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Hemlock (Molecule of the Month for March 2001)


Hemlock has achieved a certain notoriety through its implementation in the state execution of Socrates. Although that event occurred several millennia ago its fame and credentials as a poison par excellence have been assured ever since. The eyewitness reports of Socrates' death are principally to thank for this, however hemlock's toxicity is also referred to in other ancient texts, including the Old Testament, which proves that hemlock's reputation was well established long before Socrates was put to death.

There are two varieties of hemlock: poison hemlock (the one used to assassinate Socrates) and water-hemlock. In spite of its more innocuous sounding name, water-hemlock is just as deadly as its famous relative. Although they are related, water hemlock and poison hemlock act on the body in very different ways. I am only interested in the effects of the former, so from henceforth I shall concentrate exclusively on poison hemlock. Poison hemlock (conium maculatum) is native to most parts of Europe and since its introduction to the USA has become well established there too. It grows to heights of about 6-10 ft. It has fleshy white taproots, which are frequently mistaken for wild parsnips or carrots and its leaves resemble those of parsley, which is a member of the same family.

Unfortunately, all parts of hemlock are poisonous so its resemblance to other edible plants is the most common cause of hemlock poisoning. The seeds contain the highest concentration of poison. The name 'hemlock' comes from the Anglo-Saxon hemleac (meaning 'shore-plant'), whilst its botanical name is derived from the Greek word 'konas' (to whirl about) since one of the main symptoms of hemlock poisoning is unsteadiness.

The "active ingredients" in poison hemlock are alkaloids. Alkaloids are compounds that contain N in a heterocyclic ring. They are formed as metabolic by-products from amino acids: Amino acids are decarboxylated to amines, these then react with amine oxides to form aldehydes. Mannich-type condensation of the aldehyde and amine groups creates the characteristic heterocyclic ring. The alkaloids that are found in hemlock are known (imaginatively) as conium alkaloids.

Conium alkaloids are structurally similar to nicotine and have a similar pathophysiology. Initially, nicotinic activation from poison hemlock leads to stimulation of the central nervous system (CNS). Symptoms at this stage of hemlock poisoning include: headache, unsteadiness (ataxia), salivation, profuse sweating (diaphoresis) and a rapid heart rate (tachycardia). In severe cases the stimulation phase is later followed by a depressant phase characterized by slow heart rate (bradycardia), ascending motor paralysis, CNS depression and, ultimately, respiratory paralysis from nondepolarizing blockade at neuromuscular junctions.

Formal Chemical Name (IUPAC)

Picture of Hemlock

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Picture of Hemlock

Update by Karl Harrison
(Molecule of the Month for March 2001 )