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Ionic polymer-coated laccase with high activity and enhanced stability: application in the decolourisation of water containing AO7.

Zhang X, Hua M, Lv L, Pan B - Sci Rep (2015)

Bottom Line: The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity.Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7.The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, P.R. China.

ABSTRACT
Eliminating dyes in environmental water purification remains a formidable challenge. Laccase is a unique, environmentally friendly and efficient biocatalyst that can degrade pollutants. However, the use of laccase for the degradation of pollutants is considerably limited by its susceptibility to environmental changes and its poor reusability. We fabricated a novel biocatalyst (LacPG) by coating polyethylenimine onto the native laccase (Lac) followed by crosslinking with glutaraldehyde. The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity. Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7. LacPG was separated from the AO7 solution using an ultrafiltration unit. The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling. LacPG exhibited enhanced stability, high catalytic activity and favourable properties for membrane separation; therefore, LacPG could be continuously reused in an enzymatic membrane reactor with a high efficiency for decolourising water containing AO7. The developed strategy appears to be promising for enhancing the applicability of laccase in practical water treatment.

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Zeta potentials of Lac and LacPG; error bars show standard deviations for at least five measurements.
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f2: Zeta potentials of Lac and LacPG; error bars show standard deviations for at least five measurements.

Mentions: Figure 1(a) presents a schematic that illustrates the fabrication of LacPG. Briefly, native laccase (denoted as Lac) was modified by PEI to produce Lac-PEI, which was then crosslinked by GA to produce the novel biocatalyst LacPG. UV-Vis spectra (Supplementary Fig. S1) revealed that a significant increase in the absorption intensity occurred for LacPG from 310 to 550 nm compared to a mixture of Lac and PEI-G (which corresponded to the solution of PEI that was crosslinked by GA) at the same concentration level, indicating that LacPG was a new product rather than a simple mixture. A topographic image of LacPG is shown in Fig. 1(b), in which LacPG is observed as shadows with an average size of approximately 20 nm. The size distributions of Lac and LacPG were measured by dynamic light scattering (DLS) (Fig. 1(c)), which indicated a Lac diameter within 4–6 nm, in agreement with the previously reported value for Trametes versicolor laccase38; however, a larger average diameter of 15–17 nm was observed for LacPG, which was consistent with the results shown in Fig. 1(b). Figure 1(d) shows the molecular weight (Mw) of Lac and LacPG determined by size exclusion chromatography (SEC). Lac molecules had a molecular weight of 67 kDa, consistent with the previously reported Mw of laccase from Trametes versicolor of 69 kDa38, whereas most of the LacPG molecules had larger Mw of 206 kDa. In addition to the aforementioned changes in size or molecular weight, the zeta potentials of Lac and LacPG (see Fig. 2) revealed that the isoelectric point (PI) for LacPG (≃6.8) was considerably higher than that for Lac (≃2.9), primarily because the PEI coating on the Lac molecule contained an abundance of positively charged groups. The surface chemistry alteration of LacPG grant more opportunity for anionic substrate to react with LacPG through enhanced electrostatic attraction, which is favourable for decolourisation of water containing anionic azo dye, as elucidated below.


Ionic polymer-coated laccase with high activity and enhanced stability: application in the decolourisation of water containing AO7.

Zhang X, Hua M, Lv L, Pan B - Sci Rep (2015)

Zeta potentials of Lac and LacPG; error bars show standard deviations for at least five measurements.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4317704&req=5

f2: Zeta potentials of Lac and LacPG; error bars show standard deviations for at least five measurements.
Mentions: Figure 1(a) presents a schematic that illustrates the fabrication of LacPG. Briefly, native laccase (denoted as Lac) was modified by PEI to produce Lac-PEI, which was then crosslinked by GA to produce the novel biocatalyst LacPG. UV-Vis spectra (Supplementary Fig. S1) revealed that a significant increase in the absorption intensity occurred for LacPG from 310 to 550 nm compared to a mixture of Lac and PEI-G (which corresponded to the solution of PEI that was crosslinked by GA) at the same concentration level, indicating that LacPG was a new product rather than a simple mixture. A topographic image of LacPG is shown in Fig. 1(b), in which LacPG is observed as shadows with an average size of approximately 20 nm. The size distributions of Lac and LacPG were measured by dynamic light scattering (DLS) (Fig. 1(c)), which indicated a Lac diameter within 4–6 nm, in agreement with the previously reported value for Trametes versicolor laccase38; however, a larger average diameter of 15–17 nm was observed for LacPG, which was consistent with the results shown in Fig. 1(b). Figure 1(d) shows the molecular weight (Mw) of Lac and LacPG determined by size exclusion chromatography (SEC). Lac molecules had a molecular weight of 67 kDa, consistent with the previously reported Mw of laccase from Trametes versicolor of 69 kDa38, whereas most of the LacPG molecules had larger Mw of 206 kDa. In addition to the aforementioned changes in size or molecular weight, the zeta potentials of Lac and LacPG (see Fig. 2) revealed that the isoelectric point (PI) for LacPG (≃6.8) was considerably higher than that for Lac (≃2.9), primarily because the PEI coating on the Lac molecule contained an abundance of positively charged groups. The surface chemistry alteration of LacPG grant more opportunity for anionic substrate to react with LacPG through enhanced electrostatic attraction, which is favourable for decolourisation of water containing anionic azo dye, as elucidated below.

Bottom Line: The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity.Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7.The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, P.R. China.

ABSTRACT
Eliminating dyes in environmental water purification remains a formidable challenge. Laccase is a unique, environmentally friendly and efficient biocatalyst that can degrade pollutants. However, the use of laccase for the degradation of pollutants is considerably limited by its susceptibility to environmental changes and its poor reusability. We fabricated a novel biocatalyst (LacPG) by coating polyethylenimine onto the native laccase (Lac) followed by crosslinking with glutaraldehyde. The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity. Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7. LacPG was separated from the AO7 solution using an ultrafiltration unit. The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling. LacPG exhibited enhanced stability, high catalytic activity and favourable properties for membrane separation; therefore, LacPG could be continuously reused in an enzymatic membrane reactor with a high efficiency for decolourising water containing AO7. The developed strategy appears to be promising for enhancing the applicability of laccase in practical water treatment.

Show MeSH
Related in: MedlinePlus