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Analytical Chemistry

Vetiver

In my experience, most organic and medicinal chemists are always ready to hear about the latest results in two branches of the science: things that explode and things with weird smells. Maybe we are in our way “singularly in touch with the primitive promptings of humanity”, as Captain Grimes says in Decline and Fall (although let it be noted that he had something very different in mind). So let’s do a bit of solid, 100% odoriferous chemistry today as a brief change of pace from vaccine work. Ever heard of vetiver? It’s a tropical grass, very large and sturdy, with an extremely deep, dense root system that’s led to the plant’s use in soil stabilization. But those roots have long been used for something else entirely: perfume.

There are a lot of plants in that category – not just flowers, but thing like sandalwood and patchouli. The problem is that in many cases it’s just not possible to grow enough of some of these to meet the fragrance industry’s needs. True sandalwood, for example, has been ferociously overharvested over the decades and is now a protected species. This C&E News article is a nice look at the problem, and at the balance between supply chain needs, cost of ingredients and many consumer’s stated preference for “all-natural” formulations. This can be an opportunity for organic synthesis to step in with larger-scale production, either from other chemical feedstocks or from natural products that can be harvested from more easily grown plants. Medicinal chemists will immediately recall the situation with the natural product taxol, whose use in chemotherapy threatened to make the Pacific yew extinct at one point (the inner bark of the tree had to be stripped). A semisynthetic route was developed at Bristol-Myers Squibb from a related intermediate that could be harvested from pine needles, and now there is even commercial production from plant cell culture.

Now, you don’t hear too much demand from oncologists for all-natural paclitaxel, but all of these techniques do raise questions about what can be called natural and what can’t. It should go without saying that (for example) pure vanillin made in an industrial reactor is exactly the same as pure vanillin isolated from the tropical bean. But it should also go without saying that the extract from the plant will likely contain all sorts of other constituents (some of them at very low levels) that add depth and complexity to an aroma or flavor. Isoamyl acetate, for example, is by far the dominant note in the smell and taste of a banana. But by itself, it smells like banana candy more than it smells like a fresh banana, thanks to all the other components. (Note: I’ve heard the story about how isoamyl acetate was marketed to mimic an earlier variety of banana, but that doesn’t quite hold up). Similarly, ethyl methylphenylglycidate is a big part of the smell of a strawberry, but definitely comes across as artificial and cheap-candy-like on its own.

Most natural extracts have been investigated to the point that we know their “principle”, as the perfume industry calls it. Instead of trying to source original sandalwood oil (not easy on a commercial scale) or deal with the various other oils from related trees and shrubs, you can go get some santalols made by fermentation processes, or buy some sandalore or brahmanol, or try “Dreamwood“, a macrocyclic lactone in a totally different structural class that also recreates much of the effect. Vetiver, though, has been a tough one.

Vetiver itself is a lot easier to cultivate than sandalwood, but harvesting and distilling tons of vetiver root is still something that might be improved on just a bit. But despite decades of effort, no one has quite pinned down which of the hundreds of compounds in vetiver oil really carries the bulk of its distinctive character. Until now, apparently. This new paper seems to have tracked it down, and it took a fair amount of synthetic chemistry to confirm it.

You can see some of those components above (graphic from Angewandte Chemie/Wiley). And you’ll notice that some of these things are pretty easy to smell, like beta-vetivone with a threshold of 0.3 nanograms/liter of air. But it smells more like grapefruit than it does vetiver oil itself, so that can’t be the principle (rather, it’s one of the “top notes” of the overall scent). You may be surprised to see geosmin in there – now that’s a compound with a low detection threshold, and you’ve certainly smelled it, whether you know it or not. It’s the smell of fresh dirt, or the smell you get as a rainstorm starts to wet the ground. There’s a tiny bit of that in the overall vetiver profile, too. But there’s a unique-to-vetiver part of that profile that people have been trying to track down all these years. As the paper details, khusimone (lower left) has long been thought to be that principle, but although its in the right ballpark, its odor detection threshold is just too high for it to be the real candidate.

