Potential Of Small Molecular Diketones As Mediators For Laccase

Laccase-mediator systems(LMS)have been extensively studied for the degradation of variant recalcitrant compounds,but their practical application in wastewater treatment is hampered by the high cost,toxic risks,and poor recyclability of the synthetic mediators,and high costs of separation and purification,and unkown toxicity of natural mediators.Therefore,low cost,environmentally friendly and good recyclable mediators are still highly needed to facilitate the application of laccase in various biotechnological processes for wastewater treatmentIn the present study,the potential of three diketones,biacetyl,acetylacetone(AA),and acetonylacetone,as mediators for laccase were investigated.The two widely-used laccase mediators,1-hydroxybenzotriazole(HBT)and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)were employed as references.Experimental results demonstrate that all the three diketones could act as effective mediators in LMS for dye degradation,and exhibited different degradation performace for the different substrates,suggesting that diketones are similar to the the widely-used HBT and ABTS.The LMSs composed of laccase and diketones were substrate-selective.In cycling runs for enzymatic degradation of dyes,the diketones showed much better reusability than HBT.According to the UV-Vis spectra and HPLC profiles,less degradation products were generated in the laccase-diketone systems than those in the laccase-HBT system.More intensified new products were formed in the laccase-HBT system,implying more possible intensified toxic risks.Young Daphnia magna(6-24 h of life)was investigated to evaluate the toxicity of mediators,substrate solutions before and after degradation in laccase-only and laccase-mediator systems.Results showed that as compared with HBT and ABTS,diketones are of low toxicity and could detoxify substrate solutions.The degradation mechanism in the laccase-AA system was investigated by electron paramagnetic resonance analysis.Possible mechanisms were proposed,including hydrogen atom transfer or electron transfer mechanism between laccase and AA.Overall,the eco-friendly small diketones with relatively low cost,good detoxification ability,and decent enhancing effect on the catalytic efficiency of laccase in cycling runs endow them with several merits as ideal redox mediators.These characteristics made the diketone-mediated enzymatic degradation processes much more cost effective and promising in practical application.