Spectroscopic Detection Of Pesticide Residues Based On Porphyrins And Study On Their Molecular Interaction

Pesticides play an irreplaceable role in agriculture to assure agricultural product inquality and quantity, but residues from pesticide abuse has become a worldwide issuebecause it is harmful to food, environment and export. To solve the problem, it isextremely urgent to develop a new method for pesticide residues detection with highsensitivity, rapidity and reliability. Based on its low cost, high sensitivity, wideapplicability and easy popularization, UV-Visable spectrometry association with highphotosensitive porphyrins was proposed to detect pesticide residues, and theirinteraction mechanism was initially discussed. Specifically, the thesis was completed asfollows:1. Four porphyrins including5-（4-carboxyphenyl）-10,15,20-triphenylporphyrin（CTPP）,5-（4-carboxyphenyl）-10,15,20-triphenylporphyrin zinc （ZnCTPP）,5-（4-aminophenyl）-10,15,20-triphenylporphyrin （ATPP） and5-（4-aminophenyl）-10,15,20-triphenylporphyrin zinc （ZnATPP） were synthesized for pesticide residues detection.Their structures were characterized by UV-Visible spectrophotometry, FT-IRspectrometry and1HNMR spectrometry.2. Four typical pesticides including organophosphorus chlorpyrifos,organochlorine triadimefon, carbamate carbendazim and pyrethroid decamethrin weredetected with four as-prepared porphyrins by UV-Visible spectrophotometry. Aftersystematic data processing, the absorance-concentration relationship, calibration curve,sensitivity and detection limit were obtained. Based on the national standard of pesticideresidues and linear relationship of the results, ATPP, CTPP and ZnATPP were selectedas the superior porphyrins to detect chlorpyrifos with detection limits of1ppb,10ppband10ppb, individually. Meanwhile, CTPP and ZnATPP were more suitable fortriadimefon with detection limits of1ppb and10ppb. CTPP and ATPP were not only fitfor carbendazim but also decamethrin with detection limits of0.1ppb,10ppb,0.1ppband1ppb, individually.3. Molecular interactions of porphyrins with pesticides were initially investigatedby molecular docking modul of Sybyl. The results showed CTPP was best for pesticidesdetection because of their interaction by hydrogen bonding and π-π facial stacking,while other three porphyrins only via π-π facial stacking. 4. Molecular interactions incluing association constants and themodynamicconstants of CTPP with four pesticides were studied by UV-Visible spectrophotometry.The results demonstrated CTPP as the electron receptor and pesticides as the electrondonor coordinated via hydrogen bonding and π-π facial stacking with coordinationnumber of1：1. Their association constants of CTPP with chlorpyrifos, triadimefon,carbendazim and decamethrin at298.15K were6.02×10²M^-1,6.44×10²M^-1,26.30×10²M^-1and27.30×10²M^-1, individually. And they decreased with temperatureincreased, which indicated lower temperature benefits to the reactions. However, it wasfound that CTPP showed stronger binding ability to carbendazim and decamethrinbecause of higher association constants. Moreover, the standard molar enthalpy change（rHm^θ） and standard molar entropy change （rSm^θ） of the four reaction systems wereinvestigated, which indicated chlorpyrifos coordinating with CTPP was a entropydecreased exothermic reaction, while other three pesticides with CTPP were entropyincreased exothermic reactions.