| In this thesis, three kinds of organic pollutants including fenvalerate,nonylphenol and polycyclic aromatic hydrocarbons (PAHs) are selected as theresearch objects. For the two research fields of degradation mechanism and thequantum structure-activity relationship (QSAR), by using density functional theory,the research includes five aspects: the photodegradation mechanism of fenvalerate inwater; the photodegradation mechanism of4-n-nonylphenol in water; a QSAR studyon the biodegradation of PAHs in aged contaminated sedments; QSAR for predictingbiodegradation rates of PAHs in aqueous systems; a QSAR study on thephotodegradation of PAHs in aqueous systems. On one hand, the transition states,intermediates and reaction pathways for the photodegradation of fenvalerate andnonylphenol are confirmed and the full reaction mechanisms are obtained. On theother hand, quantum structure-activity relationship on the biodegradation andphotodegradation of PAHs in different surroundings are established. The researchresults can provide certain theoretical basis for the degradation and transformation oforganic pollutants in marine environment.(1) The photodegradation mechanism of fenvalerate in water has beeninvestigated by density functional theory. The geometries of reactants, transition states,intermediates and products are optimized at B3LYP/6-31G*level. The calculatedresults indicate that the reaction process mainly includes the nucleophilic attack andthe substitution reaction by hydroxyl radical to carbonyl group. By vibrationalfrequency analysis and intrinsic reaction coordinate method, the transition state and itsreaction pathway are confirmed. Moreover, the changes of natural population analysis,calculated using Natural bond orbital method, are analyzed along with the degradationreaction which can explain the variation of chemical bonds. Additionally, the solventeffect is also investigated and the results show that the reaction preferably takes placein water. (2) The photodegradation mechanism of nonylphenol in water induced by·OHhas been investigated by density functional theory. By the analysis of NBO charges,we speculate the main reaction for·OH and nonylphenol include carbon addition tobenzene ring and hydrogen abstraction to phenolichydroxyl. The geometries ofreactants, transition states, intermediates and products are optimized atB3LYP/6-31G*level. By vibrational frequency analysis and intrinsic reactioncoordinate method, the transition state and its reaction pathway are confirmed. Theconfirmed intermediates and products are agree with the experimental results.(3) The relationship between the chemical structure and biodegradation activityof17PAHs was studied using density functional theory and stepwise multiple linearregression analysis methods. The equilibrium geometries and vibration frequencyhave been investigated at B3LYP/6-31+G(d,p) level. One high correlation coefficientwas found between the wagging vibration frequency of the whole molecule and-logt1/2, which is resulted by the special structural characteristic with a bigconjugated system. By means of regression analysis, the main factors influencingbiodegradation activity were screened, and the equations of quantitativestructure-activity relationship were established-logt1/2=12.049-0.013Freq-0.159N-5.329ELUMO+16.528NEHOMO-0.003IRIn. The evaluation of the developed QSARshowed that the relationships are significant and the model had good predictive ability.The QSAR model showed that the biodegradation activity was closely related tomolecular structure: the chemical bond strength of benzene ring played an importantrole in biodegradation process; In addition, low molecular weight PAHs are moredegradable than the high molecular weight compounds.(4) The relationship between chemical structures and biodegradation rateconstants of22PAHs was studied using density functional theory and stepwisemultiple linear regression analysis method. The equilibrium geometries and vibrationfrequency have been investigated at B3LYP/6-31+G(d,p) level by thinking Solventeffects using a selfconsistent reaction field based on the polarizable continuum model.It was concluded that the biodegradation rate was closely related to its molecularstructure, and there was one high correlation coefficient between the in-plane bending vibration frequency of the conjugated ring of PAHs and biodegradation rate constant.By means of regression analysis, the main factors affected biodegradation rate wereobtained and the equation of QSAR was successfully established kb=-0.653+0.001Freq+0.068Q C+0.049N1. Statistical evaluation of the developed QSAR showedthat the relationships are statistically significant and the model had good predictiveability. The fact that a bending frequency is more important than the HOMO orLUMO energies in predicting kb suggests that the bend of benzene ring might play animportant role in the enzymatic catalysis of the initial oxidation step.(5) The relationship between chemical structures and photodegradation activityof12PAHs was studied using density functional theory and stepwise multiple linearregression analysis method. The equilibrium geometries and vibration frequency havebeen investigated at B3LYP/6-31+G(d,p) level by thinking Solvent effects using aselfconsistent reaction field based on the polarizable continuum model. It wasconcluded that the photodegradation activity was closely related to its molecularstructure. By means of regression analysis, the main factors affectingphotodegradation rate include the energy of the highest occupied orbital EHOMOandthe number of benzene ring N1, and the equation of QSAR was successfullyestablished logkb=6.046+54.830EHOMO+0.272N1. Statistical evaluation of thedeveloped QSAR showed that the relationships are statistically significant and themodel had good predictive ability. EHOMOis the most important factor influcing thephotodegradation of PAHs, because the higher EHOMOis, the more easily electron willbe excited and the more easily molecular will be degraded. |
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