The structure of native cellulose

Current models in bacterial hemicellulase-encoding gene regulation

The discovery and characterization of bacterial carbohydrate-active enzymes is a fundamental component of biotechnology innovation, particularly for renewable fuels and chemicals; however, these studies have increasingly transitioned to exploring the complex regulation required for recalcitrant polysaccharide utilization. This pivot is largely due to the current need to engineer and optimize enzymes for maximal degradation in industrial or biomedical applications. Given the structural simplicity of a single cellulose polymer, and the relatively few enzyme classes required for complete bioconversion, the regulation of cellulases in bacteria has been thoroughly discussed in the literature. However, the diversity of hemicelluloses found in plant biomass and the multitude of carbohydrate-active enzymes required for their deconstruction has resulted in a less comprehensive understanding of bacterial hemicellulase-encoding gene regulation. Here we review the mechanisms of this process and common themes found in the transcriptomic response during plant biomass utilization. By comparing regulatory systems from both Gram-negative and Gram-positive bacteria, as well as drawing parallels to cellulase regulation, our goals are to highlight the shared and distinct features of bacterial hemicellulase-encoding gene regulation and provide a set of guiding questions to improve our understanding of bacterial lignocellulose utilization. KEY POINTS: • Canonical regulatory mechanisms for bacterial hemicellulase-encoding gene expression include hybrid two-component systems (HTCS), extracytoplasmic function (ECF)-σ/anti-σ systems, and carbon catabolite repression (CCR). • Current transcriptomic approaches are increasingly being used to identify hemicellulase-encoding gene regulatory patterns coupled with computational predictions for transcriptional regulators. • Future work should emphasize genetic approaches to improve systems biology tools available for model bacterial systems and emerging microbes with biotechnology potential. Specifically, optimization of Gram-positive systems will require integration of degradative and fermentative capabilities, while optimization of Gram-negative systems will require bolstering the potency of lignocellulolytic capabilities.

Stimuli-Responsive Chiral Cellulose Nanocrystals Based Self-Assemblies for Security Measures to Prevent Counterfeiting: A Review

The proliferation of misleading information and counterfeit products in conjunction with technical progress presents substantial worldwide issues. To address the issue of counterfeiting, many tactics, such as the use of luminous anticounterfeiting systems, have been investigated. Nevertheless, traditional fluorescent compounds have a restricted effectiveness. Cellulose nanocrystals (CNCs), known for their renewable nature and outstanding qualities, present an excellent opportunity to develop intelligent, optically active materials formed due to their self-assembly behavior and stimuli response. CNCs and their derivatives-based self-assemblies allow for the creation of adaptable luminous materials that may be used to prevent counterfeiting. These materials integrate the photophysical characteristics of optically active components due to their stimuli-responsive behavior, enabling their use in fibers, labels, films, hydrogels, and inks. Despite substantial attention, existing materials frequently fall short of practical criteria due to limited knowledge and poor performance comparisons. This review aims to provide information on the latest developments in anticounterfeit materials based on stimuli-responsive CNCs and derivatives. It also includes the scope of artificial intelligence (AI) in the near future. It will emphasize the potential uses of these materials and encourage future investigation in this rapidly growing area of study.

Action of AA9 lytic polysaccharide monooxygenase enzymes on different cellulose allomorphs

Lytic polysaccharide monooxygenase (LPMO)-catalyzed oxidative processes play a major role in natural biomass conversion. Despite their oxidative cleavage at the surface of polysaccharides, understanding of their mode of action, and the impact of structural patterns of the cellulose fiber on LPMO activity is still not fully understood. In this work, we investigated the action of two different LPMOs from Podospora anserina on celluloses showing different structural patterns. For this purpose, we prepared cellulose II and cellulose III allomorphs from cellulose I cotton linters, as well as amorphous cellulose. LPMO action was monitored in terms of surface morphology, molar mass changes and monosaccharide profile. Both PaLPMO9E and PaLPMO9H were active on the different cellulose allomorphs (I, II and III), and on amorphous cellulose (PASC) whereas they displayed a different behavior, with a higher molar mass decrease observed for cellulose I. Overall, the pretreatment with LPMO enzymes clearly increased the accessibility of all types of cellulose, which was quantified by the higher carboxylate content after carboxymethylation reaction on LPMO-pretreated celluloses. This work gives more insight into the action of LPMOs as a tool for deconstructing lignocellulosic biomass to obtain new bio-based building blocks.

Characterizing Macroporous Ion Exchange Membrane Adsorbers for Natural Organic Matter (NOM) Removal-Adsorption and Regeneration Behavior

Addressing the characterization of Natural Organic Matter (NOM) removal by functionalized membranes in water treatment, this study evaluates the effectiveness of two commercial ion-exchange membrane adsorbers: Sartobind® Q (with quaternary amines) and D (with tertiary amines). Using Suwannee River NOM (SRNOM) as a surrogate, Langmuir adsorption isotherms revealed maximum capacities (Qmax) of 2966 ± 153 mg C/m2 and 2888 ± 112 mg C/m2, respectively. Variations in flux from 50 to 500 LMH had a minimal impact on breakthrough times, proving low diffusion limitations. The macroporous (3-5 µm) functionalized cellulose-based membranes exhibited high permeabilities of 10,800 L/(h m2 bar). Q maintained positive zeta potential vs. pH, while D's zeta potential decreased above pH 7 due to amine deprotonation and turning negative above an isoelectric point of 9.1. Regeneration with 0.01 M NaOH achieved over 95% DOC regeneration for Sartobind® D, characterizing reversibility through a pH-swing. Cyclic adsorption showed that Q maintained its capacity with over 99% DOC regeneration, while D required acidic conditioning after the first regeneration cycle to mitigate capacity reduction and re-deprotonate the adsorber. These results have demonstrated the potential suitability of adsorber membranes, designed originally for biotechnological purposes, for the possible removal of disinfection byproduct precursors in drinking water treatment.