The paper is a joint effort from the Max Planck Institute in Mülheim and from Givaudan (a big player in the fragrance industry), and it mentions an effort at the latter company to carefully distill 800g of vetiver oil through a Sulzer column and then a Spaltrohr. Even a lot of synthetic organic chemists will be saying “Through a what and a which?” to that one. Sulzer is a Swiss company that makes all sorts of fluid-handling equipment, including many high-end distillation column systems. A look through their material will take you into a whole new world of chemical engineering for such hardware, if you’ve never had to worry about such things. (I haven’t myself – the most hardcore distillation I’ve ever done was with a spinning band column back in 1985 or so, and that was a one time event!) A Spaltrohr distillation (the second step in the Givaudan work) is a tube-within-a-tube column with only a very small separation between the tube surfaces. It’s typically used for small scale vacuum distillation work, although I don’t think “typical” is the right word for what’s a rather uncommon piece of equipment. You’ve got to take those things up very slowly, but you can get some pretty amazing separations if you have the patience.

Now, if you put vetiver oil into a gas chromatograph system, you get hundreds of peaks for different compounds, so isolating things through fractional distillation is not something you’d undertake lightly. A mere 155 of those peaks, by the way, have ever been firmly identified. But you can narrow things down with an interesting GC accessory called a “nose port”, which is exactly what it sounds like: you sniff the separated eluent from the column and use the human nose (which can be a startlingly good detector) to figure out where your compounds of interest lies. Not recommended for ordinary use in the lab, but for flavor-and-fragance work it’s just the thing. That showed a key region eluting at between 45 and 46 minutes with the sought-after aroma, but there were still a number of different peaks in there. And the problem with all research on olfaction is that trace constituents, things that you would hardly even notice in such a forest of GC peaks, can have enormous impacts on smell.

So the only way to be sure was to synthesize some of these things, and that’s what the team in Mülheim did. An earlier attempt to deconvolute both vetiver oil and the vetiver oil literature, which was hardly in better shape due to such trace-component problems, suggested the ziza‐6(13)en‐3‐on skeleton compounds as candidates, but no one had ever prepared these in enough quantity to see if they came at the right spot in the GC smell traces. The Givaudan work agreed with this, pointing especially to compound 10 in the graphic above as a likely winner. Chemistry time! The synthesis (which gives three stereoisomers that are then separated) is about ten steps from cyclopentenone, and involves a tricky intramolecular Pauson-Khand for ring formation. The double bond left from the starting material turned out to be a real pain to reduce selectively in the presence of the exo-alkene left over from the Pauson-Khand, and as you can see from the structure above, that latter one needs to be in the final product. You can tell that this is not what the team was looking to be fighting ten steps into the synthesis, but they got around the problem by epoxidizing the exo-alkene. Hydrogenation then knocks down the enone double bond while converting the epoxide into a hydroxymethyl, which is then eliminated.

And sure enough, compound 10 had a unique odor that hit the elusive “transparent woody-amber” note of vetiver. It’s at least 150 times more detectable to the nose than khusimone, down to 0.03 ng/l of air or below. The authors noted that its scent is rather similar to arborone, which is the active component of a well-known fragrance ingredient called Iso E Super (and other other names as various mixtures of stereoisomers). Those compounds don’t look a heck of a lot alike at first glance, but are quite similar stereoelectronically in a 3-D overlay, which makes sense. Iso E Super has been described as “remarkably pleasant”, and apparently compound 10 is as well. You can bet that the fragrance chemists are modeling the two of them as we speak to figure out some other interesting molecules that might share the same property!

68 comments on “Vetiver”

  1. Marko says:

    Derek sniffing his lady’s perfume : ” That’s lovely. Lemme guess : It’s 2-epi-ziza-6(13)-en-3-one. Amirite?”

    1. Anonymous says:

      I made a trimethylsilylmethylcyclopropylmethanol thingie that smelled fantastic – um, 1-trimethylsilylmethyl-1-hydroxymethylcyclopropane? It’s been awhile since I had to do nomenclature.

      Mentioned to a fellow grad student that her perfume smelled just like it – she was not amused.

      1. kultakutri says:

        People are dumbasses. But then, I was pretty much into perfumes and mixing one’s own stuff is fun and, anyways, and people seemed to take offence when I remarked that they smell good.

  2. Tom says:

    I was curious about those detection limits. I came across some reference items that listed methyl mercaptan, the natural gas odorant, in the 2 ng/L range. So some of these compounds you list really tickle the nose.
    At the extreme end 1-p-menthene-8-thiol has a claimed limit of 0.000034 ng/L in air. It’s in grapefruit.
    Ref.: https://pubs.acs.org/doi/10.1021/acs.jafc.6b01645
    Also thanks for the tip on geosmin. From a light search I see it’s the compound responsible for the “smell after rain” phenomenon called petrochor. My new factoid for today.

    1. kultakutri says:

      I have a bottle of 1% geosmin somewhere and it doesn’t smell like earth after rain started. It’s an interesting smell – and it’s a bit of pain because the smell seems to stick to everything and annoy for days.

  3. rhodium says:

    We need someone to start a wine column for chemists. Instead of notes of grapefruit and chocolates we could have a lambda max of 488 nm with strong nootkatone and hints of. cis-jasmone . It should drive the prices down.

    1. Aaron says:

      LOL, nice. I think you could make a hilarious sketch comedy based on that.

    2. LdaQuirm says:

      Hah! Reminds me of “Good taste” by Isaac Asimov. https://sites.google.com/site/asimovgoodtaste/

    3. Dave says:

      Many already have started doing this with alcoholic beverages. Startup companies have attempted to deconstruct wines and Champaigns to obtain the “exact” nose and palette of expensive wines, using HPLC and GC-MS. Then they replicate the target product with a profile of scents and flavorants. The final products don’t match exactly, of course, but to the average untrained wine drinker, the results were apparently very good. I am aware of one company that launched products, but regulatory issues around product labeling caused them to pivot. They are now making whiskeys and other spirits whose profile mimics those of much more expensive brands.

    4. Kaleberg says:

      Actually, there’s a whole business of tastes-like or in-the-style-of wines that use a variety of synthetics and natural extracts to get the desired flavor and scent profile. A business might want a branded wine, perhaps a cabernet sauvignon, in the style of a 1992 Mondavi Reserve or a 1986 Streblow. In theory, this involves finding similar grapes and duplicating the process somehow, and a lot of luck. Instead, they find a batch of suitable grape juice, usually the same varietal, ferment it and match the notes to create a wine that tastes like or is in the style of the original. If it has a sandalwood note, it is likely because it has some sandalwood synthetic or extract in it, note due to an artifact of the aged oak barrels or whatever. There’s a whole similar business for fragrances, as in, we want a laundry soap that smells like Arpege or Bois des Isle, and good luck with the pH chemistry. That’s how those celebrity fragrances start.

      Who says chemistry doesn’t pay? (OK, half the commenters here.)

    5. Moses says:

      @Rhodium.
      I attended a comp. chem conference in Germany’s Rhine valley in the late 90s where the conference banquet was accompanied by a lecture on the flavour molecules & other characteristics of six wines, one per course, together with a full glass of each wine as they were discussed. Happy days.

  4. CET says:

    In the past, I’ve used vetiver extract to add an interesting note bourbon cocktails (at near-homeopathic dilutions in simple syrup, otherwise the whole drink tastes like cologne). I’d be curious what folks think about the likely low-dose toxicity of that collection of enones and enals though. I might have to rethink my recipes.

    1. metaphysician says:

      My first instinct is “probably trivial compared to the existing toxicity of the alcohol”, but IANAC ( I Am Not A Chemist ).

      1. BV says:

        Well, these things are detectable at nanograms per liter, while alcohol is present in wines at maybe 10-15% by weight. So perhaps the alcohol isn’t as dangerous as you suppose.

  5. Eugene says:

    Last I had heard, no one even knows how the Olfactory sense works at the molecular level. That would be the real breakthrough for perfume technology. Imagine the design software that would be created chemical smell-cad.

    1. Kaleberg says:

      Scent involves hundreds of chemical sensors each reacting at some level to a chemical shape and firing the appropriate neurons. Everyone has their own set of such sensors. It’s not as varied nor as variable as the immune system, but it’s not like they eye with four basic sensors or the ear with a frequency scale. What people – not fragrance experts – typically consider a scent is detected as a pattern of olfactory stimuli. Since everyone has a different set of sensors and those patterns have to be learned, there is no one has perfect scent they some have perfect pitch or perfect color. The folks in the fragrance business spend a lot of time training people to produce calibrated responses.

