Tabun

Tabun (NATO designation GA) is an extremely toxic compound and nerve agent chemical weapon of the organophosphate family. It is not present in nature. At room temperature, the pure compound is a clear and viscous liquid. However, impurities imparted during its manufacture are almost always present, turning it yellow or brown. Exposed to environs, it slowly evaporates into the atmosphere, with the vapor having a slight fruity or almond-like odor. As the compound has a much higher molecular mass (162 g/mol) compared to air, tabun gas tends to accumulate in low-lying areas.

It is a potent inhibitor of acetylcholinesterase, a key enzyme within the human body as well as in other animals. Acetylcholinesterase is responsible for breaking down acetylcholine, a neurotransmitter released into the synaptic cleft by motor neurons. The presence of acetylcholine within the cleft signals the post-synaptic (downstream) motor neuron to contract the neuron's associated muscle fibers, and vice versa. By irreversibly phosphorylating the enzyme, tabun accomplishes a constant and involuntary contraction of the affected muscles, as the acetylcholine is not recycled and continues to build up within the cleft. Death of the organism ensues when respiratory muscles, such as the diaphragm and intercostals, become exhausted and paralyzed from constant contraction, leading to loss of respiratory functions.