Role of Natural Binding Proteins in Therapy and Diagnostics

This review systematically investigates the critical role of natural binding proteins (NBPs), encompassing DNA-, RNA-, carbohydrate-, fatty acid-, and chitin-binding proteins, in the realms of oncology and diagnostics. In an era where cancer continues to pose significant challenges to healthcare systems worldwide, the innovative exploration of NBPs offers a promising frontier for advancing both the diagnostic accuracy and therapeutic efficacy of cancer management strategies. This manuscript provides an in-depth examination of the unique mechanisms by which NBPs interact with specific molecular targets, highlighting their potential to revolutionize cancer diagnostics and therapy. Furthermore, it discusses the burgeoning research on aptamers, demonstrating their utility as 'nucleic acid antibodies' for targeted therapy and precision diagnostics. Despite the promising applications of NBPs and aptamers in enhancing early cancer detection and developing personalized treatment protocols, this review identifies a critical knowledge gap: the need for comprehensive studies to understand the diverse functionalities and therapeutic potentials of NBPs across different cancer types and diagnostic scenarios. By bridging this gap, this manuscript underscores the importance of NBPs and aptamers in paving the way for next-generation diagnostics and targeted cancer treatments.

The plant cell wall-dynamic, strong, and adaptable-is a natural shapeshifter

Mythology is replete with good and evil shapeshifters, who, by definition, display great adaptability and assume many different forms-with several even turning themselves into trees. Cell walls certainly fit this definition as they can undergo subtle or dramatic changes in structure, assume many shapes, and perform many functions. In this review, we cover the evolution of knowledge of the structures, biosynthesis, and functions of the 5 major cell wall polymer types that range from deceptively simple to fiendishly complex. Along the way, we recognize some of the colorful historical figures who shaped cell wall research over the past 100 years. The shapeshifter analogy emerges more clearly as we examine the evolving proposals for how cell walls are constructed to allow growth while remaining strong, the complex signaling involved in maintaining cell wall integrity and defense against disease, and the ways cell walls adapt as they progress from birth, through growth to maturation, and in the end, often function long after cell death. We predict the next century of progress will include deciphering cell type-specific wall polymers; regulation at all levels of polymer production, crosslinks, and architecture; and how walls respond to developmental and environmental signals to drive plant success in diverse environments.

H2O/HF Scavenging Mechanism in Cellulose-Based Separators for Lithium-Ion Batteries with Enhanced Cycle Life

Lithium-ion batteries (LIBs) are increasingly being integrated into the transportation industry due to their high energy density, durability, and low cost. With the growing demand for transportation and other emerging applications, there is a concurrent rise in concern over LIB material sourcing and recycling. This urges the development of LIBs with extended cycle lifespans. One mechanism of capacity fading in LIBs is the dissolution of transition metals into the electrolyte after the cathode is etched with hydrofluoric acid (HF). HF is readily generated by the hydrolysis of the LIB electrolyte salt, lithium hexafluorophosphate (LiPF6), which makes minimizing moisture in the electrolyte a priority in manufacturing. In this study, a nonwoven, cellulose-based separator (CBS) is introduced as an alternative separator for battery technologies to scavenge residual water and HF from the electrolyte. The CBS is shown to be capable of scavenging varying amounts of water from the electrolyte based on different drying processes of the CBS, and a mechanism for this water scavenging is identified based on the materials present in the CBS. In addition, the chemical and electrochemical performance of the CBS in real battery conditions is investigated. Results suggest an effective H2O/HF scavenging capability in the CBS that allows LIB coin cells to have over 17% higher capacity retention than those with conventional separators. Furthermore, studies of the industrially manufactured, commercially relevant cylindrical and pouch cells show remarkable 761 and 103% improvements in the 60% capacity lifetime, respectively. The environmental friendliness, low cost, and easy application empowered by the cycle life improvements shown in this work make this nonwoven CBS a promising candidate for improving industry-level LIB performance.

Effects of hydrolysis conditions on the morphology of cellulose II nanocrystals (CNC-II) derived from mercerized microcrystalline cellulose

The properties of cellulose nanocrystals with allomorph II (CNC-II) vary with the sources and the treatments received. In this work, the influences of hydrolysis time, temperature, and the applied acid concentration on the crystal size of CNC-II were investigated by the surface response experimental design. The results showed that temperature was the most significant factor affecting the crystal size of CNC-II during hydrolysis from mercerized cellulose. Then the morphology and colloidal properties of CNC-II were revealed by dynamic laser scattering (DLS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), etc. XRD results indicated that CNC-II had slightly lower crystallinity (80.89 % vs 82.7 %) and larger crystallite size (5.21 vs. 5.13 nm) than CNC-I. TEM and AFM results showed that the morphology of CNC-II were disc-like and rod-like particles, with an average diameter of 14.6 ± 4.7 nm (TEM) and a thickness of 4- 8 nm (AFM). TG and XPS revealed the reduced thermal stability was due to the introduced sulfate groups in CNC-II during hydrolysis. This investigation has addressed the features of CNC-II derived from mercerized cellulose, and it would be promising in fabricating advanced materials.

