Laccase Catalysis Research Articles

Injectable enzyme-crosslinking antioxidant hydrogel for stem cells protection and application in skeletal muscle regeneration

Repair of large and irregular skeletal muscle defects by cell therapy has been one of the major challenges in tissue engineering and regenerative medicine because of some major hurdles including stem cell death, function decline rapidly, and low retention in situ. Commercially available hydrogels for encapsulating stem cells are usually not suitable for uses in deep and irregular defects due to the limitations of crosslinking approaches as well as that of antioxidant properties. In this work, an injectable and self-healing hydrogel was developed, which is composed of caffeic acid grafted-gelatin molecules cross-linked through laccase catalysis reaction. Mechanical properties, swelling and degradation rates, cell compatibility, ROS-scavenging ability, and anti-senescence potentials of the hydrogels were characterized and investigated with varying caffeic acid contents. Result showed that the hydrogels hold features of strong capacity of scavenging reactive oxygen species, appropriated mechanical modulus falling in the range of that for bone marrow, and relative low oxygen microenvironment, which enabled the hydrogels to reduce the senescence of bone marrow-derived mesenchymal stem cells (BMSCs) and preserved their stemness. When applied to a mouse model of large and deep skeletal muscle defects, the hydrogel encapsulation increased BMSC retention in situ, improved the cell viability, and differentiation function, promoting myofiber regeneration, vascularization, and M2 macrophage polarization. In conclusion, this study highlights the superior ability of the hydrogel to preserve BMSCs’ stemness and enhance their therapeutic potential, offering a promising strategy for BMSCs protection and application to the repair of deep and large skeletal muscle defects in situ.

Highly Efficient Degradation of 2-Methylisoborneol by Laccase Assisted by a Micro-Electric Field

Taste and odor (T&O) compounds have emerged as crucial parameters for assessing water quality. Therefore, identifying effective methodologies for the removal of these compounds is imperative. In this study, an effective approach utilizing laccase assisted by a micro-electric field was developed for the degradation of 2-methylisoborneol (2-MIB). For this purpose, the optimal conditions for the laccase-catalyzed degradation of 2-MIB were determined, and they were pH 4.0, 25 °C, 150 rpm, 0.1 U/mL of laccase, and 200 ng/L of 2-MIB. Under these specified conditions, the degradation efficiency of 2-MIB was approximately 78% after a 4 h reaction period. Subsequently, the introduction of an electric field yielded a synergistic effect with the enzyme for 2-MIB degradation. At an electric current intensity of 0.04 A over a 4 h duration, the degradation efficiency increased to 90.78%. An analysis using SPME-GC/MS provided information on the degradation intermediates of 2-MIB resulting from laccase-catalyzed degradation, electrocatalytic degradation, and micro-electric-assisted laccase degradation. The potential degradation pathways of 2-MIB illustrated that these three methods result in common degradation products, such as capric aldehyde, nonylaldehyde, and 2-ethylhexanol, and their final products include 3-pentanone, acetone, and 2-butanone. This study provides an enzyme–electrochemical method for the efficient and rapid degradation and removal of 2-MIB. The strategy of laccase catalysis assisted by a micro-electric field has good potential for the removal of pollutants from the natural environment.

Bio-coloration and Antibacterial Function of Wool grafted with pomegranate peel polyphenols catalyzed by laccase

With the deterioration of environmental problems and world energy consumption, the improvement of textile dyeing has been paid more and more attention by researchers. The application of natural dyes in the dyeing of wool fabrics had become a research hotspot. However, the main drawback of the application of natural dyes lies in the poor color stability on wool fabrics. Therefore, research on environmentally and economically friendly dyeing processes has gained crucial importance. In this paper, the effect of pomegranate pigment on the functional dyeing of wool fabric under the catalysis of laccase was discussed. The dyeing effect of different methods on wool fabric was compared and the laccase catalytic dyeing process was optimized. Firstly, the properties of pomegranate peel pigment were analyzed by Ultraviolet-visible absorption spectrum (UV-Vis) and Fourier infrared spectroscopy (FTIR). Then the surface morphology and properties of wool fabric were observed by scanning electron microscope (SEM), microscope and FTIR. Lastly the function and stability of dyed wool fabric were tested by color characteristic value, UV resistance, antibacterial property, color fastness and tensile strength. The results showed that better dyeing effect of wool fabric were obtained by dyeing firstly with pomegranate peel and then catalysis with laccase. The optimum process of laccase catalysis was as follows: catalysis time 8 h, laccase dosage 3.3 U, temperature 50℃, pH 5. The results of SEM, FTIR and microscope tests showed that the phenolic compounds in the pigment of pomegranate peel was catalyzed by laccase to form the deepened coloration polymers and the phenolic polymers were finally combined with the wool fabric. Laccase-catalyzed dyed wool fabric showed good performance stability, such as color fastness to rubbing and soap-washing, strong antibacterial property, great enhancement of UV resistance and excellent tensile strength. The application of laccase in the natural dyeing process of textiles can provide a better way to improve the dyeing properties.

