How nose perceives common class of odours decoded

Researchers have found an unexpected chemical strategy employed by the mammalian nose to detect chemicals known as aldehydes.
According to a team led by The City College of New York Associate Professor of Chemistry Kevin Ryan and colleagues, some of the nose's many aldehyde receptors don't detect the aldehyde by its structure and shape directly.
Rather, the aldehyde is recognised by its ability to undergo a chemical reaction with water, likely after entering the nose.
Odourant receptors make up a large family of cell membrane proteins that monitor inhaled air on neurons within the nose.
Aldehydes, meanwhile, are found in a variety of natural sources like herbs, flowers and fruit. They are typically fresh-smelling chemicals, and synthetic aldehydes are important to the flavour and fragrance industry.

"Once exposed to air, aldehydes have a limited lifetime as oxygen slowly converts them into less savoury, even malodorous chemicals," said Ryan.

"It's not surprising then that the nose is adept at detecting aldehydes, and distinguishing them from structurally similar chemical groups," Ryan said.
His team found that for some receptors it's the aldehyde's chemical reactivity, not its inherent shape, that tells the nose there are aldehydes in the air.
"In our experiments, some of the many odourant receptors that detected the eight-carbon aldehyde octanal recognised the aldehyde portion of the molecule by its ability to morph into a completely different chemical group, known as a gem-diol," Ryan added.

"Since this reaction is unique to aldehydes, it serves as a means to discriminate them from similarly shaped chemical groups," he said.
The research will be published in the journal ACS Chemical Biology.