QSAR Models For Predicting Reaction Rate Constants Of Typical Organic Contaminants With Hydrated Electrons And Their Mechanistic Pathways

The hydrated electron(eaq-)-based reduction processes are promising for removing organic pollutants in water engineering systems.The second order rate constants(keaq-)of eaq-with organic compounds is important for evaluating the removal efficiency of organic pollutants in advanced reduction system.At present,there are only hundreds of experimental keaq-values for organic compounds.Due to the high cost and time consumption of experimental methods,it is unrealistic to obtain keaq-for the large number of chemicals by experimental determination.Thus,it is necessary to empoly computational simulation methods to predict the keaq-of organic compounds.In this study,the keaq-values for aliphatic compounds and phenyl-based compounds are,for the first time,modeled by the quantitative structure-activity relationship(QSAR)method.Quantum chemical calculations are conducted to investigate the feasibility of these reduction reactions and the pathway of single electron transfer(SET).Additionally,the impacts of the functional groups on keaq-and the thermodynamic viability of the reactions are also investigated to better understand the reactivity of organic compounds with eaq-.The main results are as follows:(1)Based on quantum chemical descriptors and molecular structure parameters,QSAR models for predicting the keaq-of aliphatic compounds and phenyl-based compounds are constructed by employing stepwise multiple linear regression(MLR)and support vector machine(SVM)methods.All QSAR models have satisfactory goodness-of-fit(R2adj,tr>0.700),robustness(Q2LOO>0.650)and good predictability(Q2ext>0.700).In addition,the performances of SVM models are generally better than that of MLR models.(2)It is revealed that the energy of the lowest unoccupied molecular orbital(ELUMO),one-electron reduction potential(ERED)and polarizability(a)are the most important descriptors governing the reactivity of two classes of organic compounds toward eaq-.(3)Quantum chemical calculations are employed to probe into the feasibility of the SET pathway in the eaq--based reduction process.The computational results show that the compounds with electron-withdrawing groups tend to possess higher keaq.and lower Gibbs free energy(?GSET)and Gibbs free energies of activation(?(?)G0SET)than the ones with electron-donating groups,indicating that the compounds containing electron-withdrawing functional groups tend to have higher reactivity with eaq-.(4)It is also found that the refractory halogenated alphatic compounds can achieve dehalogenation via the SET pathway.However,whether the halogenated aromatic compounds can achieve dehalogenation depends on the substituents of benzene rings and LUMO distribution to some degree.