NMR Study on Laccase Polymerization of Kraft Lignin Using Different Enzymes Source.

The usage of laccases is a sustainable and environmentally friendly approach to modifying the Kraft lignin structure for use in certain applications. However, the inherent structure of Kraft lignin, as well as that resulting from laccase modification, still presents challenges for fundamental comprehension and successful lignin valorization. In this study, bacterial and fungal laccases were employed to modify eucalypt Kraft lignin. To evaluate the type and range of the chemical and structural changes of laccase-treated lignins, different NMR techniques, including solution 1H and 2D NMR (heteronuclear single quantum correlation (HSQC)), and solid-state 13C NMR, were applied. Size exclusion chromatography and infrared spectroscopy were also used. Interestingly, HSQC analysis showed substantial changes in the oxygenated aliphatic region of lignins, showing an almost complete absence of signals corresponding to side-chains due to laccase depolymerization. Simultaneously, a significant loss of aromatic signals was observed by HSQC and 1H NMR, which was attributed to a deprotonation of the lignin benzenic rings due to polymerization/condensation by laccase reactions. Then, condensed structures, such as α-5', 5-5', and 4-O-5', were detected by HSQC and 13C NMR, supporting the increment in molecular weight, as well as the phenolic content reduction determined in lignins.

Green solvents extraction-based detoxification to enhance the enzymatic hydrolysis of steam-exploded lignocellulosic biomass and recover bioactive compounds.

A novel strategy for pre-treated biomass detoxification combining emerging green solvents and low environmental impact extraction technologies was evaluated. Steam-exploded biomass was subjected to microwave-assisted or orbital shaking extraction using bio-based or eutectic solvents. The extracted biomass was enzymatically hydrolysed. The potential of this detoxification methodology was studied in terms of phenolic inhibitors extraction and sugar production improvement. The effect of adding a post-extraction water washing step before hydrolysis was also evaluated. Excellent results were achieved when steam-exploded biomass was subjected to the microwave-assisted extraction combined with the washing step. The highest sugar production was achieved when ethyl lactate was used as extraction agent (49.80 ± 3.10 g total sugar/L) over the control (30.43 ± 0.34 g total sugar/L). Results suggested that a detoxification step based on green solvents would be a promising option to extract phenolic inhibitors, which can be revalorized as antioxidants, and improve the sugar production from the extracted pre-treated biomass.

Chemical, Thermal and Antioxidant Properties of Lignins Solubilized during Soda/AQ Pulping of Orange and Olive Tree Pruning Residues.

Some agroforestry residues such as orange and olive tree pruning have been extensively evaluated for their valorization due to its high carbohydrates content. However, lignin-enriched residues generated during carbohydrates valorization are normally incinerated to produce energy. In order to find alternative high added-value applications for these lignins, a depth characterization of them is required. In this study, lignins isolated from the black liquors produced during soda/anthraquinone (soda/AQ) pulping of orange and olive tree pruning residues were analyzed by analytical standard methods and Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (solid state 13C NMR and 2D NMR) and size exclusion chromatography (SEC). Thermal analysis (thermogravimetric analysis (TGA), differential scanning calorimetry (DSC)) and antioxidant capacity (Trolox equivalent antioxidant capacity) were also evaluated. Both lignins showed a high OH phenolic content as consequence of a wide breakdown of ß-aryl ether linkages. This extensive degradation yielded lignins with low molecular weights and polydispersity values. Moreover, both lignins exhibited an enrichment of syringyl units together with different native as well as soda/AQ lignin derived units. Based on these chemical properties, orange and olive lignins showed relatively high thermal stability and good antioxidant activities. These results make them potential additives to enhance the thermo-oxidation stability of synthetic polymers.

Comparison of the efficiency of bacterial and fungal laccases in delignification and detoxification of steam-pretreated lignocellulosic biomass for bioethanol production.

