NEET Chemistry Notes Chemistry in Everyday Life -Antimicrobials
Antibiotics These are the chemicals synthesised from microbes and have either cidal (killing) effect or a static (inhibitory) effect on microbes. A few examples of the two types of antibiotics are as follows :
(a) Bactericidal, e.g. penicillin (a narrow spectrum antibiotic), ampicillin and amoxicillin (semisynthetic modification of pencillin), ofloxacin (broad spectrum), aminoglycosides (streptomycin) (broad spectrum), etc.
(b) Bacteriostatic, e.g. erythromycin, tetracycline, chloramphenicol (a broad spectrum antibiotic) etc.
Antiseptics These are applied to the living tissues such as wounds, cuts, ulcers and diseased skin surfaces. Examples are furacine, soframycine, dettol (a mixture of chloroxylenol and a-terpinol), 0.2 per cent solution of phenol. Bithionol (also called bithional) is added to soaps, iodine, iodoform, etc.
Disinfectants These are applied to inanimate objects such as floors, drainage system. Examples, one per cent solution of phenol, chlorine and S02 (in very low concentrations), are disinfectants.
- These have lead to the concept of family planning. Birth control pills essentially contain a mixture of synthetic estrogen and progesterone derivatives, e.g. norethindrone (synthetic progesterone) and the estrogen derivative in combination with progesterone derivative, (ethinylestradiol) (novestrol) etc.
- The therapeutic properties of a drug depends upon its relative toxicity to the parasite and the host.
- The ratio of the maximum tolerated dose (MTD) to that
required for a maximum curative dose (MCD) is known as therapeutic index. .
Therapeutic index (TI)
- The higher the therapeutic index ratio, the safer the drug will be.
Chemicals in Food
Substances which are added to food either to improve its taste and flavour or to preserve it, are called food additives. Main categories of food additives are as follows :
- Food colours
- Flavours and sweeteners
- Fat emulsifiers and stabilising agents
- Flour improvers-antistaling agents and bleaches
- Nutritional supplements such as minerals, vitamins and amino acids.
Artificial Sweetening Agents
Some examples of artificial sweetening agents are saccharin (ortho-sulphobenzimide), aspartame (nutra sweet), sucralose, alitame etc. Alitame is high potency sweetener, although it is more stable than aspartame. Sucralose is trichloro derivative of sucrose. Its appearance and taste are sugar like. It is stable at cooking temperature. Hence, its use is of great value to diabetic persons who need to control intake of calories.
Food preservatives prevent spoilage of food due to microbial growth. Examples are sodium benzoate, salts of sorbic acid and propanoic acid, etc.
Antioxidants are added to many foods to prevent autoxidation and spoilage and allow long-term storage.
e.g. BHT (butylated hydroxy toluene)
BHA (butylated hydroxy anisole)
These protective agents function by interrupting the chain reaction of the autoxidation process.
S02 and Na2S03 are useful antioxidants for wine and beers, sugar-syrups, peelled fruits, vegetables.
These are also known as surfactants or surface active agents. In fact, those chemicals which concentrate at the surface of the solution or interfaces or surface films, reduce surface tension of the solution and help in removing dirt and dust by emulsifying grease are known as surfactants. Soaps and detergents belong to this class.