Comparison of Non-Covalent and Covalent Interactions between Lactoferrin and Chlorogenic Acid.

Adding polyphenols to improve the absorption of functional proteins has become a hot topic. Chlorogenic acid is a natural plant polyphenol with anti-inflammatory, antioxidant, and anticancer properties. Bovine lactoferrin is known for its immunomodulatory, anticancer, antibacterial, and iron-chelating properties. Therefore, the non-covalent binding of chlorogenic acid (CA) and bovine lactoferrin (BLF) with different concentrations under neutral conditions was studied. CA was grafted onto lactoferrin molecules by laccase catalysis, free radical grafting, and alkali treatment. The formation mechanism of non-covalent and covalent complexes of CA-BLF was analyzed by experimental test and theoretical prediction. Compared with the control BLF, the secondary structure of BLF in the non-covalent complex was rearranged and unfolded to provide more active sites, the tertiary structure of the covalent conjugate was changed, and the amino group of the protein participated in the covalent reaction. After adding CA, the covalent conjugates have better functional activity. These lactoferrin-polyphenol couplings can carry various bioactive compounds to create milk-based delivery systems for encapsulation.

Covalent conjugation of Inca peanut albumin and polyphenols with different phenolic hydroxyl numbers through laccase catalysis to improve functional properties.

Enzymatic crosslinking is a method that can be used to modify Inca peanut albumin (IPA) using polyphenols, and provides desirable functionalities; however, the effect of polyphenol structures on conjugate properties is unclear. In this study, we selected four polyphenols with different numbers of phenolic hydroxyl groups [para-hydroxybenzoic acid (HBA), protocatechuic acid (PCA), gallic acid (GA), and epigallocatechin gallate (EGCG)] for covalent modification of IPA by enzymatic crosslinking, and explored the structure-function changes of the IPA-polyphenol conjugates. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis showed that laccase successfully promoted covalent crosslinking of IPA with polyphenols, with the order of degree of conjugation as EGCG > GA > PCA > HBA, the IPA-EGCG conjugate showed the highest polyphenol binding equivalents (98.35 g kg-1 protein), and a significant reduction in the content of free amino, sulfhydryl, and tyrosine group. The oxidation of polyphenols by laccase forms quinone or semiquinone radicals that are covalently crosslinked to the reactive groups of IPA, leading to significant changes in the secondary and tertiary structures of IPA, with spherical structures transforming into dense lamellar structures. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability and emulsification stability of IPA-EGCG conjugates improved by almost 6-fold and 2.7-fold, respectively, compared with those of unmodified IPA. These data suggest that the higher the number of polyphenol hydroxyl groups, the higher the degree of IPA-polyphenol conjugation; additionally, enzymatic crosslinking can significantly improve the functional properties of IPA. © 2024 Society of Chemical Industry.

Mold Resistance of Bamboo after Laccase‐Catalyzed Fixation of Lignin Nanoparticles

AbstractIn this study lignin nanoparticles (LNPs) and iodolignin nanoparticles (ILNPs) were prepared in aqueous medium and subsequently deposited on the bamboo surfaces via laccase catalyzed reaction. The SEM micrographs of blocks treated with LNPs and ILNPs revealed a layer of nanoparticles with a mean particles size of 100 nm and 215 nm. Besides that, the fungal isolates from the bamboo culm of Dendrocalamus asper shared 99 %, 98 % and 100 % similarity with Penicillium sumatrense, Pleosporales and Cunninghamella species. The treatment of ILNPs exhibited maximum biocidal efficacy at 91 % against P. sumatrense, Pleosporales sp. and Cunninghamella sp. After leaching with ultrapure water, LNPs‐treated blocks exhibited a reduced biocidal effectiveness with an efficacy of 67 %. In contrast, bamboo treated with ILNPs exhibited a higher level of resistance to decay than LNPs. The reduction in mass of 2 %, 3 %, and 1 % was observed when subjecting P. sumatrense, Cunninghamella, and Pleosporales species to treatment with ILNPs. This study demonstrates the application of laccase catalysis in both LNPs and ILNPs, indicating a potentially effective approach for providing surface protection to bamboo against plant pathogenic fungi.

