Immobilization of Adenosine Derivatives onto Cellulose Nanocrystals via Click Chemistry for Biocatalysis Applications

Adenosine triphosphate (ATP) is a central molecule of organisms and is involved in many biological processes. It is also widely used in biocatalytic processes, especially as a substrate and precursor of many cofactors─such as nicotinamide adenine dinucleotide phosphate (NADP(H)), coenzyme A (CoA), and S-adenosylmethionine (SAM). Despite its great scientific interest and pivotal role, its use in industrial processes is impeded by its prohibitory cost. To overcome this limitation, we developed a greener synthesis of adenosine derivatives and efficiently selectively grafted them onto organic nanoparticles. In this study, cellulose nanocrystals were used as a model combined with click chemistry via a copper-catalyzed azide/alkyne cycloaddition reaction (CuAAC). The grafted adenosine triphosphate derivative fully retains its biocatalytic capability, enabling heterobiocatalysis for modern biochemical processes.

Pomelo peel derived nanocellulose as Pickering stabilizers: Fabrication of Pickering emulsions and their potential as sustained-release delivery systems for lycopene

Two kinds of nanocellulose (cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) were synthesized from pomelo peels via a facile approach of TEMPO oxidation and sulfuric acid treatment respectively. The FTIR results illustrated that hemicelluloses and lignin were completely removed from the pomelo peel cellulose substrate. The obtained CNFs and CNCs possessed a uniform morphology and nanoscale particle size. The stability of CNF-based Pickering emulsions was higher than that of emulsions stabilized with CNCs, due to the formation of gel structure induced by the CNFs' longer fibrils. Increased oil fractions enhanced the viscoelasticity of CNF-based Pickering emulsions. The in vitro digestion results suggested that increased oil fractions decreased the lipolysis degree, as a result of the larger droplet size and higher viscoelasticity of emulsion. The release of lycopene showed a trend similar to that of FFA release, suggesting that higher oil fractions were beneficial for controlling lycopene release during gastrointestinal digestion.

Effects of the surface chemical groups of cellulose nanocrystals on the vulcanization and mechanical properties of natural rubber/cellulose nanocrystals nanocomposites

Cellulose nanocrystals (CNCs), as the promising reinforcing fillers in the rubber industry, their surface chemical groups have vital effects on the vulcanization kinetics, cross-linking densities, and mechanical properties of rubber composites. Herein, CNCs with acidic carboxyl (CCA) and alkaline amino groups (CCP) were produced by modifying the sulfonic CNCs (CCS) in environment-friendly ways. Studies found the CCS and CCA with acid groups have obvious inhibiting effects on the vulcanization of natural rubber (NR), while CCP with alkaline amino groups accelerates the vulcanization of NR. Differential scanning calorimeter, Fourier transform infrared spectroscopy, and Electron paramagnetic resonance, etc. were performed to clarify the effecting mechanisms of CNCs surface groups on NR vulcanization. It was found that NR/CCS and NR/CCA nanocomposites vulcanize through radical reactions, and the surface acidic groups of CCS and CCA, i.e., hydroxyl, sulfonate, and carboxyl groups inactivate the sulfur radicals generated during vulcanization and depress the vulcanization activity. The amino groups of the polyethyleneimine of CCP promote the ring opening of sulfur (S₈) or the breaking of polysulfide bonds connected to NR molecular chains to form sulfur anion with a strong nucleophilic ability, which leads to the cross-linking of NR/CCP reacts via ionic reaction mainly. The vulcanization rate and cross-linking density of NR/CCP are improved by the ionic reaction. And benefiting from the higher cross-linking density and the reinforcement of CCP, NR/CCP had the best physical and mechanical properties. Our work elucidates the mechanism of the surface chemical groups of CNCs affecting NR vulcanization and may provide ideas for the preparation of high-performance rubber composites reinforced by CNCs.

