Practice English Speaking&Listening with: Luca Turin: The science of scent

Difficulty: 0

The fragrance that you will smell, you will never be able to smell this way again.

Its a fragrance called Beyond Paradise,

which you can find in any store in the nation.

Except here its been split up in parts by Estée Lauder

and by the perfumer who did it, Calice Becker,

and I'm most grateful to them for this.

And its been split up in successive bits and a chord.

So what youre smelling now is the top note.

And then will come what they call the heart, the lush heart note.

I will show it to you.

The Eden top note is named after the Eden Project in the U.K.

The lush heart note, Melaleuca bark note -- which does not contain any Melaleuca bark,

because its totally forbidden.

And after that, the complete fragrance.

Now what you are smelling is a combination of --

I asked how many molecules there were in there, and nobody would tell me.

So I put it through a G.C., a Gas Chromatograph that I have in my office,

and its about 400.

So what youre smelling is several hundred molecules

floating through the air, hitting your nose.

And do not get the impression that this is very subjective.

You are all smelling pretty much the same thing, OK?

Smell has this reputation of being somewhat different for each person.

Its not really true.

And perfumery shows you that cant be true,

because if it were like that it wouldnt be an art, OK?

Now, while the smell wafts over you, let me tell you the history of an idea.

Everything that youre smelling in here

is made up of atoms that come from what I call

the Upper East Side of the periodic table -- a nice, safe neighborhood.


You really dont want to leave it if you want to have a career in perfumery.

Some people have tried in the 1920s

to add things from the bad parts, and it didnt really work.

These are the five atoms from which just about everything

that youre going to smell in real life, from coffee to fragrance, are made of.

The top note that you smelled at the very beginning,

the cut-grass green, what we call in perfumery -- theyre weird terms --

and this would be called a green note,

because it smells of something green, like cut grass.

This is cis-3-hexene-1-ol. And I had to learn chemistry on the fly

in the last three years. A very expensive high school chemistry education.

This has six carbon atoms, so "hexa," hexene-1-ol.

It has one double bond, it has an alcohol on the end,

so its "ol," and thats why they call it cis-3-hexene-1-ol.

Once you figure this out, you can really impress people at parties.

This smells of cut grass. Now, this is the skeleton of the molecule.

If you dress it up with atoms, hydrogen atoms --

thats what it looks like when you have it on your computer --

but actually its sort of more like this, in the sense that the atoms have a certain

sphere that you cannot penetrate. They repel.

OK, now. Why does this thing smell of cut grass, OK?

Why doesnt it smell of potatoes or violets? Well, there are really two theories.

But the first theory is: it must be the shape.

And thats a perfectly reasonable theory in the sense that

almost everything else in biology works by shape.

Enzymes that chew things up, antibodies, its all, you know,

the fit between a protein and whatever it is grabbing, in this case a smell.

And I will try and explain to you whats wrong with this notion.

And the other theory is that we smell molecular vibrations.

Now, this is a totally insane idea.

And when I first came across it in the early '90s, I thought my predecessor,

Malcolm Dyson and Bob Wright, had really taken leave of their senses,

and Ill explain to you why this was the case.

However, I came to realize gradually that they may be right --

and I have to convince all my colleagues that this is so, but Im working on it.

Heres how shape works in normal receptors.

You have a molecule coming in, it gets into the protein, which is schematic here,

and it causes this thing to switch, to turn, to move in some way

by binding in certain parts.

And the attraction, the forces, between the molecule and the protein

cause the motion. This is a shape-based idea.

Now, whats wrong with shape is summarized in this slide.

The way --I expect everybody to memorize these compounds.

This is one page of work from a chemists workbook, OK?

Working for a fragrance company.

Hes making 45 molecules, and hes looking for a sandalwood,

something that smells of sandalwood.

Because theres a lot of money in sandalwoods.

And of these 45 molecules, only 4629 actually smells of sandalwood.

And he puts an exclamation mark, OK? This is an awful lot of work.

This actually is roughly, in man-years of work, 200,000 dollars roughly,

if you keep them on the low salaries with no benefits.

So this is a profoundly inefficient process.