Suspension Culture System for Isolating Cancer Spheroids using Enzymatically Synthesized Cellulose Oligomers

Isolating cancer cells from tissues and providing an appropriate culture environment are important for a better understanding of cancer behavior. Although various three-dimensional (3D) cell culture systems have been developed, techniques for collecting high-purity spheroids without strong stimulation are required. Herein, we report a 3D cell culture system for the isolation of cancer spheroids using enzymatically synthesized cellulose oligomers (COs) and demonstrate that this system isolates only cancer spheroids under coculture conditions with normal cells. CO suspensions in a serum-containing cell culture medium were prepared to suspend cells without settling. High-purity cancer spheroids could be separated by filtration without strong stimulation because the COs exhibited antibiofouling properties and a viscosity comparable to that of the culture medium. When human hepatocellular carcinoma (HepG2) cells, a model for cancer cells, were cultured in the CO suspensions, they proliferated clonally and efficiently with time. In addition, only developed cancer spheroids from HepG2 cells were collected in the presence of normal cells by using a mesh filter with an appropriate pore size. These results indicate that this approach has potential applications in basic cancer research and cancer drug screening.

Bacterial cellulose: Biopolymer with novel medical applications

Due to the growing importance of green chemistry, the search for alternatives to cellulose has begun, leading to the rediscovery of bacterial cellulose (BC). The material is produced by Gluconacetobacter and Acetobacter bacteria, mainly Komagataeibacter xylinus. It is a pure biopolymer, without lignin or hemicellulose, forming a three-dimensional mesh, showing much lower organization than its plant counterpart. Thanks to its design, it has proven itself in completely unprecedented applications - especially in the field of biomedical sciences. Coming in countless forms, it has found use in applications such as wound dressings, drug delivery systems, or tissue engineering. The review article focuses on discussing the main structural differences between plant and bacterial cellulose, methods of bacterial cellulose synthesis, and the latest trends in BC applications in biomedical sciences.

Anisotropic Wooden Electromechanical Transduction Devices Enhanced by TEMPO Oxidization and PDMS

In order to increase the number and contact probability of electric dipole on cellulose, acid and alkali treatment was employed to extract hemicellulose and lignin from original wood to gain a highly oriented cellulose frame. The combined means with 2,2,6,6-tetramethylpiperidine-1-oxyl-NaBr-NaClO oxidation and impregnation of PDMS with compression was subsequently used to enhance its mechanical performance and electromechanical conversion. The assembled wooden electromechanical device (10 mm × 10 mm × 1 mm) exhibits the maximum open-circuit voltage (V _OC) of 11.75 V and short-circuit current (I _SC) of 211.01 nA as stepped by foot. It can be sliced to fabricate a flexible sensor with high sensitivity displaying V _OC of 2.88 V and I _SC of 210.09 nA under the tapped state. Its highly oriented wood fiber makes it display significant anisotropy in terms of mechanical and electromechanical performance for multidirectional sense. This strategy will exactly provide reference for developing other high-performance piezoelectric devices.

Flame-Retardant Foamed Material Based on Modified Corn Straw Using Two Nitrogenous Layers

Foamed materials based on a biopolymer of crop straws are environmentally friendly, but ignitability limits their application. In this study, two nitrogenous layers were introduced onto corn straw by esterification and grafting for flame-retardant purposes. The inner thin nitrogenous layer consisted of imidazole rings, and the outer thick nitrogenous layer consisted of grafted acrylamide by a free-radical polymerization. The outer nitrogenous layer was simultaneously introduced into the system with a foaming process at 150 °C. Azodiisobutyronitrile acted both as initiator of the polymerization and the main foaming agent, and deionized water acted both as a plasticizing agent and an auxiliary foaming agent, which simplified the process and formula. It was found that cavities of two different sizes were formed. The nonuniformity of the foamed material was ascribed to the heterogeneous foaming precursor consisting of a rigid core and a soft shell. Its excellent flame-retard rating of UL-94 V-0 was ascribed to the two nitrogenous layers, which provides a sufficient nitrogen source for non-combustible gases. A relatively high compression strength of 17.7 MPa was partly due to the fiber of corn straw.

Tailoring a bio-based adsorbent for sequestration of late transition and rare earth elements

The demand for new renewable energy sources, improved energy storage and exhaust-free transportation requires the use of large quantities of rare earth (REE) and late transition (LTM, group 8-12) elements. In order to achieve sustainability in their use, an efficient green recycling technology is required. Here, an approach, a synthetic route and an evaluation of the designed bio-based material are reported. Cotton-derived nano cellulose particles were functionalized with a polyamino ligand, tris(2-aminoethyl) amine (TAEA), achieving ligand content of up to ca. 0.8 mmol g^-1. The morphology and structure of the produced adsorbent were revealed by PXRD, SEM-EDS, AFM and FTIR techniques. The adsorption capacity and kinetics of REE and LTM were investigated by conductometric photometric titrations, revealing quick uptake, high adsorption capacity and pronounced selectivity for LTM compared to REE. Molecular insights into the mode of action of the adsorbent were obtained via the investigation of the molecular structure of the Ni(II)-TAEA complex by an X-ray single crystal study. The bio-based adsorbent nanomaterial demonstrated in this work opens up a perspective for tailoring specific adsorbents in the sequestration of REE and LTM for their sustainable recycling.

Identification of Chitin Allomorphs in Poorly Crystalline Samples Based on the Complexation with Ethylenediamine

Chitin is a key component of hard parts in many organisms, but the biosynthesis of the two distinctive chitin allomorphs, α- and β-chitin, is not well understood. The accurate determination of chitin allomorphs in natural biomaterials is vital. Many chitin-secreting living organisms, however, produce poorly crystalline chitin. This leads to spectrums with only broad lines and imprecise peak positions under conventional analytical methods such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy, resulting in inconclusive identification of chitin allomorphs. Here, we developed a novel method for discerning chitin allomorphs based on their different complexation capacity and guest selectivity, using ethylenediamine (EDA) as a complexing agent. From the peak shift observed in XRD profiles of the chitin/EDA complex, the chitin allomorphs can be clearly discerned. By testing this method on a series of samples with different chitin allomorphs and crystallinity, we show that the sensitivity is sufficiently high to detect the chitin allomorphs even in near-amorphous, very poorly crystalline samples. This is a powerful tool for determining the chitin allomorphs in phylogenetically important chitin-producing organisms and will pave the way for clarifying the evolution and mechanism of chitin biosynthesis.

