Wednesday, December 7, 2011

The chemistry of essential oils: Terpenes revisited

This post was originally written on December 30, 2010, but I've added and updated it! 

So what the heck are terpenes?

Terpenes are organic compounds, the major building blocks within nearly every living creature. For instance, steroids are derivatives of the triterpene squalene. (Quote from Wikipedia .) They are derived from units of isoprene (that's the picture up there, with a formula of C5H8) called the isoprene rule or C5 rule. Terpenes are created out of multiples of those isoprene units. When they are modified chemically through oxidation or rearrangement of the carbon skeleton, they become terpenoids or isoprenoids (terpenoids are not the same as terpenes as they have been modified in some way, but some people group them together.) These can be cyclical or linear.

Terpenes are everywhere in our products, especially in oils and essential oils.

These contain 10 carbons and 2 isoprene units. They tend to be used as flavouring and fragrancing ingredients, but they often have other great qualities. Limonene is a great example of a monoterpene, and we know it acts as a good degreaser (you can see the isoprene unit at the top and bottom of the ring). Linalool, which is found in roses and lavender, is often used as a fragrance ingredient. Other monoterpenes of interest are camphor, menthol, citronellal, thymol, and carvacrol.

We find major monoterpenes in plants or spices like black pepper, peppermint leaf, cardamom, rosemary, bitter orange peel, camphor, caraway, and thyme.

Some monoterpenes can stimulate mucous membranes and help with congestion, respiratory issues, and phlegm - think about Vick's for a moment with the camphor, eucalyptus, and menthol (but don't think about Buckley's cough syrup because it really tastes awful!). You'll find 1,8-cineole (aka eucalyptol) in tea tree oil and eucalyptus, both of which can stimulate mucous membranes but can be irritating at higher levels. And there is some indication that monoterpenes might have some anti-cancer properties (click this link for the summary of the study).

These contain 15 carbons and 3 isoprene units. They are found abundantly in plants and some of the major ones are alpha-bisabolol in chamomile and parthenolide in feverfew, both of which are potent anti-inflammatories, and ß-caryophyllene (the picture to the left), found in rosemary, cloves, cinnamon, and the essential oils of cannabis. Studies are still testing to see if the the ß-caryophyllene has anti-inflammatory properties in humans. Chamazulen, also found in chamomile, is a fantastic anti-inflammatory.

Another important sesquiterpene is farnesol, found in citronella, neroli, lemon grass, tuberose, rose, musk, and balsam. It's used in products to enhance the fragrance, but it's also a natural pesticide for mites and is active against yeasts.
For more on sesquiterpenes, click here.

These have 20 carbons and 4 isoprene units. The most significant one is phytol, which constitutes the lipophilic side chain of chlorophyll in plans. It forms a part of Vitamin E (tocopherol). (Vitamin A contains 20 carbon atoms but it's formed from a cleavage of a tetraterpene.) Some of the other important diterpenes are stevioside from stevia (which I enjoy in my tea every morning) and ginkgolides from ginko.

These contain 30 carbons and have 6 isoprene units. The most important one is squalene, which makes up about 12% of our skin's sebum, so our skin identifies it as "ours" and soaks it up quickly. Squalene is a vital part of cholesterol, steroid, and Vitamin D synthesis in our bodies. It penetrates the skin quickly offering softening and moisturizing to even really chapped or cracked skin.

We find it in lanosterol, one of the ingredients in Croda's Super Sterol product.

In this category we also find curcurbitane, which is found in cucumber extract, and is a very good anti-inflammatory and analgesic. And we also find dammarenediols in ginseng extract, which might help with penetration of actives into our skin.

These contain 40 carbons and 8 isoprene units. The major tetraterpenes of interest in this category are ß-carotene, lycopene (pigment in tomatoes), and capsanthin (pigment in red peppers)

The main terpenes we'll be seeing in essential oils are the monoterpenes and sesquiterpenes. Tomorrow we'll spend some time with the terpene alcohols like monoterpene alcohol and sesquiterpene alcohol, but first, we need to know what an alcohol means in chemistry!


goodgirl said...

Thank you Susan! I really appreciate you posts and explanations and scientific view of things.

Anonymous said...

thank you Susan, I really like how much information you have provided me with! this is really useful for my school chem project!