Synthesis And Performance Of Indicators For Chemical Warfare Agents

The production,storage and use of chemical warfare agents（CWAs）,including nerve agents and blister agents,pose a great threat to national and public security.The effective detection of CWAs can reduce or even eliminate casualties for the alarm of chemical attack,the guidance of subsequent protection and decontamination operation.Rapid,simple and effective detection method for CWAs are therefore the focus of research in the field of chemical defense and counter-terrorism.Among the methodologies proposed,chromo-fluorogenic detection by organic small molecules and enzyme gains much attention due to its portable,cost-effective and“naked-eye”detection through the change of color and fluorescence.A typical indicator of organic small molecular is usually formed by a chromo-fluorogenic reporter group and a reactive group,the nucleophilic reaction between indicator and chemical agents can cause the change of intramolecular charge and then the reporter group translates the binding event into the change of color and fluorescence.Otherwise,the hydrolysis of acetylthiocholine（ATC）by acetylcholinesterase（AChE）could be inhibited by nerve agents,which reduces the production of thiocholine（TCh）,and thus leads to the change of surface plasmon resonance（SPR）and color in the presence of gold nanoparticles（Au NPs）.Based on the ideas above,thiourea-based and thiolactam-based rhodamine compounds were designed and synthesized in this thesis.In addition,a novel system composed of CdSe/12ZnS core/shell quantum dots（CdSe/12ZnS QDs）and AuNPs composite,AChE and ATC was also proposed.At last,the three indicators were applied in the detection of chemical warfare agents and their simulants.The concrete contents are as follows:1.Thiourea-based rhodamine indicator for the detection of nerve agents.Thiourea was proposed as the reactive group of indicators based on its reactivity to nerve agents,for the poor stability of hydroxyl group.A thiourea-based rhodamine compound N-（rhodamine B）-lactam-2-（4-cyanophenyl）as a chromo-fluorogenic indicator thiourea（RB-CT）of nerve agent and its simulant diethyl chlorophosphate（DCP）was introduced.The synthesized probe enabled a rapidly and highly sensitive response to DCP with clear fluorescence and color changes in several seconds.The limit of detection（LOD）was as low as 2×10^-66 M.Excellent performance was also showed in aqueous phase and the LOD for naked eye was 1.0×10^-5 M.RB-CT exhibited high detecting selectivity for DCP,among other organophosphorus compounds.The sensing mechanism showed that opening of the spirolactam ring following the phosphorylation of thiosemicarbazides group formed a seven-membered heterocycle adduct,according to MS analysis,³¹P NMR and density functional theory（DFT）calculations.Moreover,two test kits were employed and successfully used to detect real nerve agent Soman in liquid and gas phase（40 mg/m³）.All above suggested RB-CT was able to be used to the naked eye,in-situ,fast,effective and selective detection of nerve agents and their simulant,which gives a valuable reference for the design and synthesis of indicators.2.Thiolactam-based rhodamine indicator for the detection of sulfur mustard.Thiolactam was proposed as the reactive group of indicators based on the S-alkylation of sulfur mustard with thiourea for most of indicators of sulfur mustard are toxic or need complex operation.A thiolactam-based rhodamine compound N-（rhodamine B）-thiolactam-2-n-butane（SRB-NB）as a chromo-fluorogenic indicator of sulfur mustard and its simulant 2-chloroethyl ethyl sulfide（2-CEES）was introduced.The synthesized probe enabled a remarkable response to 2-CEES in the solvent of methanol/trichloroethane 4:1,v/v within 1 h at room temperature or 2 min at 60℃,accompanied with clear fluorescence and color changes.The LOD was as low as 3×10^-6M.Good performance was also showed in aqueous phase.SRB-NB exhibited high detecting selectivity for 2-CEES,among other halogenated alkanes and organophosphorus compounds.The sensing mechanism showed that opening of the thiolactam ring following the S-alkylation,according to MS analysis and DFT calculations.Moreover,two test kits were employed and used to detect 2-CEES in liquid and gas phase（125 mg/m³）.Clear response was also observed in 1 min to sulfur mustard.All above suggest SRB-NB can effectively and selectively detect sulfur mustard and simulant by naked eye and in-situ,which means its potential application in the field of the detection of the agent.3.QDs/Au NPs composite-based system for the detection of nerve agent simulant.CdSe/nZnS QDs were prepared and CdSe/12ZnS QDs was chose to assemble with Au NPs after optimization,the obtained CdSe/12ZnS QDs/Au NPs composite was used for the highly sensitive detection of nerve agent mimic diethyl cyanophosphonate（DCNP）based on inhibition mechanism of AChE.The efficient FRET between CdSe/12ZnS QDs and AuNPs results in good fluorescence quenching while the fluorescence can be recovered in the presence of AChE and ATC as QDs can be replaced by thiocholine.The fluorescence quenching and recovery of QDs showed the maximum efficiency when the concentration ratio of QDs and Au NPs is 20:1 and the concentration of AChE is 1.0×10^-3 U/L,respectively.DCNP can cause the reduction of fluorescence recovery effect and the detection can be realized by evaluating the fluorescence emission intensity.Optimally,a linear relationship of recovery percentage on the logarithmic concentration of DCNP in the range of 5.0×10^-9-5.0×10^-4 M was observed,and the LOD was 5.0×10^-9 M.Otherwise,the color change from black to wine red in the process indicates the achievement of naked eye detection to nerve agent simulant.High sensitivity and low limit of detection demonstrate good prospects for its application in the detection of nerve agents.