The first evidence from tests on people that our ability to distinguish between different scents involves quantum mechanics has reopened a long-standing debate.
Most researchers think a molecule's odour is determined by its shape, with ells triggered when the molecule enters a suitably shaped receptor in the nose, like a key entering a lock. Luca Turin of the Fleming Biomedical Research Sciences Centre in Vari, Greece disagrees, because some molecules with different shapes have similar ells.
In 1996 he proposed that a ell receptor would only fire when a molecule vibrated at the right frequency. These vibrations provide enough energy to trigger a quantum tunnelling effect, causing an electron to pass across the receptor and trigger a ell.
One way to test the theory is replacing the hydrogen atoms in a molecule with deuterium, a hydrogen isotope with a nucleus of a neutron and a proton, rather than just a proton. The shape of the molecule barely changes, but the added neutrons alter the frequency of its vibrations. Turin's previous experiments have shown fruit flies can distinguish between the original and altered versions of acetophenone, a common perfume ingredient, but similar tests on humans had failed.
Now Turin and colleagues have attempted the same experiment with larger molecules and discovered that humans can detect a significant difference in odour. They put this down to an increased number of carbon-hydrogen bonds in the larger molecules, as these bonds maybe responsible for the vibrational effect.
Researchers supporting the shape model of ell remain unconvinced though, with Tim Jacob of Cardiff University, UK telling the BBC that the new results were "supportive but not conclusive".
Meanwhile, Ilia Solov'yov of the University of Illinois at Urbana-Champaign, told Chemistry World he was "not convinced" the results prove humans could ell the difference between the two types of molecules.
More broadly, there is increased interest in the quantum biology, including recent evidence that birds may use quantum mechanics to navigate.
