In situ encapsulation of laccase in microfibers by emulsion electrospinning: preparation, characterization, and application

Activity of laccase immobilized on TiO2-montmorillonite complexes

The TiO₂-montmorillonite (TiO₂-MMT) complex was prepared by blending TiO₂ sol and MMT with certain ratio, and its properties as an enzyme immobilization support were investigated. The pristine MMT and TiO₂-MMT calcined at 800 °C (TiO₂-MMT800) were used for comparison to better understand the immobilization mechanism. The structures of the pristine MMT, TiO₂-MMT, and TiO₂-MMT800 were examined by HR-TEM, XRD and BET. SEM was employed to study different morphologies before and after laccase immobilization. Activity and kinetic parameters of the immobilized laccase were also determined. It was found that the TiO₂ nanoparticles were successfully introduced into the MMT layer structure, and this intercalation enlarged the “d value” of two adjacent MMT layers and increased the surface area, while the calcination process led to a complete collapse of the MMT layers. SEM results showed that the clays were well coated with adsorbed enzymes. The study of laccase activity revealed that the optimum pH and temperature were pH = 3 and 60 °C, respectively. In addition, the storage stability for the immobilized laccase was satisfactory. The kinetic properties indicated that laccase immobilized on TiO₂-MMT complexes had a good affinity to the substrate. It has been proved that TiO₂-MMT complex is a good candidate for enzyme immobilization.

Adsorption and transformation of PAHs from water by a laccase-loading spider-type reactor

The remediation of polycyclic aromatic hydrocarbons (PAHs) polluted waters has become a concern as a result of the widespread use of PAHs and their adverse impacts on water ecosystems and human health. To remove PAHs rapidly and efficiently in situ, an active fibrous membrane, laccase-loading spider-type reactor (LSTR) was fabricated by electrospinning a poly(D,L-lactide-co-glycolide) (PDLGA)/laccase emulsion. The LSTR is composed of beads-in-string structural core-shell fibers, with active laccase encapsulated inside the beads and nanoscale pores on the surface of the beads. This structure can load more laccase and retains higher activity than do linear structural core-shell fibers. The LSTR achieves the efficient removal/degradation of PAHs in water, which is attributed to not only the protection of the laccase activity by the core-shell structure but also the pre-concentration (adsorption) of PAHs on the surface of the LSTR and the concentration of laccase in the beads. Moreover, the effects of pH, temperature and dissolved organic matter (DOM) concentration on the removal of PAHs by the LSTR, in comparison with that by free laccase, have been taken into account. A synergetic mechanism including adsorption, directional migration and degradation for PAH removal is proposed.

Immobilization of horseradish peroxidase by electrospun fibrous membranes for adsorption and degradation of pentachlorophenol in water

Horseradish peroxidase (HRP) is successfully in situ encapsulated into the poly(D,L-lactide-co-glycolide) (PLGA)/PEO-PPO-PEO (F108) electrospun fibrous membranes (EFMs) by emulsion electrospinning. The adsorption and degradation of pentachlorophenol (PCP) by HRP-EFMs are investigated. The experimental results show that the sorption kinetic of PCP on EFMs follows the pseudo-second-order model, and the sorption capacity is as high as 44.69 mg g(-1). The sorption mechanisms of EFMs for PCP can be explained by hydrogen bonding interactions, hydrophobic interactions and π-π bonding interactions. Profiting from the strong adsorption, the removal of PCP can be dramatically enhanced by the interaction of adsorbed PCP and HRP on the surface of EFMs. For PCP degradation, the optimal pH values for free HRP and immobilized HRP are 4 and 2-4, respectively. As pH>4.7, no adsorption and degradation are observed due to the deprotonation of PCP. The removal percentages reach 83% and 47% for immobilized HRP and free HRP, respectively, at 25 ± 1°C. The presence of humic acid can inhibit the activity of HRP and decreases the adsorption capacity of PCP because of competitive adsorption. The operational and storage stability of immobilized HRP are highly improved through emulsion electrospinning.

Immobilization of laccase on magnetic bimodal mesoporous carbon and the application in the removal of phenolic compounds

A novel magnetically separable laccase immobilized system was constructed by adsorbing laccase into bimodal carbon-based mesoporous magnetic composites (CMMC). A large adsorption capacity (491.7 mg g(-1)), excellent activity recovery (91.0%) and broader pH and temperature profiles than free laccase have been exhibited by the immobilized laccase. Thermal stability was enhanced to a great extent and operational stability was increased to a certain extent. The shift of kinetic parameters indicated affinity change between enzyme and substrate. Application of the immobilized system in phenol and p-chlorophenol removal was investigated in a batch system. Adsorption effects of the support were responsible for the quick removal rate in the first hour, and up to 78% and 84% of phenol and p-chlorophenol were removed in the end of the reaction, respectively, indicating that the magnetic bimodal mesoporous carbon is a promising carrier for both immobilization of laccase and further application in phenol removal.

