Enzyme Adsorption Research Articles

An overview on the factors affecting enzymatic saccharification of lignocellulosic biomass into fermentable sugars

Abstract Lignocellulosic biomass (LCB) is a widely available and sustainable energy resource that can be directly or indirectly converted to biofuels and value-added bioproducts. In such LCB conversion, enzymatic saccharification is commonly regarded as a green alternative to chemical hydrolysis due to less energy-intensive, less toxic, and more environment-benign for efficient fermentable sugar recovery. However, enzymatic saccharification faces substantial challenges, since the complex polymeric matrices of LCB necessitates a variety of enzymes for complete and adequate saccharification. Empirical evidence on enzymatic saccharification has paved the way for optimizing the processes and design for enhancing the performance in LCB. This review examines the enzymatic saccharification of LCB, focusing on the important parameters affecting the process, such as pH, temperature, agitation, enzyme/substrate loading, residence time, and the enzymes required to degrade various LCB components. Various strategies have been reported to improve the performance in saccharification and to address the non-productive adsorption of enzymes. A preliminary economic competency valuation of enzyme-derived fermentable sugars is proposed. Wheat straw, sugarcane bagasse and corn stalk appear, in this case, to be the most economic competent LCBs for commercial enzyme-derived fermentable sugar production. Lastly, practical challenges and future research directions on the enzymatic saccharification of LCB are discussed.

Damage-free remote SF6 plasma-treated CNTs for facile fabrication of electrochemical enzyme biosensors

Remote SF6 plasma treatment of CNTs is performed to graft hydrophobic fluorine on the surface of CNTs. Fluorinated CNTs (F-CNTs) allow for the facile adsorption of enzyme molecules via hydrophobic interaction between F-CNTs and the hydrophobic patches of enzyme molecules. The loading of glucose oxidase (GOx) on F-CNTs correlates well with plasma treatment time. Interestingly, the Rct value of GOx/F-CNTs decreases when CNTs are treated with plasma for a short time such as 1 and 5 min, which is due to weakly-bound chemisorbed fluorine molecules on F-CNTs (semi-ionic C-F). As an example, the Rct value of GOx/F-CNT electrode with 1 min plasma treatment is 0.57 times lower than that of GOx/CNTs, while increasing its sensitivity by 2.5 times. Upon extending the treatment time such as 30, 45 and 60 min, the XPS results reveal the dominance of covalently-attached fluorine, leading to marginally-increased resistance and sensitivity. It is worthy of noting this work is the first report of simple enzyme adsorption on remote-plasma treated CNT surfaces together with its detailed mechanism studies, especially for the binding of enzyme molecules semi-ionic fluorine.

Effect of pretreatment severity on the inhibitory behaviors of larch lignins in enzymatic hydrolysis

To explore the underlying reasons for the decreased enzymatic hydrolysis yields of the acid pretreated softwood under the higher pretreatment severity, the residual bulk lignins, as one type lignin fraction with stronger inhibition, were isolated from larch (softwood) pretreated with different pretreatment severity in this study. The lignin structure changes during the pretreatment were comprehensively investigated by nuclear magnetic resonance (NMR) analysis. The larch lignins addition decreased the enzymatic hydrolysis of Avicel from 68.43% to 25.9–39.3%. The pretreatment intensified the inhibition of isolated lignins on enzymatic hydrolysis of Avicel. Furthermore, quartz crystal microbalance (QCM) analysis was applied to investigate the interaction between enzyme and lignins, distinguishing the reversible and irreversible enzyme adsorption. It demonstrated that the obviously higher irreversible adsorption of enzyme was observed on lignins from pretreated substrates with the higher severity. Additionally, the correlation between structure and inhibition of residual lignins in the enzymatic hydrolysis was then investigated with Pearson’s correlation heatmap. The findings can be used to develop theoretical guidelines for alleviating the residual lignin inhibition in the enzymatic hydrolysis of acidic pretreated softwood.