Preparation, structural characterization and properties of feruloyl oligosaccharide–rice protein hydrolysate conjugates

Rice protein hydrolysate (RPH) and feruloyl oligosaccharides (FOs) were conjugated under the catalysis of laccase and free radical, and the structure and properties of the resultant conjugates were studied. Electrophoresis analysis demonstrated that conjugation with FOs increased the molecular weight of some fractions in RPH, which confirmed the formation of both conjugates. The conjugation degree of laccase-induced conjugate and radical-induced conjugate was 60.45% and 22.70%, respectively. Laccase-catalyzed conjugation decreased the tyrosine residue content of RPH but had no significant effect on the free amino group content, which suggested that tyrosine residues were the conjugation site in the laccase-induced conjugate. However, radical-catalyzed conjugation decreased both the free amino group content and the tyrosine residue content, which indicated that both free amino groups and tyrosine residues were the conjugation site in the radical-induced conjugate. The ultraviolet, fluorescence and circular dichroism spectroscopy analysis revealed that conjugation with FOs significantly altered the secondary and tertiary structure of RPH. In addition, conjugation with FOs increased the solubility and antioxidant activity of RPH but decreased the emulsifying activity and stability. Particularly, the radical-induced conjugate had greater anti-aggregation capacity and antioxidant activity but lower emulsifying activity and stability than the laccase-induced conjugate, which might be due to that their conjugation site and degree were different.

Fabrication and characterization of soy protein isolation-ferulic acid antioxidant hydrogels.

Soy protein gel products are prone to direct oxidation by reactive oxygen during processing and transportation, thus reducing their functional properties and nutritional values. A covalent complex was prepared with soy protein isolate (SPI) and ferulic acid (FA) catalyzed by laccase (LC). The complex was further treated with microbial transglutaminase (TGase) to form hydrogels. The structural changes of the covalent complex (SPI-FA) and the properties and antioxidant stability of hydrogel were investigated. The SPI-FA complexes were demonstrated to be covalently bound by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and they had the least hydrophobic and free sulfhydryl groups at a 1.0 mg mL-1 FA concentration. The α-helix of complexes increased from 11.50% to 27.39%, and random coil dropped from 26.06% to 14.44%. The addition of FA caused SPI fluorescence quenching and redshift. The hydrogel was formed after the complex was induced with TGase, and its hardness and water holding capacity was increased by 50.61% and 26.21%, respectively. Scanning electron microscopy showed that a layered and ordered gel structure was formed. After in vitro digestion, the complex hydrogels maintained stable antioxidant activity, and the free radical scavenging rates of DPPH and ABTS reached 87.65% and 84.45%, respectively. SPI-FA covalent complexes were prepared under laccase catalysis, and complex hydrogels were formed by TGase. Hydrogels have stable antioxidant activity, which provides application prospects for the antioxidant development of food. © 2023 Society of Chemical Industry.

Arabic gum grafted with phenolic acid as a novel functional stabilizer for improving the oxidation stability of oil-in-water emulsion

Three kinds of phenolic acids: ferulic acid (FA), caffeic acid (CA), and gallic acid (GA) with different chemical structures were individually grafted onto Arabic gum (AG) via a laccase mediated method, and their roles in stabilizing o/w emulsions were evaluated. The total phenolic content in modified AG increased from 2.7 ± 0.2 to 18.7 ± 0.2, 19.8 ± 0.6, 22.4 ± 0.8 mg/g after 4 h of laccase catalysis, respectively. FTIR spectra of modified AGs exhibited additional phenolic characteristics, revealing the successful grafting of phenolic acids to AG structure. Compared with natural AG, modified AGs showed remarkably enhanced thermal stability, as well as antioxidant capacity in an order of gallic acid > caffeic acid > ferulic acid. The incorporation of phenolic acids into AG dramatically improved its emulsification performance. Herein, gallic acid-modified AG evinced up to 17.6 % and 12.6 % increments in emulsifying activity and emulsion stability relative to natural AG, respectively. Moreover, the oxidative stability of AG emulsions was pronouncedly meliorated by the introduced phenolic acids, especially gallic acid, as manifested by the suppressed production of primary and secondary oxidation products.

