical Properties and Enzymatic Hydrolysis

Cellulose acetate is one of the most important cellulose derivatives. The use of ionic liquids in cellulose processing was recently found to act both as a solvent and also as a reagent. A recent study showed that cellulose dissolution in the ionic liquid 1-ethyl-3-methylimidazoliumacetate (EMIMAc) mixed with dichloromethane (DCM) resulted in controlled homogenous cellulose acetylation; yielding water-soluble cellulose acetate (WSCA). This research investigated the properties of cellulose acetate prepared in this manner, in an aqueous solution. The results revealed that WSCA fully dissolves in water, with no significant sign of molecular aggregation. Its conformation in aqueous solution exhibited a very large persistence length, estimated as over 10 nm. The WSCA exhibited surface activity, significantly reducing the surface tension of water. Because of the molecular dissolution of WSCA in water, augmented by its amphiphilicity, aqueous solutions of WSCA exhibited an overwhelmingly high rate of enzymatic hydrolysis.

Effects of Pretreatment with Ionic Liquids on Cellulose Hydrolysis under Hydrothermal Conditions

Hydrothermal hydrolysis in hot pressurized liquid water (HPLW) is attractive for biomass conversion into valuable products because it achieves high reaction rates without catalysts and additives. The hydrothermal hydrolysis of high crystalline cellulose requires higher reaction temperature than polysaccharides having low crystallinity. It can be expected to increase the reaction rate or decrease temperature by decreasing the crystallinity. In the present study ashless filter paper as a fibrous pure cellulose sample was pretreated with ionic liquids (ILs) such as imidazolium chloride ILs containing alkyl side chains ranging from two to six carbons, and with an aqueous solution of bis(ethylenediamine ammonium) copper (BEDC). Herein, the pretreatment with ILs was to regenerate filter paper: dissolving in ILs at 373 K for 120 min or in an aqueous BEDC solution at room temperature, precipitating by adding water, washing the solid, and then drying. Subsequently, the pretreated filter paper samples were hydrolyzed at 533 K and 5.0 MPa in HPLW in a small semi-batch reactor, and the effects of the pretreatment with ILs or BEDC on reaction rates and product yields were examined. While the crystallinity indexes with all ILs and BEDC after the pretreatments decreased to 44 to 47 from the original sample of 87, the reaction rates and product yields were significantly affected by the IL species. At 533 K and 5.0 MPa, the dissolution rate with [AMIM][Cl] was nine times as fast as that for untreated sample.

Effects of reduced severity of ammonium sulfite pretreatment on bamboo for high cellulose recovery

In this study, the conditions for the pretreatment of bamboo by ammonium sulfite to achieve high cellulose recovery were investigated and optimized. To obtain higher cellulose recovery under low-severity pretreatment conditions such as ammonia sulfite concentration, pretreatment time and pretreatment temperature, three-factor and three-level experiments were designed by the Box–Behnken design based on response surface methodology. The results showed that the cellulose recovery yield after 48 h enzymatic hydrolysis could reach 58.36–59.87%; moreover, the recovered cellulose was pretreated with 20% ammonium sulfite at 150 °C for 6 h, and the obtained yield was in agreement with the predicted yield (58.87%). It was about 13-fold higher than that of the untreated bamboo (4.41%). Pretreatment temperature and ammonia sulfite concentration are significantly important factors than pretreatment time in the design space for achieving high cellulose recovery. Moreover, SEM analysis of the pretreated bamboo substrate under optimized conditions illustrated that the biomass surface had become more rough and porous after pretreatment.

In this study, the conditions for the pretreatment of bamboo by ammonium sulfite to achieve high cellulose recovery were investigated and optimized.

A selective fractionation method of lignocellulosic materials using electro-assisted organosolv pretreatment

Lignocellulosic materials (LCMs) extracted from waste-wood products are promising sources of renewable chemicals and fuels. Organosolv pretreatment is commonly used for the fractionation of LCMs; however, these methods require high reaction temperatures, which remain problematic. In this study, room temperature ionic liquids (RTILs) and electrochemical conversion were used for LCMs fractionation. This paper presents a modified organosolv pretreatment, termed electro-assisted organosolv pretreatment (EAOP), which utilises gamma-valerolactone and 1-Butyl-3-methylimidazolium acetate as binary solution, in the presence of electrical energy. Importantly, EAOP can selectively fractionate lignin or cellulose at temperatures lower than 80 °C. Cellulose dissolution occurred at 2.4 V whereas lignin dissolution occurred at 4.2 V. A capacitance parameter was established and validated to describe the operating condition and selectively of EAOP. Operations conducted with capacitance less than 2317 F have the potential for cellulose solubilisation, whereas at capacitance exceeding 2317, lignin solubilisation was observed. This study showed that EAOP can overcome organosolv pretreatment shortfalls.

Mixed fermentation of Aspergillus niger and Candida shehatae to produce bioethanol with ionic-liquid-pretreated bagasse

In this study, bagasse was pretreated with ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and 1% NaOH solution for initial activation of bagasse. A mixed fermentation of treated bagasse by Aspergillus niger and Candida shehatae showed the optimal conditions with the addition of C. shehatae 12 h later at a 1:1 proportion to A. niger. To further improve the ethanol production and obtain optimal fermentation conditions, a Plackett-Burman design was applied to screen the significant formulation and process variables. The optimal ethanol fermentation conditions with IL pretreated bagasse were determined using response surface methodology by Box-Behnken design. Three variables "initial pH, (NH4)2SO4, fermentation time" were regarded as significant factors in the optimization study. The resulting optimum fermentation conditions for bioethanol was identified as: initial pH of 5.89, (NH4)2SO4 concentration of 0.40 g/50 mL, and fermentation time of 3.60 days. The verification experimental ethanol concentration was 8.14 g/L, which agreed with the predicted value. An enhancement of approximately 153.58% compared with initial fermentation conditions in ethanol production was found using optimized conditions. It demonstrated that optimization methodology had a positive effect on the improvement of ethanol production. Under the optimal fermentation medium and conditions, the ethanol production with IL-pretreated bagasse and untreated bagasse was 8.14 g/L and 5.03 g/L, respectively, which exhibited 62% increase, compared to initial conditions with production of 3.21 g/L and 2.67 g/L, respectively, which displayed 20% increase. Both under optimal and original fermentation conditions, compared to the fermentation medium with untreated bagasse, all the results indicated that IL-pretreated bagasse resulted in higher ethanol production than untreated bagasse, demonstrating that IL-pretreated bagasse successfully increased the ethanol production in the mixed fermentation by A. niger and C. shehatae.

A Polar Liquid Zwitterion Does Not Critically Destroy Cytochrome c at High Concentration: An Initial Comparative Study with a Polar Ionic Liquid

A polar carboxylate-type zwitterion with a small volume of water can dissolve cytochrome c without significant disruption, compared with the case of a popular polar carboxylate-type ionic liquid, 1-ethyl-3-methylimidazolium acetate. A change in the Soret, Q, and 615nm bands was not observed in the 80 wt-% polar zwitterion solution, whereas a shift in the Soret band, diminishing Q band, and appearance of the 615nm band was found in the 80 wt-% polar ionic liquid solution. It suggests that concentrated polar ionic liquid solutions critically disrupt the structure of cytochrome c, and the polar zwitterion solution used in this study was better than a 1-ethyl-3-methylimidazolium acetate solution in a high concentration range.