      There’s no reason one couldn’t build an artificial nose with a thousand or so sensing pads and a suitable flow system. One would then need to train it, and this is actually a good use for modern machine learning systems. That first step is probably harder than it sounds, and even when some basic system is implemented, there’s the matter of finding a suitable set of shapes for sensing.

      If anyone wants to learn more about the whole fragrance business, including a lot about the chemistry, I’ll recommend ‘The Chemistry of Fragrances by the folks at Quest, one of the big fragrance houses. It gives a real view of the business from the customer putting out an RFP or a scent house pushing a new line of synthetics through the chemistry, the testing and so on.

    2. John M says:

      Since I learned about Luca Turin from comments on this blog years ago, I feel the need to reference him here for the benefit of ITP’s much-COVID-enlarged audience.

      Turin has advocated a vibrational theory of the mechanism of smell that has not gained wide acceptance (and which I’m not qualified to judge). You can read that story in Chandler Burr’s biography of Turin, “The Emperor of Scent”.

      What I can comment on is Luca Turin and Tania Sanchez’s “Perfumes: The A-Z Guide”. I guarantee you have never read such detailed and often hilarious descriptions of scents. Many of them constitute sublime poetry.

  6. Druid says:

    Sesquiterpenoids are wonderful to work with like this but can rearrange in minutes in the trace of acidity in deuterochloroform. That exo-alkene looks perfect for starting such ring migrations. I switched to deuterodichloromethane, in the days when there were not so many choices of NMR solvents.

  7. Marko says:

    I just hope all this gets figured out in time for me to be able to experience a decent home-based Smell-O-Vision.

    1. Anonymous says:

      Another use for the synthesis machine!

  8. Wallace Grommet says:

    Vetiver essential oil is a great men’s perfume. Much more agreeable and masculine than patchouli, with a subtle and profound aroma.

    1. Dave says:

      When I was a young rakish-wannabe man, I was going through all these fragrances looking for the best scent to attract a “lady.” At one point, I had this routine worked out where I took a date to a fragrance section to have her pick out a scent for me that she liked. Since I was a scientist by training, a fact that turned her on, she also got a kick out of how I dropped names like vetiver and patchouli as we playfully tried each scent. That date turned out to be an all-out seduction that worked masterfully and still brings a smile as I recall it. To be young again, with the wisdom of how to exploit that as a science geek….

  9. Aileen says:

    Not to be a pain, Derek, but I seem to recall that you studied in Germany and so I will tell you the Max-Planck Institut branch is in Mülheim an der Ruhr, not just Mülheim, to differentiate it from not too far away Koln-Mülheim.

    We in German coal country are a proud bunch, so that’s why this is the Max-Planck Institute for Coal Research.

    1. Derek Lowe says:

      Now that’s a distinction you have to be from the Ruhrgebiet to make! I’ll note that in the post. . .

      1. Aileen says:

        Thank you! My six years and counting in Essen (not at Evonik, but I did teach some of their lab staff at one point) have to be good for something. I was happy to see something from the Max Planck here, because I used to pass it on my commute and wondered what on earth they work on in a world attempting to move past coal…

        It’s certainly interesting in the Pittsburgh of Germany. They still find WW2 bombs weekly in the region, and our local energy company was in the news when they had a scrubber vomit activated charcoal over a playground.

  10. Barry says:

    Synthetic chemists may eventually be called upon to duplicate Chanel#5 to eliminate the need for”flagellated male civet cats”

  11. Elliott says:

    Wait a minute–“nose port” is a thing? Maybe over there in Mulheim an der Ruhr (I refuse to bother with umlauts) but the Big Pharma Co. that I work for here in the US would definitely consider snorting our compounds to be a firing offense.

    1. Michel tabak says:

      Yes the ‘ nose-port’ is a huge thing. The nose is much more sensitive than the GCMS that it is coupled too.

  12. FoodScientist says:

    There’s no legal definition of “natural” in the USA, so you can claim pretty much anything. Very synthetic elements would be an extreme stretch, but technically they naturally occur in supernovas for short periods of time. Certified organic or cage free are actual things, though.

