The sense of smell

[Guest 1lastdragon]

Oh how my misguided brain hurts.

 

A friend of mine is a composer working on a special project. She tells me that there was a recent paper published tha claims that the aromas we

register are not caused by the molecule but by the "frequency" that molecule is "vibrating" at. She's presently hard at work composing the "scent of geraniums". Neat stuff!

 

She has also told me that the present theory of how we smell has something to do with the "shape of the molecule", which makes no sense to me. Do molecules come in different shapes?

 

Looking for some interesting insights

[jdurg]

Well I would have to disagree with whatever paper that is based upon the information given in your post. The vibration of a molecule is its temperature. Molecules at a higher temperature vibrate more rapidly so they would have a higher frequency. To say that smell is based on the frequency of the vibration would say that your sense of smell is 100%, completely due to temperature. That is completely wrong.

 

Molecules come in many different shapes. The DNA molecules is a double-stranded helix while a benzene molecule is pretty much a flat six-sided ring. These different shapes allow for the different behavior of many molecules inside a human body. The shape is also what gives rise to a compound's odor. Molecules that are similar in shape and electronic structure tend to have similar odors. Look at the halogens; Fluorine, Chlorine, Bromine, and Iodine. They are all diatomic molecules which want to grab an electron from anything. As a result, they basically have a slightly positive effective charge on them. (This isn't entirely true, but I'm just trying to simplify things here). In your nose, all of the halogens smell pretty similar. They all have a bleach-like odor to them. This is because of the electronic structure of the halogen molecules and the shape of them.

 

Also look at molecules like benzene, toluene, phenol, etc. They have a very similar odor to each other because their shapes are very close to each other. As a result, they trigger similar receptors in your nose. Another good example is hydrogen sulfide gas. H2S gas has the same shape as a water molecule, but a different electronic configuration. H2S smells like rotten eggs. Your nose is able to detect the tiniest amount of H2S gas in the air, but after a short while you become desensitized to it. It's theorized that the gas molecule binds to the scent receptor in your nose thereby inactivating it. As a result, you no longer smell the gas. If you move into an area that is free of H2S gas, those receptors are able to clear themselves out and your ability to smell the gas comes back. This 'blocking' of your scent receptors by H2S gas is pretty nasty because the gas is also very toxic. So you might think the gas leak has gone away when in reality your nose is just numb to the odor.

 

Anyway, I hope that cleared things up a little bit without causing too much confusion. It's early for me and I've yet to wake up fully. lol.

[badchad]

Well, since we're on the topic of reports, I found a clinical study refuting the idea. Although admittedly, I only read the abstract.

 

PUBMED link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15034588

 

I also found what may be the original paper describing this phenomenon.

 

PUBMED link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=8985605

 

You can read up if you wish. From my knowledge of receptor's I tend to agree with jdurg.

[jdurg]

In reality, it's probably a combination of the two. The thing that second article mentioned was how a fully deuterated compound smells different than a normal non-deuterated version. They say that the structure is the same, but it would actually be slightly different since the deuterium atoms is VERY SLIGHTLY larger than the protium atom. It may just be a combination of the stretching and moving along the C-D/C-H bond that results in the different smells.