Chemistry Of Herbs

 

Herbs contain a vast range of chemicals, ranging from water and inorganic salts, sugars and carbohydrates to highly complex proteins and alkaloids.

Plant acids

Weak organic acids are found throughout the plant kingdom. A typical example is the citric acid found in lemons.

The organic acids can be divided into those based on a carbon chain, and those containing a carbon ring in their structure, but they all have a -COOH group in common.

The chain acids (or aliphatic acids) range from the simple formic acid we can feel in the sting of nettles to the more complex ones like citric acid and valeric acid, the latter being the basis for a sedative used in allopathic medicine.

The ring acids (aromatic acids) are an important pharmacological group. The simplest aromatic acid, benzoic acid, can be found in many resins and balsams like gum benzoin, tolu, Peru balsam and also in cranberries. It can be used as a lotion or an ointment, can be a beneficial inhalant for chronic bronchial problems, and has antiseptic, anti-pyretic and diuretic actions.

Alcohols

Alcohols are found in various forms in plants, often as constituents of volatile oils or as sterols, like the alcohol oil geraniol in attar of rose and menthol in peppermint oil. Other common forms of alcohol are waxes, combinations of alcohols and fatty acids, which are found in plants in the coating of leaves and in other parts. The commonly used carnauba wax for instance is obtained from the palm Copernicia cerifera.

Volatile oils

Most of the volatile oils are based on simple molecules like isoprene or isopentane, which can combine in many different ways to form terpenes, containing multiples of the basic 5-carbon molecules, sometimes with slight variations, making up the volatile oils.

We can find the volatile oils in the aromatic plants, such as peppermint or thyme, where different oils-sometimes up to 50 or more-combine to give the plant its particular smell. Depending on the combination of oils the smell will vary and even be slightly different within the same species, depending on the concentrations of oils.

By extracting these oils, the so-called essential or aromatic oils are produced, which can be used therapeutically, but which also are used to a large extent for the production of perfumes.

The range of aromatic oils is very large and they each have unique properties, but they also share some common actions worth mentioning.

All aromatic oils are antiseptics, good examples being eucalyptus oil, garlic oil and thyme oil. As the oils are very easily transported and distributed throughout the body, they act both locally and on the whole system. When they are taken internally or applied externally, they will soon show up in the urinary system, the lungs and the bronchiaIs, and in secretions like sweat, saliva, tears or the vaginal fluids. They can even occur in mother's milk or travel through the placenta into the fetus. Besides their direct antiseptic action they also stimulate the production of white blood-cells, thereby augmenting the body's own natural defense system.

The volatile oils stimulate the tissue they come in contact with, either leading to slight 'irritations' (as in the case of mustard oil) or to a numbing (as with menthol and camphor). They aid digestion by stimulating the lining of the colon, which sets off a reflex that increases the flow of gastric juices and induces a feeling of hunger. Also they can help to ease griping pains by relaxing the peristalsis in the lower part of the intestines.

The volatile oils also act on the central nervous system. Some will relax and sedate, like chamomile, others will stimulate, like peppermint, and all tend to induce a state of inner ease and well-being, thus reducing tension and depression. When aromatic oils are applied externally, part of their effect is due to their actions on the nose, as the olfactory nerves transmit the smell to the brain and trigger off a reaction there.

As volatile oils evaporate very easily, herbs containing these oils have to be stored carefully in well sealed containers.

Carbohydrates

A great variety of carbohydrates can be found in plants, either in the form of sugars such as glucose and fructose, or as starches, where they serve as the main energy store. They can also be in the more complex form of cellulose, which gives structural support to plants.

The large polysaccharides, like cellulose, can further bond with other chemicals and produce molecules like pectin, found for instance in apples, or seaweed gums like algin, agar or carragum, found in Irish moss. They are all very viscous and demulcent and are used to produce gels that are utilized in medicine and in food preparations.

Gums and mucilages, which are very complex carbohydrates, are contained in some excellent soothing and healing herbs, like the demulcents coltsfoot, plantain and marshmallow. Their action relaxes the lining of the gut, triggering a reflex that runs through the spinal nerves to areas related embryologically, like the lungs and the urinary system. In this way the mucilages work in a twofold manner: they reduce irritation and inflammation in the whole of the alimentary canal, reduce the sensitivity to gastric acid, prevent diarrhea and reduce the peristalsis; they also work via a reflex on the respiratory system, reducing tension and coughing and increasing the secretion of watery mucus.

Phenolic compounds

Phenol is a basic building block of many important plant constituents. Phenolic compounds may be simple in structure, or a complex combination of a range of basic molecules. One of the simple phenolics is salicylic acid, which is found often in combination with sugar, forming a glycoside, as in willow, cramp bark, wintergreen and meadowsweet. This chemical has antiseptic, pain killing and anti-inflammatory properties, and is used by allopathic medicine in the form of acetylsalicylic acid, better known as aspirin.

Eugenol, the pain-killing oil found in cloves, and thymol from oil of thyme both have similar effects to salicylic acid. Part of the antiseptic action of bearberry on the urinary system can be explained by the presence of the phenol hydroquinone.