    Natural butter flavoring extraction is a hilarious example.(diacetyl is somewhat toxic, so “natural” is preferable)

    I think shipping/hazard regulations on “NMR pure chemical made Joe in the lab” vs “various plant oil steam distilled from some roots” are somewhat practical importance. Even if they’re identical compositions. It’s kind of like GRAS(generally recognized as safe). If it didn’t kill the animal it was extracted from; It’s probably still in our biological ballpark.

    1. A Nonny Mouse says:

      You are certainly right in the USA that anything seems to go; I have spent the best part of 4 years working on a commercially viable process to (S)-nicotine (to remove cancer causing impurities which are in the natural product for those who wish to indulge in this sort of thing). This has recently gone into production.

      In the meantime, a certain other company has been selling the synthetic R/S-racemic mixture and no one seems to have batted an eyelid over it! People are consuming the R-isomer where there is no safety information at all. Whether this can be considered “GRAS” (though is nicotine consumption anyway?) is certainly a debatable point.

    2. Magrinho says:

      But the CFR (Code of Federal Regulations) contains a clear definition of ‘artificial’.

      The FDA has steadfastly refused to define ‘natural’.

    3. confused says:

      >>There’s no legal definition of “natural” in the USA, so you can claim pretty much anything.

      “Made entirely of naturally-occurring subatomic particles!”

    4. Kaleberg says:

      If you’ve been to a perfume shop lately, you may have noticed that they’ve ret-conned half of their fragrances now that the EU has banned oak moss as an ingredient. It’s really kind of sad for those of us who remember, let’s say Coco by Chanel. No, isn’t the distortion of nostalgia. You can buy old fragrances, at least in the US, from a number of sample houses, and the new stuff is overly sweet, floral and awful.

      1. metaphysician says:

        Why did they ban oak moss? Newly discovered toxicity? Population loss? Random bureaucratic stupidity?

        1. eub says:

          It’s a skin sensitizer leading to contact allergy, in pretty high numbers as cosmetics go.

        2. ppjm says:

          “Why did they ban oak moss?”

          Issue of very serious skin sensitisation. Not just banned in the EU/EEA/EFTA, but rather widely now.

  13. Eugene says:

    Derek, Thanks for the non-(virus name that shall not be mentioned) post. This is one of the obscure corners of Science that I look forward to reading. I am definitely suffering from pandemic fatigue.

  14. Scott Stewart says:

    When people are sniffing these unstudied molecules, how are they relatively sure they are not sniffing some sort of horrible cumulative toxin?

    1. Karl says:

      When they die of something else, I guess?

    2. Lane Simonian says:

      It is possible but not likely that some essential oils are carcinogens (you would likely have to be smelling them for long periods of time for years, though). More common side effects are increases in blood pressure and increased anxiety from more stimulating oils.

      Unfortunatley, the science of aromatherapy has been locked into the pseudoscience category. Due to components that are anti-bacterial, anti-viral, anti-oxidant, and anti-inflammatory, various aromatic compounds may have unlocked medical potential. One clue in this is that the loss of smell in some cases can be restored by direct inhalation aromatherapy (although some times the type of smell restored is not a perfect match to that which has been lost). The clue is that olfactory receptor are g protein-coupled receptors as are receptors nvolved in the retrieval of short-term memory, mood, sleep, social recognition, and alertness. Potentially, then, essential oil components can have a beneficial effect on some or all of these receptors.

      There are a number of reviews on essential oils for possible medical use but this is one of the best ones.

      https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6259136/

      1. metaphysician says:

        If you want essential oils to be taken seriously as medicine, than you need to take the individual components of said oils, and subject them to actual rigorous medical trials for effect. Until someone does so, then essential oils are, *and deserve to be*, considered snake oil.

        1. Lane Simonian says:

          There are multiple scientific studies examining the effects of some specific essential oil components. The clinical trials are out there as well, but they are small, relatively few, and rarely distinguish between specific constituents (whether the latter is needed or not is open to question).

      2. David L says:

        It’s practically impossible to do RCT for essential oils, as well…fragrance.

      3. T says:

        A bit of a confusing comment. It talks about aromatherapy and therapeutic use of essential oils as the same thing, which they aren’t. The recorded antibacterial effects of some of the oils that you mention, for example, might give them some kind of antiseptic action when applied topically (if not too toxic at the effective dose). But there is no reason to conclude from this that just sniffing the oil (which is what aromatherapy does) would produce any kind of antibacterial effect, any more than you’d expect sniffing cod liver oil to help with vitamin D deficiency.

