Smells copper

chemistry : Metal odor is body odor

If you touch an iron railing, a door handle or steel cutlery, you can often notice a kind of metallic smell on your hands. Dietmar Glindemann and his assistants, chemists from Leipzig University, claim, however, that it is not the metal that smells at all.

The researchers found that the musty smell comes from chemicals in the skin that are instantly converted when they come into contact with iron. Their exact results were published in the international edition of Angewandte Chemie1.

It is very similar with copper. This explains why your fingers smell of metal after paying with copper alloy coins. "If a salesman gives you a coin," says Glindemann, "you smell his body odor."

The odorous reactions of the metals give us the "sensory impression that it is the metal itself that smells right after we have touched it," according to the researchers. In other words, a "metallic" smell is merely an association-based assumption.

Hand sweat

Glindemann's investigations began years ago when he wanted to find out the cause of the garlic-like odor that iron takes on shortly after it has been touched by a sweaty hand. He found out that various acids present in human sweat trigger reactions between carbon and phosphorus impurities, which are typically found in iron, the end products of which are unpleasant-smelling volatile molecules, so-called organophosphines (1).

But the "metal smell" that remains on the hand when you touch iron or copper is different from the smell of metal that has come into contact with acids in the laboratory. "This problem bothered me for five or six years," says Glindemann.

The breakthrough came with a collaboration with Andrea Dietrich, an environmental chemist at the Virginia Polytechnic Institute and State University in Blacksburg. She was trying to find out why so many people complain about the metallic taste in drinking water.

Her investigations into the taste of metal led her to the smell of metal. So she got to Glindemann, with whom she solved the problem together.

The researchers captured the vapors escaping from the skin of people who had touched iron objects and examined their chemical composition. The gases consisted, among other things, of aldehydes and ketones, which often have a strong and distinctive odor. The popular preservative formalin, a formaldehyde solution2, is responsible for the characteristic odor of old anatomy rooms, while the ketone acetone produces the strong solvent odor of nail polish remover.

These substances are created by rapid reactions of iron or copper with fatty substances on our skin.

Are there mushrooms here?

One of these substances is called 1-octen-3-one3. It is found in the fumes from the skin that has come into contact with iron and has a particularly strong smell. Humans can perceive it even in very low concentrations, namely as a mushroom-like, metallic odor.

Scientists believe that when everyone touches metal, they produce a slightly different mixture of these fragrances, and that composition changes when they have a disease such as cancer. The analysis of the substances in the "iron smell" of a person can therefore perhaps be a new form of diagnosis. "We are currently investigating whether the odor that iron causes on the skin can provide clues to certain diseases," says Glindemann.

The reactions could also answer Andrea Dietrich's question, why you sometimes have a metallic taste in your mouth when you drink water: Organic components of food could react with rust in the water and thus produce the undesirable fragrances.

(1) Glindemann, D., et al. Angew. Chem. Int. Ed., 45.7006-7009 (2006).

This article was first published on November 2nd, 2006 at [email protected] Translation: Rainer Remmel. © 2006, Macmillan Publishers Ltd

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