Effect of Different Methods to Synthesize Polyol-Grafted-Cellulose Nanocrystals as Inter-Active Filler in Bio-Based Polyurethane Foams

Currently, the scientific community has spent a lot of effort in developing "green" and environmentally friendly processes and products, due the contemporary problems connected to pollution and climate change. Cellulose nanocrystals (CNCs) are at the forefront of current research due to their multifunctional characteristics of biocompatibility, high mechanical properties, specific surface area, tunable surface chemistry and renewability. However, despite these many advantages, their inherent hydrophilicity poses a substantial challenge for the application of CNCs as a reinforcing filler in polymers, as it complicates their dispersion in hydrophobic polymeric matrices, such as polyurethane foams, often resulting in aggregate structures that compromise their properties. The manipulation and fine-tuning of the interfacial properties of CNCs is a crucial step to exploit their full potential in the development of new materials. In this respect, starting from an aqueous dispersion of CNCs, two different strategies were used to properly functionalize fillers: (i) freeze drying, solubilization in DMA/LiCl media and subsequent grafting with bio-based polyols; (ii) solvent exchange and subsequent grafting with bio-based polyols. The influence of the two functionalization methods on the chemical and thermal properties of CNCs was examined. In both cases, the role of the two bio-based polyols on filler functionalization was elucidated. Afterwards, the functionalized CNCs were used at 5 wt% to produce bio-based composite polyurethane foams and their effect on the morphological, thermal and mechanical properties was examined. It was found that CNCs modified through freeze drying, solubilization and bio-polyols grafting exhibited remarkably higher thermal stability (i.e., degradation stages > 100 °C) with respect to the unmodified freeze dried-CNCs. In addition, the use of the two grafting bio-polyols influenced the functionalization process, corresponding to different amount of grafted-silane-polyol and leading to different chemico-physical characteristics of the obtained CNCs. This was translated to higher thermal stability as well as improved functional and mechanical performances of the produced bio-based composite PUR foams with respect of the unmodified CNCs-composite ones (the best case attained compressive strength values three times more). Solvent exchange route slightly improved the thermal stability of the obtained CNCs; however; the so-obtained CNCs could not be properly dispersed within the polyurethane matrix, due to filler aggregation.

Zirconium Phosphate Assisted Phosphoric Acid Co-Catalyzed Hydrolysis of Lignocellulose for Enhanced Extraction of Nanocellulose

The high mechanical strength, large specific surface area, favorable biocompatibility, and degradability of nanocellulose (CNC) enable it to be a potential alternative to petroleum-based materials. However, the traditional preparation of CNCs requires a large amount of strong acid, which poses a serious challenge to equipment maintenance, waste liquid recycling, and economics. In this study, a solid and easily recoverable zirconium phosphate (ZrP) was used to assist in the phosphoric acid co-catalyzed hydrolysis of lignocellulose for extracting CNCs. Due to the presence of acidic phosphate groups, ZrP has a strong active center with a high catalytic activity. With the assistance of ZrP, the amount of phosphoric acid used in the reaction is significantly reduced, improving the equipment's durability and economic efficiency. The effects of the process conditions investigated were the phosphate acid concentration, reaction temperature, and reaction time on the yield of CNCs. The Box-Behnken design (BBD) method from the response surface methodology (RSM) was applied to investigate and optimize the preparation conditions. The optimized pre-treatment conditions were 49.27% phosphoric acid concentration, 65.38 °C reaction temperature, and 5 h reaction time with a maximal cellulose yield (48.33%). The obtained CNCs show a granular shape with a length of 40~50 nm and a diameter of 20~30 nm, while its high zeta potential (-24.5 mV) make CNCs present a stable dispersion in aqueous media. Moreover, CNCs have a high crystallinity of 78.70% within the crystal type of cellulose Ⅰ. As such, this study may pioneer the horizon for developing a green method for the efficient preparation of CNC, and it is of great significance for CNCs practical production process.

Breathability and Moisture Permeability of Cellulose Nanocrystals Hollow Microsphere Coatings for PET Fabrics

In this study, cellulose nanocrystals hollow microspheres (HMs) were fabricated through Pickering emulsion polymerization, in which hydrophobically modified cellulose nanocrystals (CNCs) acted as Pickering stabilizers. The hollow interior core was prepared by solvent evaporation. This manuscript describes the synthesis of HMs in detail. The hollow structure and nanoscale size of HMs were verified using TEM. The resultant HMs could easily coat self-forming films on the surface of PET fabrics. Additionally, these coatings exhibited superior breathability and moisture permeability properties with a high one-way transport index of 936.33% and a desirable overall moisture management capability of 0.72. Cellulose nanocrystal hollow microsphere coatings could be used as a moisture-wicking functionality agent for finishing fabrics, oil-water separation, and fog harvesting.