Bioeconomic production of high-quality chitobiose from chitin food wastes using an in-house chitinase from Vibrio campbellii

Marine Vibrio species are natural degraders of chitin and usually secrete high levels of chitinolytic enzymes to digest recalcitrant chitin to chitooligosaccharides. This study used an endochitinase (VhChiA) from Vibrio campbellii to produce high-quality chitobiose from crustacean chitins. The enzyme was shown to be fully active and stable over 24 h when BSA was used as an additive. When different chitin sources were tested, VhChiA preferentially digested shrimp and squid (α) chitins compared to crab (β) chitin and did not utilize non-chitin substrates. The overall yields of chitobiose obtained from small-scale production using a single-step reaction was 96% from shrimp, and 91% from squid pen and crab-shell chitins. Larger-scale production yielded 200 mg of chitobiose, with > 99% purity after a desalting and purification step using preparative HPLC. In conclusion, we report the employment of an in-house produced chitinase as an effective biocatalyst to rapidly convert chitin food wastes to chitobiose, in a quantity and quality suitable for use in research and commercial purposes. Chitobiose production by this economical and eco-friendly approach can be easily scaled up to obtain multi-gram quantities of chitobiose for chemo-enzymic synthesis of rare chitooligosaccharide derivatives and long chain chitooligosaccharides, as well as preparation of sugar-based functionalized nanomaterials.

How hydrogen-bonding interactions and nanocrystal aspect ratios influence the morphology and mechanical performance of polymer nanocomposites reinforced with cellulose nanocrystals

The performance of polymer nanocomposites reinforced with cellulose nanocrystals (CNCs) is complicated by several factors, primarily CNC-polymer and polymer-polymer interactions. Our current work specifically seeks to address the effects of CNC geometry, CNC-polymer and polymer-polymer interactions on the structure and non-linear mechanical performance of nanocomposites prepared using two water-soluble polymers, polyethylene oxide (PEO) and polyvinyl alcohol (PVA), having different morphological and structural characteristics. PEO and PVA are chosen since they are compatible with CNCs, however, they interact quite differently with CNCs and result in different reinforcement mechanisms. PEO and PVA interact with CNCs via a nucleating effect and H-bonding, which influence the polymer structure in two opposite directions. The nucleating effect tends to lead the polymer chains to form more ordered structures, whereas H-bonding interactions restrict the mobility of the polymer chains. Since PEO has weaker interactions amongst molecular chains than PVA, the properties of PEO are more significantly influenced by CNCs.

Nanocellulose-Based Biomedical Scaffolds in Future Bioeconomy: A Techno-Legal Assessment of the State-of-the-Art

Nanocellulose is a broader term used for nano-scaled cellulosic crystal and/or fibrils of plant or animal origin. Where bacterial nanocellulose was immediately accepted in biomedicine due to its “cleaner” nature, the plant-based nanocellulose has seen several roadblocks. This manuscript assesses the technological aspects (chemistry of cellulose, nanocellulose producing methods, its purity, and biological properties including toxicity and suggested applications in final drug formulation) along with legal aspects in REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals) regulation by the European Union, EMA (European Medicine Agency). The botanical biomass processing methods leading to the nanoscale impurity (lignin and others) on nanocellulose surface, along with surface modification with harsh acid treatments are found to be two major sources of “impurity” in botanical biomass derived nanocellulose. The status of nanocellulose under the light of REACH regulation along with EMA has been covered. The provided information can be directly used by material and biomedical scientists while developing new nanocellulose production strategies as well as formulation design for European markets.

The latest achievements in plant cellulose-based biomaterials for tissue engineering focusing on skin repair

The present work reviews recent developments in plant cellulose-based biomaterial design and applications, properties, characterizations, and synthesis for skin tissue engineering and wound healing. Cellulose-based biomaterials are promising materials for their remarkable adaptability with three-dimensional polymeric structure. They are capable of mimicking tissue properties, which plays a key role in tissue engineering. Besides, concerns for environmental issues have motivated scientists to move toward eco-friendly materials and natural polymer-based materials for applications in the tissue engineering field these days. Therefore, cellulose as an appropriate substitute for common polymers based on crude coal, animal, and human-derived biomolecules is greatly considered for various applications in biomedical fields. Generally, natural biomaterials lack good mechanical properties for skin tissue engineering. But using modified cellulose-based biopolymers tackles these restrictions and prevents immunogenic responses. Moreover, tissue engineering is a quick promoting field focusing on the generation of novel biomaterials with modified characteristics to improve scaffold function through physical, biochemical, and chemical tailoring. Also, nanocellulose with a broad range of applications, particularly in tissue engineering, advanced wound dressing, and as a material for coupling with drugs and sensorics, has been reviewed here. Moreover, the potential cytotoxicity and immunogenicity of cellulose-based biomaterials are addressed in this review.