  15. heteromeles says:

    Biologist here. I’m amused because, if I remember right, geosmin is produced by cyanobacteria and actinomycetes, so naturally I wondered if the reason geosmin is showing up in vetiver extract. And it turns out there is evidence that the bacterial community associated with the root can induce expression of a Vetiver sesquiterpene synthase (https://pubmed.ncbi.nlm.nih.gov/18662308/). Not a slam dunk, but some cyanobacteria show up as nitrogen fixers in some C4 grasses, so…

  16. KN says:

    For natural compounds like this, I wonder when it will be easier to find biosynthetic path and genetically export it to some bacteria for synthesis.

  17. Yuri K. says:

    Back in 1970s, the Soviet Union imported a brand of jasmine-scented soap from India. To me, it didn’t smell like jasmine. There was so much skatole in it that I had to use a different brand of soap to get rid of the stench. https://en.wikipedia.org/wiki/Skatole

    I learned never to trust perfume reviews. The sense of smell is just too variable. Some of it is even determined in the womb. https://www.sciencedaily.com/releases/2010/12/101201095559.htm

    As an example, here is a hilarious review of a vetiver-based scent posted on Basenotes.net.

    “Out of the old man’s grumblings and rumblings, out of the dry, crusty sweat of his urine-stained trousers, out of the blunt reek of ammonia oozing from his armpits, out of the assembled smell of cats, dogs and hamsters he keeps locked up in his fetid kitchen with the closed windows, there rises up this milk of horror – they call it Route du Vetiver.” Reviewed by Naed_Nitram (Dean_Martin typed backwards)
    [ https://www.basenotes.net/fragrancereviews/fragrance/26121387/page/2 ]

    After seeing that, I bought a small sample of “Route du Vetiver” and carefully sniffed it. There was indeed a strong hint of rotting beetroot in the background but nothing horrible. Too much geosmin, perhaps? The dose makes the poison?

    1. CET says:

      Very true! I once found a vetiver and bergamot based scent I wanted to use for house candles. I thought it was charming, but my wife’s first reaction was ‘why the **** do we want the house to smell like burning hair!’

  18. Super cool!!! The “ziza” compound identified as important to vetiver smell is quite similar in overall structure to lots of woody/ambery aromachems. The 7-C & 5-C saturated carbon rings sharing one C-C bond & C-C-C loop across middle of 7-C ring is an extremely common motif in naturally occurring & synthetic woody/ambery aromamolecules. Of course, the devil is in the details, and stereochemistry of these molecules is also central to their organoleptic properties.

  19. Ren Hoeg says:

    For anyone interested in scent molecules niche fragrance brand Escentric Molecules might be worth having a look at. Their line of five “Molecule” fragrances is based on single aroma-chemicals, i.e. Iso E Super, Ambroxan, vetiveryl acetate, javanol, and cashmeran, respectively. The matching “Escentric” line of five fragrances uses the same molecules as the main ingredients but combined with other, matching ingredients.

  20. Dave says:

    I see the paper is by Philip Kraft of Givaudin. I read that he’s quite the organic chemist. He can visualize the likely structure of a molecule just by its scent. He is to the F&F field what a top notch med chemist is to small molecule biopharma. He is the co-author of “Scent and Chemistry” and author or “Perspectives in Flaors and Fragrances” which are worth reading to aspiring F&F chemist.

    1. achemist says:

      We had a lecture by him in my masters.

      Good stuff

    2. Derek Lowe says:

      Flavor and fragrance chemistry can be very tricky indeed, given the number of natural product structures in the field. Add in the complexity of the olfactory receptor system and the process chemistry implications, and there’s plenty of challenge there.

      1. Robin says:

        Derek, your comment on the wealth of natural products in the F&F industry rings true to me. There is still a lot out there to discover although this is no longer the preferred route to new molecule discoveries. I am the botanist/natural product chemist that did the original distillation and isolation (Spaltrohr, Girard etc) to find the molecule that started Dr Kraft and the team on his mission to synthesise it. I’m glad you found it interesting.