This study evaluates the potential of a bacterial laccase from Streptomyces ipomoeae (SilA) for delignification and detoxification of steam-exploded wheat straw, in comparison with a commercial fungal laccase from Trametes villosa. When alkali extraction followed by SilA laccase treatment was applied to the water insoluble solids fraction, a slight reduction in lignin content was detected, and after a saccharification step, an increase in both glucose and xylose production (16 and 6%, respectively) was observed. These effects were not produced with T. villosa laccase. Concerning to the fermentation process, the treatment of the steam-exploded whole slurry with both laccases produced a decrease in the phenol content by up to 35 and 71% with bacterial and fungal laccases, respectively. The phenols reduction resulted in an improved performance of Saccharomyces cerevisiae during a simultaneous saccharification and fermentation (SSF) process, improving ethanol production rate. This enhancement was more marked with a presaccharification step prior to the SSF process.

Influence of process variables on the properties of laccase biobleached pulps.

A laccase stage can be used as a pre-treatment of a standard chemical bleaching sequence to reduce environmental concerns associated to this process. The importance of each independent variable and its influence on the properties of the bleached pulp have been studied in depth in this work, using an adaptive network-based fuzzy inference system (ANFIS) with four independent variables (laccase, buffer, mediator and oxygen) as input. Eucalyptus globulus kraft pulp was biobleached using a laccase from Pycnoporus sanguineus and a natural mediator (acetosyringone). Later, an alkaline extraction and a hydrogen peroxide treatment were applied. Most biobleaching processes showed a decrease in kappa number and an increase in brightness with no significant impact on the viscosity values, compared with the control. Oxygen was the variable with the smallest influence on the final pulp properties while the laccase and buffer solution showed a significant influence.

Preferential adsorption and activity of monocomponent cellulases on lignocellulose thin films with varying lignin content.

Understanding the enzymatic hydrolysis of cellulose and the influence of lignin in the process are critical for viable production of fuels and chemicals from lignocellulosic biomass. The interactions of monocomponent cellulases with cellulose and lignin substrates were investigated by using thin films supported on quartz crystal microgravimetry (QCM) resonators. Trichoderma reesei exoglucanase (CBH-I) and endoglucanase (EG-I) bound strongly to both cellulose and lignin but EG-I exhibited a distinctive higher affinity with lignin, causing a more extensive inhibition of the cellulolytic reactions. CBH-I was found to penetrate into the bulk of the cellulose substrate increasing the extent of hydrolysis and film deconstruction. In the absence of a cellulose binding domain (CBD) and a linker, the CBH-I core adsorbed slowly and was not able to penetrate into the film. Conversely to CBH-I, EG-I exhibited activity only on the surface of the lignocellulose substrate even when containing a CBD and a linker. Interestingly, EG-I displayed a clearly different interaction profile as a function of contact time registered by QCM.

Effect of the combined addition of ultrasonicated kraft lignin and montmorillonite on hydroxypropyl methylcellulose bionanocomposites.

Although hydroxypropyl methylcellulose (HPMC) has been proposed as renewable substitute for traditional plastic, its barrier and active properties need to be improved. Thus, the combination of an organic residue such as kraft lignin (0-10% w/w) and a natural clay such as montmorillonite (3% w/w) by application of ultrasound can significantly improve HPMC properties. This is most likely due to the close interaction between lignin and montmorillonite, which leads to delamination of the clay and improves its dispersion within the HPMC matrix. Specifically, the addition of kraft lignin to the bionanocomposite films provided them with UV-shielding, antioxidant capacity and antibacterial activity. The incorporation of 3% montmorillonite resulted in reductions of 65.8% and 11.4% in oxygen (OP) and water vapor permeabilities (WVP), respectively. Moreover, a reduction of 43.8% in WVP was achieved when both lignin (1%) and montmorillonite (3%) were incorporated, observing a synergistic effect. Thus, the HPMC bionanocomposite with 1% lignin and 3% montmorillonite, presented good thermal stability and mechanical strength with significantly improved gas barrier permeability, as well as UV-shielding (maintaining a good transparency), antioxidant and antibacterial activities.

Enzyme-Catalyzed Polymerization of Kraft Lignin from Eucalyptus globulus: Comparison of Bacterial and Fungal Laccases Efficacy.

