Molecular vibrations reveal secrets of scent

In a study designed to find out how smell is written into a molecule’s structure, scientists used a spectroscope to test whether changing how a molecule vibrates on a nano-scale changes its smell.

In an experiment, scientists took the musk molecule, which is commonly used in perfumery, and replaced the hydrogen atoms in the molecule with the heavier isotope deuterium.

This exchange doubles the hydrogen atoms’ mass, alters the molecule’s molecular vibrations, but leaves the shape of the molecule unchanged.

Results from the study appear to show that the deuterium musk molecules smell different to the hydrogen musk molecules, confirming that a molecule’s molecular vibrations determine its smell.

The study suggests that receptors in our nose are able to detect a nano-scale quantum mechanism called ’inelastic electron tunnelling’ to detect molecular vibrations.

First proposed at UCL in 1996, the idea was initially considered outlandish, although physicists confirmed the mechanism worked in theory.

Mr Simon Gane, a co-author of the study from the London Centre for Nanotechnology (LCN) and a surgeon at the UCL Ear Institute, said: “Changing the mass of some atoms inside certain molecules can affect the way they smell to humans, even though that does not change their shape in a large way. This is difficult to explain without the vibrational theory.”