Research On The Photo And Photosensitive Degradation Of PCBs

Based on the density functional theory and time dependent density functional theory, the mechanism of direct photo degradation and the photosensitive degradation in natural organic matter for PCBs were studied, by the method of QST3, the transition state and reaction mechanism of the ring-opening reaction for PCBs were discussed. Meanwhile, in order to investigate the effects of natural organic matter on the degradation of PCBs, combined with the polarized continuum model (PCM), the solvent effect on the photo degradation of PCBs were analyzed based on the ground state and the excited state parameters. At last, by setting the strongest peak of the ultraviolet absorption spectrum of the PCB-52 molecule as the dependent variable and the filtered PCB-52 quantization parameter based on the correlation analysis and the principal component analysis as the independent variable, the quantitative structure-activity relationship (QSAR) model is built based on the quantum-chemical parameters.This study found that the degradation reaction activity of PCBs in symmetrical structure is lower than that in the asymmetric structure, the degradation reaction activity for C-Cl bond in different positions is different (ortho position> inter position> para position), and the number of C-Cl bond does not affect the degradation reaction activity of PCBs. However, as the only one has two ortho C-Cl bond in symmetric structure, the degradation reaction activity of PCB-4 is not in accordance with the above rules; the open-loop point, transition state and the energy barrier in the process of ring opening reaction were found, there is a remarkable correlation between the strongest peak of the ultraviolet absorption spectrum of the PCB-52 molecule and its structural parameters (3) and the energy parameters of the ground state and excited state (17) (sig. is 0.034<0.05). The established quantitative structure-activity relationship (QSAR) model was tested by a validation set composed of PCBs detected in the Arctic with a coefficient of simulation equal to 0.98>0.9. The sensitivity analysis of the QSAR model shows that the energy parameters, excitation energy (6), oscillator strength and structure parameter of the C-Cl bond-length are the most significant parameters affecting the strongest peak of the ultraviolet absorption spectrum of PCB molecules.