Spectroscopic Studies Interaction Mechanism Of Three Potential Carcinogenic Pesticides With Calf Thymus DNA

In recent years, the incidence of the cancer-causing pesticides shows an increasing trend. DNA which is the main target of carcinogens is becoming the focus of research pesticides carcinogenic mechanism. In this thesis, fluorescence spectroscopy, UV-visible spectroscopy, infrared spectroscopy, circular dichroism, NMR, atomic force microscopy combined with fluid dynamics method were applied to study the the mechanism of interaction calf thymus DNA(ctDNA) with several pesticides of (cyanazine, folpet and triadimenol) from different angles which were reported to have potential carcinogenicity by U.S. Environmental Protection Agency (EPA). The goal is to clarify how these carcinogenic pesticides damage DNA, prevent pesticide poisoning, and provide a theoretical basis for the development of new low-toxicity pesticides. The paper is divided into four parts:(1) the recent status of pesticide carcinogenic, carcinogenic, research tools, research of the interaction between pesticides and ctDNA, methods as well as chemometrics were reviewed;(2) the binding mechanism of cyanazine to ctDNA and investigate the thermodynamic characteristic was explored using multispectroscopic methods including UV-vis absorption, fluorescence, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy, coupled with viscosity measurements under physiological pH conditions. The results revealed that intercalation binding should be the interaction mode of cyanazine to ctDNA. In addition, the intention was to study the changes and progress of the ctDNA-cyanazine interaction based on the concentration information and corresponding pure spectra of the reaction components by resolving the measured absorption spectral data of the competitive reaction between cyanazine and ethidium bromide probe with ctDNA with the aid of alternate least squares (ALS) which indicated that cyanazine intercalated into ctDNA by substituting for EB in the ctDNA-EB complex.(3) In this work, the hydrolytic process of folpet in the absence and presence of ctDNA in pH7.4Tris-HCl buffer was investigated using UV-vis absorption spectroscopy. ALS was applied to analyze the absorption spectra data, which revealed there were four components (folpet, phthalimide, phthalic acid, and an unstable intermediate) during the hydrolytic process. Their pure spectra and concentration profiles throughout the process were simultaneously extracted to monitor the hydrolytic process. The results of DNA binding test indicated that folpet or the intermediate can intercalate into the double-helix of ctDNA, while phthalic acid bound to DNA by a non-classical intercalation. Phthalimide could not interact with DNA;(4) the interaction between triadimenol (NOL) and calf thymus DNA in a pH7.4tris-HCl buffer was investigated by multispectroscopic methods including UV-vis absorbtion, fluorescence, circular dichroism (CD), Fourier transform infrared (FT-IR), and nuclear magnetic resonance (1H NMR) spectroscopy, coupled with viscosity measurements, atomic force microscopy (AFM) and molecular docking technique. The results suggested that NOL interacted with ctDNA by intercalation mode which resulted in regional cleavage of the two DNA strands and a specific binding mainly exists between NOL and G-C base pairs of the ctDNA where two hydrogen bonds form. Moreover, the effect of Ca2+and Mg2+on this interaction were studied which indicated that both of the two metal ions could enhance the interaction between ctDNA and NOL. The binding constants of ctDNA-NOL complex tended to increase initially and then decrease as the concentrations of the two metal ions increased. Therefore, the effect of metal ions on the binding between NOL and DNA mainly depends on the relative affinity between metal ions and NOL, DNA basic groups or phosphate groups.