Chitosan-based Maillard products for enzyme immobilization in multilayers structure: Its application in electrochemical sensing

In this work we demonstrate for the first time the advantages of using water-soluble chitosan polycation obtained by Maillard reaction with glucose (G-Chit) or lactose residues for the immobilization of glucose oxidase (GOx) and lactate oxidase by the layer-by-layer adsorption method onto carbon paste electrodes. Besides its solubility in enzyme-compatible media, these polymers have a suitable charge density for electrostatic adsorption and allow adequate charge transfer at the electrode-solution interface. Based on the analysis of the effect of the type of chitosan derivative on the enzymatic response; we built an efficient biosensor based on G-Chit and GOx. The multilayered structure made of three bilayers of G-Chit and GOx showed the best performance; the biosensor exhibits a sensitivity of (12.4 ± 0.3) µA mM−1 cm−2 in a glucose concentration range from 180 µM to 1.75 mM. In addition, the analytical response of this biosensor was tested in milk samples with negligible effects of the matrix. The results confirm the suitability of these chitosan derivatives for the adsorption of enzymes and the construction of supramolecular structures. The favorable environment for the enzymatic activity results in bioelectrodes with fast responses for quantification of glucose even in a complex matrix like milk.

Fate of the capping agent of biologically produced gold nanoparticles and adsorption of enzymes onto their surface

Enzymotherapy based on DNase I or RNase A has often been suggested as an optional strategy for cancer treatment. The efficacy of such procedures is limited e.g. by a short half-time of the enzymes or a low rate of their internalization. The use of nanoparticles, such as gold nanoparticles (AuNPs), helps to overcome these limits. Specifically, biologically produced AuNPs represent an interesting variant here due to naturally occurring capping agents (CA) on their surface. The composition of the CA depends on the producing microorganism. CAs are responsible for the stabilization of the nanoparticles, and promote the direct linking of targeting and therapeutic molecules. This study provided proof of enzyme adsorption onto gold nanoparticles and digestion efficacy of AuNPs-adsorbed enzymes. We employed Fusarium oxysporum extract to produce AuNPs. These nanoparticles were round or polygonal with a size of about 5 nm, negative surface charge of about − 33 mV, and maximum absorption peak at 530 nm. After the adsorption of DNAse I, RNase A, or Proteinase K onto the AuNPs surface, the nanoparticles exhibited shifts in surface charge (values between − 22 and − 13 mV) and maximum absorption peak (values between 513 and 534 nm). The ability of AuNP-enzyme complexes to digest different targets was compared to enzymes alone. We found a remarkable degradation of ssDNA, and dsDNA by AuNP-DNAse I, and a modest degradation of ssRNA by AuNP-RNase A. The presence of particular enzymes on the AuNP surface was proved by liquid chromatography–mass spectrometry (LC–MS). Using SDS-PAGE electrophoresis, we detected a remarkable digestion of collagen type I and fibrinogen by AuNP-proteinase K complexes. We concluded that the biologically produced AuNPs directly bound DNase I, RNase A, and proteinase K while preserving their ability to digest specific targets. Therefore, according to our results, AuNPs can be used as effective enzyme carriers and the AuNP-enzyme conjugates can be effective tools for enzymotherapy.

Fed-batch enzymatic hydrolysis of steam-exploded sugarcane bagasse

Statistical design and mathematical modeling were used to investigate the fed-batch enzymatic hydrolysis of steam-exploded sugarcane bagasse (195 °C, 7.5 min). First, a Box-Behnken experimental design was used to evaluate the effect of enzyme loading (8, 24, and 40 FPU g-1 glucans of Cellic CTec3®), stirring speed (100, 150, and 200 rpm), and substrate total solids (5, 12.5, and 20 wt%) on the release of glucose equivalents (GlcEq, mostly glucose) after hydrolysis for 48 h in batch mode. A simplified kinetic model was used to fit the experimental data, in which specific activities in Cellic CTec3 were not differentiated, enzyme adsorption was ignored, and end-product inhibition was only attributed to glucose accumulation. The adjusted kinetic model was used to predict the effects of substrate and enzyme intermittent feedings in fed-batch hydrolysis experiments. Compared with batch experiments at 20 wt%, the proposed fed-batch procedure was able to increase GlcEq productivity by nearly 68% using the same enzyme loading, producing substrate hydrolysates containing 91.8 g L-1 GlcEq.