Solid-State Nuclear Magnetic Resonance as a Tool to Probe the Impact of Mechanical Preprocessing on the Structure and Arrangement of Plant Cell Wall Polymers

Efficient separation of the plant cell wall polymers during lignocellulose processing has been historically challenging due to insolubility of the polymers and their propensity for recalcitrant reassembly. Methods, such as "lignin first" extraction techniques, have advanced efficient biomass use, but the molecular mechanisms for recalcitrance remain enigmatic. Here, we discuss how solid-state Nuclear Magnetic Resonance (NMR) approaches report on the 3D organization of cellulose, xylan, and lignin in the plant cell wall. Recent results illustrate that the organization of these polymers varies across biomass sources and sample preparation methods, with even minimal physical processing causing significant effects. These structural differences contribute to variable extraction efficiencies for bioproducts after downstream processing. We propose that solid-state NMR methods can be applied to follow biomass processing, providing an understanding of the polymer rearrangements that can lead to poor yields for the desired bioproducts. The utility of the technique is illustrated for mechanical processing using lab-scale vibratory ball milling of Sorghum bicolor.

Unraveling aerobic cultivable cellulolytic microorganisms within the gastrointestinal tract of sheep (Ovis aries) and their evaluation for cellulose biodegradation

Anaerobic cellulolytic microbes in gastrointestinal tract (GT) of ruminants have been well-documented, however, knowledge of aerobic microbes with cellulolytic activities in ruminant GT is comparably limited. Here, we unraveled aerobic cultivable cellulolytic microbes in GT of Ujimqin sheep (Ovis aries) and evaluated the cellulolytic potential of promising isolates. Twenty-two strains were found to possess cellulose degrading potential by Congo-red staining and phylogenetic analysis of the 16S rDNA/ITS sequence revealed that all strains belonged to nine genera, i.e., Bacillus, Streptomyces, Pseudomonas, Lactobacillus, Brachybacterium, Sanguibacter, Rhizobium, Fusarium, and Aspergillus. Strains with high cellulolytic activities were selected to further evaluate the various enzyme activities on lignocellulosic alfalfa hay (Medicago sativa). Among them, isolate Bacillus subtilis RE2510 showed the highest potential of cellulose degradation considering the high endoglucanase (0.1478 ± 0.0014 IU ml-1), exoglucanase (0.1735 ± 0.0012 IU ml-1) and β-glucosidase (0.3817 ± 0.0031 IU ml-1) after 10-day incubation with alfalfa hay. A significant destruction effect of the cellulose structure and the attachment of B. subtilis RE2510 to the hay were also revealed by using scanning electron microscope. This study expands our knowledge of aerobic cellulolytic isolates from GT of sheep and also highlights their potential application as microbial additive in the aerobic process of cellulose bioconversion.

Pyrolytic activation of cellulose: Energetics and condensed phase effects

Bottom-up design of lignocellulose pyrolysis to optimize the quality and yield of bio-oil is hindered by the limited knowledge of the underlying condensed phase biomass chemistry. The influence of condensed...

Combining Computational Chemistry and Crystallography for a Better Understanding of the Structure of Cellulose

The approaches in this article seek to enhance understanding of cellulose at the molecular level, independent of the source and the particular crystalline form of cellulose. Four main areas of structure research are reviewed. Initially, the molecular shape is inferred from the crystal structures of many small molecules that have β-(1→4) linkages. Then, conformational analyses with potential energy calculations of cellobiose are covered, followed by the use of Atoms-In-Molecules theory to learn about interactions in experimental and theoretical structures. The last section covers models of cellulose nanoparticles. Controversies addressed include the stability of twofold screw-axis conformations, the influence of different computational methods, the predictability of crystalline conformations by studies of isolated molecules, and the twisting of model cellulose crystals.

Ultrastructural change in lignocellulosic biomass during hydrothermal pretreatment

In recent years, visualization and characterization of lignocellulose at different scales elucidate the modifications of its ultrastructural and chemical features during hydrothermal pretreatment which include degradation and dissolving of hemicelluloses, swelling and partial hydrolysis of cellulose, melting and redepositing a part of lignin in the surface. As a result, cell walls are swollen, deformed and de-laminated from the adjacent layer, lead to a range of revealed droplets that appear on and within cell walls. Moreover, the certain extent morphological changes significantly promote the downstream processing steps, especially for enzymatic hydrolysis and anaerobic fermentation to bioethanol by increasing the contact area with enzymes. However, the formation of pseudo-lignin hinders the accessibility of cellulase to cellulose, which decreases the efficiency of enzymatic hydrolysis. This review is intended to bridge the gap between the microstructure studies and value-added applications of lignocellulose while inspiring more research prospects to enhance the hydrothermal pretreatment process.

On cellulose spatial organization and interactions as unraveled by diffraction and spectroscopic methods throughout the 20th century

This contribution attempts to describe the path towards determination of cellulose crystal structure down to atomic coordinates, towards the determination of its molecular conformation, as well as towards the details of the intricate pattern of hydrogen bonds and their dynamics. This path started at the beginning of the 20th century with X-ray diffraction, continued with electron diffraction, infrared and Raman spectroscopy, and significant knowledge was gained by methods of NMR spectroscopy. Towards the end of the 20th century and at the beginning of the 21st century, X-ray diffraction in conjunction with neutron diffraction provided the position of hydrogens, which led to detailed description of the geometry of hydrogen bonding network in cellulose. Quantum chemical and molecular dynamics calculations, polarized infrared spectroscopy and sum frequency generation vibrational spectroscopy were used to identify the origins of the vibrational modes in cellulose and to describe their extensive coupling mediated by hydrogen bonds. The role of amphiphilic character of cellulose macromolecule (and consequent hydrophobic interactions) in cellulose properties and behavior has been gaining more recognition in the 21st century.

