Field of Science

Inert gases aren't always inert

Earlier this week I posted about the intoxicating effects of nitrogen gas at high pressures, which leads divers to substitute helium for nitrogen. An astute reader wondered in the comments why argon wasn't used, as it is substantially cheaper. It turns out that argon is even more potent intoxicant than nitrogen at high pressures! But aren't argon and helium inert gases?

The elements in the last column in the periodic table comprise what IUPAC (the International Union of Pure and Applied Chemists is to chemists what the IOC is to sports) calls Group 18, but what most of us learned in high school to call the noble or rare, gases. Helium, argon, neon, krypton, xenon and radon are indeed all gases under standard conditions, but the modifier misses the mark by a bit.

Rare? Take a deep breath, you've just inhaled about 100 mg of argon. Almost 1% of the atmosphere is argon; there is almost three times as much argon in the air as there is CO2. "Noble" generally means "unreactive" to a chemist. The noble metals, such as gold and platinum are resistant to oxidation - they don't rust - unlike the "base" metals such as iron and copper. Much like gold and platinum, under the right conditions these inert gases can be made to react. The first noble gas compound - xenon hexafluoroplatinate - was synthesized in 1962, but there were earlier clues that these gases might not be completely unreactive. The anesthetic effect of xenon had been observed in the 1930s, and reports of its use in clinical settings appeared in the late 1940s.

The mechanism by which nitrogen, argon and xenon behave as anesthetics isn't completely understood. The best theories at the moment suggest that the gases interact with ion channels - but whether they binding chemically or physically is not clear.


  1. Given the anesthetic action of large, round, lipophilic, soft Lewis base molecules... is buckminsterfullerene anesthetic?

  2. I'd be very surprised if the anesthetic properties of Argon were due to a chemical reaction. from what I recall, the chemistry of noble gases tends to take place lower down in the periodic table. Interactions with proteins tend to occur in an aqueous environment which I think would be incompatible with known noble gas chemistries. I believe that cyclopropane has been used as an anesthetic and that hydrogen has been used in diving gas mixtures.

  3. I work in protein crystallography, and Xenon is used to "derivatize" proteins. Simply incubate your protein crystals in a high pressure atmosphere of Xenon and some atoms will interact (not covalently) with the protein, in specific locations. Not a strong interaction, but enough to distort the structure of the protein just a little bit and to make some Xenon gases occupy well defined positions in the proteins. Remove the pressure and the Xenon quickly flies away.
    So Xenon can affect proteins without really needing to "react" with them.


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