This post was written by IU undergraduate student Yiling Dong. It is the third in a series of featured stories written for a ScIU in the Classroom collaboration with Dr. Cathrine Reck in the Department of Chemistry.
“Good source of B17” sounds legit, right? A quick internet search will lead you to thousands of results touting the anti-cancer benefits of vitamin B17 that are found in the pits of apricots, the seeds of apples, and in bitter almonds. B17 is being sold to consumers as a health food supplement, but dig a little deeper (perhaps try the second page of Google) and you’ll find a completely different story. B17 is not actually a vitamin and is instead a compound called “amygdalin.“ And the thing about amygdalin? It can be broken down into cyanide in the body after consumption .
I’m sure we all know about cyanide. A popular poison, it has been shown in countless movies and was famously used in real-life in Nazi gas chambers as well as during the Jonestown Massacre. In short, not really something you would want to be putting into your body. But how does cyanide work and why exactly is it so deadly? The cyanide used in poisonings is usually a salt of cyanide made by combining a metal such as sodium with cyanide to form what are known as cyanides or cyanide salts. Once in the body, cyanide salts (NaCN) can react with aqueous hydrochloric acid (HCl) in the stomach in the following manner :
HCl + NaCN → HCN + NaCl
This reaction proceeds because hydrocyanic acid (HCN) is a more stable product than HCl due to the chemical concept known as pKa. pKa is a measure of acid strength and can be used to predict the reaction outcome. A higher pKa value means that the acid is weaker, more stable, and less reactive. Just think, if you were forced to hold a bomb, you would much prefer to hold a weaker bomb. In other words, reactions will always proceed towards the side with the acid of a higher pKa, signaling a weaker acid. If we examine our two acids, HCl and HCN, you will find that HCl has a pKa of -7 and HCN has a pKa of 9. Now picture a set of scales with the arrow in the chemical equation separating the contents of the two sides of the scales. Imagine that the pKa values are actually weight values. Which side would the scales tip to? They would tip towards the heavier side or the side with the higher weight values. Reactions proceed in a similar manner with reactions tipping towards the side with the higher pKa value. In this reaction, it means that HCN is formed.
The formed cyanides, like HCN, are so dangerous because they are water soluble. Water soluble means that they will dissolve in water in a similar manner to how table salt dissolves when placed into a glass of water. In the case of our apricot pits, the amygdalin found there reacts with the water in saliva to form HCN and sugar. You know what contains a lot of water? Blood. This means that HCN is able to dissolve in blood which allows it to be circulated throughout the body. While in the blood, HCN gets into the mitochondria inside the cells and binds to an enzyme called “cytochrome c oxidase”. Cytochrome c oxidase normally binds to oxygen and aids in the production of adenosine triphosphate (ATP), the source of energy in cells. If this were a game of monkey in the middle, cytochrome c oxidase would be trying to pass a ball to help score ATP, but HCN would be the monkey blocking cytochrome c oxidase’s attempts. In this game of monkey in the middle, the stakes are high because without oxygen, ATP will not form. In other words, no energy = no life .
Cyanide is a fast-acting poison, so symptoms such as headaches, nausea, and vomiting can be seen quickly. At high doses, death is almost instantaneous. While it is not likely that one would consume a lethal dose of apricot seeds (around 50-60 seeds), smaller doses could still cause symptoms of cyanide poisoning. The Canadian government’s health department recommends that adults eat no more than three seeds per day . I don’t know about you, but if I’m snacking, I’m eating far more than three seeds in one sitting. The lesson in all of this? Watch what you are eating. Apricot seeds are advertised as a “seed for life,” but that “life” could actually be a reference to the afterlife.
Edited by Victoria Kohout
 Rietjens, I. M., Martena, M. J., Boersma, M. G., Spiegelenberg, W., & Alink, G. M. (2005). Molecular mechanisms of toxicity of important food‐borne phytotoxins. Molecular nutrition & food research, 49(2), 131-158.
 Kampe, S., Iffland, R., Korenkov, M., & Diefenbach, C. H. (2000). Survival from a lethal blood concentration of cyanide with associated alcohol intoxication. Anaesthesia, 55(12), 1189-1191.
 Cyanide Poisoning, Health Canada Warns.” CBC News, 6 Dec. 2017, http://www.cbc.ca/news/health/