Quantum stink?

[Rum]

From the Beeb: http://www.bbc.co.uk/news/science-environment-21150046

'Quantum smell' idea gains ground
By Jason Palmer Science and technology reporter, BBC News



A controversial theory that the way we smell involves a quantum physics effect has received a boost, following experiments with human subjects.

It challenges the notion that our sense of smell depends only on the shapes of molecules we sniff in the air.

Instead, it suggests that the molecules' vibrations are responsible.

A way to test it is with two molecules of the same shape, but with different vibrations. A report in PLOS ONE shows that humans can distinguish the two.

Tantalisingly, the idea hints at quantum effects occurring in biological systems - an idea that is itself driving a new field of science, as the BBC feature article Are birds hijacking quantum physics? points out.

But the theory - first put forward by Luca Turin, now of the Fleming Biomedical Research Sciences Centre in Greece - remains contested and divisive.

The idea that molecules' shapes are the only link to their smell is well entrenched, but Dr Turin said there were holes in the idea.

He gave the example of molecules that include sulphur and hydrogen atoms bonded together - they may take a wide range of shapes, but all of them smell of rotten eggs.

"If you look from the [traditional] standpoint... it's really hard to explain," Dr Turin told BBC News.

"If you look from the standpoint of an alternative theory - that what determines the smell of a molecule is the vibrations - the sulphur-hydrogen mystery becomes absolutely clear."

Molecules can be viewed as a collection of atoms on springs, so the atoms can move relative to one another. Energy of just the right frequency - a quantum - can cause the "springs" to vibrate, and in a 1996 paper in Chemical Senses Dr Turin said it was these vibrations that explained smell.

The mechanism, he added, was "inelastic electron tunnelling": in the presence of a specific "smelly" molecule, an electron within a smell receptor in your nose can "jump" - or tunnel - across it and dump a quantum of energy into one of the molecule's bonds - setting the "spring" vibrating.

But the established smell science community has from the start argued that there is little proof of this.
Of horses and unicorns

One way to test the idea was to prepare two molecules of identical shape but with different vibrations - done by replacing a molecule's hydrogen atoms with their heavier cousins called deuterium.

Leslie Vosshall of The Rockefeller University set out in 2004 to disprove Dr Turin's idea with a molecule called acetophenone and its "deuterated" twin.

The work in Nature Neuroscience suggested that human participants could not distinguish between the two, and thus that vibrations played no role in what we smell.

But in 2011, Dr Turin and colleagues published a paper in Proceedings of the National Academy of Sciences showing that fruit flies can distinguish between the heavier and lighter versions of the same molecule.

A repeat of the test with humans in the new paper finds that, as in Prof Vosshall's work, the subjects could not tell the two apart. But the team then developed a brand new, far larger pair of molecules - cyclopentadecanone - with more hydrogen or deuterium bonds to amplify the purported effect.

In double-blind tests, in which neither the experimenter nor the participant knew which sample was which, subjects were able to distinguish between the two versions.

Still, Prof Vosshall believes the vibrational theory to be no more than fanciful.
Molecular model of cyclopentadecanone The new experiments hinged on making a brand-new molecule - in "heavy" and "light" versions

"I like to think of the vibration theory of olfaction and its proponents as unicorns. The rest of us studying olfaction are horses," she told BBC News.

"The problem is that proving that a unicorn exists or does not exist is impossible. This debate on the vibration theory or the existence of unicorns will never end, but the very important underlying question of why things smell the way they do will continue to be answered by the horses among us."

Tim Jacob, a smell researcher at the University of Cardiff, said the work was "supportive but not conclusive".

"But the fact is that nobody has been able to unequivocally contradict [Dr Turin]," he told BBC News.

"There are many, many problems with the shape theory of smell - many things it doesn't explain that the vibrational theory does."

And although many more scientists are taking the vibrational theory seriously than back in 1996, it remains an extraordinarily polarised debate.

"He's had some peripheral support, but... people don't want to line up behind Luca," Prof Jacob said. "It's scientific suicide."

Columbia University's Richard Axel, whose work on mapping the genes and receptors of our sense of smell garnered the 2004 Nobel prize for physiology, said the kinds of experiments revealed this week would not resolve the debate - only a microscopic look at the receptors in the nose would finally show what is at work.

"Until somebody really sits down and seriously addresses the mechanism and not inferences from the mechanism... it doesn't seem a useful endeavour to use behavioural responses as an argument," he told BBC News.