Inhibition of Extracellular Enzyme Activity by Reactive Oxygen Species upon Oxygenation of Reduced Iron-Bearing Minerals.

The dual roles of minerals in inhibiting and prolonging extracellular enzyme activity in soils and sediments are governed by enzyme adsorption to mineral surfaces. Oxygenation of mineral-bound Fe(II) generates reactive oxygen species (ROS), yet it is unknown whether and how this process alters the activity and functional lifespan of extracellular enzymes. Here, the effect of mineral-bound Fe(II) oxidation on the hydrolytic activity of a cellulose-degrading enzyme β-glucosidase (BG) was studied using two pre-reduced Fe-bearing clay minerals (nontronite and montmorillonite) and one pre-reduced iron oxide (magnetite) at pH 5 and 7. Under anoxic conditions, BG adsorption to mineral surfaces decreased its activity but prolonged its lifespan. Under oxic conditions, ROS was produced, with the amount of •OH, the most abundant ROS, being positively correlated with the extent of structural Fe(II) oxidation in reduced minerals. •OH decreased BG activity and shortened its lifespan via conformational change and structural decomposition of BG. These results suggest that under oxic conditions, the ROS-induced inhibitory role of Fe(II)-bearing minerals outweighed their adsorption-induced protective role in controlling enzyme activity. These results disclose a previously unknown mechanism of extracellular enzyme inactivation, which have pivotal implications for predicting the active enzyme pool in redox-oscillating environments.

Interactions of Catalytic Enzymes with n-Type Polymers for High-Performance Metabolite Sensors.

The tight regulation of the glucose concentration in the body is crucial for balanced physiological function. We developed an electrochemical transistor comprising an n-type conjugated polymer film in contact with a catalytic enzyme for sensitive and selective glucose detection in bodily fluids. Despite the promise of these sensors, the property of the polymer that led to such high performance has remained unknown, with charge transport being the only characteristic under focus. Here, we studied the impact of the polymer chemical structure on film surface properties and enzyme adsorption behavior using a combination of physiochemical characterization methods and correlated our findings with the resulting sensor performance. We developed five n-type polymers bearing the same backbone with side chains differing in polarity and charge. We found that the nature of the side chains modulated the film surface properties, dictating the extent of interactions between the enzyme and the polymer film. Quartz crystal microbalance with dissipation monitoring studies showed that hydrophobic surfaces retained more enzymes in a densely packed arrangement, while hydrophilic surfaces captured fewer enzymes in a flattened conformation. X-ray photoelectron spectroscopy analysis of the surfaces revealed strong interactions of the enzyme with the glycolated side chains of the polymers, which improved for linear side chains compared to those for branched ones. We probed the alterations in the enzyme structure upon adsorption using circular dichroism, which suggested protein denaturation on hydrophobic surfaces. Our study concludes that a negatively charged, smooth, and hydrophilic film surface provides the best environment for enzyme adsorption with desired mass and conformation, maximizing the sensor performance. This knowledge will guide synthetic work aiming to establish close interactions between proteins and electronic materials, which is crucial for developing high-performance enzymatic metabolite biosensors and biocatalytic charge-conversion devices.

Revealing adsorption of mixed enzymes onto lignin resulted from integration of hydrothermal and chemi-mechanical pretreatment

Lignin is the main factor inhibiting enzymatic hydrolysis of lignocellulosic biomass. Different pretreatments can alter chemical and structural characteristics of lignin, thus affecting its adsorption capacity of enzymes. Herein, enzymatic mild acid lignin (EMAL) was separated from poplar branch wood chips as substrates resulted from different combined pretreatments, and then characterized and adsorbed by enzymes, so as to study the effects of different pretreatments on enzyme adsorption capacity. The results showed that the phenolic hydroxyl content and CC bond number of lignin increased after hydrothermal pretreatment, which increased the unproductive adsorption of mixed enzymes through hydrophobic interaction and hydrogen bonds. Chemical pretreatment after hydrothermal pretreatment can further reduce the unproductive adsorption of lignin on mixed enzymes, improving the enzymatic hydrolysis of substrates. This study would help to unmask the adsorption of mixed enzymes on lignin resulted from combined pretreatments, and facilitate the rapid development of efficient pretreatment for lignocellulosic biomass.

