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How to Smell (2018)
- cwkoss 7y agoInteresting article, will be thinking about smell this week. Anyone have more articles about honing sense of smell? I have wondered about making a 'calibration array' of esters with increasing lengths of carbon chains or something like that. What are the receptors in our noses detecting? Do similar smells always imply chemical similarities? Can a trained nose eventually achieve something like "this smells like it has a 3 carbon chain hanging off the 4-position on an indole ring"?
- cwkoss 7y agoWhoa "Although deuteration does not appreciably change molecular shape, atom size, or bond length or stiffness, it doubles hydrogen mass, thus affecting the overall vibrational modes of an odorant. Therefore, if recognition of molecular shape alone was the sole determinant for odor character (2, 3), then flies should not respond differentially to deuterated [d, where d(x) denotes replacement of x nonexchangeable hydrogens with deuterium atoms] and nondeuterated/normal (i.e., H-) odorants. To address this hypothesis, we took advantage of the commercial availability of acetophenone (ACP) carrying three, five, or eight deuterium atoms (d3, d5, and d8) in place of the respective hydrogens in the normal molecule (h-ACP). Equal amounts (75 μL) of each odorant were diluted to 1 mL in isopropyl myristate and we quantified (Fig. 1A) the response of groups of flies to each odorant versus unscented air traversing the arms of a standard T-maze (Materials and Methods) (19, 20). When given a choice between normal ACP (i.e., h-ACP) and air, the excess flies present in the odor-delivering maze arm indicated that, at the dilution used, the odorant was attractive. However, replacing only three hydrogen atoms with deuterium eliminated this spontaneous preference as the flies distributed nearly equally in the arms of the maze. The d5-ACP was mildly aversive and the fully substituted d8-ACP was the most aversive of the four isotopes." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3048096/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3048096/
- _carl_jung 7y agoThanks for this. I recently read a simple book on organic chemistry and wondered the same thing.
- cwkoss 7y agoNote that this was done in flies, and a similar test in humans did not find ability detect deuteration.
- amelius 7y agoDoesn't the increase in mass change the diffusion characteristics?
- kieckerjan 7y agoActually scientists are still grappling with how the sense of smell works. Two basic observations about smell combine to make it hard to explain. Firstly, it is more or less instantaneous. Secondly, we can discern new smells, even smells that did not exist before. Now, we know biological receptors that are very fast (tastebuds, say) but they can typically detect only a few, fixed sensations. And we know biological systems that can learn new stuff but they are relatively slow: the immune system, for instance, takes hours to days to learn to recognize something new. Here is "smell professor" Luca Turin explaining his theory: https://www.youtube.com/watch?v=yzOcvINn8Iw https://www.youtube.com/watch?v=yzOcvINn8Iw
- jfengel 7y agoAs far as I can tell, Turin is the only one still pursuing this theory, and he hasn't made a lot of headway. About five years ago he was trying to prove his theory by producing molecules with heavy hydrogen, which would smell different by his theory and the same under conventional theory, and the results were inconclusive. He seems to have moved on to other areas. His theory has a fascinating way of explaining what it means for novel smells to be judged similar, but nobody can find a mechanism that would allow it to work. That's not proof that it doesn't work that way, but the conventional theory is proving very productive in research, and his hasn't.
- kieckerjan 7y agoThanks for the update! Would love to see some pointers.
- adim86 7y agoThis article is very interesting. For some reason, somewhere down the line humans evolved to use smell as a way to decide if something is worth engaging with or not (Food, people etc) or to detect danger (smoke from a fire) but like the author said. There is a whole world of smells that are just interesting in themselves but humans never explore. I have never entertained the intricacies of a smell I stop at if it is good or bad.
- z3t4 7y agoIn the server room next to my office I have a air cleaner/fan/filter so that I do not have to clean the servers from dust as often. It will ramp up if it detects dust or smell. It will for example ramp up if someone farts nearby which is quite funny. I however have social anxiety, and when I'm on a phone call, or just thinking about talking to someone I don't like, it will also ramp up. I wonder what this smell does to someone's subconscious when I meet them in person ...
- deleted 7y ago[deleted]
- z3t4 7y agoIn chemistry we learned to explicitly not put our nose against something to smell it, instead wave your hand to get the particles into the air, and smell carefully from a distance.
- bloak 7y agoYes, it's definitely good to avoid accidentally snorting the unknown substance.
- magic_beans 7y agoThe rules of chemistry vary greatly from the rules of real life.
- sizzle 7y agoMy chemistry teacher loved to use the term "waft"
- ibudiallo 7y agoSince I read Perfume by Patrick Süskind, I smell everything. And the sense I had associated with good or bad smells is disappearing. Now I just smell things and etch the moment in my memory. At night, I lay down and replay my day. I can still smell the moist in the air before it rained today.
- s5ma6n 7y agoThis book and for that matter the movie has reignited my enthusiasm about the smells. Whenever I go out for shopping, I stop by a perfumery to try random perfumes. In time, I noticed that I can now identify some of the ingredients of the perfumes. I highly recommend this practice as it also teaches you to identify the quality of fruits/vegetables easily.
- newnewpdro 7y agoThis reminded me of the anecdote in Surely You're Joking, Mr. Feynman! where he had his wife pick a book from a shelf and return it without his watching then using smell alone successfully identified the book she had handled.
- mjlee 7y agoWhen smelling lots of things that are somewhat similar (wines, coffees, etc.) I have found you can get some sort of smell fatigue and stop being able to easily differentiate smells. One trick I have been taught is to smell something that's very different to reset your senses. I've seen people use their clothes, the back of their hand, etc.
- hammock 7y agoCoffee beans are the go to for this. You'll find them in perfume stores, wineries, etc. I guess it doesn't work when you're already smelling coffees though..
- jpalla 7y agoIn some sommellerie school in France, you train your nose using an "aroma box" (https://aromaster.com/fr/produit/coffret-master-aromes-du-vin/ https://aromaster.com/fr/produit/coffret-master-aromes-du-vi...). Being interested into owning one for quite some time now.
- smoll 7y agoIf I was any more in tune with my sense of smell, I don’t think I could live in New York. Walking through most neighborhoods in Manhattan is an assault on most of my senses, smell especially. I haven’t lived in any other large cities in the United States (only a handful in Australia), but is this a common experience for people living in other large, dirty cities or am I just being overly dramatic?
- carlmr 7y agoI wasn't trained in smelling, but I definitely agree New York is a smelly city. That's one of my biggest memories how smelly it was. Berlin can be quite smelly, too. Not every big city is smelly though.
- rinchik 7y agoI wouldn't say it's true for every major city in US, but yes, unfortunately NYC is decaying. NYC is mess you can't compare to Boston or, let's say, Chicago. Current infrastructure is already stretched very thin, but that's one thing, corrupt and incompetent local government deserves it's own story. If residents don't get their shit together and start voting for the change, it will all end badly.