Application of Laccase Catalysis in Bond Formation and Breakage: A Review

Laccase belongs to the superfamily of multicopper oxidases and has been widely investigated in recent decades. Due to its mild and efficient oxidation of substrates, laccase has been successfully applied in organic catalytic synthesis, the degradation of harmful substances, and other green catalytic fields. Nevertheless, there are few reports on the green catalysis with laccase. This review focuses on reporting and collating some of the latest interesting laccase-catalyzed bond formation and breakage research. This is discussed with a focus on the effects of the medium system on the laccase-catalyzed reaction, as well as the formation and the breakage of C–N, C–C, and C–O bonds catalyzed by laccase. It provides abundant references and novel insights for furthering the industrial applications of laccase.

Laccase immobilization on hierarchical micro/nano porous chitin/graphene oxide beads prepared via Pickering emulsion template for dye decolorization

Nowadays, the removal of dye molecules from water sources is a major environmental concern and challenge. Enzymatic degradation (biological) and adsorptive (physical) dye removal are considered to be the most effective dye removal techniques. Laccase catalysis is a reliable method to remove synthetic dyes from water to reduce environmental pollution, but free laccase has the disadvantages of low stability and non-reusability. In this study, stable Pickering emulsions were prepared using chitin (Ch) and graphene oxide (GO) composite solutions. Ch/GO composite aerogel beads with hierarchical porous structure were obtained by emulsion template method combined with freeze-drying, and then used for laccase immobilization and dye decolorization experiments. The results showed that the immobilized laccase had better thermal stability compared to the free enzyme, and it was found that the optimum pH of the immobilized laccase was 3.4 and the optimum temperature was 55 °C. In the cyclic decolorization experiments of acid Big Red GR, the decolorization rate of CH/GO-30 was maintained at 100% after 5 cycles of ABTS (2,2-biazo-bis(3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt) by enzyme catalysis and carrier adsorption synergistically. The preparation of Ch/GO composite aerogel beads by the Pickering emulsion template method is simple and green, without the use of surfactants, avoiding secondary pollution to the environment, and has potential industrial applications in the decolorization and biodegradation of dye wastewater.

Recent Advances in Molecular Oxygen Assisted Laccase Catalyzed Sustainable Organic Transformations

AbstractBio‐catalysis is a versatile and powerful tool in organic synthesis, hazardous chemical remediation, biosensors, and industrial sectors. It has been claimed that laccases can function as an intriguing class of biocatalyst in organic chemistry. They are highly favourable catalysts and offer advantages over conventional oxidants and toxic metal catalysts by exhibiting high activity in aqueous media under mild conditions and also work on diverse functional groups possessing substrates maintaining the atom economy. They coordinate well with molecular oxygen and perform chemo selective oxidation reactions, as well as a plethora of other reactions. However, this review is intended to cover molecular oxygen‐assisted laccase catalysis in organic transformations and its significance in industry.

Laccase‐Triggered Surface Co‐Deposition of Gentisic Acid and Chitosan for Multifunctional Polymer Membranes

AbstractCo‐deposition of phenols and amines inspired by mussel‐inspired chemistry has attracted much attention in the field of surface and interface science and technology. However, most deposition systems are still limited to phenols with at least one catechol group. In this work, a novel enzyme‐triggered co‐deposition system based on a natural phenol (gentisic acid, GA) and a kind of biomacromolecule (chitosan, CS) is reported. With the catalysis of laccase, GA can be oxidized and further react with CS to form effective surface coatings on various substrates such as polypropylene microfiltration membrane (PPMM). The co‐deposition process takes only 40 min at room temperature and endows the membrane with superhydrophilicity and underwater superoleophobicity. The modified membranes show excellent separation performance, reusability, and long‐term stability for the separation of oil‐in‐water emulsions. The modified membranes are highly charged (pI ≈7.2) and capable of efficient dye adsorption. In addition, the modified membranes possess better protein resistance properties compared with the nascent membranes. This work demonstrates a green, mild, and highly efficient surface modification process based on laccase catalysis. The co‐deposition system comes from natural sources and expands the phenol family for constructing multi‐functional surface coatings.