A potential application of a novel synergistic catalytic nanocluster system composed of biological enzymes and nanozyme in glycerol bioconversion

The integration of multimodal chemical/biocatalysis technology has provided a broad prospect in the efficiency of cascade reactions for a long time. Inspired by the intricate structure and superior efficiency of natural multi-enzyme systems, it is attractive for developing the next generation of high-performance orderly enzyme cascade biological platforms, combined with the catalase-like activity and immobilization properties of nanozymes. In our simple and convenient design, a biomimetic multi-enzyme hybrid nanocluster with excellent catalytic activity was synthesized by in-situ adsorption and immobilization of biological enzyme on nanozyme Fe3O4@OA. The combination of nanozyme Fe3O4@OA with single enzyme (concatenated alditol oxidase, catAldO) or double enzymes (catAldO and concatenated dihydroxy-acid hydrolyase, catDHAD) enjoys outstanding synergistic biocatalytic ability. Nanozyme Fe3O4@OA alternatives catalase to catalyze H2O2 cycle and regenerate O2, which implements the internal circulation of O2 → H2O2 → O2 system and accelerates the conversion of glycerol. It realized the high efficiency synergistic catalysis of nanozyme and biological enzyme successfully. In contrast to simple biocatalyst mixtures in solution, the prepared multienzyme hybrid resulted in the obvious improvements in activity for tandem reactions. The cascade bioactivity of the multienzyme complex was enhanced by the synergistic effect of the immobilization of nanozyme Fe3O4@OA, the opening of substrate channel between the enzyme and nanozyme, and the effective reduction of the transport distance among intermediate metabolites. In this study, it highlights the superiority of synergistic bioreactor integrated with nanoclusters contain Fe3O4@OA nanozyme and biological enzyme, realizing rapid recovery and multiple reusability of nanoclusters, and suggesting great application potential in multi-enzyme synergistic cascade catalysis.

Gas Plasma Surface Modification for Biological Assays.

Surface chemistry plays an important role in the adsorption and immobilization of enzymes and antibodies. Gas plasma technology performs surface preparation that assists in the attachment of molecules. Surface chemistry helps to manage a material's wetting, joining, or thereproducibility of surface interactions. There are numerous examples of commerically available products that utilize gas plasma in their manufacturing process.Examples of products treated by gas plasmaare well plates, microfluidic devices, membranes, fluid dispensers, and some medical devices. This chapter presents an overview of gas plasma technology and provides a guide for using gas plasma for designing surfaces in product development or research.

Beneficial effect of surfactant in adsorption/desorption of lignocellulose-degrading enzymes on/from lignin with different structure

Nonionic surfactant Tween 80 is effective in alleviating the adsorption of lignocellulose-degrading enzymes onto lignin. However, the impacts of lignin structural characteristics on this mitigation effect of Tween 80 were still not clear. Herein, effects of Tween 80 on cellulase and xylanase adsorption on different enzymatic residual lignins (ERLs) and poplar samples were investigated. Besides, effects of Tween 80 on desorption of the two enzyme preparations from different ERLs and poplar samples were also evaluated. By adding Tween 80, the inhibition of ERLs to cellulase hydrolysis was offset and the positive role of Tween 80 in Avicel hydrolysis with presence of ERLs was more effective. Binding strength of cellulase with ERLs was alleviated from 236.0 − 410.9 to 43.9 − 116.6 mL/g after adding 0.5 mg/mL Tween 80. When ERLs was more hydrophobic and had more condensed phenolic OH, the alleviation effect of Tween 80 on cellulase adsorption on ERLs was intensified but its positive effect on enhancing cellulase desorption was weakened. Tween 80 was effective in increasing xylanase activity and preventing xylanase deactivation. With the increase of lignin content and phenolic OH in pretreated poplar, the effect of Tween 80 in alleviating xylanase adsorption on poplar samples was intensified but the effect in enhancing xylanase desorption from poplar samples was weakened. The results provided distinct findings to understand the interaction between Tween 80 and cellulase/xylanase in enzymatic saccharification of lignocelluloses.

