CHAPTER 23: Unit 5. Focus on Health and Medicine: Hydrogen cyanide
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| The reactions detailed in the electron transport chain and oxidative phosphorylation are so crucial for the health of an organism that disruption of even a single step can have disastrous consequences. When any one step is inhibited, energy production ceases, and an organism cannot survive. |
| i) Naturally Occurring HCN |
| HCN is obtainable from fruits that have a pit, such as cherries, apricots, apples, and bitter almonds, from which almond oil and flavoring are made. Many of these pits contain small amounts of cyanohydrins such as mandelonitrile and amygdalin, which slowly release hydrogen cyanide.A few naturally occurring compounds that contain CN groups form HCN when they are hydrolyzed in the presence of certain enzymes. As an example, amygdalin is present in the seeds and pits of apricots, peaches and wild cherries. |
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| AmygdalinAmygdalin and its close relative laetrile, were once touted as anti-cancer drugs, and are still available in some countries for this purpose. |
| ii) Hydrogen Cyanide |
| Hydrogen cyanide (HCN), sometimes called prussic acid, is a chemical compound[11] with the chemical formula HCN. It is a colorless, extremelypoisonous and flammable liquid that boils slightly above room temperature, at 25.6 °C (78.1 °F).[12] HCN is produced on an industrial scale and is a highly valuable precursor to many chemical compounds ranging from polymers to pharmaceuticals.Hydrogen cyanide (AC) is a chemical warfare agent (military designation, AC). It is used commercially for fumigation, electroplating, mining, chemical synthesis, and the production of synthetic fibers, plastics, dyes, and pesticides.Cyanide is a fast-acting, potentially deadly chemical that prevents the cells of the body from using oxygen properly. When this happens, the cells die. Cyanide is released from natural substances found in some foods, such as apple seeds and peach pits, and in certain plants.Hydrogen cyanide is highly toxic because it inhibits cellular oxidative processes. An adult human can withstand 50–60 parts of hydrogen cyanide per million parts of air for an hour without serious consequences, but exposure to concentrations of 200–500 parts per million of air for 30 minutes is usually fatal. A method of inflicting capital punishment consists of administering a fatal dose of hydrogen cyanide gas.Hydrogen cyanide may be isolated in small quantities from plants, where it occurs in combination with sugars. Large quantities of hydrogen cyanide for laboratory and commercial use are synthesized by three principal methods: (1) treatment of sodium cyanide with sulfuric acid; (2) catalytic oxidation of a methane–ammonia mixture; and (3) decomposition of formamide (HCONH2). Hydrogen cyanide is an excellent solvent for many salts, but it is not widely used as a solvent because of its toxicity. In pure form, hydrogen cyanide is a stable compound, but it polymerizes readily in the presence of basic substances, such as ammonia or sodium cyanide. The salts are used in the extraction of ores, in electrolytic processes, and in the treatment of steel. Among the important reactions with organic compounds are those with aldehydes and ketones, forming cyanohydrins, which serve as intermediates in many organic syntheses, and with ethylene oxide, forming an intermediate product that is converted to acrylonitrile (CH2=CHCN).What immediate health effects can be caused by exposure to hydrogen cyanide? Breathing small amounts of hydrogen cyanide may cause headache, dizziness, weakness, nausea, and vomiting. Larger amounts may cause gasping, irregular heartbeats, seizures, fainting, and even rapid death. Generally, the more serious the exposure, the more severe the symptoms. Similar symptoms may be produced when solutions of hydrogen cyanide are ingested or come in contact with the skin. Can hydrogen cyanide poisoning be treated? The treatment for cyanide poisoning includes breathing pure oxygen, and in the case of serious symptoms, treatment with specific cyanide antidotes. Persons with serious symptoms will need to be hospitalized. Call your doctor or the Emergency Department if you develop any unusual signs or symptoms within the next 24 hours, especially:* difficulty breathing, shortness of breath, or chest pain* confusion or fainting* increased pain or a discharge from your eyes* increased redness, pain, or a pus-like discharge in the area of a skin burnAre any future health effects likely to occur? A single small exposure from which a person recovers quickly is not likely to cause delayed or long term effects. After a serious exposure, a patient may have brain or heart damage. What tests can be done if a person has been exposed to hydrogen cyanide? Specific tests for the presence of cyanide in blood and urine generally are not useful to the doctor. If a severe exposure has occurred, blood and urine analyses and other tests may show whether the brain or heart has been injured. Testing is not needed in every case. |
| iii) HCN and its Health Affect |
| As Hydrogen cyanide (HCN) is a colorless, rapidly acting, highly poisonous gas or liquid that has an odor of bitter almonds. Most HCN is used as an intermediate at the site of production. Major uses include the manufacture of nylons, plastics, and fumigants. Exposures to HCN may occur in industrial situations as well as from cigarette smoke, combustion products, and naturally occurring cyanide compounds in foods. Sodium nitroprusside (Na2[Fe(CN)5 NO]·2H2O), which has been used as an antihypertensive in humans, breaks down into nonionized HCN.HCN is a systemic poison; toxicity is due to inhibition of cytochrome oxidase, which prevents cellular utilization of oxygen. Inhibition of the terminal step of electron transport in cells of the brain results in loss of consciousness, respiratory arrest, and ultimately, death. Stimulation of the chemoreceptors of the carotid and aortic bodies produces a brief period of hyperpnea; cardiac irregularities may also occur. The biochemical mechanisms of cyanide action are the same for all mammalian species. HCN is metabolized by the enzyme rhodanese which catalyzes the transfer of sulfur from thiosulfate to cyanide to yield the relatively nontoxic thiocyanate.Human exposures with measured concentrations were limited to occupational reports. Symptoms of exposed workers ranged from no adverse health effects to mild discomfort to frank central nervous system effects. Repeated or chronic exposures have resulted in hypothyroidism. Inhalation studies resulting in sublethal effects, such as incapacitation, and changes in respiratory and cardiac parameters were described for the monkey, dog, rat, and mouse; lethality studies were available for the rat, mouse, and rabbit.The AEGL-1 is based on human monitoring studies in which the preponderance of data as a weight-of-evidence consideration indicates that an 8-h exposure to HCN at 1 parts per million (ppm) would be without adverse health effects for the general population.Chronic exposures (5–15 years [y]) in three electroplating plants to mean concentrations of 6, 8, and 10 ppm produced exposure-related symptoms including headache, weakness, and objectionable changes in taste and smell. Over half of the workers presented with enlarged thyroids (characteristically observed in cases of chronic cyanide exposure), which may have been responsible for certain symptoms. In a study of National Research Council (NRC) subcommittee concluded that a 1-h exposure at 8 ppm would cause no more than mild headache in healthy adults.Reference: https://www.ncbi.nlm.nih.gov/books/NBK207601/ |