The second part of the series on poisons deals with cyanide, another notorious murder cause. It plays a role in the genocide, in suicide pills and occurs in small quantities in the seeds of numerous fruits. Why is cyanide so toxic and why are deaths from cyanide poisoning less rare than those caused by arsenic poisoning these days?
Cyanide is the CN ion, and as a poison it is usually administered as one of the three compounds shown in the figure: hydrogen cyanide, a volatile, colorless liquid, and potassium and sodium cyanide, both white powders. Both potassium and sodium cyanide react with gastric acid to produce hydrogen cyanide, which may then cause toxic effects.
Although cyanide has been used as a poison for centuries, it was first isolated in 1782 by Swedish chemist Carl Scheele in Sweden. While various sources tell different stories, some claim that exposure to cyanide was one of Scheele's early deaths at the age of 43. Scheele's early death is not surprising, considering how many toxic substances he has worked throughout his career. He was also the first to notice the bitter almond smell of hydrogen cyanide - a smell that, as it turns out, can only be detected by 40% of humans for genetic reasons.
So what happens if a person is poisoned with cyanide? It is one of the fastest acting known poisons. If a significant amount is absorbed, it can quickly kill you. When ingested, it binds to hemoglobin, the molecule in red blood cells that is responsible for transporting oxygen to the cells in our body. Hemoglobin then transports it to the tissues of the body where it can bind to an enzyme called cytochrome oxidase. This enzyme is an important tool that cells need to use oxygen, and they are unable to do so with the cyanide attached.
Symptoms of cyanide exposure are rapid and include headache, nausea, vomiting, and increased respiratory and heart rates. With a suitable dose, these symptoms can quickly lead to loss of consciousness, respiratory arrest and death. The exact dose that causes death depends on the form of cyanide administered. However, lethal doses of only one milligram per kilogram of body weight have been reported.
Cyanide poisoning can also originate from improbable sounding sources. One study reported a woman who ate 20 apricot kernels and subsequently suffered from cyanide poisoning. Apricot kernels and seeds of other fruits such as apples and peaches contain a compound called amygdalin, which contains a cyanide moiety. When this compound comes into contact with the stomach acid, hydrogen cyanide is produced, which can then lead to poisoning. Fortunately, a significant number of fruit seeds are needed to achieve a lethal cyanide dose - the woman mentioned in the study recovered completely.
Probably the best-known use of cyanide as a poison was in the concentration camps of the Nazis of World War II. There, the Nazis used Zyklon B, a cyanide-based pesticide that released hydrogen cyanide to kill millions. Cyanide was also involved in the war later; Although it is widely believed that Hitler committed suicide by shooting himself in the head, the evidence indicates that he and Eva lost their lover to a pill containing potassium cyanide.
Cyanide poisoning is still not uncommon, although exposure is often random. In particular, plastics such as nylon and polyurethanes release cyanide on burning, so that cyanide poisoning can often occur in fires. In 2009, more than 150 people died in a fire in a Russian nightclub. A number of these deaths were thought to be due to the inhalation of cyanide and other toxic gases from the burning of plastics.
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