Organic phosphates Insecticides

Moeller HC, Rider JA. 1959. The effects of various organic phosphate insecticides on RBC and plasma cholinesterase in humans [Abstract]. Fed Proc 18 424. 

Van Bao T, Szabo I, Ruzicska P, et al. 1974. Chromosome aberrations in patients suffering acute organic phosphate insecticide intoxication. Humangenetik 24 33-57. 

DuBois KP, Kinoshita FK. 1968. Influence of induction of hepatic microsomal enzymes by phenobarbital on toxicity of organic phosphate insecticides. Proc Soc Exp Biol Med 129 699-702. 

Metrifonate, which was originally introduced as an organic phosphate insecticide, is a pro-drug for dichlorovos,10 a potent acetylcholinesterase inhibitor (Chapter 8) to which it is nonenzymatically metabolized spontaneously in vitro even at neutral pH (Eq. 7.11). The drug s clinical application is exclusively against S. hematobium infections. Although some effectiveness against other schistosomes exists, this is not achieved at safe doses. 

Uses Emulsifier for organic phosphate insecticides Properties Liq. oil-sol. 

Of the three organic phosphorus insecticides—hexaethyl tetraphosphate, tetraethyl pyrophosphate, and parathion—the first two have been shown to be mixtures (36) that contain tetraethyl pyrophosphate as the principal active ingredient. Several methods have been proposed for the determination of this compound in the commercial products (25, 35). All are based on the separation of the tetraethyl pyrophosphate from the related ethyl phosphates, followed by its hydrolysis to diethyl orthophosphoric acid and titration with standard alkali. Both hexaethyl tetraphosphate and tetraethyl pyrophosphate are soluble in water and are rapidly hydrolyzed to monoethyl and diethyl orthophosphoric acid. This rapid hydrolysis to nontoxic products greatly limits the duration of the in- secticidal effectiveness of tetraethyl pyrophosphate, but it also eliminates the danger of toxic residues on the crops treated. 

In spite of their toxicity, alkyl phosphites have been used extensively as lubricant additives, corrosion inhibitors, and antioxidants. In addition to their use as intermediates in synthesis, organophosphorus compounds are useful for separating heavy metals by solvent extraction. Several insecticides that were formerly in widespread use are derivatives of organic phosphates. Two such compounds are malathion and parathion. 

Organic phosphates, phosphonates, and analogues are of interest in medicinal chemistry as drugs or prodrugs, and in toxicology mainly as plasticizers, insecticides, or warfare agents. Their breakdown by enzymatic routes has received marked attention since many years, but it is most unfortunate for the advancement of science that an unknown number of highly relevant results remain classified information. 

Pesticides Carbamate insecticides and herbicides, chlorinated pesticides (for example aldrin, dieldrin, heptachlor, DDT, DDE, HCB, HCH isomers), dithiocarbamate fungicides, organic phosphates, triazine herbicides... 

Phenol Red. The first publications of an automated procedure for the measurement of cholinesterase inhibitors are those of Winter 14) and Winter and Ferrari (15). The method employed an Autoanalyzer instrumental system wherein the extracts containing the insecticide were incubated with a standard cholinesterase solution at 37 °G. A continuous sample from the incubation bath is buffered and mixed with acetylcholine iodide. After a second incubation, the acetic acid released by the action of the uninhibited cholinesterase is measured colorimetrically, using phenol red as the indicator. More recently, Fischl et al. 16) reported a method for rapid detection of organic phosphate pesticides in serum. Strips of filter paper were impregnated with a buffered acetylcholine substrate solution containing phenol red as an indicator. When no inhibition is present, the acid released from the action of cholinesterase turns the paper yellow. When cholinesterase has been inhibited, the paper turns pink-to-violet. 

Why then, since such an abundance of metabolic inhibitors is available, do so few of them find practical application Examples are the folic acid reductase inhibitors, such as aminopterin, the purine and pyrimidine analogs used as cytostatics in cancer chemotherapy and known for their high toxicity in a wide variety of species, and the organic phosphates and carbamates used as insecticides but also highly toxic to mammals. Lack of selectivity in the action of metabolic inhibitors is inherent in their mechanism of action due to the universality of biochemical processes and principles throughout nature. Selectivity in action requires species differences in biochemistry. For the antivitamins, for instance, there is not only a lack of species differences in action in addition, the fact that vitamins often serve as cofactors for a variety of enzymes is a serious drawback to endeavors to obtain agents with species-selective action. 

Extension to insecticides of the idea that receptors could occur on enzymes was made soon after the end of the Second World War, when organic phosphates began to be used for their inhibition of AChase in insects. The hydroxy-group of serine in this enzyme was pinpointed as the receptor site for organophosphate insecticides (Section 13.3). 

Many simpler carbamates, as well as organic phosphates, which have this property of blocking acetylcholinesterase, are used in treating glaucoma, also as anthelmintics and insecticides (see Section 13.3). 

For the analysis of organic phosphorous compounds in human serum after acute poisoning, the procedure proposed by Futagami et al. may be used. They applied HPTLC for the detection of 25 commonly used organic phosphorous insecticides in human serum. These organo-phosphates were separated on plates with three different separating systems within 6-18 min and detected by means of UV radiation and coloring reactions. 

Hyde of mineral elements-it can deal life or death. As white phosphorus, it s the flame of incendiary bombs as red phosphorus, it s the heart of the common match as organic phosphate, it s nerve gas and insecticides and as organic combinations, it s a constituent of every cell and fluid of the body. Without phosphorus, no cell divides, no heartbeats, and no baby grows. 

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