Kraft lignin, a side-stream from the pulp and paper industry, can be modified by laccases for the synthesis of high added-value products. This work aims to study different laccase sources, including a bacterial laccase from Streptomyces ipomoeae (SiLA) and a fungal laccase from Myceliophthora thermophila (MtL), for kraft lignin polymerization. To study the influence of some variables in these processes, a central composite design (CCD) with two continuous variables (enzyme concentration and reaction time) and three levels for each variable was used. The prediction of the behavior of the output variables (phenolic content and molecular weight of lignins) were modelled by means of response surface methodology (RSM). Moreover, characterization of lignins was performed by Fourier-transform infrared (FTIR) spectroscopy and different nuclear magnetic resonance (NMR) spectroscopy techniques. In addition, antioxidant activity was also analyzed. Results showed that lignin polymerization (referring to polymerization as lower phenolic content and higher molecular weight) occurred by the action of both laccases. The enzyme concentration was the most influential variable in the lignin polymerization reaction within the range studied for SiLA laccase, while the most influential variable for MtL laccase was the reaction time. FTIR and NMR characterization analysis corroborated lignin polymerization results obtained from the RSM.

Lignocellulosic-Based Nanoparticles with Photoluminescent Properties for Bioimaging.

Natural and renewable resources from plants or animals are an important source of biomaterials due to their biocompatibility and high availability. Lignin is a biopolymer present in the biomass of plants, where it is intertwined and cross-linked with other polymers and macromolecules in the cell walls, generating a lignocellulosic material with potential applications. We have prepared lignocellulosic-based nanoparticles with an average size of 156 nm that exhibit a high photoluminescence signal when excited at 500 nm with emission in the near-infrared (NIR) region at 800 nm. The advantage of these lignocellulosic-based nanoparticles is their natural luminescent properties and their origin from rose biomass waste, which eliminates the need for encapsulation or functionalization of imaging agents. Moreover, the in vitro cell growth inhibition (IC50) of lignocellulosic-based nanoparticles is about 3 mg/mL, and no in vivo toxicity was registered up to 57 mg/kg, which suggests that they are suitable for bioimaging applications. In addition, these nanoparticles can circulate in the blood and are excreted in urine. The combined high luminescence signal in NIR, small size, low in vitro toxicity, low in vivo toxicity, and blood circulation support the potential of lignin-based nanoparticles as a novel bioimaging agent.

Bicomponent lignocellulose thin films to study the role of surface lignin in cellulolytic reactions.

Ultrathin bicomponent films of cellulose and lignin derivatives were deposited on silica supports by spin coating, and after conversion into the respective polymer precursor, they were used as a model system to investigate interfacial phenomena relevant to lignocellulose biocatalysis. Film morphology, surface chemical composition, and wettability were determined by atomic force microscopy, X-ray photoelectron spectroscopy, and water contact angle, respectively. Phase separation of cellulose and lignin produced structures that resembled the cell wall of fibers and were used to monitor enzyme binding and cellulolytic reactions via quartz crystal microgravimetry. The rate and extent of hydrolysis was quantified by using kinetic models that indicated the role of the surface lignin domains in enzyme inhibition. Hydrophobic interactions between cellulases and the substrates and their critical role on irreversible adsorption were elucidated by using acetylated lignin films with different degrees of substitution. Overall, it is concluded that sensors based on the proposed ultrathin films of lignocellulose can facilitate a better understanding of the complex events that occur during bioconversion of cellulosic biomass.

Emulsion Stabilization by Cationic Lignin Surfactants Derived from Bioethanol Production and Kraft Pulping Processes.

