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Terpene

May 15, 2017

While modern man is generally concerned about his body odor, it appears that prehistoric man was not. Flowers would have been an abundant natural source of pleasant fragrance for primitive man. There is evidence that Neanderthals adorned themselves with bird feathers,[1] but they do not seem to have adorned themselves with flowers. There is evidence, however, of the use of flowers in prehistoric burials.[2]

As civilization progressed, so did concerns about body odor. The ancient Greeks had developed a perfume industry at least as far back as the 4th century BC. Theophrastus (c. 371 - c. 287 BC), whose mineralogy treatise, "On Stones (Περι λιθων)," was mentioned in several articles on this blog (Pyroelectric Energy Harvesting, October 15, 2010, Rise and Fall of Coal, February 4, 2016, and Triboelectric Generators, February 8, 2016), described the perfumer's art in another short treatise on odors.

Theophrastus succeeded Aristotle as leader of the Peripatetic school; and, like Aristotle, he wrote in many subject areas. Theophrastus wrote a lengthy treatise on botany, Enquiry into Plants (Περι φυτων ιστορια, Historia Plantarum), so he is often called the "father of botany." On Odors is usually placed as an appendix to the Enquiry into Plants.[3-4] On Odors describes the perfumers' secrets of his age (see figure).

Portion of 'On Odors' by Theophrastus

A portion of Theophrastus', "On Odors," that discusses the oil extraction of fragrant compounds. "Now the composition and preparation of perfumes aim entirely, one may say, at making the odours last. That is why men make oil the vehicle of them, since it keeps a very long time and also is most convenient for use. By nature indeed oil is not at all well suited to take in an odour, because of its close and greasy character: and of particular oils this is specially true of the most viscous, such as almond-oil, while sesame-oil and olive-oil are the least receptive of all." (Original Greek and English translation from Theophrastus, "De odoribus (Concerning Odours)," vol. II of Loeb Classical Library edition of the Enquiry into Plants, 1926.)[3)]


Chemistry has developed to the point at which most fragrances are produced synthetically, usually by chemical analysis of natural fragrances to produce the same chemical compounds, or as an aid in the search for functional analogs. Most natural odorants are a class of chemicals called terpenes, and there are thousands of terpenes to be found in both natural and synthetic fragrances.

The smaller terpene molecules are more strongly fragrant, so oxygenated monoterpenes are the most widely used and investigated. The higher molecular weight terpenes have lower volatility, which makes their scents more tenacious, so they're often used as a vehicle for other terpene fragrances.

Alpha-terpineol molecule

α-Terpineol

Alpha-Terpineol has a lilac scent.

Although it's used as a fragrance in products such as soap, I used this compound as part of the electrolyte mixture in an electrochemical process.

(Via Wikimedia Commons.)


The five principal fragrance terpenes are Geraniol-nerol, linalool, citronellol, citronellal and citral. These, and derived compounds such as their esters and alcohols are widely used. They are used, also, as reagents for synthesis of other terpenes. The following table lists some important terpene-derived chemicals.[5]

  Material Odor
  Geraniol-nerol Rose
  linalool Floral, wood
  citronellol, citronellal and citral Rose
  Dihydromyrcenol Citrus, floral
  Hydroxycitronellal Lily of the valley
  (Methyl)ionones Violet
  Linalyl acetate Lavender
  Borneol/isoborneol and acetate Pine
  α-Terpineol and acetate Lilac
  Amberlyn® Ambergris
  Carvone Spearmint
  Menthol Mint
  Acetylated cedarwood Cedar

While body odor, both pleasant and unpleasant, sends signals to those nearby, scent is not our primary mode of communication. Chemical signalling, however, is the principal communications channel for simpler organisms such as bacteria. As most people likely know, bacteria are the principal lifeform, there being an estimated 1030 bacteria on Earth. Each bacterium is small, but in such a number bacterial mass easily exceeds the mass of all plants and animals.

A team of biologists from the Netherlands Institute of Ecology (NIOO-KNAW, Wageningen, The Netherlands), Wageningen University and Research Centre (Wageningen, The Netherlands), the University of Greifswald (Greifswald, Germany), and the Erasmus University Medical Center (Rotterdam, The Netherlands) has looked at the bacterial production of the terpene, sodorifen, in response to volatile organic compounds (VOCs), primarily terpenes, emitted by fungi. They suggest that VOCs are used as a communication channel between fungi and bacteria.[6-7]

The plant pathogenic fungus, Fusarium culmorum, and the rhizobacterium, Serratia plymuthica PRI-2C, were selected for this study.[6] While the role of VOCs in organism communication has been known for more than 30 years, the response of bacteria to fungal VOCs has not been studied.[6] VOCs are effective for communication, since their low molecular weights, boiling points, and high vapor pressures allow their speedy diffusion in both aqueous and atmospheric environments.[6]

A good sense of environment is important for an organism's survival, so it's plausible that microorganisms will sense the VOCs in their environment and adapt accordingly.[6] In the case of the experimental organisms, this involves activation of the genes that produce the fragrance chemicals.[7]

Says Paolina Garbeva, group leader of the study,
"We have known for some time that plants and insects use terpenes to communicate with each other. But we've only just begun to realize that it's actually much wider. There is a much larger group of 'Terpene-speakers': micro-organisms... Serratia, a soil bacterium, can 'smell' the fragrant terpenes produced by Fusarium, a plant pathogenic fungus. It responds by becoming motile and producing a terpene of its own."[7]

Fungal VOC effect on bacterial growth

Fungal VOC effect on bacterial growth.