Reductive Amination Reaction for the Functionalization of Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) represent intriguing biopolymeric nanocrystalline materials, that are biocompatible, sustainable and renewable, can be chemically functionalized and are endowed with exceptional mechanical properties. Recently, studies have been performed to prepare CNCs with extraordinary photophysical properties, also by means of their functionalization with organic light-emitting fluorophores. In this paper, we used the reductive amination reaction to chemically bind 4-(1-pyrenyl)butanamine selectively to the reducing termini of sulfated or neutral CNCs (S_CNC and N_CNC) obtained from sulfuric acid or hydrochloric acid hydrolysis. The functionalization reaction is simple and straightforward, and it induces the appearance of the typical pyrene emission profile in the functionalized materials. After a characterization of the new materials performed by ATR-FTIR and fluorescence spectroscopies, we demonstrate luminescence quenching of the decorated N_CNC by copper (II) sulfate, hypothesizing for these new functionalized materials an application in water purification technologies.

Structure and dynamics of sodium alginate as elucidated by chemical shift anisotropy and site-specific spin-lattice relaxation time measurements

The biocompatible, biodegradable, linear copolymer sodium alginate is fabricated from [Formula: see text] linked [Formula: see text]-D-mannuronic acid (M block) and [Formula: see text]-L-guluronic acid (G-block). It has wide applications in drug delivery, cell encapsulation, and commercial application in the textile, cosmetics, paper, food, biomedical, and pharmaceutical industries. The structure and dynamics of sodium alginate were here investigated by measuring chemical shift anisotropy (CSA) parameters, spin-lattice relaxation time, and molecular correlation time. The principal components of the CSA tensor were determined by two-dimensional phase-adjusted spinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) SSNMR. The alternating M and G blocks of both equatorial and axial links are associated with greater overall flexibility. The molecular correlation time of the carboxyl carbon of both G and M blocks is faster than for the anomeric carbon and pyranose carbon. This is further experimental evidence of the coexistence of two different dynamics within the polysaccharide chains of sodium alginate, which was previously established by ¹H-¹³C dipolar profile analysis. The relaxation time of the para-crystalline region of sodium alginate is comparable with that of chitosan, but it is much shorter than that of cellulose and chitin. The order of the molecular correlation time of sodium alginate and chitosan is also the same. Hence, it can be concluded that sodium alginate exhibits greater flexibility than cellulose and chitin. These types of investigation into the local electronic configuration and nuclear spin dynamics at various carbon nuclei sites of the biopolymer at atomic-scale resolution will help in the design of biomimetic materials.

Approaches in Animal Proteins and Natural Polysaccharides Application for Food Packaging: Edible Film Production and Quality Estimation

Natural biopolymers are an interesting resource for edible films production, as they are environmentally friendly packaging materials. The possibilities of the application of main animal proteins and natural polysaccharides are considered in the review, including the sources, structure, and limitations of usage. The main ways for overcoming the limitations caused by the physico-chemical properties of biopolymers are also discussed, including composites approaches, plasticizers, and the addition of crosslinking agents. Approaches for the production of biopolymer-based films and coatings are classified according to wet and dried processes and considered depending on biopolymer types. The methods for mechanical, physico-chemical, hydration, and uniformity estimation of edible films are reviewed.

On the orientation of the chains in the mercerized cellulose

The cold alkaline treatment or mercerization of cellulose is widely used in industry to enrich the cellulose raw with high-molecular-weight [Formula: see text]-cellulose. Washing out of hemicelluloses by alkalies is accompanied by the rearrangement of the cellulose chains' packing, well known as a transition between cellulose I and cellulose II. Cellulose II can also be produced by the precipitation of the cellulose solutions (regeneration). The currently accepted theory implies that in cellulose II, both mercerized and regenerated, the macromolecules are arranged antiparallelly. However, forming such a structure in the course of the mercerization seems to be significantly hindered, while it seems to be quite possible in the regeneration process. In this work, we discuss the sticking points in the theory on the antiparallel structure of mercerized cellulose from a theoretical point of view summarizing all of the available experimental data in the field.

Temperature-triggered formation of a cellulose II nanocrystal network through regioselective derivatization

The two ends of rodlike cellulose II nanocrystals (CNC-II) were regioselectively functionalized either with gold nanoparticles or thermosensitive polymer chains. In the first case, after the introduction of sulfur atoms at both ends of the rods, CNC-II were labelled using a method based on the in situ nucleation and growth of gold nanoparticles (AuNPs) from soluble derivatives. Transmission electron microscopy (TEM) images showed that such a method resulted in the grafting of one monodisperse AuNP at each extremity of the CNC-II, i.e. to the formation of hybrid dumbbell-shaped objects. No AuNP was detected on the lateral surfaces of the CNC-II and almost all observed CNC-II exhibited this dual labeling. This result confirmed with a good statistics when compared to previous works the possibility to derivatize only the two ends of the CNC-II, thanks to the antiparallel arrangement of cellulose chains in these nanoparticles. In the second case, the localized grafting of temperature-sensitive macromolecules onto the ends of the CNC-II was performed using an oxidation reaction followed by a peptide coupling. This end-specific grafting of thermosensitive chains onto CNC-II enhanced their colloidal stability when the temperature was below the lower critical solution temperature (LCST) of the polymer. Above the LCST, the TEM images revealed the formation of a network extending to tens of microns resulting from end-to-end associations of the derivatized rods through attractive interactions between collapsed polymer chains. Rheology experiments further evidenced a temperature-induced sol-gel transition from a liquid-like (sol) behavior below the LCST to solid-like (gel) behavior above the LCST, in agreement with a change from purely repulsive interactions to interconnections via the hydrophobic collapsed chains. Importantly, all results concurred with a full reversibility of the phenomena upon cooling and reproducibility when samples were subjected to temperature cycles around the LCST. This work reveals that the dual site-specific derivatization of CNC-II can provide symmetric hybrid particles with innovative assembling and macroscopic properties that cannot be obtained through homogeneous chemical modifications.