3D Printed Porous Nanocellulose-Based Scaffolds As Carriers for Immobilization of Glycosyltransferases.

Biocatalysis is increasingly becoming an alternative method for the synthesis of industrially relevant complex molecules. This can be realized by using enzyme immobilized polysaccharide-based 3D scaffolds as compatible carriers, with defined properties. Especially, immobilization of either single or multiple enzymes on a 3D printed polysaccharide scaffold, exhibiting well-organized interconnected porous structure and morphology, is a versatile approach to access the performance of industrially important enzymes. Here, we demonstrated the use of nanocellulose-based 3D porous scaffolds for the immobilization of glycosyltransferases, responsible for glycosylation in natural biosynthesis. The scaffolds were produced using an ink containing nanofibrillated cellulose (NFC), carboxymethyl cellulose (CMC), and citric acid. Direct-ink-writing 3D printing followed by freeze-drying and dehydrothermal treatment at elevated temperature resulted in chemically cross-linked scaffolds, featuring tunable negative charges (2.2-5.0 mmol/g), pore sizes (10-800 μm), fluid uptake capacity, and exceptional dimensional and mechanical stability in the wet state. The negatively charged scaffolds were applied to immobilize two sugar nucleotide-dependent glycosyltransferases (C-glycosyltransferase, Zbasic2-CGT; sucrose synthase, Zbasic2-SuSy), each harboring a cationic binding module (Zbasic2) to promote charge-based enzyme adsorption. Both enzymes were immobilized at ∼30 mg of protein/g of dry carrier (∼20% yield), independent of the scaffold used. Their specific activities were 0.50 U/mg (Zbasic2-CGT) and 0.19 U/mg (Zbasic2-SuSy), corresponding to an efficacy of 37 and 18%, respectively, compared to the soluble enzymes. The glycosyltransferases were coimmobilized and shown to be active in a cascade reaction to give the natural C-glycoside nothofagin from phloretin (1.0 mM; ∼95% conversion). All enzyme bound scaffolds showed reusability of a maximum of 5 consecutive reactions. These results suggest that the 3D printed and cross-linked NFC/CMC-based scaffolds could present a class of solid carriers for enzyme (co)-immobilization, with promising applications in glycosyltransferase-catalyzed synthesis and other fields of biocatalysis.

Physical and chemical evolution of sugar beet pulp during aqueous ammonia pretreatment and its impacts on the recalcitrance of cellulose

Recognition and deconstruction of biomass recalcitrance are essential steps in fuel ethanol production. Aqueous ammonia (AA) is an efficient pretreatment to improve the enzymatic digestibility of sugar beet pulp (SBP), but the precise mechanism is still ambiguous. Multidimensional methods, e.g., physical properties, wet chemistry compositions, and glycome profiling were integrated to elucidate the impacts of AA pretreatment on recalcitrance of SBP semi-quantitatively. Additionally, the variations in enzyme adsorption and cell wall morphology during the enzymatic hydrolysis were systematically observed. The results confirmed that the constitution, association, and distribution of glycan epitopes within cell walls significantly correlated to recalcitrance. Specifically, the arabinogalactan and rhamnogalacturonan epitopes negatively correlated to the recalcitrance. And xylans only bound to cellulose contributed to recalcitrance. Dislocation and fragmentation of cell walls through sequential removal of several glycan epitopes could facilitate enzymatic digestibility, in terms of enzyme adsorption, reducing sugar yields, and enzymatic saccharification behaviors. Whereas, cell corners seemed to be highly resistant to enzymatic digestion due to some gathered epitopes. The maximum reducing sugar yields ranging from 437.7 to 441.48 mg/g were obtained from the pretreated SBP (3, 5, and 7 h), which nearly increased by 87% compared to the control. Selecting a proper pretreatment to precisely strip out the vital glycan epitopes might be an economically feasible strategy in fuel ethanol production.

