Design, Synthesis And Research Of Photoresponsive Chitosan Derivatives As Nanopesticide

In modern agriculture,the use of pesticides plays a substantial role in ensuring global food production.However,traditional pesticide preparations have the problems of low utilization rate and large dosage,which have caused a series of adverse effects on the safety of agricultural products,human health and ecological environment.Therefore,the development of safe and environmentally friendly green nano pesticide preparations is of great significance to ensure the safety of agricultural products and reduce environmental pollution,showing a good application prospect in promoting the reduction of pesticide application and efficiency and promoting the sustainable development of the pesticide industry.In this study,the photoresponsive chitosan based nanomicelles were designed and developed using biodegradable,cheap and readily available natural polymer chitosan as raw materials,and the nanoparticle loaded with pesticides was prepared by in-situ drug loading method,and its photoresponsive properties and controlled release characteristics of pesticides were studied.The aim is to provide theoretical guidance and technical support for the research and development of new pesticide dosage forms and the reduction of pesticide application and efficiency.The following work has been carried out:(1)Preparation of visible Light responsive Carboxymethyl chitosan derivatives(CMCS-DEACMS)nanocarriers and controlled release of pesticides:Cmcs-deacms were prepared by covalently coupling hydrophobic[7-diethylaminocoumarin-4-]methyl succinate(DEACMS)on the main chain of hydrophilic carboxymethyl chitosan(CMCS)using carboxymethyl chitosan as raw material and EDC/NHS as activator through amide bond.We confirmed the successful synthesis of CMCS-DEACMS polymer by FTIR and NMR.Amphiphilic CMCS-DEACMs were self-assembled into spherical micelles in water.The critical micelle concentration(CMC)of CMCS-DEACMs decreased with the increase of CMCS substitution by DEACMS,ranging from 0.013 mg/m L to 0.042 mg/m L,and was used as a photoresponsive nano pesticide carrier.The particle size,morphology,photophysical properties and photolysis properties of CMCS-DEACMS micelles under simulated sunlight were studied by dynamic light scattering(DLS),transmission electron microscopy(TEM),UV-visible absorption spectroscopy(UV-vis)and fluorescence spectroscopy.In addition,2,4-dichlorophenoxyacetic acid(2,4-D)was used as model pesticide and encapsulated in CMCS-DEACMS micelles.In these micelle forms,simulated sunlight promoted the release of 2,4-D,during which coumarin partially dissociated from the CMCS main chain,resulting in changes and instability in the hydrophilic and hydrophobic balance of micelles.2.4-D/CMCS-DEACMS controlled release data were consistent with first-order model,and the regression coefficients(R~2)of light and light avoidance were 0.9198 and 0.9145,respectively.In addition,biometric studies have shown that micelles containing 2,4-D have good biological activity against target plants and do not cause harm to non-target plants.Therefore,photoresponsive CMCS-DEACMS micelles provide an intelligent delivery platform for agricultural chemicals.(2)Preparation of poly(ethylene glycol)chitosan amphiphilic polymer grafted with azobenzene and its application in avermectin preparation:m PEG-CS-AZO was prepared by covalently coupling azobenzene and poly(ethylene glycol)monomethyl ether to the main chain of chitosan by amide bond using chitosan as raw material and EDC/NHS as activator.We confirmed the successful preparation of m PEG-CS-AZO polymer by FTIR and NMR.The amphiphilic m PEG-CS-AZO can be self-assembled into micelles in water with a critical micelle concentration(CMC)of 0.024mg/m L,and can be used as a photoresponsive nano pesticide carrier.Dynamic light scattering(DLS)was used to study the particle size of polymer micelles.The photoresponse of micelles was studied by UV-vis and NMR.In addition,m PEG-CS-AZO polymer has a unique uv blocking property,which is used in the encapsulation of the photodegradable pesticide avermectin(AVM).The controlled release and photolysis properties of m PEG-CS-AZO micelles were studied by HPLC.The results showed that EE value and LC value of m PEG-CS-AZO micelles were 74.8%and 22.44%respectively.The cumulative release amount of AVM/m PEG-CS-AZO micelles after120 h was 91.89%.The AVM/m PEG-CS-AZO sustained-release data fit Higuchi model,and the regression coefficients(R~2)of UV exposure and light avoidance were0.9992 and 0.9966,respectively.The decomposition rate of AVM/m PEG-CS-AZO was still lower than 42%after 60 h UV irradiation.m PEG-CS-AZO polymer has good photolysis and controlled release properties for AVM.Photoresponsive AVM/m PEG-CS-AZO green nano pesticide formulation provides an efficient nano platform for the sustainable development of agriculture.