The smell of iron

"That we are smelling the metal itself is actually an illusion." In conjunction with a team of researchers from the Virginia Polytechnic Institute and State University in the United States, The University of Leipzig and the Leipzig Environmental Research Center, Germany, he has tracked down the responsible scent molecules.

Seven test subjects immediately recognized the "musty" metallic odor when their hands came into contact with metallic iron or a solution containing iron ions with a twofold positive charge. In contrast, solutions of iron with a triple negative charge did not cause the odor. Analysis of gas samples from the skin of the test subjects pointed to a bouquet of different organic compounds that seemed to be characteristic of the metallic smell.

The key component is called 1-octen-2-one, which smells fungal-metallic even when highly diluted. The precursors to the odor molecules are lipid peroxides, which are produced when oils on skin are oxidized by certain enzymes or other processes (e.g. under UV light). These lipid peroxides are then decomposed by the doubly negative iron ions, which are consequently reduced to triply negative iron ions. When touching objects made of iron, the required doubly negative ions are formed when perspiration on the skin corrodes the iron.

Rubbing blood over skin results in a similar metallic smell based on the same scent molecules. Blood also contains iron atoms. Says Glindemann, "That humans can 'smell' iron can be interpreted as a sense for the smell of blood. Early humans were thus probably able to track down wounded prey or tribe members."

Based on this new knowledge, medical researchers should be able to further develop iron tests for skin, blood and tissues in order to identify specific "fingerprints" of volatile scent molecules as markers for individual body odor, oxidative stress, and diseases.

The researchers were also able to characterize another iron-type smell: carbon- and phosphorus-containing cast iron and steel develop a metallic-garlic odor when exposed to acids. Until now, metallurgists ascribed this to the gas phosphine (PH₃). However, at breathable concentrations, pure phosphine (also known as a pesticide) is basically odorless. The true culprits are organophosphines, especially those champions among intensively smelly compounds like methylphosphine and dimethylphosphine. Their structure is like that of a phosphine molecule in which one or two of the hydrogen atoms are replaced with methyl (CH₃) groups.

Citation: Dietmar Glindemann, The Two Odors of Iron when Touched or Pickled: (Skin) Carbonyl Compounds and Organophosphines, Angewandte Chemie International Edition 2006, 45, No. 42, 7006–7009, doi: 10.1002/anie.200602100

Source: Angewandte Chemie

Researchers find the smell of metal can be deceiving
In the process of conducting research on iron plumbing infrastructure and drinking water quality, two Virginia Tech researchers in the College of Engineering uncovered that the smell of iron when you touch metal is really not iron at all.
Key site in iron metabolism aids in diagnosing anemia of chronic disease
University of Utah School of Medicine researchers have developed a new tool that facilitates diagnosis of anemia related to chronic illness, as well as diseases of iron overload. The results of a study detailing the new tool are published in the August 2008 issue of the journal Cell Metabolism, a publication of Cell Press.
Fortified cassava could provide a day's nutrition in a single meal
Scientists have determined how to fortify the cassava plant, a staple root crop in many developing countries, with enough vitamins, minerals and protein to provide the poor and malnourished with a day's worth of nutrition in a single meal.
The structure of XPD sheds light on cancer and aging
The protein XPD is one component of an essential repair mechanism that maintains the integrity of DNA. XPD is unique, however, in that pinpoint mutations of this single protein are responsible for three different human diseases: in xeroderma pigmentosum, extreme sensitivity to sunlight promotes cancer; Cockayne syndrome involves stunted growth and premature aging; trichothiodystrophy, characterized by brittle hair and scaly skin, is another form of greatly accelerated aging.
'Dynamic duo' develops framework for Earth's inaccessible interior
A new model of inner Earth constructed by Arizona State University researchers pulls past information and hypotheses into a coherent story to clarify mantle motion.
Vitamin D in brain function
In a definitive critical review, scientists at Children’s Hospital & Research Center Oakland ask whether there is convincing biological or behavioral evidence linking vitamin D deficiency to brain dysfunction. Joyce C. McCann, Ph.D., assistant staff scientist and Bruce N. Ames, Ph.D., senior scientist at Children’s Hospital Oakland Research Institute (CHORI) conclude that there is ample biological evidence to suggest an important role for vitamin D in brain development and function, and that supplementation for groups chronically low in vitamin D is warranted. Their conclusions will be published on April 22, 2008 in the Federation of American Societies for Experimental Biology (FASEB) Journal.
How water shrews find prey in the dark
Shrews are tiny mammals that have been widely characterized as simple and primitive. This traditional view is challenged by a new study of the hunting methods of an aquatic member of the species, the water shrew. The research reveals that the small animal possesses remarkably sophisticated methods for detecting prey that allow it to catch small fish and aquatic insects as readily in the dark as in daylight.
Researchers investigate links between prostate, cadmium, zinc
Cadmium exposure is a known risk factor for prostate cancer, and a new University of Rochester study suggests that zinc may offer protection against cadmium.

The smell of iron

Related stories:

News discussion: