Study On Degradation Of Polycyclic Aromatic Hydrocarbons Based On Biosurfactant Laccase Reverse Micelle System

Polycyclic aromatic hydrocarbons（PAHs）are a class of organic compounds composed of two or more fused aromatic rings,which can be formed during the thermal decomposition of organic molecules and their subsequent recombination.They can be produced not only naturally from fire and fossil fuels,but also from incomplete combustion of organic chemicals.The intensification of human activities has caused a large amount of pollutants to be released into the ubiquitous air,soil and water.Especially in the aquatic environment,due to their high hydrophobicity,they tend to adsorb on the particulate matter,and remain adsorbed for a long time,making it difficult to wash away PAHs.At the same time,PAHs can also cause many adverse effects on aquatic organisms,including endocrine changes,hindering growth,DNA damage,and malformations of embryos and larvae.At present,the degradation of polycyclic aromatic hydrocarbons by enzymes is a good method of biological management.However,the direct contact between enzymes and organic reagents will reduce the enzyme activity and affect the effective degradation of polycyclic aromatic hydrocarbons.The construction of the mediator system can enable enzymes to oxidize compounds with higher redox potentials than themselves.However,it has disadvantages of low repeated utilization rate and high molar ratio of mediator to substrate.It is necessary to find a new enzyme catalytic system to exert the catalytic ability of laccase better.The unique pool of reverse micelles can be regarded as a nanoreactor,which will protect the enzyme from denaturation caused by direct contact with organic solvents and promote the enzyme to show super activity.Biosurfactant is a degradable surfactant.Compared with other surfactants produced by chemical synthesis or petroleum refining methods,it has the advantages of non-toxic,biodegradable,ecological safety and high surface activity.So the use of biosurfactants with good biocompatibility instead of chemical surfactants to construct reverse micelle enzyme systems can help to protect the environment.In the study,taking the laccase as the core,the well-characterized reverse micelles were formed by rhamnolipid（RL）.And it was used to degrade phenanthrene,benz（a）anthracene and benzo（b）fluoranthene.Based on the system,the effect of some relevant parameters,such as water content,pH,temperature and RL concentration had been explored and the optimum condition was found:w_o（20）,pH（4.8）,t（35°C）and RL concentration（150 CMC）.The highest degradation rates of phenanthrene,benz（a）anthracene and benzo（b）fluoranthene were 52.22%、35.25%and28.92%,respectively.Meanwhile,based on the research of the laccase kinetics,the maximum velocity(v_max)and the Michaelis constant（K_m）were obtained under the circumstance that phenanthrene and benz（a）anthracene was as the substrate respectively.In addition,at the variety of p H and temperature,the structural change of laccase in the reaction system have been investigated by CD（circular dichroism）.The results showed that mutual conversion occurred betweenβ-sheet and random coil,and the content ofα-helix andβ-turn fluctuated within a narrow range in the degradation process.The detection of intermediate for degradation of benzo（a）anthracene by laccase rhamnolipid reverse micelle system by gas chromatography-mass spectrometry showed the superior catalytic properties of laccase under this system.The appearance characteristic of reverse micelle was deaminated by using Phase contrast,NMR,Cryo-sem and confocal technics.Reverse micelle with low w_o present smaller,spherical and having signal layer characters.As with the increase of w_o,reverse micelle turns to be bigger,with more layers.At last,through the related quantum chemistry calculations of Hishfeld charge,Fukui function,and the atomic contribution of carbon atoms in HOMO and LUMO,the initial degradation sites of benzo（a）anthracene catalyzed by laccase were predicted.