Organophosphate

Phosphoric acid esters (also: alkyl phosphates ) are esters of orthophosphoric acid, which are formally or in fact, by the reaction of the acid and alcohol with elimination of water. They can be called organic phosphates / organophosphates, but not belong to the group of the organophosphorus compounds, since no carbon-phosphorus bond is present.

Structure

A distinction is made between monoesters, diesters and triesters:

They differ from the esters of diphosphoric acids and Triphosphorsäuren (see triphosphate ), both of which are monoesters.

Phosphoric acid esters in the organism are essential, because they are involved as intermediates in numerous metabolic processes in virtually all biological processes ( see, for example adenosine triphosphate). To be distinguished from the phosphoric esters are also counted among the organophosphorus compounds, some highly toxic, thiophosphorus and dithiophosphoric.

Importance in biochemistry

Phosphates or phosphate residues play an important role in the biochemistry of living organisms. They are involved in the formation of biologically important molecules, such as deoxyribonucleic acid ( DNA). In phosphodiester / phosphotriester system of adenosine diphosphate (ADP) and adenosine triphosphate ( ATP) ADP is " energetically charged " by transferring a phosphate group (ADP Pi energy ⇒ ATP) and ATP can by cleavage of a phosphate group - elsewhere in the cell - restore energy emit (ATP ADP Pi energy ⇒ ). Important in biochemistry is the phosphorylation, i.e., the selective transfer of phosphate to proteins. Covalently bound to proteins phosphate acts as a molecular switch and allows regulation of metabolic processes. They are transmitted here from the large class of protein kinases, protein phosphatases again split off from.

Other examples are:

• Nucleotides
• Phospholipids

Use (general)

Phosphoric acid esters are used in plastics and coatings as plasticizers, flame retardants, hardeners, as seed dressing and adhesive during application of paints and coatings in the metal surface treatment as purifying, anti-corrosion and adhesion-promoting substances, as aids for textiles and paper, as a cleaner and cleaning products, hydraulic fluid, oil and fuel additives.

Use as pesticides and chemical warfare agents

Organophosphorus compounds and phosphoric acid esters are the most extensive and most diverse group of agents against insects ( insecticides) and mites ( acaricides ). Examples of this class of insecticides are phoxim, dichlorvos ( DDVP ), fenthion, chlorpyrifos, parathion (E 605 ) and its methyl and ethyl derivatives, and tetraethyl pyrophosphate ( Bladan ).

History

The development of this class of compounds began in early 1900 through August Michaelis and Alexander Arbuzov, who are the founder of classical phosphorus chemistry. The biological effect of the organic phosphoric acid ester, however, was detected only in the mid -1930s by Gerhard Schrader, the synthesized in the search for acaricides and insecticides, the agents Tabun (1936) and Sarin ( 1939). Later, the nerve agents soman and VX were developed.

Properties

• Easily hydrolyzed ( cleaved by water ) and also easily enzymatic and abiotic degradation
• Sometimes very fat-soluble ( lipophilic)
• High toxicity and therefore lower application rate
• Wide variability of the compounds, i.e., there are many different compounds are possible, so that the risk of the emergence of resistance is reduced.

Toxic effect

The toxic effects in humans based on the inhibition of esteratischen Centre ( irreversible) of acetylcholinesterase and thus leads initially to an acetylcholine - flooding with muscarinic and nicotinic symptoms ( see also acetylcholine receptors). In the following, it comes through the permanent nerve impulses to cramping and then death due to respiratory arrest. The toxicity of the individual compounds is, however, very different. Other symptoms may include slow heart rate, constricted pupils, increased salivation and dyspnea, as well as nausea, diarrhea, and urinary incontinence. To antagonize is administered in emergency medicine atropine and obidoxime chloride.