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phosphate toxants work by inhibiting acetylcholinesterase, leading to excess acetylcholine at the neuromuscular junction which can, in turn, cause paralysis of the muscles needed for breathing and stopping the beating of the heart. Many orga› nophosphates have neurotoxic effects on developing organ› isms, even at low exposure levels. Their toxicity is not limited to an acute phase, however, and chronic effects have long been noted. 

[0013] Some organophosphate compounds are also potent pesticides and are classified as weapons of mass destruction by the United Nations according to UN Resolution 687 (passed in April 1991 ). Their production and stockpiling was outlawed by the Chemical Weapons Convention of 1993, which officially took effect on Apr. 29, 1997. 

[0014] The term "organophosphate" has, in recent years, also been used more generically to describe virtually any organic phosphorus (V)-containing compound, especially when dealing with neurotoxic compounds. Many compounds that are included within the organophosphate class actually contain carbon-phosphate bonds. For instance, the nerve agent sarin has the IUPAC name 0-isopropyl meth› ylphosphonofluoridate, and is derived from phosphorous acid (HP(O)(OH)$_{2}$ ), rather than phosphoric acid (P(O)(OH) 3 ). Also, many compounds that are derivatives of phosphinic acid are used as neurotoxic organophosphates. Organophos› phate pesticides, as well as sarin and the VX nerve agent, irreversibly inactivate acetylcholinesterase, which is essen› tial to nerve function in insects, humans, and many other animals. Organophosphate pesticides affect this enzyme in varied ways, and thus vary in their potential for poisoning. For example, parathion, one of the first organophosphates com› mercialized, is many times more potent than malathion, an insecticide used in combating the Mediterranean fruit fly (Med-fly) and West Nile Virus-transmitting mosquitoes. 

[0015] Many, but not all, organophosphate pesticides degrade rapidly by hydrolysis on exposure to sunlight, air, and soil. However, small amounts of these compounds can still be detected in food and drinking water. The ability to degrade over time has made them an attractive alternative to the persistent organochloride pesticides, such as DDT, aldrin, and dieldrin. Although organophosphates degrade faster than the organochlorides, they have greater acute toxicity, posing risks to people who may be exposed to large amounts of these compounds. Common organophosphates which have been used as pesticides include parathion, malathion, methyl par› athion, chlorpyrifos, diazinon, dichlorvos, phosmet, tetra› chlorvinphos, and azinphos methyl. 

[0016] VX is an extremely toxic organophosphate and is so dangerous, even in extremely small volumes, that its only application is in chemical warfare as a nerve agent. VX is also the most toxic of the deployed chemical weapons and is classified as a weapon of mass destruction by the United Nations in UN Resolution 687. Like other organophosphorus nerve agents, VX may be destroyed by reaction with strong nucleophiles such as pralidoxime. The reaction ofVX with concentrated aqueous sodium hydroxide results in competing cleavage of P---0 and P-S esters, with P-S cleavage domi› nating. This can be a problem when hydrogen peroxide is used as a decontaminant, since one by-product of P---0 bond cleavage (named EA 2192) is nearly as toxic as VX itself and is far more persistent in the environment. In contrast, reaction with the anion of percarboxylic acids (perhydrolysis) leads to exclusive cleavage of the P-S bond: 

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[0017] The H-class (known as "blister agents" or "sulfur mustards") are not organophosphates. Rather, these com› pounds are a class of cytotoxic, vesicant CBW agents with the ability to form large blisters on exposed skin. Vesicants are highly active corrosive materials, even at extremely low con› centrations. Compounds of this type comprise the structural element BCH$_{2}$CH$_{2}$X, where B is any leaving group and X is a Lewis base. Such compounds can form cyclic "onium" ions (sulfonium, ammoniums, etc.), which are good alkylating agents. Examples of blister agents include, but are not limited to, bis(2-chloroethyl)ether, the (2-haloethyl) amines (nitro› gen mustards) and sulfur sesquimustard, which has two ~-chloroethyl thioether groups (CIH$_{2}$C----CH$_{2}$-S-) con› nected by an ethylene (----CH$_{2}$CH$_{2}$ -) group. These com› pounds have a similar ability to alkylate DNA, but their physi› cal properties, e.g., melting point, can vary considerably. Some of these compounds have melting points well below the freezing point of water. The most well known of these com› pounds is commonly referred to as "mustard gas" (bis-(2- chloroethyl) sulfide or 1,1’-thiobis(2-chloroethane)), and, in its pure form, is a colorless, odorless, viscous liquid desig› nated as HD, which is a ~-chloro thioether with the formula C$_{4}$H$_{8}$Cl$_{2}$ S. HD is a liquid at room temperature and has melt› ing point of 14° C. (57° F.). 

[0018] These vesicant agents can be quite deadly as they have a high solubility in lipids ( e.g., fatty tissues). Symptoms of exposure to mustard gas include conjunctivitis, blindness, cough, edema of the eyelids, and erythema or necrosis of the skin. When inhaled, this can severely and irreparably damage the respiratory tract. In addition, mustard gas is also a car› cinogen. Vesicants have other uses besides chemical warfare, however, the vesicating properties of these compounds are an undesirable/unwanted side effect. For example, some chemo› therapy drugs are mild vesicants, as are a variety of industri› ally useful chemical intermediates. 

[0019] The term "biopathogen" encompasses CBW agents that are infectious biological agents which can cause disease 

P-S Cleavage 

P-S Cleavage 