Improving the anti-mould capacity of bamboo through sequential alkaline extraction and laccase-mediated thymol modification

• An integrated anti-mould treatment of bamboo was effectively established. • Nearly no mould could grow on the modified bamboo with high hydrophobicity under investigation. • Relationships between anti-mould capacity and bamboo properties were summarized. The poor solubility of thymol restricts laccase catalytic efficiency for enhancing bamboo durability against exogenous mould. Herein, an integrated process of bamboo modification was established to improve the anti-mould capacity of bamboo through alkaline extraction and laccase-mediated thymol modification. The results showed that increased thymol dosages from 0 to 10.0% could significantly extend mould resistance activity persistence under laccase catalysis. Nearly no moulds could be found on the L-0.25Thy surface through the integrated strategy under a 30-day mould resistance test. The surface hydrophobicity of the modified bamboo increased from 52.5° to 123.5° due to various extents of thymol fixation. Multiple characterisation methods were employed to better grapple with the modified bamboo's chemical changes. This work demonstrates the complex dependence of improving the anti-mould capacity of bamboo through sequential alkaline extraction and laccase-mediated thymol modification to unlock the potential avenue to bamboo preservation.

Covalent interaction of soy protein isolate and chlorogenic acid: Effect on protein structure and functional properties

Covalent interaction of soy protein isolate (SPI) and chlorogenic acid (CA) through laccase catalysis was studied. The structure, interfacial properties (foaming and emulsifying properties) and antioxidant activities of soy protein isolate-chlorogenic acid (SPI-CA) adducts were characterized. The formation of covalent adducts was indicated by the result of the SDS-PAGE analysis. The UV–vis and FTIR analysis indicated that the addition of CA resulted in changes in the secondary structure of the protein. The spectroscopy analysis indicated that the structure of SPI tended to unfold. The emulsifying activity of SPI-CA80 (CA concentration is 80 μmol/g protein) adducts was the highest, which increased by 34.77%. Additionally, SPI-CA100 adducts exhibited high antioxidant capacity, with ABTS and DPPH radical scavenging rates increased by 24.83% and 14.41%, respectively. The results showed that the interfacial properties of SPI were correlated with changes in the concentration of CA. Overall, this study demonstrates that covalent binding of SPI to CA enhances the potential application of SPI as a functional ingredient in food.

Effect of Cu2+ on the Laccase-Inducted Formation of Non-Extractable Residues of Tetrabromobisphenol A in Humic Acids.

We used 14C-radiolabelling to study the non-extractable residues (NERs) formation of tetrabromobisphenol A (TBBPA) in a humic acid (HA) suspension under catalysis of laccase in the presence of copper. When entering the suspension after TBBPA adsorbing to HA supramolecular associates, Cu2+ at low concentrations (even without toxicity to laccase) significantly reduced the amount and first-order kinetic constant of the NER formation, while Cu2+ had no significant effect on the formation after it was complexed with HA. The inhibition effect of Cu2+ on the NER formation is explained to be attributed to the prevention of laccase-induced oxidation of TBBPA in the voids of HA associates by complexation of Cu2+ with periphery molecules of the associates. The results provide insights into varying effects of heavy metals on the environmental fate of organic contaminants and suggest that co-existing heavy metals could increase their environmental risk by reducing their NER formation.

Degradation of bisphenol A enhanced by dialysis membrane enclosed laccase catalysis

Bisphenol A (BPA) as an important industrial material has attracted substantial interests due to its environmental concerns. Here in dialysis membrane enclosed laccase catalysis (DMELC) strategy was adopted firstly to degrade BPA. The feasibility and efficiency of DMELC (81.7% increase) for enhancing BPA degradation were demonstrated experimentally by comparing with the process without dialysis membranes. The enhanced BPA degradation with DMELC could be realized by varying the execution time, initial BPA concentration, pH, temperature, running mode, laccase concentration, surface area-to-volume ratio (SA: V), and laccase mediators. BPA degradation with DMELC was not significantly affected by rotating speed. Four degradation products of BPA with DMELC including 4-(prop-1-en-2-yl) phenol, 3-methyl-2,3-dithtdrobenzofuran, 2-methyl-2,3-dithtdrobenzofuran, and 1-methyl-4-(prop-1-en-2-yl)cyclohex-2-en-1-ol were identified by GC–MS, and the possible degradation pathways were proposed. According to Cramer rules 4-(prop-1-en-2-yl) phenol has a low toxicity, and the other products had high toxicity. In addition, 4-(prop-1-en-2-yl) phenol and 1-methyl-4-(prop-1-en-2-yl)cyclohex-2-en-1-ol are easily biodegradable compounds, whereas 3-methyl-2,3-dithtdrobenzofuran and 2-methyl-2,3-dithtdrobenzofuran are persistent chemicals. The toxicological risk and biodegradability of the degraded products should be investigated experimentally further. The findings provide new insights into the elimination of hazardous pollutants by enzymes and highlight the potential applications in the industrial waste water treatment. • Enhancing BPA degradation by 81.7% was obtained by DMELC. • Substrate structural features induce the behavior difference of rotating speed. • BPA degradation pathway by DMELC was clarified. • Influencing mechanisms of DMELC on BPA degradation were evaluated.