And my definition of a theory is, its not just something

that you teach people; its labor saving.

A theory is something that enables you to do less work.

I love the idea of doing less work. So let me explain to you why -- a very simple fact

that tells you why this shape theory really does not work very well.

This is cis-3-hexene-1-ol. It smells of cut grass.

This is cis-3-hexene-1-thiol, and this smells of rotten eggs, OK?

Now, you will have noticed that vodka never smells of rotten eggs.

If it does, you put the glass down, you go to a different bar.

This is -- in other words, we never get the O-H --

we never mistake it for an S-H, OK?

Like, at no concentration, even pure, you know,

if you smelt pure ethanol, it doesnt smell of rotten eggs.

Conversely, there is no concentration at which the sulfur compound will smell like vodka.

Its very hard to explain this by molecular recognition.

Now, I showed this to a physicist friend of mine who has a profound distaste

for biology, and he says, "Thats easy! The things are a different color!"


We have to go a little beyond that. Now let me explain why vibrational theory has

some sort of interest in it. These molecules, as you saw in the beginning,

the building blocks had springs connecting them to each other.

In fact, molecules are able to vibrate at a set of frequencies

which are very specific for each molecule and for the bonds connecting them.

So this is the sound of the O-H stretch, translated into the audible range.

S-H, quite a different frequency.

Now, this is kind of interesting, because it tells you

that you should be looking for a particular fact, which is this:

nothing in the world smells like rotten eggs except S-H, OK?

Now, Fact B: nothing in the world has that frequency except S-H.

If you look on this, imagine a piano keyboard.

The S-H stretch is in the middle of a part of the keyboard

that has been, so to speak, damaged,

and there are no neighboring notes, nothing is close to it.

You have a unique smell, a unique vibration.

So I went searching when I started in this game

to convince myself that there was any degree of plausibility

to this whole crazy story.

I went searching for a type of molecule, any molecule,

that would have that vibration and that -- the obvious prediction

was that it should absolutely smell of sulfur.

If it didnt, the whole idea was toast, and I might as well move on to other things.

Now, after searching high and low for several months,

I discovered that there was a type of molecule called a Borane

which has exactly the same vibration.

Now the good news is, Boranes you can get hold of.

The bad news is theyre rocket fuels.

Most of them explode spontaneously in contact with air,

and when you call up the companies, they only give you minimum ten tons, OK?


So this was not what they call a laboratory-scale experiment,

and they wouldnt have liked it at my college.

However, I managed to get a hold of a Borane eventually, and here is the beast.

And it really does have the same -- if you calculate,

if you measure the vibrational frequencies, they are the same as S-H.

Now, does it smell of sulfur? Well, if you go back in the literature,

theres a man who knew more about Boranes than anyone

alive then or since, Alfred Stock, he synthesized all of them.

And in an enormous 40-page paper in German he says, at one point --

my wife is German and she translated it for me --

and at one point he says, "ganz widerlich Geruch,"

an "absolutely repulsive smell," which is good. Reminiscent of hydrogen sulfide.

So this fact that Boranes smell of sulfur

had been known since 1910, and utterly forgotten until 1997, 1998.

Now, the slight fly in the ointment is this: that

if we smell molecular vibrations, we must have a spectroscope in our nose.

Now, this is a spectroscope, OK, on my laboratory bench.

And its fair to say that if you look up somebodys nose,

youre unlikely to see anything resembling this.

And this is the main objection to the theory.

OK, great, we smell vibrations. How? All right?

Now when people ask this kind of question, they neglect something,

which is that physicists are really clever, unlike biologists.


This is a joke. Im a biologist, OK?

So its a joke against myself.

Bob Jacklovich and John Lamb at Ford Motor Company,

in the days when Ford Motor was spending vast amounts of money

on fundamental research, discovered a way

to build a spectroscope that was intrinsically nano-scale.

In other words, no mirrors, no lasers, no prisms, no nonsense,

just a tiny device, and he built this device. And this device uses electron tunneling.

Now, I could do the dance of electron tunneling,

but Ive done a video instead, which is much more interesting. Heres how it works.

Electrons are fuzzy creatures, and they can jump across gaps,

but only at equal energy. If the energy differs, they cant jump.