Amorphous cellulose nanofiber supercapacitors

Despite the intense interest in cellulose nanofibers (CNFs) for biomedical and engineering applications, no research findings about the electrical energy storage of CNF have been reported yet. Here, we present the first electroadsorption effects of an amorphous cellulose nanofiber (ACF) supercapacitor, which can store a large amount of electricity (221 mJm⁻², 13.1 Wkg⁻¹). The electric storage can be attributed to the entirely enhanced electroadsorption owing to a quantum-size effect by convexity of 17.9 nm, an offset effect caused by positive polar C₆=O₆ radicles, and an electrostatic effect by appearance of the localised electrons near the Na ions. The supercapacitor also captures both positive and negative electricity from the atmosphere and in vacuum. The supercapacitor could illuminate a red LED for 1 s after charging it with 2 mA at 10 V. Further gains might be attained by integrating CNF specimens with a nano-electromechanical system (NEMS).

Chemical Modification of Reducing End-Groups in Cellulose Nanocrystals

Native plant cellulose has an intrinsic supramolecular structure. Consequently, it can be isolated as nanocellulose species, which can be utilized as building blocks for renewable nanomaterials. The structure of cellulose also permits its end-wise modification, i.e., chemical reactions exclusively on one end of a cellulose chain or a nanocellulose particle. The premises for end-wise modification have been known for decades. Nevertheless, different approaches for the reactions have emerged only recently, because of formidable synthetic and analytical challenges associated with the issue, including the adverse reactivity of the cellulose reducing end and the low abundance of newly introduced functionalities. This Review gives a full account of the scientific underpinnings and challenges related to end-wise modification of cellulose nanocrystals. Furthermore, we present how the chemical modification of cellulose nanocrystal ends may be applied to directed assembly, resulting in numerous possibilities for the construction of new materials, such as responsive liquid crystal templates and composites with tailored interactions.

Engineering of sustainable biomaterial composites from cellulose and silk fibroin: Fundamentals and applications

This review addresses composites prepared from cellulose (Cel) and silk fibroin (SF) to generate multifunctional, biocompatible, biodegradable materials such as fibers, films and scaffolds for tissue engineering. First, we discuss briefly the molecular structures of Cel and SF. Their structural features explain why certain solvents, e.g., ionic liquids, inorganic electrolyte solutions dissolve both biopolymers. We discuss the mechanisms of Cel dissolution because in many cases they also apply to (much less studied) SF dissolution. Subsequently, we discuss the fabrication and characterization of Cel/SF composite biomaterials. We show how the composition of these materials beneficially affects their mechanical properties, compared to those of the precursor biopolymers. We also show that Cel/SF materials are excellent and versatile candidates for biomedical applications because of the inherent biocompatibility of their components.

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.

Phosphorylase-catalyzed bottom-up synthesis of short-chain soluble cello-oligosaccharides and property-tunable cellulosic materials

Cellulose-based materials are produced industrially in countless varieties via top-down processing of natural lignocellulose substrates. By contrast, cellulosic materials are only rarely prepared via bottom up synthesis and oligomerization-induced self-assembly of cellulose chains. Building up a cellulose chain via precision polymerization is promising, however, for it offers tunability and control of the final chemical structure. Synthetic cellulose derivatives with programmable material properties might thus be obtained. Cellodextrin phosphorylase (CdP; EC 2.4.1.49) catalyzes iterative β-1,4-glycosylation from α-d-glucose 1-phosphate, with the ability to elongate a diversity of acceptor substrates, including cellobiose, d-glucose and a range of synthetic glycosides having non-sugar aglycons. Depending on the reaction conditions leading to different degrees of polymerization (DP), short-chain soluble cello-oligosaccharides (COS) or insoluble cellulosic materials are formed. Here, we review the characteristics of CdP as bio-catalyst for synthetic applications and show advances in the enzymatic production of COS and reducing end-modified, tailored cellulose materials. Recent studies reveal COS as interesting dietary fibers that could provide a selective prebiotic effect. The bottom-up synthesized celluloses involve chains of DP ≥ 9, as precipitated in solution, and they form ~5 nm thick sheet-like crystalline structures of cellulose allomorph II. Solvent conditions and aglycon structures can direct the cellulose chain self-assembly towards a range of material architectures, including hierarchically organized networks of nanoribbons, or nanorods as well as distorted nanosheets. Composite materials are also formed. The resulting materials can be useful as property-tunable hydrogels and feature site-specific introduction of functional and chemically reactive groups. Therefore, COS and cellulose obtained via bottom-up synthesis can expand cellulose applications towards product classes that are difficult to access via top-down processing of natural materials.

Study of cellular architecture and micromechanical properties of cuajilote fruits (Parmentiera edulis D.C.) using different microscopy techniques

The cuajilote (Parmentiera edulis D.C.) tree produces fibrous fruits with a high content of lignocellulosic compounds. However, this fruit and their fibers have been scarcely studied. For this reason, an integral study of their cellular architecture, physicochemical, micromechanical, and structural properties in two maturity stages were carried out. Physicochemical tests, light, confocal and electron microscopy, microindentation, and X-ray diffraction were used for the characterization of fruit and their fibers. Chemical analysis showed that the unripe fruits have the highest cellulose content (42.17%), but in ripe fruit the cellulose content decreases (32.76%) while lignin content increases from 35.26 to 40.79%, caused by the lignification of the sclerenchyma fibers. Microstructural and micromechanical studies in the different regions of the fruit provided relevant information about its cellular architecture, distribution of lignocellulosic compounds and its role in the micromechanical properties of their fibers. The thickening cell wall of sclerenchyma fibers was caused by the cellular lignification of the ripe fruits. According to the physicochemical and structural studies, cuajilote fibers are comparable to other fibers obtained from crops rich in lignocellulosic compounds. The current study provided new knowledge about the cellular architecture of fruit and criteria for selecting the ripening stage adequate for the extraction of cellulose or lignin. Furthermore, information regarding the micromechanical properties of their fibers and which structural arrangement could be more convenient for mechanical reinforcement of biodegradable materials was obtained.