Stabilization of Pickering emulsions via synergistic interfacial interactions between cellulose nanofibrils and nanocrystals

Nanocellulose is a promising stabilizer for industrial emulsions that offers the advantages of sustainability, biodegradability and nontoxicity. Emulsions prepared using cellulose nanofibrils (CNF) and nanocrystals (CNCs) in mildly acidic lithium bromide trihydrate (MALBTH) were characterized in this study. At fixed CNCs concentration (0.3 wt%), increasing the CNF content from 0 to 0.9 wt% clearly influenced the stability and microstructure of Pickering emulsions. The Oil droplets size decreased and stabilized with increasing CNF loading. This emulsification behavior was attributed to the irreversible adsorption of CNCs on the surface of the oil droplets and the formation of a dense CNF network in the aqueous phase, thereby improving the emulsion stability. The universal applicability of the proposed method was verified using cyclohexane and edible olive oil as oil phases. Overall, this study may provide a novel means of producing all-natural, low-oil, food-grade emulsions with adjustable stability.

Photo-curable carboxymethylcellulose composite hydrogel as a promising biomaterial for biomedical applications

A series of carboxymethylcellulose (CMC) functionalized with glycidyl methacrylate (GMA) was successfully synthesized for producing of CMC-g-GMA copolymer. Water-soluble CMC-g-GMA copolymer was photo-crosslinked while Irgacure-2959 was used as a UV-photo-initiator at 365 nm. On the other hand, cellulose nanocrystals (CNCs) from sugarcane were graft-copolymerized in an aqueous solution utilizing cerium ammonium nitrate (CAN) as an initiator in a redox-initiated free-radical approach. CNCs were grafted with GMA to enhance their physicochemical and biological characteristics. Factors affecting hydrogel formation, e.g. CMC-g-GMA copolymer concentration, irradiation time and incorporation of different concentration of CNCs-g-GMA nano-filler, were discussed in dependance on the swelling degree and gel fraction of the produced hydrogels. Notably, the addition of CNCs-g-GMA nanofillers increased progressively thermal stability of the prepared hydrogel. CMC-g-GMA filled with CNCs-g-GMA composite hydrogel showed antimicrobial activity against multidrug resistance pathogens. Thus, CMC-g-GMA filled with CNCs-g-GMA composite hydrogel could be endorsed as compatible biomaterials for versatile biomedical applications.

Polymer ultrastructure governs AA9 lytic polysaccharide monooxygenases functionalization and deconstruction efficacy on cellulose nano-crystals

Lytic Polysaccharide MonoOxygenases display great variability towards cellulose ultrastructure while performing oxidative functionalization of the polymers. Aiming at employing AA9-LPMOs for isolation of cellulose nano-crystals (CNCs), the ratio between functionalization/crystalline degradation became a crucial parameter. Here are reported the constraints posed by the substrate ultrastructure on the activity of seven different AA9 LPMOs representative of various regioselectivity and substrate affinity: TtAA9E, TaAA9A, PcAA9D, MtAA9A, MtAA9D, MtAA9I-CBM and MtAA9J. The substrate crystallinity and dry matter loading greatly affected the seven AA9s in an enzyme-specific manner, impacting their efficiency for CNCs functionalization purposes. X-ray diffraction pattern analyses were used to assess the cracking efficacy of the enzymatic treatment to de-crystallize CNCs, revealing that those AA9s with minor efficiency in releasing oligosaccharides resulted instead the most disruptive towards the crystal lattice and in reducing the particle sizes. These non-catalytic effects were found comparable with the one caused by the expansin BsEXLX1 enzyme.

Lytic polysaccharide monooxygenases as powerful tools in enzymatically assisted preparation of nano-scaled cellulose from lignocellulose: A review

Nanocellulose, either in the form of fibers or crystals, constitutes a renewable, biobased, biocompatible material with advantageous mechanical properties that can be isolated from lignocellulosic biomass. Enzyme-assisted isolation of nanocellulose is an attractive, environmentally friendly approach that leads to products of higher quality compared to their chemically prepared counterparts. Lytic polysaccharide monooxygenases (LPMOs) are enzymes that oxidatively cleave the β-1,4-glycosidic bond of polysaccharides upon activation of O₂ or H₂O₂ and presence of an electron donor. Their use for treatment of cellulose fibers towards the preparation of nano-scaled cellulose is related to the ability of LPMOs to create nicking points on the fiber surface, thus facilitating fiber disruption and separation. The aim of this review is to describe the mode of action of LPMOs on cellulose fibers towards the isolation of nanostructures, thus highlighting their great potential for the production of nanocellulose as a novel value added product from lignocellulose.