  21. Josh Vura-Weis says:

    Anyone curious about the “nose port” should check out something called “coupled gas chromatography – electroantennographic detection”: https://www.srs.fs.usda.gov/idip/tools/gc-ead/ . You wire electrodes to an insect’s body or antennae, then flow the output of the GC over it. When a molecule of interest to the bug wafts over it, there is a spike in current that can be correlated with the mass of the molecule. Another option is to put a moth into a little box with a laser beam just over its wings. When it smells an interesting molecule, it flaps and blocks the beam, which basically records “Molecule with mass 123.45 is interesting to the moth”.

    I learned about this in a talk by Prof. Rebecca Whelan of Notre Dame, who works with Prof. Mary Garvin at Oberlin. Want to know why some birds are vectors for West Nile virus but not others? Swap secretions from the butts of difference birds, put them into the GC-EAD, and see which pheremones trigger a response in a mosquito. As someone who builds big, expensive laser systems, the idea of ‘mosquito as detector’ blew my mind.

  22. TheNylonDon says:

    The GC “Nose Port” is both hilarious and my favorite piece of analytical equipment I’ve learned about in a very, very long time.

  23. luysii says:

    Surprising that the word terpene does not appear in post or comments. Nearly all of the structures shown are terpenes. Play the terpene game and find all the 2 methyl butane carbon chains in the structures. Amazing the way nature tacks them together

  24. Vetiver grass (oil )also deters termites (Henderson), and releases a pheromone that attracts Stem borer moths, like Chilo partellus, that lay their eggs on the vetiver, the hatched larvae are then killed by a chemical in the vetiver that destroys their digestive enzymes (recent Chinese research). Indeed a unique and complex plant!

  25. Christophe L Verlinde says:

    It’s so refreshing to read a non-COVID related post, Derek!

  26. li zhi says:

    “pure” vanillin is pure vanillin? Is this a statement of religious doctrine or an aspiration or what? I find it a bit difficult to believe that commercially available synthetic vanillin and commercially available naturally derived vanillin (if there is any such thing) are (or would be) indistinguishable. Although that possibility exists – but at what (trace) level? %, ppm, ppb, ppt, …?
    BTW. That nose port sounds cool; do they also have a mouth (tongue) port and a vein (artery) port? (this humor from a guy who washed up during and after shift in a paint lab with benzene; it tended to dry out my skin.)

    1. Flavor says:

      Tasting is also a thing, but dilutions at low concentrations depending on origins. For vanillin authenticity you can use GC-IRMS; looking at isotope ratios. https://pubs.acs.org/doi/10.1021/jf503055k
      For synthetic routes there is/used to be approved methods and unapproved. And you look for residuals of the process to determine the route.

  27. Gghhjnnbcddffgghhg says:

    Biden sucks dicks in hell

  28. Anon says:

    I am a Tamil speaking native and the name Vetiver has its origin in an ancient, Tamil language. Vetiver is a complex word made up of two words Vetti (useless) and ver (root) roughly translated as….useless root! This is one rare exception where in the the “pleasant odor” is concentrated in the roots and not on other parts of this plant. A bunch of Vetiver root was usually tossed in Earthen pots in Southern India so that people can have a cool and flavored water during punishing summer. It is still practiced in some part of Southern India.

  29. Belgian Grad student says:

    Thanks for the post Derek. Do you know of any good books on the chemistry of perfumes?

  30. Cymantrene says:

    Spaltrohr is a fascinating equipment indeed. The one i worked with had a 80-100 effective theoretical plate number, at least accoring to manual. Fractioning 1-2 ml material was feasible even at below 1 mbar vacuum, but it could handle some hundred ml as well. That was an old one, at least 40 years old equipment, but it still produced in the same form (regarding glass parts)

  31. Cymantrene says:

    Similar components in rose oil are beta-damascone, beta-damascenone and their relatives. Bulk of rose oil are some well known essential oils, as geraniol, nerol and so on, but the key factors are the damasc*. They have very low organoleptic (rhinometric…) detection limit. Once upon a time we produced some via oxydation, and we used water ring pump for vacuum evaporation of solvents. Even in the waste water their concantration was too high to have proper rose scent, instead we felt some fruity smells, raspberry for most people.

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