"Don't get me wrong, I'm not writing off this theory, but I need data and it hasn't been presented."

[Thinking Aloud]

Uh oh. The Psychedelics were right all along...

This garden universe vibrates complete...

... and the word is: Om.

[Audley Strange]

I read about this sort of thing a few years back in Neal Stephenson's Anathem, there is an entire part about scent being a quantum process and how they cannot process non local aromas.

[pErvinalia]

Uh oh. The Psychedelics were right all along...

This garden universe vibrates complete...

... and the word is: Om.

Haha yeah, I was just thinking of 'auras' and "energy" (as used by hippies).

[Clinton Huxley]

I say, I say, I say! My dog has no nose!

How does he smell?

He uses inelastic quantum tunnelling!

Nah.

Sent from my KFTT using Tapatalk 2

[mistermack]

I suppose this is possible.
But how would this evolve? Presumably a sense of smell started simple and got better and better.
How would simple cells start reacting differently to quantum effects of incoming molecules? Maybe they were already doing it.

Maybe, when they start really looking, there might be lots of quantum triggers right inside animal tissue, that act as signals telling proteins and cells what to do.
Like in our immune systems etc.

[Jason]

So, what you're saying is, by the use of quantum entanglement we can have Smell-O-Vision?

[laklak]

Fresh dogshit smells worse than old dogshit, because the molecules in old dog shit are tired and aren't vibrating as fast.

Sounds legit.

[Azathoth]

Fresh dogshit smells worse than old dogshit, because the molecules in old dog shit are tired and aren't vibrating as fast.

Sounds legit.

But how do you explain the old dogshit that forms a crust around a soft centre of inexplicable vileness?

[mistermack]

If you were going to be executed by the Nazis, but they would spare you, if you ate shit, and you had to choose between human or dog shit, which would you choose?

[pErvinalia]

I'd eat Charlize Theron's shit.

[Calilasseia]

The BBC TV programme Horizon covered this topic a while back. They mentioned that tests were performed by trying to find substances with matching bond energies, to see if they produced the same olfactory sensations. One of the compounds tested was decaborane. This was chosen because the S-H bond and the B-H bond have very similar binding energies, and are therefore expected to smell similarly to receptors that are reliant on bond energy. Lo and behold, decaborane has a strongly sulphurous smell, despite containing no sulphur.

Trouble is, the bond energy related theory of olfaction (which is what leads to the electron tunnelling effects cited) runs into the buffers when you consider carvone. This is a chiral compound, existing as two stereoisomers, and the two stereoisomers have different odours associated with them. R(-)-carvone smells like spearmint, whilst S(+)-carvone smells like the caraway seeds for which it is named (said seeds producing only the S-isomer). Oddly enough, several Labiate (Mint Family) plants produce R(-)-carvone, including the Spear Mint. The carvone case requires receptors that are triggered by molecular shape. But of course, there's no reason why the nose cannot have both varieties of receptor, is there?

Oh, that Horizon documentary was from 1995 - A Code In The Nose. Here's part one:

[JimC]

The BBC TV programme Horizon covered this topic a while back. They mentioned that tests were performed by trying to find substances with matching bond energies, to see if they produced the same olfactory sensations. One of the compounds tested was decaborane. This was chosen because the S-H bond and the B-H bond have very similar binding energies, and are therefore expected to smell similarly to receptors that are reliant on bond energy. Lo and behold, decaborane has a strongly sulphurous smell, despite containing no sulphur.

Trouble is, the bond energy related theory of olfaction (which is what leads to the electron tunnelling effects cited) runs into the buffers when you consider carvone. This is a chiral compound, existing as two stereoisomers, and the two stereoisomers have different odours associated with them. R(-)-carvone smells like spearmint, whilst S(+)-carvone smells like the caraway seeds for which it is named (said seeds producing only the S-isomer). Oddly enough, several Labiate (Mint Family) plants produce R(-)-carvone, including the Spear Mint. The carvone case requires receptors that are triggered by molecular shape. But of course, there's no reason why the nose cannot have both varieties of receptor, is there?

In fact, with natural selection, one expects not a perfectly honed blueprint by some sort of purist engineer, but a mish-mash of cobbled together solutions, as long as they do the job, and can derive from some earlier architecture.

So there would be no reason in principle why olfaction has to restrict itself to one particular chemical technique.

[Tyrannical]

It's been known for years dogs can smell the difference between normal and heavy water. I'd be surprised a bit if the average human could tell it apart.