Oil-in-water bitumen emulsions stabilized by biobased surfactants such as lignin are in line with the current sustainable approaches of the asphalt industry involving bitumen emulsions for reduced temperature asphalt technologies. With this aim, three lignins, derived from the kraft pulping and bioethanol industries, were chemically modified via the Mannich reaction to be used as cationic emulsifiers. A comprehensive chemical characterization was conducted on raw lignin-rich products, showing that the kraft sample presents a higher lignin concentration and lower molecular weight. Instead, bioethanol-derived samples, with characteristics of non-woody lignins, present a high concentration of carbohydrate residues and ashes. Lignin amination was performed at pH = 10 and 13, using tetraethylene pentamine and formaldehyde as reagents at three different stoichiometric molar ratios. The emulsification ability of such cationic surfactants was firstly studied on prototype silicone oil-in-water emulsions, attending to their droplet size distribution and viscous behavior. Among the synthetized surfactants, cationic kraft lignin has shown the best emulsification performance, being used for the development of bitumen emulsions. In this regard, cationic kraft lignin has successfully stabilized oil-in-water emulsions containing 60% bitumen using small surfactant concentrations, between 0.25 and 0.75%, which was obtained at pH = 13 and reagent molar ratios between 1/7/7 and 1/28/28 (lignin/tetraethylene pentamine/formaldehyde).

Different Kraft lignin sources for electrospun nanostructures production: Influence of chemical structure and composition.

This work focuses on the structural features and physicochemical properties of different Kraft lignins and how they can influence the electrospinning process to obtain nanostructures. Structural features of Kraft lignins were characterized by nuclear magnetic resonance, size exclusion chromatography, fourier-transform infrared spectroscopy, and thermal analysis, whereas chemical composition was analyzed by standard method. The addition of cellulose acetate (CA) improves the electrospinning process of Kraft lignins (KL). Thus, solutions of KL/CA at 30 wt% with a KL:CA weight ratio of 70:30 were prepared and then physicochemical and rheologically characterized. The morphology of electrospun nanostructures depends on the intrinsic properties of the solutions and the chemical structure and composition of Kraft lignins. Then, surface tension, electrical conductivity and viscosity of eucalypt/CA and poplar/CA solutions were suitable to obtain electrospun nanostructures based on uniform cross-linked nanofibers with a few beaded fibers. It could be related with the higher purity and higher linear structure, phenolic content and S/G ratios of lignin samples. However, the higher values of electrical conductivity and viscosity of OTP/CA solutions resulted in electrospun nanostructure with micro-sized particles connected by thin fibers, due to a lower purity, S/G ratio and phenolic content and higher branched structure in OTP lignin.

Properties versus application requirements of solubilized lignins from an elm clone during different pre-treatments.

Kraft pulping, organosolv process and acid hydrolysis were applied on an elm clone. The solubilized lignins were recovered and analyzed. Kraft pulping and acid hydrolysis led to lignins with higher phenolic OH content as result of extensive cleavage of ß-O-4' linkages, as revealed by 13C solid state and 13C-1H heteronuclear single quantum coherence nuclear magnetic resonance. This depolymerization also yielded lower molecular weight lignins inferred by size exclusion chromatography. Contrarily, organosolv process gave rise to a lignin with a more preserved structure, maintaining a large number of ß-O-4' linkages. Consequently, organosolv lignin presented lower phenolic OH content and higher molecular weight. Moreover, the high content of the labile native ß-O-4' linkages in organosolv lignin resulted in a lower thermostability as compared to the kraft and acid lignins. On the other hand, the solubilized lignins from kraft and acid processes displayed an enrichment of S-units, whereas lignin from organosolv process was slightly enriched in G-units, containing all of them different native as well as pre-treatment derived units. These results could help to increase the inventory of lignin sources available for future lignin-based products, for which knowledge of the lignin properties versus application requirements is crucial.

Hydrophobic composite foams based on nanocellulose-sepiolite for oil sorption applications.

TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl)-oxidized cellulose nanofibers (CNF) were assembled to fibrous clay sepiolite (SEP) by means of a high shear homogenizer and an ultrasound treatment followed by lyophilization using three different methods: normal freezing, directional freezing, and a sequential combination of both methods. Methyltrimethoxysilane (MTMS) was grafted to the foam surface by the vapor deposition method to introduce hydrophobicity to the resulting materials. Both the SEP addition (for the normal and directional freezing methods) and the refreezing preparation procedure enhanced the compressive strength of the foams, showing compressive moduli in the range from 28 to 103 kPa for foams loaded with 20% w/w sepiolite. Mercury intrusion porosimetry shows that the average pore diameters were in the range of 30-45 µm depending on the freezing method. This large porosity leads to materials with very low apparent density, around 6 mg/cm3, and very high porosity >99.5%. In addition, water contact angle measurement and Fourier-transform infrared spectroscopy (FTIR) were applied to confirm the foam hydrophobicity, which is suitable for use as an oil sorbent. The sorption ability of these composite foams has been tested using olive and motor oils as models of organophilic liquid adsorbates, observing a maximum sorption capacity of 138 and 90 g/g, respectively.

Populus alba L., an Autochthonous Species of Spain: A Source for Cellulose Nanofibers by Chemical Pretreatment.

In order to identify new sustainable sources for producing cellulose nanofibers (CNFs), fast-growing poplar (Populus alba L.) wood was evaluated herein. For that purpose, bleached poplar kraft pulp was produced and submitted to TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) mediated oxidation (TEMPO-ox) chemical pretreatment followed by microfluidization. The resulting CNFs were thoroughly characterized, including a rheological study at different pH values. Poplar CNFs showed properties comparable to eucalypt CNFs (reference material for CNFs production), showing high carboxylate content (1048 ± 128 µmol g-1), fibrillation yield (87.3% ± 8.1%), optical transmittance (83% at 700 nm) and thermal stability (up to more than 200 °C). Regarding the rheological study, whereas pH from 4 to 10 did not produce significant changes in rheological behavior, a reduction of pH down to 1 led to an order-of-magnitude increase on the viscoelastic functions. Therefore, poplar CNF shows potential in the pH-sensitive hydrogels application field. Finally, the possible ecotoxicity of poplar CNF was assessed. The decrease in cell viability was very low so that only concentrations causing a 10% cytotoxicity could be calculated for the assay detecting alterations in cell metabolism (10 µg mL-1) and plasma membrane integrity (60 µg mL-1).

Alginate bionanocomposite films containing sepiolite modified with polyphenols from myrtle berries extract.

Alginate nanocomposite films incorporating sepiolite (Sep) modified with myrtle berries extract (MBE) rich in polyphenols were prepared by solution casting method. The effects of different extract concentrations on the film properties were determined by measuring physicochemical, mechanical and antioxidant properties of the films. Fourier transform infrared (FTIR) spectra indicated that strong interactions between the polyphenols present in the MBE and sepiolite were involved in the films. The results suggested that incorporation of Sep-MBE hybrids into the films improved elongation at break, tensile strength, water vapor and UV barrier properties compared to the control film. The antioxidant activity of the films was significantly improved and raised with increasing content of MBE. The release kinetics results of MBE polyphenols from the active films into alcoholic food simulant indicated that the addition of Sep-MBE hybrids to alginate film is able to slow the release of MBE polyphenols. This study revealed the benefits of incorporation of Sep-MBE hybrids into the alginate films and their potential application as active packaging films or coating material.

Evaluation of lignin-enriched side-streams from different biomass conversion processes as thickeners in bio-lubricant formulations.

This study explores the suitability of residual lignin-containing fractions generated as side-streams in different conversion processes of eucalypt and pine woods as thickening agents in bio-lubricant formulations. These conversion processes included fermentable sugars extraction by autohydrolysis or steam explosion and kraft pulping. Structural properties of lignin fractions were characterized by FTIR, 1H and 13C NMR, two-dimensional NMR, TGA and SEC, whereas their compositions were analysed by standard analytical methods. On the other hand, chemical oleogels were prepared with NCO-functionalized residual lignin fractions, and characterized by means of rheological, tribological and AFM techniques. Hydrolysis lignin fractions exhibited a great content of carbohydrates, especially glucose (46.0-48.5%), xylose (4.3-15.6%) and lignin (32.5-39.9%) with a well-maintained structure, displaying the main inter-unit linkages and low phenolic content. By contrast, kraft lignin fractions presented a lower carbohydrate content, mainly xylose (3.4-4.3%), and higher content (44.9-67%) of severely degraded lignin, showing a dramatic reduction of inter-unit linkages, and thereby high phenolic content. The rheological response of NCO-functionalized lignin fractions-based oleogels is highly influenced by the composition and chemical structure of residual lignin fractions. Moreover, these oleogels presented suitable tribological properties with values of the friction coefficient lower than those typically exhibited by standard lubricating greases.

