Mechanism Of Oxidative Degradation And Biodegradation Of PCBs Based On DFT And Molecular Docking

Polychlorinated biphenyls are widely used in heat exchange agent,lubricant,insulation transformer and capacitor,plasticizers and flame retardants and other important chemical products,is present in the environment of a kind of typical chlorinated organic pollutants,a large number of PCBs products are released into the environment causing serious pollution and adverse effects,ecological system and because of its semi volatile,persistence,bioaccumulation and high toxicity characteristics by the United Nations Environment Programme needs to be listed as the first batch of persistent organic pollutant reduction and control of the 12 kinds of persistent organic pollutants such as.PCBs toxicity is very strong,the transformation in the environment and the removal pathway has been a hot issue the concern of the people.The reaction pathways of PCB-77 in the atmosphere with OH,O2,NOx,and1O2 were inferred based on density functional theory calculations with the 6-31G*basis set.The structures the reactants,transition states,intermediates,and products were optimized.The energy barriers and reaction heats were obtained to determine the energetically favorable reaction pathways.To study the solvation effect,the energy barriers and reaction rates for PCB-77 with different polar and nonpolar solvents(cyclohexane,benzene,carbon tetrachloride,chloroform,acetone,dichloromethane,ethanol,methanol,acetonitrile,dimethylsulfoxide,and water)were calculated.The results showed that ·OH preferentially added to the C5 atom of PCB-77,which has no Cl atom substituent,to generate the intermediate IM5.This intermediate subsequently reacted with O2 via pathway A to generate IM5a,with an energy barrier of 7.27 kcal/mol and total reaction rate of 8.45×10-8 cm3 molecule-1 s-1.Pathway B involved direct dehydrogenation of IM5 to produce the OH-PCBs intermediate IM5b,with an energy barrier of 28.49 kcal/mol and total reaction rate of 1.15×10-5 cm3 molecule-1 s-1.The most likely degradation pathway of PCB-77 in the atmosphere is pathway A to produce IM5a.The solvation effect results showed that cyclohexane,carbon tetrachloride,and benzene could reduce the reaction energy barrier of pathway A.Among these solvents,the solvation effect of benzene was the largest,and could reduce the total reaction energy barrier by 25%.Cyclohexane,carbon tetrachloride,benzene,dichloromethane,acetone,and ethanol could increase the total reaction rate of pathway A.The increase in the reaction rate of pathway A with benzene was 8%.The effect of solvents on oxidative degradation of PCB-77 in the atmosphere is important.Microbial degradation of PCBs is the effective way of soil and PCBs in water environment degradation that can achieve complete mineralization.Using dioxin like polychlorinated biphenyls(PCBs)degradation products of atmospheric oxidation of two hydroxy PCBs and 2,3 two hydroxy biphenyl dioxygenase(Bphc,PDBID:IKW6)were constructed by molecular docking.The molecular structure parameters as independent variables,scoring function(Kd value,on behalf of docking activity)as the dependent variable molecular similarity index analysis(CoMSIA)and the related molecular hologram quantitative structure-activity relationship(HQSAR)model,and molecular modification of two hydroxy PCBs,in order to improve the two docking activity of OH-PCBs.The results showed that Bphc enzyme of two hydroxy PCBs have different degrees of degradation,the effect of amino acid residues of Bphc enzyme activity for docking:His145,Val147,ILE174,His194,His208,Hi S209,His240,ASN242,TYR249,THR280,and two more hydrogen bonds of Oh PCBs and amino acid residues in the formation of the docking docking,the higher the activity.In addition,the molecular model of CoMSIA in electrostatic field is the main factor affecting two hydroxy PCBs and Bphc enzyme docking intensity,but the electrostatic potential map of the three-dimensional block area is too large unable to determine the precise sites,the effect of molecular substitution activity,molecular and HQSAR model activity contribution diagram,can make up for the CoMSIA model can not precisely locate the activity of the substituent shortcomings.Accordingly,the scoring function of lower two hydroxy polychlorinated biphenyl 5,6-2OH-CB60 as target molecule,design a new type of 8 kinds of scoring function significantly improved the molecules.The docking activity increased 65%?85%and decreased 10%-83%(IC50)molecular toxicity,bioaccumulation(BCF)decreased 4%-27%migration(KOA)and half-life(t1/2)increase decline basically unchanged.The design of a new type of molecular reaction Path inference can be verified further by two hydroxy polychlorinated biphenyls 5,6-2OH-CB60 new 5,6-2OH-CB60 molecular design and activity of free radicals or reactive molecules generated in the reaction and in the environment,the new two hydroxy PCBs dioxin like PCBs that can be generated by atmospheric oxidation degradation enzyme degradation significantly improved,to further control the dioxin like PCBs the purpose of the behavior.