Stimuli-responsive self-assembly of cellulose nanocrystals (CNCs): Structures, functions, and biomedical applications

Cellulose nanocrystals (CNCs) have received a significant amount of attention from the researchers. It is used as a nanomaterial for various applications due to its excellent physiochemical properties for the last few decades. Self-assembly is a phenomenon where autonomous reorganization of randomly oriented species occurs elegantly. Self-assembly is responsible for the formation of the hierarchical cholesteric structure of CNCs. This process is highly influenced by several factors, such as the surface chemistry of the nanoparticles, intermolecular forces, and the fundamental laws of thermodynamics. Various conventional experimental designs and molecular dynamics (MD) studies have been applied to determine the possible mechanism of self-assembly in CNCs. Different external factors, like pH, temperature, magnetic/electric fields, vacuum, also influence the self-assembly process in CNCs. Notably, better responses have been observed in CNCs-grafted polymer nanocomposites. These functionalized CNCs with stimuli-responsive self-assembly have immense practical applications in modern biotechnology and medicine. Herein, we have concisely discussed the mechanism of the self-assembled CNCs in the presence of different external factors such as pH, temperature, electric/magnetic fields, and their biomedical applications.

Molecular Dynamics Simulation of Cellulose I-Ethylenediamine Complex Crystal Models

Cellulose I fibrils swell on exposure to ethylenediamine (EDA), which forms the cellulose I-EDA complex. These are regarded as host materials with guest intercalation. The present study reports molecular dynamics (MD) simulations of cellulose I-EDA crystal models with finite fiber to reproduce desorption of EDA molecules. The force field parameters for EDA were improved. Part of the EDA molecules was desorbed only from the surfaces of the crystal models, not from their interiors. The EDA molecules diffused through a hydrophilic channel composed of the hydrophilic edges of the cellulose chains, and their conformations and orientations changed. With the configuration of the cellulose chains being held, the vacant hydrophilic channel was immediately filled with water molecules. The innermost part of the crystal models, defined as a core unit, was partly deformed from the initial crystal structure, including the changes in the exocyclic group conformations of the cellulose chains and the orientations of the EDA molecules, coupled with partial reconfiguration of the intermolecular hydrogen bonding scheme. A possible crystalline conversion scheme after complete desorption of EDA has been discussed based on the present findings.

Thermal Response in Cellulose Iβ Based on Molecular Dynamics

The structural details of cellulose I β were discussed according to molecular dynamics simulations with the GLYCAM-06 force field. The simulation outcomes were in agreement with previous experimental data, including structural parameters and hydrogen bond pattern at 298 K. We found a new conformation of cellulose Iβ existed at the intermediate temperature that is between the low and high temperatures. Partial chain rotations along the backbone direction were found and conformations of hydroxymethyl groups that alternated from tg to either gt or gg were observed when the temperature increased from 298 K to 400 K. In addition, the gg conformation is preferred than gt. For the structure adopted at high temperature of 500 K, major chains were twisted and two chains detached from each plain. In contrast to the observation under intermediate temperature, the population of hydroxymethyl groups in gt exceeded that in gg conformation at high temperature. In addition, three patterns of hydrogen bonding were identified at low, intermediate and high temperatures in the simulations. The provided structural information indicated the transitions occurred around 350 K and 450 K, considered as the transitional temperatures of cellulose Iβ in this work.

Investigation of the internal structure and dynamics of cellulose by 13C-NMR relaxometry and 2DPASS-MAS-NMR measurements

Internal structure and dynamics of commercial and natural cellulose were studied by measuring chemical shift anisotropy (CSA) parameters, and spin-lattice relaxation rate (1/T₁) at each and every chemically different carbon nuclear site. CSA parameters were measured by ¹³C two-dimensional phase adjusted spinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) NMR experiment. Site specific spin-lattice relaxation time was measured by Torchia-CP method. Anisotropy parameters of C4 and C6 regions are higher than C1 and C235 regions and asymmetry of C4 line is lower than any other carbon site. The higher values of CSA parameters of C4 and C6 nuclei arise due to the rotation of O4-C4, C1-O4, O5-C5-C6-O6 and C4-C5-C6-O6 bonds at torsion angles ψ, Φ, χ and χ' respectively and the influence of interchain and intrachain hydrogen bondings. Two distinct peaks are also observed for C4 and C6 resonance line position-one peak arises primarily due to the nuclei in amorphous region and another one arises due to the same nuclei resides in paracrystalline region. The spin-lattice relaxation time and the CSA parameters are different at these two distinct peak positions of C4 and C6 line. Molecular correlation time of each and every chemically different carbon site was calculated with the help of CSA parameters and spin-lattice relaxation time. The molecular correlation time of the amorphous region is one order of magnitude less than the crystalline region. The distinction between amorphous and paracrystalline regions of cellulose is more vividly portrayed by determining spin-lattice relaxation time, CSA parameters, and molecular correlation time at each and every chemically different carbon site. This type of study correlating the structure and dynamics of cellulose will illuminate the path of inventing biomimetic materials.