Controls (blue) and specimens (red) after 48 hours (t1) and 72 hours (t2) exposure.

(Fig. 1(b) of ref. 6, modified, licensed under the Creative Commons Attribution 4.0 International license)[6)]


While organisms produce a variety of VOCs, terpenes are the ones most often produced.[7] As the authors summarize in their paper, "We actually believe that terpenes are the most popular chemical medium on our planet to communicate through."[7]

References:

  1. Clive Finlayson, Kimberly Brown, Ruth Blasco, Jordi Rosell, Juan José Negro, Gary R. Bortolotti, Geraldine Finlayson, Antonio Sánchez Marco, Francisco Giles Pacheco, Joaquín Rodríguez Vidal, José S. Carrión, Darren A. Fa, and José M. Rodríguez Llanes, "Birds of a Feather: Neanderthal Exploitation of Raptors and Corvids," PLOS ONE, vol. 7, no. 10, Article no. 0045927, October 12, 2012, https://doi.org/10.1371/journal.pone.0045927. This is an open access publication with a PDF file available here.
  2. Brian F. Byrd and Christopher M. Monahan, "Death, Mortuary Ritual, and Natufian Social Structure," Journal of Anthropological Archaeology. vol. 14, no. 3 (September, 1995), pp. 251-287, https://doi.org/10.1006/jaar.1995.1014.
  3. Theophrastus, "De odoribus (Concerning Odours)," vol. II of the Loeb Classical Library edition of the Enquiry into Plants, 1926, via the University of Chicago.
  4. Theophrastus, "Enquiry into plants and minor works on odours and weather signs," Greek with an English translation by Sir Arthur Hort, vol. 2, W. Heinemann (London, 1916), pp. 524.
  5. D.H. Pybus, and C.S. Sell, "The Chemistry of Fragrances," Chapter 4, Royal Society of Chemistry, December 31, 1999, pp. 276, ISBN-13: 978-0854045280.
  6. Ruth Schmidt, Victor de Jager, Daniela Zühlke, Christian Wolff, Jörg Bernhardt, Katarina Cankar, Jules Beekwilder, Wilfred van Ijcken, Frank Sleutels, Wietse de Boer, Katharina Riedel and Paolina Garbeva, "Fungal volatile compounds induce production of the secondary metabolite Sodorifen in Serratia plymuthica PRI-2C," Scientific Reports, vol. 7, Article no. 862, April 13, 2017, doi:10.1038/s41598-017-00893-3. This is an open access article with a PDF file at the same link.
  7. The world's most spoken language is...Terpene, Netherlands Institute of Ecology Press Release, April 13, 2017.

Permanent Link to this article

Linked Keywords: Modern history; modern man; body odor; primitive culture; prehistoric man; flower; nature; natural; aroma compound; fragrance; Neanderthal; bird; feather; burial; civilization; ancient Greece; ancient Greeks; perfume; industry; 4th century BC; Theophrastus (c. 371 - c. 287 BC); mineralogy; treatise; On Stones; odor; Aristotle; Peripatetic school; botany; Historia Plantarum; Enquiry into Plants; addendum; appendix; secret; oil; extraction; fragrant compound; vehicle; quasi-solid; grease; viscosity; viscous; almond-oil; sesame-oil; olive-oil; De odoribus (Concerning Odours); Loeb Classical Library; chemistry; chemical synthesis; synthetic; analytical chemistry; chemical analysis; chemical compound; functional analog; terpene; molecules; oxygenated; monoterpene; molecular mass; molecular weight; volatility; α-Terpineol; Syringa vulgaris; lilac; soap; electrolyte; mixture; electrochemistry; electrochemical process; Wikimedia Commons; geraniol; nerol; linalool; citronellol; citronellal; citral; ester; alcohol; reagent; rose; floral; wood; dihydromyrcenol; citrus; hydroxycitronellal; lily of the valley; (Methyl)ionone; viola; violet; linalyl acetate; lavandula; lavender; borneol; isoborneol; pine; ambergris; carvone; spearmint; menthol; mentha; mint; Acetyl; Acetylated; cedarwood; cedar; communication; bacteria; organism; lifeform; Earth; plant; animal; biologist; Netherlands Institute of Ecology (NIOO-KNAW, Wageningen, The Netherlands); Wageningen University and Research Centre (Wageningen, The Netherlands); University of Greifswald (Greifswald, Germany); Erasmus University Medical Center (Rotterdam, The Netherlands); sodorifen; volatile organic compound; fungus; fungi; pathogen; pathogenic; Fusarium culmorum; rhizobacterium Serratia plymuthica PRI-2C; boiling point; vapor pressure; diffusion; aqueous; atmospheric; environment; microorganism; experiment; experimental; regulation of gene expression; gene activation; Paolina Garbeva; insect; motility; motile; fungal; scientific control; biological specimen; Creative Commons Attribution 4.0 International license; author.

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