Eco-friendly and mildly modification of wood cell walls with heat treated wood extracts to improve wood decay resistance

Wood protection using plant-derived extracts has shown some promise but the extracts are often easily leached making them less attractive for long-term wood protection. The potential of extracts from heat treated wood sawdust as a natural substitute for wood preservatives was explored, and a mild enzyme-catalyzed method was used to improve its leaching resistance. Laccase was used to catalyze grafting reactions of extracts from heat treated spruce (Picea asperata Mast.) and larch (Larix gmelinii (Rupr.) Kuzen.). The resulting extracts were screened for antifungal activity and then impregnated into poplar blocks (Populus tomentosa Carr.). Fourier Transform Infrared Spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize extracts reactions. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the grafted compounds. Acetone extracts from both heat treated spruce and larch exhibited good activity against the test fungi. Heat treated spruce and larch acetone extracts grafted on modified poplar and subjected to leaching showed better activity against the white-rot fungus, Trametes versicolor (L. ex Fr.) Quél. than the brown-rot fungus, Gloeophyllum trabeum (Pers.: Fr.) Murr. FTIR and XPS results indicated that heat-treated spruce and larch extracts were grafted on poplar by laccase catalysis. Squalene, 3-hydroxy-4-methoxybenzoic acid, and n-hexadecanoic acid were among those compounds suggested to be grafted. The results suggest that laccase-mediated pre-treatment of plant extracts has the potential to increase resistance to leaching. Trials with additional plant-extracts are recommended.

Enhanced removal of ibuprofen in water using dynamic dialysis of laccase catalysis

Ibuprofen (IBU) is one of the most commonly detected active compounds in water, and its presence has raised serious concerns about the risks it poses. The dynamic dialysis of laccase catalysis (DDLC) was investigated in order to improve IBU removal from water. Laccase retention and IBU permeability were assessed during the dialysis process in order to achieve IBU removal via static laccase catalysis dialysis (SDLC). The molecular weight cut-off (MWCO) and surface area-to-volume ratio of dialysis membrane were screened by SDLC, respectively. The effects of laccase concentration, initial IBU concentration, pH, and the flow rate on IBU removal by DDLC were investigated thoroughly. In comparison to SDLC and laccase catalysis without the membrane, DDLC shows considerable advantages in improved IBU cleanup (76% IBU removal) and time efficiency. 1-isobutyl-4-vinylbenzene as the degradation product was identified by GC–MS and FTIR, and a degradation pathway involving hydroxylation, decarboxylation, and dehydration was proposed. This work represents a novelty DDLC process towards the enhancement of IBU removal using laccase. These findings provide new insights into the elimination of pollutants by enzymes and highlight the potential applications in the industrial wastewater treatment.

Formation and nature of non-extractable residues of emerging organic contaminants in humic acids catalyzed by laccase

Formation of non-extractable residues (NERs) is the major fate of most environmental organic contaminants in soil, however, there is no direct evidence yet to support the assumed physical entrapment of NERs (i.e., type I NERs) inside soil humic substances. Here, we used 14C-radiotracer and silylation techniques to analyze NERs of six emerging and traditional organic contaminants formed in a suspension of humic acids (HA) under catalysis of the oxidative enzyme laccase. Laccase induced formation of both type I and covalently bound NERs (i.e., type II NERs) of bisphenol A, bisphenol F, and tetrabromobisphenol A to a large extent, and of bisphenol S (BPS) and sulfamethoxazole (SMX) to a less extent, while no induction for phenanthrene. The type I NERs were formed supposedly owing to laccase-induced alteration of primary (active groups) and secondary (conformation) structure of humic supramolecules, contributing surprisingly to large extents (23.5%–65.7%) to the total NERs, particularly for BPS and SMX, which both were otherwise not transformed by laccase catalysis. Electron-withdrawing sulfonyl group and bromine substitution significantly decreased amount and kinetics of NER formation, respectively. This study provides the first direct evidence for the formation of type I NERs in humic substances and implies a “Trojan horse” effect of such NERs in the environment.