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Archive for July 19th, 2016

Scientists tell us that the way things work at quantum level are unlike what we experience in our visible world. In macroscopic world “classical” physics of Newton et al rules the roost.

Fundamental particles of the quantum realm behave in seemingly impossible ways: they can exist in two places at once, or disappear and reappear somewhere else instantly. It is so weird that ‘spooky science’ fits the label under which they operate.

Quantum processes may occur not quite so far from our ordinary world as we once thought. Quite the opposite: they might be at work behind some very familiar processes, from the photosynthesis that powers plants – and ultimately feeds us all – to the familiar sight of birds on their seasonal migrations. Quantum physics might even play a role in our sense of smell.

A well-trained human nose can distinguish between thousands of different smells. But how this information is carried in the shape of the smelly molecule is a puzzle. Many molecules that are almost identical in shape, but jigger with one by swapping around an atom or two shall have very different smells. Vanillin smells of vanilla, but eugenol, which is very similar in shape, smells of cloves. Some molecules that are a mirror image of each other – just like your right and left hand – also have different smells. But equally, some very differently shaped molecules can smell almost exactly the same. Luca Turin, a chemist at the BSRC Alexander Fleming institute in Greece observes that there are inconsistencies.

He argues that the molecule’s shape alone isn’t enough to determine its smell. He says that it’s the quantum properties of the chemical bonds in the molecule that provides the crucial information.

According to Turin’s quantum theory of olfaction, when a smelly molecule enters the nose and binds to a receptor, it allows a process called quantum tunnelling to happen in the receptor.

In quantum tunnelling, an electron can pass through a material to jump from point A to point B in a way that seems to bypass the intervening space. For the same reason in photosynthesis of plants how electrons achieve efficiency in photosynthesis owes to the same tunneling. As with the bird’s quantum compass, the crucial factor is resonance. A particular bond in the smelly molecule, Turin says, can resonate with the right energy to help an electron on one side of the receptor molecule leap to the other side. The electron can only make this leap through the so-called quantum tunnel if the bond is vibrating with just the right energy.

When the electron leaps to the other site on the receptor, it could trigger a chain reaction that ends up sending signals to the brain that the receptor has come into contact with that particular molecule. This, Turin says, is an essential part of what gives a molecule its smell, and the process is fundamentally quantum.

The strongest evidence for the theory is Turin’s discovery that two molecules with extremely different shapes can smell the same if they contain bonds with similar energies.

Turin predicted that boranes – relatively rare compounds that are hard to come by – smelled very like sulphur, or rotten eggs. He’d never smelt a borane before, so the prediction was quite a gamble.

He was right. Turin says, “Borane chemistry is vastly different – in fact there’s zero relation – to sulphur chemistry. So the only thing those two have in common is a vibrational frequency. They are the only two things out there in nature that smell of sulphur.”

While that prediction was a great success for the theory, it’s not ultimate proof.

 

Whether or not nature has evolved to make use of quantum phenomena to help organisms make fuel from light, tell north from south, or distinguish vanilla from clove, the strange properties of the atomic world can still tell us a lot about the finer workings of living cells.

(To be concluded)

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