Hierarchically Ultrasmall Hf-Based MOF: Mesopore Adjustment and Reconstruction by Recycle Using Acid Etching Strategy

Benefiting from their unique properties including faster mass transfer, more exposed active sites and large molecule recognition, hierarchically porous metal–organic frameworks (HP-MOFs), in the form of ultrasmall nanoparticles (NPs) and having self-assembled interparticle mesopores, have garnered greater attention in recent years that given to typical MOFs. However, controllable synthesis of HP-MOFs on the nanoscale remains a significant challenge. Herein, for the first time, a facile top-down acid etching strategy was developed to fabricate a series of nanosized (∼15 nm) mesoporous MOF, HP-UiO-66-NH2(Hf). The sizes of mesopores in this material can be effectively tuned by simply controlling the concentration of propionic acid (PA) utilized in the preparation solution. Interestingly, the generated mesoporous HP-UiO-66-NH2(Hf) has excellent stability and can be readily constructed by using PA etching solution that has been recycled at least four times. Remarkably, HP-UiO-66-NH2(Hf) displays a high size-selectivity for adsorption of enzymes. Associated with its highly matched mesopore size, the nanocomposite generated by complexation with glucose oxidase (GOD), GOD@HP-UiO-66-NH2(Hf) has a higher catalytic activity and a significantly enhanced stability (recycled at least 7 times) in promoting oxidation of glucose compared to its MOF counterpart, GOD@UiO-66-NH2(Hf) and native GOD.

Enhancing ethylene glycol and ferric chloride pretreatment of rice straw by low-pressure carbon dioxide to improve enzymatic saccharification

Ethylene glycol and ferric chloride pretreatment assisted by low-pressure carbon dioxide (1 MPa CO2) realized the targeted deconstruction of lignocelluloses at 170 °C for 5 min, achieving 98 % cellulose recovery with removal of 92 % lignin and 90 % hemicellulose. After the pretreatment, the formation of stable platform mono-phenol components would be with the destruction of the lignin-carbohydrate complexes structure, and the surface of rice straw became rough, with a less negative charge and higher specific surface area, while the enzyme adsorption rate increased by 8.1 times. Furthermore, the glucose yield of pretreated straw was remarkably increased by 5.6 times that of the untreated straw, reaching 91 % after hydrolyzed for 48 h. With Tween 80 added in concentrated solid (12 %) hydrolysis at low cellulase loading (3 FPU/g dry substrate), half of the hydrolysis time was shortened than that without Tween 80, with 45 % higher glucose yield.

AFM Investigation of the Influence of Steam Flow through a Conical Coil Heat Exchanger on Enzyme Properties.

The present study is aimed at the revelation of subtle effects of steam flow through a conical coil heat exchanger on an enzyme, incubated near the heat exchanger, at the nanoscale. For this purpose, atomic force microscopy (AFM) has been employed. In our experiments, horseradish peroxidase (HRP) was used as a model enzyme. HRP is extensively employed as a model in food science in order to determine the influence of electromagnetic fields on enzymes. Adsorption properties of HRP on mica have been studied by AFM at the level of individual enzyme macromolecules, while the enzymatic activity of HRP has been studied by spectrophotometry. The solution of HRP was incubated either near the top or at the side of the conically wound aluminium pipe, through which steam flow passed. Our AFM data indicated an increase in the enzyme aggregation on mica after its incubation at either of the two points near the heat exchanger. At the same time, in the spectrophotometry experiments, a slight change in the shape of the curves, reflecting the HRP-catalyzed kinetics of ABTS oxidation by hydrogen peroxide, has also been observed after the incubation of the enzyme solution near the heat exchanger. These effects on the enzyme adsorption and kinetics can be explained by alterations in the enzyme hydration caused by the influence of the electromagnetic field, induced triboelectrically by the flow of steam through the heat exchanger. Our findings should thus be considered in the development of equipment involving conical heat exchangers, intended for either research or industrial use (including miniaturized bioreactors and biosensors). The increased aggregation of the HRP enzyme, observed after its incubation near the heat exchanger, should also be taken into account in analysis of possible adverse effects from steam-heated industrial equipment on the human body.

