Passage Cyanide (CN − ) is a powerful, rapid toxin that binds to the cellular respiratory enzyme cytochrome c oxidase. The resulting enzyme-cyanide complex blocks the transfer of electrons to oxygen in the last step of the electron transport chain. This results in cytotoxic anoxia, causing asphyxiation at the cellular level.Exposure to cyanide can occur from dietary sources, medical treatments, industrial applications, smoke inhalation (structural fires), and intentional use (suicide). While dietary exposure from moderate consumption of naturally occurring plant compounds such as cyanogenic glycosides rarely results in acute adverse effects in humans, chronic effects have been observed from prolonged diets with significant levels of these compounds. In the developed world, risk of significant cyanide exposure is most likely to result from smoke inhalation during building fires or from industrial/occupational exposures.The impact of a given exposure depends on the amount (dose, duration), the chemical composition of the cyanide compound (HCN, NaCN, KCN), and the route of exposure (inhalation, absorption, ingestion). The ionic salts (NaCN, KCN) and free acid (HCN) forms of cyanide each have different acid-base properties that interact differently under the physiological conditions associated with each route of exposure.To better understand the toxicity of different forms of cyanide, animal models have been studied for comparison to known human exposure case studies. Table 1 presents a summary of selected animal toxicity studies that examine exposure via ingestion. The table provides the lethal dose to 50% of the population (LD 50 ) in milligrams of cyanide per kilogram of body weight (mg/kg).Table 1 Compilation of LD 50 Cyanide Values in Various Animal Species Based on animal models, one treatment developed for cyanide poisoning involves assisting the rhodanese enzyme in metabolizing CN − to SCN − via an intravenous solution of NaNO 2 and Na 2 S 2 O 3 . The Na 2 S 2 O 3 assists in the formation of a reactive S-SH (persulfide) bond in the enzyme on cysteine-247 (Reaction 1), which then reacts with the cyanide ion to form thiocyanate (Reaction 2). Adapted from: Hall AH, Isom GE, Rockwood GA. Toxicology of Cyanides and Cyanogens, Experimental, Applied and Clinical Aspects. John Wiley & Sons; 2015: 1-20; and Egekeze JO, Oehme FW. Cyanides and their toxicity: A literature review. Vet Q. 1980; 2(2): 104-114. -In an aqueous solution of 1 × 10⁻³ M HCN (K_a ≈ 1 × 10⁻⁹), HCN can best be described as a:

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11ecba2d_11c8_8084_a3bf_d321f33253bf_MD0008_00 A large acid dissociation constant (K_a > 1) indicates that a reaction favors the products whereas a small value indicates that a reaction favors the reactants. A small acid dissociation constant (K_a < 1) indicates that the ionization equilibrium for the H-A bond favors the non-ionized HA reactant. Because strong acids ionize essentially 100% in aqueous solutions (giving large values for the ionization constant), a small K_a value indicates that the acid is weak. The small K_a value for HCN indicates that the non-ionized form is favored, and it is a weak acid. Evaluation of the [H⁺] gives [H⁺] = 1 × 10⁻⁶ M. This [H⁺] is much less than the HCN concentration (1 × 10⁻³ M) and confirms that only a small percentage of the dissolved HCN molecules in solution are ionized (consistent with a weak acid). (Choice B) Strong acids ionize essentially 100% into H⁺ and A⁻. If HCN were a strong acid, the [H⁺] would be very close to 1 × 10⁻³ M (the initial HCN concentration). (Choice C) Although the nitrogen atom of the cyanide group does have an available lone pair of electrons that could act as a weak proton acceptor (weak base), HCN is donating protons (acting as a weak acid). The calculated value of [H⁺] = 1 × 10⁻⁶ M (pH 6) is greater (more acidic) than a neutral solution ([H⁺] = 1 × 10⁻⁷ M, pH 7) and confirms that HCN acts overall as a weak acid rather than as a weak base. (Choice D) A strong base would fully dissociate and provide a large [OH⁻]. This would result in a very small [H⁺] and a solution pH much higher than 7. An [H⁺] ≈ 1 × 10⁻³ M would indicate acidic conditions. Educational objective: In aqueous solutions, strong acids ionize essentially 100%, giving large values of K_a and high [H⁺]. Weak acids ionize only to a small extent, giving small values of K_a and [H⁺] that are much lower than the concentration of the non-ionized acid.

Passage Cyanide (CN−) Is a Powerful, Rapid Toxin That Binds to to the Cellular

Passage Cyanide (CN⁻) Is a Powerful, Rapid Toxin That Binds to to the Cellular