Substances which prevent polymerization or oxidative reactions from occurring are well known. Such substances have been termed antioxidants or inhibitors . A considerable amount of research has been devoted to the study of these inhibitors of reactions or negative catalysts during the past 30 years. It is pointed out that certain substances susceptible to polymerization or oxidation must be protected. Leather oils, rubber, fats, unsaturated hydrocarbons, aldehydes, and some vitamins and their precursors are substances which are either easily oxidized or are subject to polymerization. Consequently, if their usefulness to man is to be retained they must be protected from oxidative deterioration or polymerization into unwanted substances.
Some aromatic amines are known to protect rubber and oils from aging. The polymerization of acrolein may be diminished by the addition of small quantities of resorcinol or other phenolic substances. Tetraethyl lead prevents the oxidation of benzaldehyde in motor fuels, and vitamin S is a well-known antioxygenic substance for fats.
Much of the research done on antioxidants has been in the test tube with homogeneous systems. However, in biological systems one is not dealing with homogeneous conditions, thus the study of biological antioxidants becomes complicated. In addition, most metabolic processes cannot be controlled in living organisms as one may regulate the temperature of a test tube reaction, or control the concentration of the reacting substances therein.
It has been demonstrated in the test tube that antioxidants can function by breaking chain reactions involving free radicals and by being reversibly oxidized and reduced very easily. Some evidence seems to point to these phenomena taking place with biological antioxidants. The question of how biological antioxidants function in living organisms remains unanswered
