vendredi 18 novembre 2011

Warfare: Arsenite poisoning.

Lewisite (2-chlorovinyldichlorarsine) is an arsenic organic compound (halide arsine) that looks like a viscous liquid and has been used as a toxic agent during the first world war and the war between China and Japan (1937-1945). 



Winford Lee Lewis, chemist in the US army found the recipe needed to synthesize this compound in the thesis of a young student (obviously) from Washington DC. Its first nam was "The dew death" because of its activity in cold condition, its unflammability, its almost colorless liquid aspect and because it is almost inodor (scented geranium).

It can easily penetrate ordinary clothing and even rubber; upon skin contact it causes immediate pain and itching with a rash and swelling. Large, fluid-filled blisters develop after approximately 12 hours. These are severe chemical burns. Sufficient absorption can cause systemic poisoning leading to liver necrosis or death.
Inhalation causes a burning pain, sneezing, coughing, vomiting, and possibly pulmonary edema. Ingestion results in severe pain, nausea, vomiting, and tissue damage. The results of eye exposure can range from stinging and strong irritation to blistering and scarring of the cornea. Generalised symptoms also include restlessness, weakness, subnormal temperature and low blood pressure.

Lewisite as all halide arsine compounds reacts with water leading to formation of free Arsenic and ionic arsenite. The effects of Lewisite on the body come from the vesicant (allergic effect leading to the formation of blisters) properties of the halide form and the poisonous arsenic and arsenites molecules. 

Some enzymes need cofactors (other molecules or enzymes) to perform their task. Arsenite and Arsenic reacts with thiol groups (sulphur) of an enzyme cofactor called dihydrolipoate (lipoic acid). The enzymes concerned by this cofactor are responsible for cellular respiration and glycolysis metabolic pathway and are then inhibited by Lewisite. The cell dies because of lack of energy or because of a too high concentration of glucose in the blood (peripheral organes are affected by this glucose toxicity).

The antidote is the 2,3-dimercaptopropanol. This molecule has a structure really close to dihydrolipoate but arsenic derivatives binds tighter to the former. Then, the complex formed can be washed away by the kidneys.

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