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发信人: foolfish (科研农民), 信区: Physics 标题: Rogue theory of smell gets a boost 发信站: BBS 珞珈山水站 (Wed Dec 13 16:20:44 2006) Rogue theory of smell gets a boost Physicists check out a bold hypothesis for how the nose works. Philip Ball Smell might be down to the vibrations of molecules rather than their shape. Punchstock A controversial theory of how we smell, which claims that our fine sense of od our depends on quantum mechanics, has been given the thumbs up by a team of ph ysicists. Calculations by researchers at University College London (UCL) show that the i dea that we smell odour molecules by sensing their molecular vibrations makes sense in terms of the physics involved1. That's still some way from proving that the theory, proposed in the mid-1990s by biophysicist Luca Turin2, is correct. But it should make other scientists t ake the idea more seriously. "This is a big step forward," says Turin, who has now set up his own perfume c ompany Flexitral in Virginia. He says that since he published his theory, "it has been ignored rather than criticized." Odd smell Most scientists have assumed that our sense of smell depends on receptors in t he nose detecting the shape of incoming molecules, which triggers a signal to the brain. This molecular 'lock and key' process is thought to lie behind a wi de range of the body's detection systems: it is how some parts of the immune s ystem recognise invaders, for example, and how the tongue recognizes some tast es. But Turin argued that smell doesn't seem to fit this picture very well. Molecu les that look almost identical can smell very different — such as alcohols, w hich smell like spirits, and thiols, which smell like rotten eggs. And molecul es with very different structures can smell similar. Because it was an interesting idea, I thought I should prove it couldn't work . Marshall Stoneham, University College London. Most strikingly, some molecules can smell different — to animals, if not nece ssarily to humans — simply because they contain different isotopes (atoms tha t are chemically identical but have a different mass). Turin's explanation for these smelly facts invokes the idea that the smell sig nal in olfactory receptor proteins is triggered not by an odour molecule's sha pe, but by its vibrations, which can enourage an electron to jump between two parts of the receptor in a quantum-mechanical process called tunnelling. This electron movement could initiate the smell signal being sent to the brain. This would explain why isotopes can smell different: their vibration frequenci es are changed if the atoms are heavier. Turin's mechanism, says Marshall Ston eham of the UCL team, is more like swipe-card identification than a key fittin g a lock. Vibration-assisted electron tunnelling can undoubtedly occur — it is used in an experimental technique for measuring molecular vibrations. "The question is whether this is possible in the nose," says Stoneham's colleague, Andrew Hors field. Unbelievable Stoneham says that when he first heard about Turin's idea, while Turin was him self based at UCL, "I didn't believe it". But, he adds, "because it was an int eresting idea, I thought I should prove it couldn't work. I did some simple ca lculations, and only then began to feel Luca could be right." Now Stoneham and his co-workers have done the job more thoroughly, in a paper soon to be publi shed in Physical Review Letters. The UCL team calculated the rates of electron hopping in a nose receptor that has an odorant molecule bound to it. This rate depends on various properties o f the biomolecular system that are not known, but the researchers could estima te these parameters based on typical values for molecules of this sort. The key issue is whether the hopping rate with the odorant in place is signifi cantly greater than that without it. The calculations show that it is — which means that odour identification in this way seems theoretically possible. ADVERTISEMENT Click here to subscribe But Horsfield stresses that that's different from a proof of Turin's idea. "So far things look plausible, but we need proper experimental verification. We'r e beginning to think about what experiments could be performed." Meanwhile, Turin is pressing ahead with his hypothesis. "At Flexitral we have been designing odorants exclusively on the basis of their computed vibrations, " he says. "Our success rate at odorant discovery is two orders of magnitude b etter than the competition." At the very least, he is putting his money where his nose is. Visit our newsblog to read and post comments about this story. Top References 1. Brookes J. C., et al. Preprint, http://www.arxiv.org/abs/physics/0611205 (2006). 2. Turin L., . Chem. Senses , 21 . 773 - 791 (2006). -- 人丑，不要怨父母命苦，就去骂政府 ※ 来源:·珞珈山水BBS站 http://bbs.whu.edu.cn·[FROM: 202.114.78.*]
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发信人: foolfish (科研农民), 信区: Physics
标  题: Rogue theory of smell gets a boost
发信站: BBS 珞珈山水站 (Wed Dec 13 16:20:44 2006)

Rogue theory of smell gets a boost
Physicists check out a bold hypothesis for how the nose works.

