Chemical Glossary

Acid a substance that can form hydrogen ions when dissolved in water. Aqueous solutions of acids typically have a sharp taste and turn litmus paper red. Most organic acids have the C(0)OH grouping but they may have other acid groups, e.g. the sulphonic group:- S(02)OH. Acids can vary in strength according to the degree of ionization in solution. alcohol an organic compound with one or more hydroxyl (-OH) groups attached directly to a carbon atom. This is a large assemblage of compounds that forms part of waxes, esters, Aldehydes, ketones and volatile oils. Alcohols may be in the solid or liquid form depending on the size of the carbon chain.

Aldehydes organic compounds with a carbonyl group joined directly to another carbon atom. Aldehydes may be either solids or colourless liquids.

Alkali the name given to a substance that gives a solution in water with a pH of greater than seven. They may also be called a base.

Alkaloid probably the most important chemicals found in plants, as they usually have a medical action. They are organic substances, found in association with organic acids in most plant groups, particularly the flowering plants. Alkaloids are alkaline and combine with acids to form crystalline salts which are water-soluble in most cases. The alkaloids themselves are generally insoluble in water but dissolve well in alcohol or ether. Alkaloids include a number of important drugs, e.g. morphine, caffeine, atropine, quinine and nicotine and many of these chemicals are very poisonous with characteristic physiological effects.

Anthraquinones glycoside compounds present in some plants and that are used to prepare dyes and purgative drugs.

Bitters the name given to herbs that have a bitter taste. It may be due to a combination of chemicals within the plant. The herbs include angostura, yellow gentian, nux vomica and wormwood and they can be used as appetite stimulants, relaxant drugs and for their antiinflammatory action.

Carbohydrates these compounds are formed in plants as a result of photosynthesis. They include sugars, starches and cellulose which all have an important nutritional value. A polysaccharide is made up of hundreds of sugar molecules linked together, and they form part of compounds such as mucilage or pectin which help protect the alimentary canal. Carbohydrates are one of the main classes of naturally-derived organic compounds.

Coumarins glycoside compounds widely distributed in plants. They provide the distinctive smell of many grass species.

Esterorganic compounds produced when an acid and an alcohol react. They often have distinctive fruity odours and are found naturally in fruits. An ester is generally a volatile liquid but may exist in a solid form.

Fatty Acids: an organic compound made up of a hydrocarbon chain and a terminal carboxyl group (-COOH). The chain can range in length from one to thirty carbon atoms and branches can occur in the compound. Fatty acids are classified as saturated or unsaturated depending on the presence of a double bond in the chain structure. In nature, fatty acids form part of glycerides, that make up part of many important tissues and are important in many energy-releasing processes in the body.

Flavonoid Glycosides compounds made up of glycoside sugars and a flavone compound. The flavones are a group of chemicals, that give a yellow pigmentation to plants. This group of compounds is widely distributed through the plant kingdom, and they can have diuretic antispasmodic or stimulating effects on the body.

Glucoside a term given to glycoside chemicals that contain glucose as the sugar.

Glycoside molecules made up of two sections, a sugar and another chemical group. This name is given to all compounds independent of the sugar within them. As a class, glycosides are colourless, crystalline and bitter and are very common in plants. There are various classes of glycosides including cardiac glycosides, e.g. foxglove/digitalis and purgative glycosides, e.g. the anthraquinone chemicals in senna and rhubarb.

Gum complex polysaccharides, that contain several different sugar and acid groups. They are generally soluble in water and produce viscous solutions, that are sometimes called mucilages. They are normally insoluble in organic solvents and are found in variable quantities in plant tissues.

Hydrocarbons compounds made up of carbon and hydrogen alone. There are various categories of compounds, depending upon the arrangement of carbon atoms in the molecule and the number of double bonds in the molecule.

Isomer compounds can have the same chemical composition and molecular weight but differ in their physical structure and hence are termed isomers. These isomers can have different physical and physiological qualities. Isomers can differ in the order in which the atoms are joined together (structural isomers) or they differ in the spatial orientation of atoms in the molecule (stereo-isomerism).

In plants, two isomeric forms of an active chemical may exist with one form having beneficial medical effects, and the other having no impact or a deleterious impact on the body. Care must be taken where several isomers of a chemical exist to utilize the correct form.

Mucilage a gum-like substance found in the cell walls or seed coats of plants. They are polysaccharides that have a soothing effect on inflamed tissues, and they are used as an ingredient in some cosmetic preparations.

Phenols slightly acidic compounds with at least one hydroxyl (-OH) group bonded to a carbon atom in an aromatic ring. They are widely found in natural plant constituents, e.g. tannins, anthocyanine glucoside pigments and salicylic acid, salicylic acid frequently combines with a sugar to form a glycoside that has antiseptic properties, e.g. in crampbark, meadowsweet and white willow.

Resin a naturally-produced acidic polymer obtained from trees. It is thought to help protect the tree from physical or mechanical damage, and attack by fungi and insects, in a similar way to how gums or mucilage protect green plants. It is a high molecular weight class of compounds usually produced by coniferous trees.

Saponins glycosides that form a lather when shaken with water. They are found in two groups; the steroidal saponins that mimic the precursors of female sex hormones and the tri-terpenoid saponins that mimic the adrenocorticotropic hormone ACTH. They occur in a wide variety of plant groups and also act as a poison affecting fish.

Starch a complex polysaccharide carbohydrate made by green plants during photosynthesis and which forms one of the plants' main energy stores. It is composed of water-soluble amylose and amylopectin, which forms a mucilaginous paste in water. Starch grains formed in the plant vary in size and shape according to the plant that produced them. Starch is used in industry as a food thickener, an adhesive and for sizing paper and cloth.

Sugars a group of water-soluble carbohydrates with a sweet taste. They can contain six or twelve carbon units in each molecule and the simple sugar units or monosaccharides can combine to form more complex sugar groups. It is a crystalline substance, found in many forms in plants.

Tannins a group of complex organic chemicals found in the leaves, unripe fruits and bark of trees. They generally taste astringent and may be a protective mechanism against the grazing of some animals. They have commercial uses in treating cattle hides to produce leather, in producing ink and as mordants in the textile industry.

Terpenes a group of unsaturated hydrocarbons, made up of multiples of isoprene units. The group includes vitamins A, E and K, carotene and other carotenoid pigments and squalene, the precursor to cholesterol. The terpenes are of great scientific and industrial importance. They are very reactive chemicals, with characteristic and pleasant odours that are used in perfumery.

Volatile Oil these compounds are formed from an alcohol and a hydrocarbon. They are found in many plants and can give a plant a characteristic taste and flavour. Many volatile oils have medicinal properties and are used as antifungal, antiseptic or aromatic oils taken internally or externally. They are very important oils in herbal medicine.

waxes fatty acid esters of alcohols with a high molecular weight. They are normally solid and have water-repellent properties. Waxes form a protective coating on animal skin, fur or feathers and also reduce water loss in leaves and fruits. The waxes are used for various commercial uses including polishes, textiles and pharmaceuticals.