Hydrocarbons → Monoterpenes
Formula: C10H16
Ending: -ene
Monoterpenes are extremely lipophilic (fat-soluble), fluid, and volatile. These small molecules can easily penetrate the skin. However, if they are not stored correctly—exposed to light, heat, or oxygen—they can oxidize rapidly, leading to breakdown products that may irritate the skin or trigger allergic reactions.
Physical and chemical properties:
- Colourless, mobile liquids;
- Highly volatile, low boiling points, evaporate very quickly;
- Weak, uninteresting odours;
- Fairly reactive, prone to oxidation (reaction with oxygen) even under cool conditions.
Therapeutic properties:
Physical effects: Essential oils rich in monoterpenes provide a stimulating, warming, pain-relieving, and anti-inflammatory effect, making them particularly beneficial for rheumatic issues and acute pain. Mild skin irritations can indirectly enhance the production of natural anti-inflammatory substances, as they stimulate the release of analgesic mediators. This beneficial response, resulting from skin irritation, is known as a counterirritant effect. It may seem contradictory that substances applied externally, which irritate the skin and cause inflammation, can lead to overall anti-inflammatory effects in muscles, nerves, and joints. However, this phenomenon has been recognized and validated through numerous experiments over time.
Moreover, monoterpenes, especially alpha- and beta-pinene, exhibit effects similar to cortisone by modulating adrenal cortex activity. They positively influence the autonomic nervous system, targeting the smooth muscles of various organ systems, such as the kidneys and gastrointestinal tract. Oils high in monoterpenes also possess antiviral and antibacterial properties and act as immune stimulants, effectively activating the immune system.
Psychic Effect: Monoterpenes typically provide a tonic effect, boosting concentration and mental stimulation while promoting a sense of structure. They encourage a mild sense of fearlessness and necessitate mental strength and logical reasoning.
Structure:
Two isoprene units linked together in a head-to-tail fashion serve as the foundation for all monoterpenes, which consist of 10 carbon atoms arranged in a linear chain. Occasionally, this chain can bend back on itself, creating a ring-like structure while still maintaining its 10-carbon composition. When this bending occurs, the terpene is classified as monocyclic, indicating the formation of a single loop, and is referred to as a monocyclic monoterpene. It is also possible for multiple loops to form within the chain, leading to the existence of bicyclic and tricyclic monoterpenes. Conversely, if the structure remains a straight chain without any loops, it is categorized as acyclic. Our understanding of the pharmacological effects of these compounds found in essential oils is still limited, making it unclear how variations in their structure might influence their effects. The situation becomes even more intricate when double bonds are introduced through oxidation or removed via reduction.
Exemples:
Acyclic: Myrcene, Ocimene
Monocyclic: Limonene, Phellandrene, Terpinene, Sylvestrene
Bicyclic: Pinene, Thujene, Carene
Aromatic: para-Cymene, ortho-Cymene, Cumene, 2,5-Dimethylstyrene
Safety warnings:
* Skin and mucous membrane irritating if oxidised (pinenes and delta-3-carene) → DILUTE!
Properties of Monoterpenes
para-Cymene is a cyclic monoterpene known for its analgesic properties and has been described as having 'excellent' anti-nociceptive potential for neurogenic and inflammatory pain.
d-Camphene s a bicyclic monoterpene known for its remarkable antinociceptive properties. It has demonstrated antioxidant and scavenging capabilities in vitro. This, together with its anti-inflammatory effects, is related to the inhibition of prostaglandin synthesis. Importantly, it does not inhibit motor activity.
Limonene is found in citrus fruits and has a citrusy scent. It is associated with mood enhancement, stress reduction, and possible anti-inflammatory benefits. Some studies indicate that it may also have anti-anxiety and antidepressant qualities.
Myrcene is often found in hops, mango, and thyme. It has a rich, earthy, musky scent. Myrcene is thought to have calming effects and may act as a muscle relaxant. It may also enhance the absorption of other cannabinoids.
Ocimene, known for its antifungal and anti-inflammatory potential, this terpene is also accompanied by a woody and floral scent with some citrus undertones.
Pinene, as its name suggests, has a pine-like odor and is found in pines, rosemary, and basil. It is associated with increased alertness and concentration. Furthermore, pinene might possess anti-inflammatory qualities and has been researched for its potential bronchodilator effects. Additionally, it may provide possible anti-cancer, antioxidant, and neuroprotective advantages.
Sabinene is a bicyclic monoterpene known for its anti-inflammatory properties. It is found in notable amounts in nutmeg, yarrow, and plantain, and can exceed 10% in others. In isolation, sabinene has demonstrated significant anti-inflammatory effects, functioning by sequestering and inhibiting nitric oxide.
Terpinene this antioxidant and anti-microbial agent, is often used as a flavoring additive for its lemony taste.
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