Field of Science

Bizarre halloween paper of the year

If there was a prize for "Bizarre paper published to celebrate halloween", this paper may get it. On a more serious note, it's an interesting paper published in this week's ACIE that tackles a very common phenomenon- the metallic odor of iron that we all perceive. As the authors demonstrate, the odor is more likely to be from carbonyl compounds produced by the reduction of lipoperoxides in the skin by Fe2+. They also analyze the garlicky odor produced when iron is 'pickled' with phosphorus, commonly attributed to phosphine (PH3) and argue that this odor too is due to organophosphines rather than phosphine itself. Some of their statements and conlcusions (not to mention the title: The Two Odors of Iron when Touched or Pickled: (Skin) Carbonyl Compounds and Organophosphines) really merit Transylvanian attention:
"Humans are perplexed by the metallic odor from touching iron metal objects, such as tools, cutlery, railings, door handles, firearms, jewelry, and coins. Phosphorus-containing iron which is under acid attack gives rise to a different carbide or garlic odor which metallurgists have attributed to the gas phosphine (PH3); however, we found that purified PH3 at breathable dilution has hardly any odor. The aim of our research is to understand the chemical causes of these two iron smells in our engineered metal environment."

"1) Ironically, the iron odor on skin contact is a type of human body odor"

"Blood iron: Blood of one of the authors rubbed onto his own skin resulted in similar metallic odor and the same odorants (78±7 nmol dm-2, 4 repetitions) as in the above experiments. Controls by addition of FerroZine which is a blood-iron chelator suppressed the reaction (4±0.4). Aerated and homogenized blood also developed metallic odor on its own. There are reports that blood iron[10] can decompose blood lipidperoxides and that FerroZine inhibits this reaction.[11] This finding confirms that blood iron can trigger the metallic odor on skin or in blood itself."

"Sweaty skin corrodes iron metal to form reactive Fe2+ ions that are oxidized within seconds to Fe3+ ions while simultaneously reducing and decomposing existing skin lipidperoxides to odorous carbonyl hydrocarbons that are perceived as a metallic odor. This fast reaction creates the sensory illusion that it is the metal in itself that we smell right after touching it."

Several of the experiments made me a little edgy; breathing phosphine to detect its odor (I have always been looking for a reference to the man/woman who first described the taste of KCN) and blood rubbed on to skin. These guys' work sure is interesting; what I am not sure of is whether I want to do a postdoc with them. Interestingly, pure phosphine, just like pure methane, is odorless.

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