Study On The DNA Interaction Targeting Mechanism Of Several Organic Pesticides

Chemical pesticides are a kind of considerable contaminants in the environmentwith potential hazard. Their widespread use had brought serious threat to humanhealth. They can be bioaccumulated in organism through the food chain and producebiologic toxicity at the doses escalated to a certain point. Deoxyribonucleic acid(DNA) is the substance basis for the gene expression, and is also regarded as the mainmolecular target of exogenous chemical substances. The comprehension of themechanism of DNA with chemical pesticides has contributed to evaluate and forecastthe toxicological effect to human at the molecular level. In this thesis,multispectroscopic and chemometrics approaches, coupled with the moleculardocking techniques, DNA viscosity and melting measurements were introduced toprobe the interaction mechanism of calf thymus DNA with several pesticides (dicofol,chlorpropham, metolcarb) in detail.The main contents in the thesis are summarized as follows:1. The chemical and biological characters of DNA were introduced simply, thenthe binding mode, research methods and basic theories of the interaction betweensmall molecules and DNA were described. Moreover, the great significances of theresearch were reviewed.2. The interaction between dicofol (DCF) and calf thymus DNA (ctDNA) wasinvestigated in physiological buffer (pH7.4) with the use of ethidium bromide (EB)as a spectral probe by fluorescence, circular dichroism (CD), and fourier transforminfrared (FT IR) spectroscopy coupled with DNA melting studies and viscositymeasurements. It can be found that DCF molecules could intercalate into the basepairs of ctDNA as evidenced by significant fluorescence quenching of the ctDNA–EBcomplex, and increase in melting temperature and relative viscosity of ctDNA.Analysis of the FT IR and CD spectra suggested that DCF mainly bound to guanineand cytosine bases and led to some changes in base stacking and double helix ofctDNA.3. This study was designed to investigate the binding properties includingbinding mode, binding constant, binding force and binding sites between herbicide chlorpropham (CIPC) and calf thymus DNA (ctDNA) in vitro by fluorescence,UV vis absorption, circular dichroism (CD) and Fourier transform infrared (FT IR)spectroscopy coupled with denature temperature, viscosity changes and molecularmodeling method. The results indicated that CIPC was intercalated with G base ofctDNA and their binding constant was computed in the order of104L mol1.Furthermore, a chemometrics approach, multivariate curve resolution-alternating leastsquares (MCR–ALS) was used to analyze the combined UV vis absorption datamatrix from the reaction system. The concentration profiles of the reactioncomponents (CIPC, ctDNA and ctDNA–CIPC complex) and their pure spectra weresuccessfully obtained. The concentration profiles reflected the interaction process.Besides, the molecular docking study was used to forecast their interaction andillustrate the possible binding gesture visually.4. The interaction of pesticide metolcarb (MTMC) with calf thymus DNA(ctDNA) was discussed from different aspects (fluorescence quenching, fluorescencepolarization, ion effect, single stranded quenching efect, UV–vis absorption changesand viscosity variations and so on) by multispectroscopic methods and fluid dynamicsmethod. Analysis of the FT IR suggested that MTMC mainly bound to guanine andcytosine bases of ctDNA. And the molecular docking result verified and described theintercalation binding mode. The concentration profiles of the three reactioncomponents and their pure spectra were successfully obtained by MCR ALS.Furthermore, the three-way synchronous fluorescence spectra data procured from theinteraction between MTMC and ctDNA–AO were resolved by parallel factor analysis(PARAFAC), and the competitive binding between MTMC with AO with ctDNA canbe explained from the concentration information of MTMC, AO and ctDNA–AO.