It is widely known that, to cows, wilted cherry leaves are deadly poisonous. Every cattle farmer is well acquainted with this fact. Yet, I, as a chemist, for years have wondered why. Surely it has to be a matter of chemistry, I realized. Indeed, that is the case.
Wild cherries are bitter, but to the aficionado (and I am one), the tiny fruits called wild cherries, are quite delicious, especially when made into the intensely-flavored wild cherry jelly. Curiously, these fruits contain substances that could be quite dangerous, except for the lack of substances called enzymes that would convert them into poisons.
One of those chemicals is amygdalin, seen in the image below. Note—in the upper right-hand corner of the molecule—are two atoms. One of the atoms is carbon, the other nitrogen. The two are joined by a triple bond. They seem harmless enough. The combination is written simply,
If they are joined by a hydrogen atom (H), the result becomes,
This is usually simply written HCN. But that’s the chemical formula for hydrogen cyanide!
Fortunately for fruit-lovers, wild cherries do not contain a chemical required to break off the cyanide group in the fruit itself. Such a chemical is called an enzyme. Such enzymes are, however, found in various parts of the wild cherry tree.
Other Parts of the Wild Cherry
Amygdalin and related compounds (glycosides) are present throughout the cherry tree’s component parts. As for the seeds within the fruit, if these are crushed, there are enzymes present that will attack the glycosides, liberating the hydrogen cyanide. There are two steps we will elucidate here.
The first involves the enzyme prunasin beta-glucosidase. Amygdalin and the enzyme react in the presence of moisture to form D-glucose sugar plus mandelonitrile. So far, we don’t see mention of the word hydrogen cyanide, do we? But there is another enzyme present, mandelonitrile lyase. Mandelonitrile plus that enzyme, again in the presence of moisture, reacts to form benzaldehyde, and—yes—cyanide!
Wilted Cherry Leaves
Curiously, if a cherry tree is chopped, or a branch breaks (perhaps due to a summer storm)—perhaps falling to the ground—the resulting wilted leaves contain a relatively large amount of cyanide and cyanide precursors. Cyanide in wilted cherry leaves sickens and kills a cow. It ought to be mentioned that there are other plants occasionally guilty of doing the same thing (see the second reference, listed below).