March 25, 2011

Quantum Smell Theory ‘Gaining Traction’

A controversial idea that sense of smell can be explained by quantum physics is gaining traction in the science world, according to researchers.

Researchers, reporting at the American Physical Society meeting in Dallas, say the key to proving how such a theory would work revolves around tiny packets of energy -- or quanta -- lost by electrons.

The scientists performed experiments using tiny wires and showed that as electrons move on proteins within the nose, odor molecules could absorb these quanta and therefore be detected.

Advanced research has delved into how a detected molecule is translated into a smell within the brain. But how well an odorant molecule is detected remains a mystery. By extending studies, researchers think an "electronic nose" superior to any chemical sensor could be created.

As molecular interactions drive scientists' understanding of enzymes and drugs, the very shape of odorant molecules has been assumed to be the way it is detected in the nose. Molecules are seen to be the "key" that fits neatly into a detector molecule in the nose that acts as a lock.

But in 1996, Luca Turin, now of the Massachusetts Institute of Technology, suggested that the "vibrational modes" of an odorant were its signature. Molecules can be viewed as a collection of atoms on springs, and energy of just the right frequency - a quantum - can cause the spring to vibrate. Since different types of molecules have different characteristic frequencies, Turin proposed that these vibrations could act as a molecular signature.

The theory revolving around the topic has been debated in the scientific world for some time, but presentations at the American Physical Society meeting put the theory on stronger ground.

Turin recently published a new paper showing that flies can distinguish between molecules that are chemically similar but in which a heavier version of hydrogen had been substituted.

The flies appeared to notice when vibration frequencies were lowered, Turin noted.

"There's still lots to understand, but the idea that it cannot possibly be right is no longer tenable really," Andrew Horsfield, of Imperial College London, told BBC's Jason Palmer. "The theory has to at least be considered respectable at this point."

Horsfield's research revolves around demonstrating how the vibration might be detected. The idea is that an electron on one part of a protein may move, and arrive at another part lacking a quantum of vibrational energy.

"The electron starts at one end of the room, if you like, and it can only make it to the other end if it gives up energy to the molecule in the middle of the room," explained Horsfield. "Once it's arrived, you say 'Aha! The fact that it's here means that somewhere between where it started and where it is now there's a molecule with the right vibrational frequency'."

He noted that it is difficult to demonstrate a physical system where this type of study can be accomplished. Horsfield and his colleagues demonstrated the use of nanowires that can act as the "room" of the analogy.

They demonstrated how electrons could arrive at one end of the nanowires and give away what molecules they had encountered along the way.

"It's a very interesting idea; there's all sorts of interesting biological physics that implement quantum processes that's cropping up," said Jennifer Brookes, a University College London researcher based at MIT.

"I believe it's time for the idea to develop and for us to get on with testing it," she told BBC News.

She suggested that vibrational theory of smell, at least as quantum physics is concerned, is a reasonable one. "Mathematically, the theory is robust, and even if it's not happening in smell, it's interesting to think it might be a discriminatory process in nature in other ways."


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