Unlike us, they wont fall off the cliff.

OK. Now. If something absorbs the energy, the electron can travel.

So here you have a system, you have something --

and theres plenty of that stuff in biology --

some substance giving an electron, and the electron tries to jump,

and only when a molecule comes along that has the right vibration

does the reaction happen, OK?

This is the basis for the device that these two guys at Ford built.

And every single part of this mechanism is actually plausible in biology.

In other words, Ive taken off-the-shelf components,

and Ive made a spectroscope.

Whats nice about this idea, if you have a philosophical bent of mind,

is that then it tells you that the nose,

the ear and the eye are all vibrational senses.

Of course, it doesnt matter, because it could also be that theyre not.

But it has a certain --


-- it has a certain ring to it which is attractive to people

who read too much 19th-century German literature.

And then a magnificent thing happened:

I left academia and joined the real world of business,

and a company was created around my ideas

to make new molecules using my method,

along the lines of, lets put someone elses money where your mouth is.

And one of the first things that happened was

we started going around to fragrance companies

asking for what they needed, because, of course,

if you could calculate smell, you dont need chemists.

You need a computer, a Mac will do it, if you know how to program the thing right,

OK? So you can try a thousand molecules,

you can try ten thousand molecules in a weekend,

and then you only tell the chemists to make the right one.

And so thats a direct path to making new odorants.

And one of the first things that happened was

we went to see some perfumers in France --

and heres where I do my Charles Fleischer impression --

and one of them says, "You cannot make a coumarin."

He says to me, "I bet you cannot make a coumarin."

Now, coumarin is a very common thing, a material,

in fragrance which is derived from a bean that comes from South America.

And it is the classic synthetic aroma chemical, OK?

Its the molecule that has made mens fragrances

smell the way they do since 1881, to be exact.

And the problem is its a carcinogen.

So nobody likes particularly to -- you know, aftershave with carcinogens.


There are some reckless people, but its not worth it, OK?

So they asked us to make a new coumarin. And so we started doing calculations.

And the first thing you do is you calculate the vibrational spectrum

of coumarin, and you smooth it out,

so that you have a nice picture of what the sort of chord, so to speak, of coumarin is.

And then you start cranking the computer to find other molecules,

related or unrelated, that have the same vibrations.

And we actually, in this case, Im sorry to say,

it happened -- it was serendipitous.

Because I got a phone call from our chief chemist

and he said, look, Ive just found this such a beautiful reaction,

that even if this compound doesnt smell of coumarin,

I want to do it, its just such a nifty,

one step -- I mean, chemists have weird minds --

one step, 90 percent yield, you know, and you get this lovely

crystalline compound. Let us try it.

And I said, first of all, let me do the calculation on that compound, bottom right,

which is related to coumarin, but has an extra pentagon inserted into the molecule.

Calculate the vibrations, the purple spectrum is that new fellow,

the white one is the old one.

And the prediction is it should smell of coumarin.

They made it ... and it smelled exactly like coumarin.

And this is our new baby, called tonkene.

You see, when youre a scientist, youre always selling ideas.

And people are very resistant to ideas, and rightly so.

Why should new ideas be accepted?

But when you put a little 10-gram vial on the table in front of perfumers

and it smells like coumarin, and it isnt coumarin,

and youve found it in three weeks,

this focuses everybodys mind wonderfully.



And people often ask me, is your theory accepted?

And I said, well, by whom? I mean most, you know -- theres three attitudes:

Youre right, and I dont know why, which is the most rational one at this point.

Youre right, and I dont care how you do it, in a sense;

you bring me the molecules, you know.

And: Youre completely wrong, and Im sure youre completely wrong.

OK? Now, were dealing with people who only want results,

and this is the commercial world.

And they tell us that even if we do it by astrology, theyre happy.

But were not actually doing it by astrology.

But for the last three years, Ive had what I consider to be

the best job in the entire universe, which is to put my hobby --

which is, you know, fragrance and all the magnificent things --

plus a little bit of biophysics, a small amount of self-taught chemistry

at the service of something that actually works.

Thank you very much.


The Description of Luca Turin: The science of scent