Cellulose nanocrystals enabled sustainable polycaprolactone based shape memory polyurethane bionanocomposites

In recent years, shape memory polyurethanes have gained substantial attention and are targeted for a range of smart and functional materials. In this work, the development of nanocrystalline celluloses (CNCs) enabled polycaprolactone-based shape memory polyurethane biocomposite using an in situ one-pot reactions is reported. The incorporation of up to 10 wt% CNCs resulted in a remarkable enhancement in the tensile strength at yield (from 0.2 MPa to 7.2 MPa), tensile strength at break (167% improvement), and modulus of elasticity (from 3.5 to 139.3 MPa) while maintaining the elongation at break. This was attributed to the simultaneous action of CNCs as a nucleating agent for crystallization and highly compatibilized reinforcing agent of the network. Moreover, the in situ incorporation of CNCs enhanced the shape memory capability of polyurethanes, which enables its employment in functional material applications, such as the biomedical sector. The intimate interfacial adhesion between the CNCs and the polymer matrix, which promoted shape fixating and recovery, was confirmed by fractured surface morphology studies. Rheology characterizations provided strong evidence that the addition of CNCs increased the shape fixity attributed to the stiffness of CNCs below the glass transition temperature (T_g) compared to the neat PU in conjuncture with the higher T_g of CNCs. Overall, the developed polymer nanocomposites are appealing materials for biomedical applications.

Surfactant-Mediated Co-Existence of Single-Walled Carbon Nanotube Networks and Cellulose Nanocrystal Mesophases

Hybrids comprising cellulose nanocrystals (CNCs) and percolated networks of single-walled carbon nanotubes (SWNTs) may serve for the casting of hybrid materials with improved optical, mechanical, electrical, and thermal properties. However, CNC-dispersed SWNTs are depleted from the chiral nematic (N*) phase and enrich the isotropic phase. Herein, we report that SWNTs dispersed by non-ionic surfactant or triblock copolymers are incorporated within the surfactant-mediated CNC mesophases. Small-angle X-ray measurements indicate that the nanostructure of the hybrid phases is only slightly modified by the presence of the surfactants, and the chiral nature of the N* phase is preserved. Cryo-TEM and Raman spectroscopy show that SWNTs networks with typical mesh size from hundreds of nanometers to microns are distributed equally between the two phases. We suggest that the adsorption of the surfactants or polymers mediates the interfacial interaction between the CNCs and SWNTs, enhancing the formation of co-existing meso-structures in the hybrid phases.

Influence of cellulose nanocrystals gellan gum-based coating on color and respiration rate of Agaricus bisporus mushrooms

The edible coating has been used for covering fruits and vegetables, bringing surface protection, and extending product shelf-life. Due to the outstanding properties, nanomaterials have become a part of the packaging/coating new generation, demonstrating improvements in the barrier capacity of materials starting from construction products to the food industry. In the food industry, on the other hand, Agaricus bisporus mushrooms have a limited shelf-life from 1 to 3 days because of their high respiration rate and enzymatic browning. With the aim to reduce these two parameters and prevent rapid senescence, the objective of this study was to incorporate a natural source of nanomaterials (cellulose nanocrystals (CNCs) into a gellan gum-based coating and sprayed the surface of the mushrooms with the coating material. To evaluate the effect of CNCs, oxygen consumption, carbon dioxide production rate, and color change were recorded during the mushroom storage at 4 ± 1 °C. Results showed that all coatings were able to decrease total color change (ΔE) of mushrooms from 12 to 8 at day 10 when the coating was applied in all samples compared to control. In addition, significant differences were observed in the respiration rate when CNCs were added to the mushrooms. Oxygen consumption results exhibited a 44 mL O2 /kg · day production at day 5 with 20% CNCs compared to 269 mL O2 /kg · day observed in noncoated samples. This trend was similarly observed in the carbon dioxide production rate. PRACTICAL APPLICATION: With this research, it was remarkable to see the presence of CNCs in the coating solution reduced the respiration rate and increased the shelf-life of mushrooms. Similar applications can be industrially scaled-up to protect fruits and vegetables by CNCs-based coating or packaging materials. A variety of sustainable materials are available nowadays that serve as packaging matrix, and scientists are working on expanding the compatibility of these nanomaterials. In addition, it has been studied that CNCs enhance the degradation of polymers, an effort that many companies are making to reduce the environmental impact in their products.