Enhanced catalytic activity of lipase encapsulated in PCL nanofibers

Use of biocatalysis for industrial synthetic chemistry is on the verge of significant growth. Enzyme immobilization as an effective strategy for improving the enzyme activity has emerged from developments especially in nanoscience and nanotechnology. Here, lipase from Burkholderia cepacia (LBC), as an example of the luxuriant enzymes, was successfully encapsulated in polycaprolactone (PCL) nanofibers, proven by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Evaluated in both organic and aqueous medium, the activation factor of the encapsulated enzymes in the hydrolysis reaction was generally higher than that in the transesterification reaction. Enhanced catalytic activities were found when 5-20 w/w % of LBC was loaded. The effect of different solvents pretreatment on the activity of immobilized LBC was also investigated. The highest activation factor was found up to 14 for the sample containing acetone-treated LBC/PCL (10 w/w %). The encapsulated lipase reserved 50% of its original activity after the 10th run in the transesterification reaction in hexane medium. The mechanism of activation of lipase catalytic ability based on active PCL nanofiberous matrix is proposed.

Degradation of high concentration 2,4-dichlorophenol by simultaneous photocatalytic-enzymatic process using TiO2/UV and laccase

Removal of 2,4-dichlorophenol (2,4-DCP) by TiO2/UV photocatalytic, laccase, and simultaneous photocatalytic-enzymatic treatments were investigated. Coupling of native laccase with TiO2/UV showed a negative synergetic effect due to the rapid inactivation of laccase. Immobilizing laccase covalently to controlled porous glass (CPG) effectively enhanced the stability of laccase against TiO2/UV induced inactivation. By coupling CPG-laccase with the TiO2/UV the degradation efficiency of 2,4-DCP was significantly increased as compared with the results obtained when immobilized laccase or TiO2/UV were separately used. Moreover, the enhancement was more remarkable for the degradation of 2,4-DCP with high concentration, such that for the degradation of 5mM 2,4-DCP, 90% removal percentage was achieved within 2h with the coupled degradation process. While for the TiO2/UV and CPG-laccase process, the removal percentage of 2,4-DCP at 2h were only 26.5% and 78.1%, respectively. The degradation kinetics were analyzed using a intermediate model by taking into account of the intermediates formed during the degradation of 2,4-DCP. The high efficiency of the coupled degradation process therefore provided a novel strategy for degradation of concentrated 2,4-DCP. Furthermore, a thermometric biosensor using the immobilized laccase as biorecognition element was constructed for monitoring the degradation of 2,4-DCP, the result indicated that the biosensor was precise and sensitive.

Fabrication of poly-DL-lactide/polyethylene glycol scaffolds using the gas foaming technique

The aim of this study was to prepare poly-DL-lactide/polyethylene glycol (PDLLA/PEG) blends to improve medium absorption and cell proliferation in the three-dimensional (3-D) structure of their scaffolds. Carbon dioxide (CO2) was used as a foaming agent to create porosity in these blends. The results of Fourier transform infrared (FTIR) spectroscopy demonstrated that the blends were homogeneous mixtures of PDLLA and PEG. The peak shifts at 1092 and 1744 cm(-1) confirmed the presence of molecular interactions between these two compounds. Increasing the PEG weight ratio enhanced the relative crystallinity and hydrophilicity. The PDLLA/PEG blends (especially 80/20 and 70/30 weight ratios) exhibited linear degradation profiles over an incubation time of 8 weeks. The mechanical properties of PDLLA/PEG blends having less than 30 wt.% PEG were suitable for the fabrication of porous scaffolds. Increasing the concentration of PEG to above 50% resulted in blends that were brittle and had low mechanical integrity. Highly porous scaffolds with controllable pore size were produced for 30 wt.% PEG samples using the gas foaming technique at temperatures between 25 and 55 °C and pressures between 60 and 160 bar. The average pore diameters achieved by gas foaming process were between 15 and 150 μm, and had an average porosity of 84%. The medium uptake and degradation rate of fabricated PDLLA/PEG scaffolds were increased compared with neat PDLLA film due to the presence of PEG and porosity. The porous scaffolds also demonstrated a lower modulus of elasticity and a higher elongation at break compared to the non-porous film. The fabricated PDLLA/PEG scaffolds have high potential for various tissue-engineering applications.

