Keith Kelsen’s Scent Narrative: Molecules of Scent (Part 2)

In Part 1, we learned that humans can distinguish over a trillion scents.  We also established that Molecules have far reaching implications in the world today.  We learned that Synthetic Molecules first created in the 1800’s then popularized in the 20th Century are the basis for the modern Fragrance Industry. We discussed the vibration of scent molecules and how that is what determines how they smell.

Behind the Art of Fragrance Chemistry is Science

Chemistry is the established foundation for modern perfumery. Modern fragrances are well within the reach of many.  Yet, before the mid-19th Century and the advent of Synthetic Molecules, only the wealthy could afford it.  Precious natural essential oils made fragrance limited in availability and to the scent of nature. In time, with the advent of Synthetic Molecules, fine fragrances became democratized and more available.  This also fueled new exploration and increased productivity.

Top Fragrance Makers Create New Molecules

Leading fragrance makers like Firmenich, International Flavors & Fragrances (IFF) and Givaudan, all look to positively contribute to the global solution. Today, these leaders in the industry, patent specialty designed molecules as trade secrets. They are continually creating many new molecules to fill the void of a trillion scents!  In fact, at Givaudan, according to their website, they have “turned chemists into molecular designers” and are “committed to bringing 2 to 5 new molecules every year to the spectrum of aroma molecules”.

Matchless by Design…There are Signatures in Molecules

Molecules are unique. They all contain a distinctive signature. By concentrating more on chemical details, functional groups of fragrant molecules can be linked to characteristic scents. The molecules hop around. Harnessing and focusing them is critical to building a scent. Linda Buck and Richard Axel won the 2004 Nobel when they discovered that our sense of scent molecules (smell) is dictated by a whole set of sensory cells. One type of fragrant molecule interacts with more than one receptor type, so the overall sensation is created by the combination of activated receptors. Buck and her co-workers found that clusters of olfactory neurons were activated when they tested a series of n-aliphatic alcohols on individual mouse neurons.[1] What does that mean?

 God is in the detail

Le bon Dieu est dans le détail”; “the good God is in the detail” as Gustave Flaubert proclaimed.  For example, the smells of “n-aliphatic alcohols”, range from herbal, rose and woody to orange. By contrast, “n-aliphatic acids” smell fatty, sour, rancid or sweaty. Wow, the difference between alcohols and acids are the difference between a symphony and just loud, discordant notes.  It is all very subtle.  Such subtle differences in the chemical composition lead to distinct scents, such as the pineapple aroma of “ethyl butyrate” and the apricot aroma of “pentyl butyrate”.

Identifying and isolating the individual scent molecule, then working with perfumers to understand which combination will create the most demand is the daily work in ‘fragrance chemistry’.

Organic Marries Synthetic to Create a Beautiful Smelling “Baby”

Marrying blends of essential oils with synthetic fragrance ingredients for long lasting freshness and fragrance is the absolute key. For perfumers, this gives a competitive, technical edge; the fragrance won’t fade if it remains stable. That high impact of scent shows how the Synthetic Molecule, joined with the Organic oil supports a structured fragrance. It is the ultimate of creations, a “baby” to its creator.

How Can One Nose be like Another?

This March, another study was conducted where computers predict molecules’ scent from their structures as the result of a massive Crowdsourcing project. Scent perception data was combined with machine-learning algorithms to “sniff out” compounds’ aroma profiles.  In a combination of chemistry, engineering, and crowd-sourcing, a team of scientists reached out to volunteers around the world to predict scent profiles. Researchers have been mystified by the relationship between the molecular structure and scent perception.

Is Artificial Intelligence Destined to Replace the Nose?

By programming machine learning into a computer, the study demonstrated that soon, computers may identify scent directly from the molecules. Pablo Meyer at IBM joined with Leslie B. Voshall and Andreas Keller at Rockefeller University to devise the crowdsourced project, the DREAM Olfaction Prediction Challenge.  The challenge’s focus was to map the chemical properties of odors to predict a given subject’s behavioral responses. The results showed that “computers can zero in on molecular characteristics responsible for odors that humans aren’t able to discern by looking at a molecule’s structure”.[2]

They crowdsourced 49 people to sniff 476 molecules. These “sniffers” categorized each molecule according to qualities such as “garlic,” “sweet,” “fruit,” “spices,” “burnt,” “urinous,” “decayed,” and “fish.” Then, the IBM-Rockefeller team provided a portion of the data to teams of computer scientists who developed machine-learning algorithms that can predict a molecule’s scent. The algorithms could accurately identify a molecule’s “pleasantness” and “intensity,” and many other “odor” qualities.

“This is a major step forward in decoding how the brain interprets messages from the nose,” says Eric Block, chemistry professor at the University at Albany, SUNY, and an olfaction chemistry expert, the identification of molecules based on their odor “may be on the horizon but is not yet in hand.”  

In an experiment, scientists took the musk molecule, which is commonly used in perfumery, and replaced the hydrogen atoms in the molecule with the heavier isotope deuterium. This exchange doubled the hydrogen atoms’ mass and alters the molecule’s vibrations, but leaves the shape unchanged. Results from the study appear to show that the deuterium musk molecules smell different to the hydrogen musk molecules, confirming that molecular vibrations determine its smell.

The study suggests that receptors in our nose can detect a “nanoscale quantum mechanism” known as ‘Inelastic Electron Tunneling’. This Inelastic Electron Tunneling will detect molecular vibrations. Over 20 years ago, it was considered outlandish when proposed at UCL in 1996. The idea was grudgingly said to initially work “in theory” by physicists; after a couple of decades, the project was completed and verified.

What’s Next for Scent Molecules?

I can conjecture that scent molecules can be created that can transport people to an altered sense of reality creating new memories associated with virtual or real experiences.  A human’s reaction to scent is personal and can mean different things to different people, based on their experience of that scent at the time of the experience. There are however common reactions that scent molecules will induce. We are at the precipice of a new journey of the senses that is going to change the world, welcome to the scent narrative.



[1] Dr. Angelika Börsch-Haubold, Small Molecules Make Scents,
[2] Computers predict molecules’ scent from their structures, Elizabeth K. Wilson Chemical & Engineering News Volume 95 Issue 9 Issue Date: February 27, 2017


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