Naked Science Forum

General Science => General Science => Topic started by: Axel2801 on 20/12/2018 04:10:51

Title: What is in a smell?
Post by: Axel2801 on 20/12/2018 04:10:51

hello everyone

I am currently researching the world of smell and would love to know of any books or websites that breakdown & describe what exactly we smell. For example a car exhaust contains carbon dioxide but also many other chemicals and gases. I would be interested to know how many separate odour there are in one subject

Axel2801

Title: Re: What is in a smell?
Post by: evan_au on 20/12/2018 10:33:50

Wine connoisseurs claim to be able to distinguish many different chemical odors associated with wine.
Other renowned experts are perfumers and makers of commercial flavors for the food industry.
But most people are not as able or experienced .

See: https://en.wikipedia.org/wiki/Aroma_of_wine

Title: Re: What is in a smell?
Post by: chiralSPO on 20/12/2018 14:55:38

Olfaction is still somewhat of a mystery, and is still being actively studied, but it appears that at least one of the smell receptors we have is a copper-containing protein complex ( https://cen.acs.org/articles/90/web/2012/02/MetalsRole-Odor-Sensing.html )

Many small molecules can bind to the copper, causing the protein to change shape, and starting the signal cascade. This includes many of the really "stinky" smells like thiols, sulfides, phosphines, amines, pyridines, alkenes (aka "olefins"), alkynes, ketones, esters etc. etc. etc.

see also:
https://en.wikipedia.org/wiki/Aroma_compound
https://www.practicallyscience.com/category/cooking/
https://www.practicallyscience.com/the-chemistry-of-food-aromas/

Title: Re: What is in a smell?
Post by: Petrochemicals on 20/12/2018 21:57:40

A delightful discovery.

https://io9.gizmodo.com/why-is-a-compound-that-smells-like-feces-put-in-perfume-1717903411

Title: Re: What is in a smell?
Post by: chiralSPO on 21/12/2018 05:05:40

Yes, the concentration-dependence of smells is a very interesting aspect. As a chemist, I have first hand (nose?) experience with many very fragrant substances. Indole is not the only one that smells awful at high levels, and nice at lower levels.

Dimethyl sulfide, at high concentrations, smells very strongly of fermenting sewage, while in very trace amounts it is quite appetizing (I know from personal experience, and I know it is used as a food additive).

3-methylbutane thiol is a major component of skunk musk (not a pleasant odor by any means, for those who are unfamiliar), but, again, in minute concentrations, is used as a component of perfumes...

I can only think of two examples of compounds for which the compound smells worse at lower concentrations:
Hydrogen sulfide, which never smells great, but at high enough levels will damage your nose, killing the ability to smell (at least temporarily).

And supposedly* thioacetone (I have never, and will never work with this particularly noxious compound!). I am not aware of any concentration at which it is remotely pleasant, but I have read that the intensity of the smell and the (initial) concentration of the compound are not monotonically related--there is a maximum somewhere below the ppb level! It is postulated that this is because it reacts with itself irreversibly (at ambient temperatures) to form oligomers and polymers, thereby having the paradoxical relationship. I also wonder if it is more like the first case, where it just kills or saturates the olfactory sensation...

*https://blogs.sciencemag.org/pipeline/archives/2009/06/11/things_i_wont_work_with_thioacetone

Title: Re: What is in a smell?
Post by: yor_on on 31/12/2018 14:48:47

Chiral " Many small molecules can bind to the copper, causing the protein to change shape, and starting the signal cascade "

To me that connects to artificial sugar in where the shape of the molecules, versus the receptors shape, are what triggers the brains impression of 'sweetness'.

So is it the geometry?
Or a combination of chemical properties and geometry?

Chemistry is indeed becoming strange :)

Title: Re: What is in a smell?
Post by: chiralSPO on 31/12/2018 18:17:46

In many ways the geometry determines the chemical properties. Shape certainly plays a role in how the smell of a compound is perceived: for instance the two enantiomers of carvone are almost perfectly identical, having the same chemical formula and same connectivity--they are perfect mirror images of each other, while still being different (like a right hand and  left hand). One of them smells like spearmint, and one of them smells of caraway!

https://en.wikipedia.org/wiki/Carvone

Title: Re: What is in a smell?
Post by: yor_on on 31/12/2018 19:28:07

I love it man, thinking of it, it opens so many possibilities.

Remember that little girl stating "I contain multitudes"?
That'¨s what you're stating now.