The pre-addition of “blocking” proteins decreases subsequent cellulase adsorption to lignin and enhances cellulose hydrolysis

The pre-adsorption of non-catalytic/blocking proteins onto the lignin component of pretreated biomass has been shown to significantly increase the effectiveness of subsequent enzyme-mediated hydrolysis of the cellulose by limiting non-productive enzyme adsorption. Layer-by-layer adsorption of non-catalytic proteins and enzymes onto lignin was monitored using Quartz Crystal Micro balancing combined with Dissipation monitoring (QCM-D) and conventional protein adsorption. These methods were used to assess the interaction between soft/hardwood lignins, cellulases and the three non-catalytic proteins BSA, lysozyme and ovalbumin. The QCM-D analysis showed higher adsorption rates for all of the non-catalytic proteins onto the lignin films as compared to cellulases. This suggested that the “blocking” proteins would preferentially adsorb to the lignin rather than the enzymes. Pre-incubation of the lignin films with blocking proteins resulted in reduced adsorption of cellulases onto the lignin, significantly enhancing cellulose hydrolysis.

Upcycling cotton textile waste into bio-based building blocks through an environmentally friendly and high-yield conversion process

This work presents mechanical refining as a chemical-free pretreatment of cotton textile waste to be converted into glucose via enzymatic hydrolysis. Both Cellic® CTec2 and CTec3 cellulase enzymes were evaluated to perform the enzymatic hydrolysis. Mechanical refining enabled cotton fiber fibrillation, thus increasing its specific surface area, water swellability, enzyme adsorption, and the efficiency of cotton conversion into sugars. Compared to conventional pretreatments, mechanical refining promoted sugar yields above 90% after enzymatic hydrolysis at lower enzyme usage (4–6 FPU/O.D g). From experimental data, a non-linear model was developed to predict cotton conversion. The predictive model allowed the optimization of the conversion process, which resulted in maximum yields of 89.3 and 98.3% when CTec2 and CTec3 were respectively used. Results from this work open the window to deploy mechanical refining as a promising and more sustainable transformation approach to produce sugar-based building blocks within the circular economy framework of textile waste.

Preferential Adsorption of Prominent Amino Acids in the Urease Enzyme of Sporosarcina pasteurii on Arid Soil Components: A Periodic DFT Study.

The urease enzyme is commonly used in microbially induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) to heal and strengthen soil. Improving our understanding of the adsorption of the urease enzyme with various soil surfaces can lead to advancements in the MICP and EICP engineering methods as well as other areas of soil science. In this work, we use density functional theory (DFT) to investigate the urease enzyme's binding ability with four common arid soil components: quartz, corundum, albite, and hematite. As the urease enzyme cannot directly be simulated with DFT due to its size, the amino acids comprising at least 5% of the urease enzyme were simulated instead. An adsorption model incorporating the Gibbs free energy was used to determine the existence of amino acid-mineral binding modes. It was found that the nine simulated amino acids bind preferentially to the different soil components. Alanine favors corundum, glycine and threonine favor hematite, and aspartic acid favors albite. It was found that, under the standard environmental conditions considered here, amino acid binding to quartz is unfavorable. In the polymeric form where the side chains would dominate the binding interactions, hematite favors aspartic acid through its R-OH group and corundum favors glutamic acid through its R-Ket group. Overall, our model predicts that the urease enzyme produced by Sporosarcina pasteurii can bind to various oxides found in arid soil through its alanine, glycine, aspartic/glutamic acid, or threonine residues.