Investigation On The Interaction Mechanism Between Pesticides And DNA

Recently, pesticides have been widely used in argricultural production andaroused serious pesticide residues. The residues of pesticides can directly affected thequality of produce, or enter human body via environmental exposal to exert toxiceffects. DNA is the material basis of biological genetic information and it is the targetof many carcinogenic pesticide molecules. Therefore, it is of great importance toinvestigate of interaction mechanism between DNA and pesticides.The interaction mechanism between calf thymus DNA (ctDNA) and severalfrequently-used pesticides were investigated with the application of multiplespectroscopy methods including ultraviolet visible (UV–vis) absorption,fluorescence, circular dichroism (CD) and fourier transform infrared spectroscopy(FT IR). Furthermore, chemometrics methods and molecular docking were employedto give out more relative information. These investigations have important theoreticalsignificance in evaluating the potential carcinogenicity of pesticides, and can provideuseful information for the invention of new effective pesticides with low toxicity.The main contents of these investigations were summarized as follows:1. A brief introduction concerning the structural and physiological properties ofDNA was presented in the first chapter. The investigating methods about theinteraction between DNA and pesticide molecules were also summarized in thischapter.2. The interaction between linuron and calf thymus DNA (ctDNA) wasinvestigated in physiological buffer (pH7.4) by UV–vis absorption, fluorescence, CDand FT–IR spectroscopies coupled with viscosity measurement and DNA meltingtechnique. The result showed that the fluorescence intensity of ctDNA–MB complexwas greatly enhanced by linuron, suggesting that there existed a strong competitionfor ctDNA binding between linuron and MB. Moreover, the relative viscosity andmelting temperature of ctDNA increased in the presence of linuron. These resultsprovided evidences that linuron intercalated into the base pairs of ctDNA. Theconstringency of CD spectral indicated the conformation conversion from B–ctDNA to C–ctDNA and the guanine and adenine were mainly influenced from the analysisof FT–IR spectra.3. A method system containing multiple spectroscopic methods, DNA viscosityand melting measurements mergering with multivariate curve resolution alternatingleast-squares (MCR ALS) chemometrics approach was built to investigate theinteraction mechanism of permethrin (PE) with ctDNA. The MCR ALS was appliedto resolve the combined spectroscopic data matrix, which was obtained by UV visand fluorescence methods. The concentration profiles of PE, ctDNA, and ctDNA PEcomplex and their pure spectra were then successfully obtained and the resultsprovided quantitive information for the interaction process. The PE molecular wasfound to be able to intercalate into the base pairs of ctDNA as evidenced by decreasesin resonance light-scattering signal and iodide-quenching effect and increase inctDNA viscosity. The results of FT–IR spectra indicated that PE was prone to bind toG C base pairs of ctDNA, and the molecular docking studies were used to validateand clarify the specific binding. The observed changes in CD signals revealed that thectDNA turned into a more highly wound form of B-conformation. The calculatedthermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS),suggested that hydrogen bonds and van der Waals forces played a predominant role inthe binding of PE to ctDNA.4. The binding properties and mode associated with calf thymus DNA (ctDNA)upon interaction with acetamiprid (ACT) was determined using spectroscopic,chemometrics, and molecular docking techniques. Fluorescence titration suggestedthat the fluorescence quenching of ACT by ctDNA was a static procedure. Thepositive values of enthalpy and entropy change suggested that the binding processwas primarily driven by hydrophobic interactions. A chemometrics approach,MCR ALS, was used to resolve the expanded UV–vis spectral data matrix. Theconcentration profiles and the spectra for the three reaction components (ACT,ctDNA, and ctDNA ACT complex) of the system were then successfully obtainedand used to evaluate the progress of ACT interacting with ctDNA. The results of thesingle-stranded ctDNA and iodide quenching experiments, ctDNA-meltinginvestigations, and viscosity measurements indicated that ACT bound to ctDNA by means of a partial intercalation. Results from fourier-transform infrared (FT–IR) andcircular dichroism (CD)spectral analysis showed that the specific binding site wasmainly located between the ACT and G–C base pairs of ctDNA, and ACT induced aconformational change from the B–ctDNA form to the A–ctDNA form.5. The binding action of propyzamide (PRO) associated with ctDNA wasexplored using spectroscopic, parallel factor analysis (PARAFAC) and moleculardocking techniques. The fluorescence spectroscopy suggested a static fluorescencequenching of PRO was induced by ctDNA and the binding reaction waspredominantly driven by hydrophobic interactions. The melting temperature andviscosity of ctDNA was enhanced upon the binding with PRO. Furthermore, thecompetitive interaction of PRO and intercalator acridine orange (AO) with ctDNAwas performed to obtain the complex three-way synchronous fluorescence spectradata, and then resolved by PARAFAC modeling to provided simultaneously theconcentration information and spectra of the three components (PRO, AO andctDNA–AO complex) for the reaction system. These results offered support for theintercalation of PRO molecule into double-helix of ctDNA. The conformationalchanges of ctDNA from B–form to A–form induced by PRO and A–T base pairs ofctDNA were the main binding sites for PRO.