Philip Ball

Smell might be down to the vibrations of molecules rather than their shape.
Punchstock
A controversial theory of how we smell, which claims that our fine sense of od
our depends on quantum mechanics, has been given the thumbs up by a team of ph
ysicists.

Calculations by researchers at University College London (UCL) show that the i
dea that we smell odour molecules by sensing their molecular vibrations makes
sense in terms of the physics involved1.

That's still some way from proving that the theory, proposed in the mid-1990s
by biophysicist Luca Turin2, is correct. But it should make other scientists t
ake the idea more seriously.

"This is a big step forward," says Turin, who has now set up his own perfume c
ompany Flexitral in Virginia. He says that since he published his theory, "it
has been ignored rather than criticized."

Odd smell

Most scientists have assumed that our sense of smell depends on receptors in t
he nose detecting the shape of incoming molecules, which triggers a signal to
the brain. This molecular 'lock and key' process is thought to lie behind a wi
de range of the body's detection systems: it is how some parts of the immune s
ystem recognise invaders, for example, and how the tongue recognizes some tast
es.

But Turin argued that smell doesn't seem to fit this picture very well. Molecu
les that look almost identical can smell very different — such as alcohols, w
hich smell like spirits, and thiols, which smell like rotten eggs. And molecul
es with very different structures can smell similar.

Because it was an interesting idea, I thought I should prove it couldn't work
.

Marshall Stoneham, University College London.

Most strikingly, some molecules can smell different — to animals, if not nece
ssarily to humans — simply because they contain different isotopes (atoms tha
t are chemically identical but have a different mass).

Turin's explanation for these smelly facts invokes the idea that the smell sig
nal in olfactory receptor proteins is triggered not by an odour molecule's sha
pe, but by its vibrations, which can enourage an electron to jump between two
parts of the receptor in a quantum-mechanical process called tunnelling. This
electron movement could initiate the smell signal being sent to the brain.

This would explain why isotopes can smell different: their vibration frequenci
es are changed if the atoms are heavier. Turin's mechanism, says Marshall Ston
eham of the UCL team, is more like swipe-card identification than a key fittin
g a lock.

Vibration-assisted electron tunnelling can undoubtedly occur — it is used in
an experimental technique for measuring molecular vibrations. "The question is
whether this is possible in the nose," says Stoneham's colleague, Andrew Hors
field.

Unbelievable

Stoneham says that when he first heard about Turin's idea, while Turin was him
self based at UCL, "I didn't believe it". But, he adds, "because it was an int
eresting idea, I thought I should prove it couldn't work. I did some simple ca
lculations, and only then began to feel Luca could be right." Now Stoneham and
his co-workers have done the job more thoroughly, in a paper soon to be publi
shed in Physical Review Letters.

The UCL team calculated the rates of electron hopping in a nose receptor that
has an odorant molecule bound to it. This rate depends on various properties o
f the biomolecular system that are not known, but the researchers could estima
te these parameters based on typical values for molecules of this sort.

The key issue is whether the hopping rate with the odorant in place is signifi
cantly greater than that without it. The calculations show that it is — which
means that odour identification in this way seems theoretically possible.

ADVERTISEMENT
Click here to subscribe
But Horsfield stresses that that's different from a proof of Turin's idea. "So
far things look plausible, but we need proper experimental verification. We'r
e beginning to think about what experiments could be performed."

Meanwhile, Turin is pressing ahead with his hypothesis. "At Flexitral we have
been designing odorants exclusively on the basis of their computed vibrations,
" he says. "Our success rate at odorant discovery is two orders of magnitude b
etter than the competition." At the very least, he is putting his money where
his nose is.

Visit our newsblog to read and post comments about this story.

     Top
References

   1. Brookes J. C., et al. Preprint,

http://www.arxiv.org/abs/physics/0611205
(2006).
2. Turin L., . Chem. Senses , 21 . 773 - 791 (2006).

--
人丑，不要怨父母
命苦，就去骂政府

※ 来源:·珞珈山水BBS站

http://bbs.whu.edu.cn·[FROM: 202.114.78.*]

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