Tannins

Tannins in herbs cause an astringent action. They act on proteins and some other chemicals and form a protective layer on the skin and the mucous membranes. Thus they can for instance bind the tissue of the gut and reduce diarrhea or internal bleeding. Externally they are useful in the treatment of burns, for sealing wounds and to reduce inflammation. Tannins help in infections of the eye (conjunctivitis), mouth, vagina, cervix and rectum.

Coumarins

The highly evocative smell of new mown hay has its basis in the coumarin group of chemicals. It is, of course, not just grass that contains these beautifully aromatic constituents; sweet woodruff is another example. Coumarin itself has limited effects on the body, but one of its metabolites, di-coumarol, is a powerful anti-clotting agent. Allopathic medicine has used the coumarins as a basis for warfarin, an anticlotting drug used as a guard against thrombosis in small dosage and as a rat poison in large doses.

Anthraquinones

Plants containing anthraquinones are known to be effective purgatives and they also happen to be good natural dyes. They appear usually in the form of glycosides (in a chemical combination with a sugar) and are found for instance in rhubarb, yellow dock, senna, buckthorn and aloe. They work by gently stimulating the colon after about 8-12 hours of ingestion by stimulating the peristalsis of the intestines, but they can do this only when natural bile is present. As there may be a tendency to colic pains through an over-stimulation of the colon wall, they are often given in combination with carminative herbs.

Flavones and flavonoid glycosides

One of the most common groups of plant constituents in herbs are the flavones and the flavonoid glycosides. They are known to have a wide range of activities, from anti-spasmodic and diuretic to circulatory and cardiac stimulants. Some, for instance, like rutin, hesperidin and the bio-flavonoid vitamin P, reduce permeability and fragility of the capillaries and so help the body to strengthen the circulatory system and to lower the blood pressure. Buckwheat is a good example of a useful herb for such problems. The bio-flavonoids are also essential for the complete absorption of vitamin C and occur in nature wherever vitamin C is present. Anther flavonoid, present in milk thistle, is responsible for its action in aiding the liver.

Saponins

The saponins have attracted the attention of pharmaceutical chemists as they can be used in the synthesis of cortisone-a strong anti-inflammatory drug-and in the synthesis of sex hormones. While the saponins contained in herbs do not directly act in the same way, the body can use them as raw materials to build up appropriate chemicals. To show the similarity between a natural saponin and the more potent synthesized drugs, we can compare cortisone with diosgenin from wild yam and see that they are very similar.

Typical anti-inflammatory herbs that contain saponins include golden rod, chickweed, figwort and wild yam.

Another important action of saponins is their expectorant action through the stimulation of a reflex of the upper digestive tract, which occurs in remedies such as primrose, mullein, violet and daisy.

Cardiac glycosides

Very similar to the saponins are the cardiac glycosides. These have been the object of intensive investigation ever since they were discovered in 1785 in foxglove, when it was recognized by medicine that these glycosides can support the failing heart.

The cardiac glycosides are formed by a combination of a sugar and a steroidal agylcone. The main activity is defined by the shape and structure of the agylcone, but it is the sugar that determines the bioavailability of the active agylcone.

Many flowering plants contain cardiac glycosides. The best known sources are foxglove, lily of the valley, squill and the Strophanthus family. In herbal medicine, lily of the valley is preferred over foxglove, as foxglove is potentially poisonous, whereas lily of the valley, quite as effective, does not lead to a build-up of toxic components in the body.

Therapeutically, the cardiac glycosides have the incredible ability to increase the force and power of the heart-beat without increasing the amount of oxygen needed by the heart muscle. They can thus increase the efficiency of the heart and at the same time steady excess heart-beats without strain to the organ.

Bitter principles

The bitter principles represent a grouping of chemicals that have an exceedingly bitter taste. Chemically they show a wide diversity of structure, with most bitters belonging to the iridoids, some to the terpenes and some to other groups.

The bitter principles have been shown to have valuable therapeutic effects. Through a reflex action via the taste buds, they stimulate the secretion of all the digestive juices and also stimulate the activity of the liver, aiding hepatic elimination. Research from China suggests that the bitter principle in Gossypium spp. may have a role as a male contraceptive by reducing the level of sperm production.

The property of bitterness imparted to plants by these principles is usually part of the overall activity of the herb, and we find sedatives such as hops and valerian, cough remedies like white horehound, anti-inflammatory such as bogbean and devil's claw, and the vulnerary marigold all sharing this valuable action.

Alkaloids

The alkaloids are perhaps the most potent group of plant constituents that act upon the human body and mind. They include the hallucinogen mescaline at one extreme and the deadly poison brucine at the other. There are alkaloids that act on the liver, the nerves, the lungs, and the digestive system. Many of the most valued herbs contain these potent chemicals. However, within the plants themselves there appears to be no important function for them, apart from possibly being a store for excess nitrogen.

The alkaloids as a group are very diverse in structure. They have nitrogen in their structure and all have a marked physiological activity. Chemically they are divided into thirteen groups based upon their structure.

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