Stability, parathion

Adhya TK, Barik S, Sethunathan N. 1981. Stability of commercial formulation of fenitrothion, methyl parathion, and parathion in anaerobic soils. J Agric Food Chem 29 90-93. 

The stability of parathion hydrolase was determined for refrigerator storage and room temperature storage. The enzyme solution is stable under refrigeration ( ) The enzyme also remains stable at room temperature for long periods ( ). 

The discovery in the early years of the 20 century that certain phosphate esters possess mammahan toxicity and insecticidal properties heightened interest in this class of compounds, both in agriculmre and as potential agents in chemical warfare. Parathion became the practical choice as a broad-spectrum insecticide because of its greater stability and lower mammalian toxicity compared to its P=0 analogue, paraoxon . 

Havens and Rase reported the immobilization of an enzyme to degrade a specific organophosphate. The organophosphate was an agricultural grade material (parathion). The enzyme was harvested from recombinant Pseudomonas diminuta and immobilized by emulsifying a solution with a prepolymer. The product of the reaction was reported to have excellent stability and the method was proposed for cleanup of small spills of parathion. 

Parathion was another widely used insecticide due to its stability in aqueous solutions and its broad range of insecticidal activity. However, its high mammalian toxicity through all routes of exposure led to the development of less hazardous compounds. Malathion [diethyl (dimethoxythiophosphorylthio)succinate], in particular, has low mammalian toxicity because mammals possess certain enzymes, the carboxylesterases, that readily hydrolyze the carboxyester link, detoxifying the compound. Insects, by... 

Garrett, S.D., DJ.A. Appleford, G.M. Wyatt, et al. 1997. Production of a recombinant anti-parathion antibody (scFv) stability in methanolic food extracts and comparison to an anti-parathion monoclonal antibody. J. Agric. Food Chem. 45 4183—4189. 

Insecticidal parathion is a phosphorothionate ester first licensed for use in 1944. Pure parathion is a yellow liquid that is insoluble in kerosene and water, but stable in contact with water. Among its properties that make parathion convenient to use as an insecticide are stability in contact with neutral and somewhat basic aqueous solutions, low volatility, and toxicity to a wide range of insects. It was applied as an emulsion in water, dust, wettable powder, or aerosol. Even before it was banned for general use, it was not recommended for applications in homes or animal shelters because of its toxicity to mammals. 

From the slope of the plot of current vs. (current/concentration of ATCh), the Km app for AChE was determined to be 0.66 mM. This biosensor also showed good precision and operational stability for the measurement of ATCh. The relative inhibition of AChE activity was calculated as a function of paraoxon concentration.. The linearity was observed up to 6.9 nM (slope, 14.36%/nM correlation coefficient, 0.9859) to 6.9 nM and the limit of detection of 0.5 nM (0.145 ppb). Moreover, the detection limit for methyl parathion using the present sensor could be expected to be 1.65 nM. Real sample analysis results were in good agreement (90%), which demonstrates the validity of this MWCNTs-SPE modified biosensor to a practical problem. 

Table 5 lists the half-lives of recovery for some OP-inhibited AChEs. In general OP-AChE complexes from dimethoxy-substituted OPs (e.g., malathion) spontaneously dephosphorylate faster than diethoxy (e.g., parathion) or diisopropoxy (e.g., DPP) complexes. Eto pointed out in 1974 that the stability of a phosphorylated AChE may be predicted from the stability of the specific OP inhibitor itself. One possibility is that methyl groups have less steric hindrance and greater electronegativity than ethyl or isopropyl groups. 

The thio analogue of paraoxon, diethyl-p-nitrophenyl phosphorothioate (parathion, 17), is practically more adequate because of its lower toxicity to warmblooded animals and higher stability against hydrolysis. It was prepared by Schrader in 1944, and the elucidation of its biological properties was due to Kiikenthal and Unterstenhofer (Schrader and Kukenthal, 1948 Unterstenhofer, 1948 Schrader, 1952b). 

Chlorthion is slightly more sensitive to hydrolysis than its analogue, parathion-methyl (24), lacking the chlorine substituent. A methyl group in the ort/io-position with respect to the nitro group thus increases and a chlorine atom decreases the stability to hydrolysis. 

It has been demonstrated that a variety of enzymes exhibited enhanced mechanical and chemical stability when immobilized on a solid support, producing a biocatalyst. Munnecke first immobilized a pesticide detoxification extract from bacteria by absorption on glass beads. The absorbed extract retained activity for what was then a remarkable full day. Wood and co-workers, using isocyanate-based polyurethane foams (Hypol ), found that a number of enzymes unrelated to OP hydrolysis could be covalently bound to this polymer. Later, Havens and Rase immobilized a parathion hydrolase. Furthermore, Turner observed that polyurethane foams are excellent adsorption materials for OP such as pesticide vapors. ... 

Four out of ten selected pesticides characterized by low polarity and low thermal stability (dimethoate, paraoxon, azinphos-methyl, azinphos-ethyl, parathion-methyl, parathion-ethyl. 

Anti-parathion-antibody (scFv), Stability in Methanolic Food Extracts and Comparison to an Anti-parathion Monoclonal Antibody , /. Agric. Food Chem., 45, 4183-4189 (1997). 

The versatility of the P450 oxygenases is summarized in Figure 9.3. Epoxides can be introduced into aromatic rings or across double bonds. The former reaction leads to a hydroxy or dihydodiol. It is most unlikely to observe aldrin in environmental samples since it is rapidly converted to dieldrin, a common environmental contaminant that is very stable. Aliphatic chains can be hydroxylated and ethers, thioethers, and substituted amines dealkylated. The conversion of parathion to the more reactive paraoxon is a factor in the mechanism of toxic action, as well as its environmental stability (see Hydrolysis, Chapter 8). The situation can be complicated by the fact that a substrate can often undergo more than one reaction. 

Persistence is related to water solubility, vapour pressure and hydrolytic stability - properties which can vary greatly from one insecticide to another (Table 12.32). Malathion, for example, persists in the soil for 1-2 weeks, whereas diazinon may remain for 3-6 months. Early highly toxic pesticides such as TEPP and parathion are now little used. 

The highly toxic parathion (12.96b), discovered in 1944 by Schrader [31], has a water solubility of 24 ppm and can be made by reaction (12.98). It has a greater hydrolytic stability than TEPP and is consequently more persistent in action. 

Uses Emulsifier for Parathion and Malathion-based insecticides dispersant, stabilizer... 

Uses Emulsifier for insecticides dispersant, stabilizer for solv.-free blends containing methyl parathion, ethyl parathion used with Toximul D and H-HF Regulatory EPA cleared Properties Dk. brn. Ilq. sol. In xylene HLB 12.0 TOXIMUL MP-26 [Stepan]... 

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