Prediction of nitrobenzene toxicity to the algae (Scenedesmus obliguus) by quantitative structure-toxicity relationship (QSTR) models with quantum chemical descriptors

In this study, Quantitative structure-toxicity relationship (QSTR) models were developed to predict the toxicity of nitrobenzene to the algae (Scenedesmus obliguus). Quantum chemical descriptors computed by PM3 Hamiltonian were used as predictor variables. The cross-validated Q²(cum) value for the optimal QSTR models is 0.867, indicating good predictive capability. The toxicity of nitrobenzenes (pC) was found to be affected by the molecular structure, the heat of formation (ΔH(f)) and dipole moment (μ(z)). Contrary to the μ(z) values of nitrobenzenes, the ΔH(f) values increase with increase in pC values and the energy of the highest occupied molecular orbital. Increasing the largest positive atomic charge on a nitrogen atom and the most positive net atomic charge on a hydrogen atom of the nitrobenzene leads to decrease in pC values. Nitrobenzenes with larger absolute hardness tend to be more stable and less toxic to the algae.

Laccase-carrying electrospun fibrous membranes for adsorption and degradation of PAHs in shoal soils

The removal of polycyclic aromatic hydrocarbons (PAHs) from soil is costly and time-consuming. The high hydrophobicity of PAHs makes PAH diffusion from soil particles by hydraulic flow difficult. The phase transfer of PAHs from soil to another available mediator is crucial for PAH removal. This study focuses on the remediation of PAH-contaminated shoal soil, located in Yangtze, China, using three types of laccase-carrying electrospun fibrous membranes (LCEFMs) fabricated via emulsion electrospinning. These LCEFMs were composed of core-shell structural nanofibers (for PAH adsorption), with laccase in the core (for PAH degradation) and pores on the shell (for mass transfer). The LCEFMs with strong adsorptivity extracted the PAHs from the soil particles, resulting in an obvious enhancement of PAH degradation. The removal efficiencies in 6 h for phenanthrene, fluoranthene, benz[a]anthracene and benzo[a]pyrene were greater than 95.1%, 93.2%, 79.1%, and 72.5%, respectively. The removal half-lives were 0.003-1.52 h, much shorter than those by free laccase (17.9-67.9 h) or membrane adsorption (1.25-12.50 h). The third-order reaction kinetics suggested that the superficial adsorption and internal diffusion were the rate-limiting steps of the overall reaction. A synergistic effect between adsorption and degradation was also proposed on the basis of the triple phase distribution and kinetics analyses.

Amine functional monodisperse microbeads via precipitation polymerization of N-vinyl formamide: immobilized laccase for benzidine based dyes degradation

Densely cross-linked poly(vinylamine) microbeads (∼ 2 μm) were prepared by precipitation copolymerization of N-vinyl formamide and ethylene glycoldimethacrylate in acetonitrile. The formamido groups of the microbeads were hydrolyzed into amino groups. Then, amino-functionalized microbeads were used for covalent immobilization of laccase via glutaraldehyde coupling. The average amount of immobilized enzyme was 18.7 mg/g microbeads. Kinetic parameters, V(max) and K(m) values were determined as 20.7 U/mg protein and 2.76 × 10(-2)mmol/L for free enzyme and 15.8 U/mg protein and 4.65 mmol/L for the immobilized laccase, respectively. The immobilized laccase was operated in a batch reactor for the degradation of two different benzidine based dyes (i.e., Direct Blue 1 and Direct Red 128). The laccase immobilized on the microbeads was very effective for removal of these dyes which interfere with the hormonal system.

Cloning and functional analysis of a new laccase gene from Trametes sp. 48424 which had the high yield of laccase and strong ability for decolorizing different dyes

The laccase gene lac48424-1 and its corresponding full-length cDNA were cloned and characterized from a novel white-rot fungi Trametes sp. 48424 which had the high yield of laccase and strong ability for decolorizing different dyes. The 1563 bp full-length cDNA of lac48424-1 encoded a mature laccase protein containing 499 amino acids preceded by a signal peptide of 21 amino acids. The deduced protein sequence of LAC48424-1 showed high similarity with other known fungal laccases and contained four copper-binding conserved domains of typical laccase protein. The functionality of lac48424-1 gene encoding active laccase was verified by expressing the gene in the yeast Pichia pastoris successfully. It was found that the recombinant laccase produced by the yeast transformant could decolorize different dyes. The 5'-flanking sequence upstream of start codon was obtained by Self-Formed Adaptor PCR. Many putative cis-acting responsive elements involved in the transcriptional regulation were identified in the promoter region of lac48424-1.