Cellulose Nanofibers from a Dutch Elm Disease-Resistant Ulmus minor Clone.

The potential use of elm wood in lignocellulosic industries has been hindered by the Dutch elm disease (DED) pandemics, which have ravaged European and North American elm groves in the last century. However, the selection of DED-resistant cultivars paves the way for their use as feedstock in lignocellulosic biorefineries. Here, the production of cellulose nanofibers from the resistant Ulmus minor clone Ademuz was evaluated for the first time. Both mechanical (PFI refining) and chemical (TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation) pretreatments were assessed prior to microfluidization, observing not only easier fibrillation but also better optical and barrier properties for elm nanopapers compared to eucalyptus ones (used as reference). Furthermore, mechanically pretreated samples showed higher strength for elm nanopapers. Although lower nanofibrillation yields were obtained by mechanical pretreatment, nanofibers showed higher thermal, mechanical and barrier properties, compared to TEMPO-oxidized nanofibers. Furthermore, lignin-containing elm nanofibers presented the most promising characteristics, with slightly lower transparencies.

Research and Patents on Coronavirus and COVID-19: A Review.

BACKGROUND: COVID-19 pandemic is a global problem that requires the point of view of basic sciences and medicine as well as social, economics and politics disciplines. Viral particles of coronaviruses including SARS-CoV-2 as well as other enveloped viruses like influenza virus could be considered as an approximation to functional core-shell nanoparticles and therefore, their study enters the realm of nanotechnology. In this context, nanotechnology can contribute to alleviate some of the current challenges posed by COVID-19 pandemic. METHODS: The present analysis contributed to diverse sources of general information, databases on scientific literature and patents to produce a review affording information on relevant areas where as nanotechnology has offered response to coronavirus challenges in the past and may be relevant now, and has offered an update of the current information on SARS-CoV-2 and COVID-19 issues. RESULTS: This review contribution includes specific information including: 1) An introduction to current research on nanotechnology and related recent patents for COVID-19 responses; 2) Analysis of nonimmunogenic and immunogenic prophylaxis of COVID-19 using Nanotechnology; 3) Tools devoted to detection & diagnosis of coronaviruses and COVID-19: the role of Nanotechnology; and 4) A compilation on the research and patents on nanotechnology dealing with therapeutics & treatments of COVID-19. CONCLUSION: Among the increasing literature on COVID-19, there are few works analyzing the relevance of Nanotechnology, and giving an analysis on patents dealing with coronaviruses that may provide useful information on the area. This review offers a general view of the current research investigation and recent patents dealing with aspects of immunogenic and non-immunogenic prophylaxis, detection and diagnosis as well as therapeutics and treatments.

Nanotechnology Responses to COVID-19.

Researchers, engineers, and medical doctors are made aware of the severity of the COVID-19 infection and act quickly against the coronavirus SARS-CoV-2 using a large variety of tools. In this review, a panoply of nanoscience and nanotechnology approaches show how these disciplines can help the medical, technical, and scientific communities to fight the pandemic, highlighting the development of nanomaterials for detection, sanitation, therapies, and vaccines. SARS-CoV-2, which can be regarded as a functional core-shell nanoparticle (NP), can interact with diverse materials in its vicinity and remains attached for variable times while preserving its bioactivity. These studies are critical for the appropriate use of controlled disinfection systems. Other nanotechnological approaches are also decisive for the development of improved novel testing and diagnosis kits of coronavirus that are urgently required. Therapeutics are based on nanotechnology strategies as well and focus on antiviral drug design and on new nanoarchitectured vaccines. A brief overview on patented work is presented that emphasizes nanotechnology applied to coronaviruses. Finally, some comments are made on patents of the initial technological responses to COVID-19 that have already been put in practice.