In this Unit, we shall learn the application of Chemistry in three important and interesting areas, namely–medicines, food materials and cleansing agents. For cleanliness, we use soaps, detergents, toothpastes, bleaches etc., which all are made up of chemical compounds.
Similarly, Clothes (Cotton, Wool, Silk, Terylene), Food materials (Carbohydrates, Proteins, Oil, Fats), Medicines (Antibiotics, Antimalarials etc.), Explosives, Fuels, Rocket propellants, Building materials etc. are all chemical compounds or derived from them.
Drugs and their Classification
Drugs are chemicals of low molecular masses (~100-500u). They produce biological response by interacting with macromolecular targets. If the biological response is therapeutic and useful, these chemicals are called medicines. They are used in diagnosis, prevention and treatment of diseases.
Classification of Drugs
Drugs can be classified mainly on the basis of following criteria :
(i) On the basis of pharmacological effect
It is useful for doctors because it provides them whole range of drugs available for treatment of particular type of problem. Eg.- Analgesic - Shows pain killing effect. Antiseptic - Kill or arrest the growth of microorganisms.
(ii) On the basis of drug action
It is based on action of drug on a particular biochemical process. Eg.- Histamines causes inflammation in the body and there are various ways in which action of histamines can be blocked. All antihistamines inhibit the action of the histamines.
(iii) On the basis of chemical structure
It is based on chemical structure of the drug. Often drugs with common structural features, have similar pharmacological activity. Sulphonamides have common structural feature as shown above. Eg.
(iv) On the basis of molecular targets
Drug possessing some common structural features, may have same mechanism of action on targets. These target molecules or drug targets are usually biomolecules such as carbohydrates, lipids, proteins and nucleic acids.
Macromolecules of biological origin perform various functions in the body. For example, Proteins which perform the role of biological catalyst in the body are called enzymes, those which are crucial to communication system in the body are called receptors. Carrier proteins carry polar molecules across the cell membrane. Nucleic acids have coded genetic information for the cell.
Enzymes as Drug Targets
(i) Catalytic action of enzymes
Enzymes perform two major functions :
(a) The first function of enzyme is to hold the substrate for chemical reaction. Enzymes have active sites, which hold the substrate molecule in a suitable position. The substrate can bind through enzyme by interactions such as ionic bonding, hydrogen bonding, van der Waals interaction or dipole-dipole interaction.
(b) The second function of enzyme is to provide functional groups that will attack the substrate and carry out chemical reaction.
(ii) Drug-enzyme interaction
Enzyme inhibitors- Drugs can inhibit the activities of enzymes. They can block the binding site of the enzyme, thus prevent the binding of substrate or they can inhibit the catalytic activity of the enzyme. Drug can inhibit the attachment of substrate on active size of enzymes in following two ways :
(a) Competitive inhibitors : These are drugs which compete with natural substrate for their attachment on the active site of enzymes.
(b) Non-competitive inhibitors : These drugs do not bind to the enzyme’s active site, rather bind to a different site of enzyme called Allosteric site and changes the shape of active site in such a way that substrate can’t recognise it.
Receptors as Drug Targets
Receptors are proteins that are crucial to body’s communication process. Receptor proteins are embedded in cell membranes in such a way that their small part possessing active site projects out of the surface of the membrane and opens on the outside region of the cell membrane.
Chemical Messengers are the chemicals in the body, through which message between two neurons or that between neurons to muscles is communicated. They are received at binding sites of receptor proteins. To accommodate a messenger, shape of receptor site changes and brings about the transfer of message into the cell. Thus, chemical messenger give message to the cell without entering the cell.
Drugs that bind to the receptor site and inhibit its natural function are called antagonists. These are useful when blocking of message is required. There are other types of drugs that mimic the natural messenger by switching on the receptor, these are called agonists. These are useful when there is lack of natural chemical messenger.
Therapeutic Action of Different Classes of Drugs
Few important classes of drugs are :
Over production of acid in stomach causes pain and irritation and in severe cases ulcers are developed. Antacids such as sodium hydrogen carbonate or mixture of aluminium and magnesium hydroxide was used. But taking excess hydrogen carbonate makes the stomach alkaline and trigger the production of even more acid. Metal hydroxides are better antacids, as they are insoluble and do not increase the pH above neutrality.
Histamine is a potent vasodilator. It has various functions, like contraction of smooth muscles in the bronchi and gut and relaxing other muscles such as those in walls of fine blood vessels. Histamines are also responsible for nasal congestion associated with common cold and allergic response to pollen. Synthetic drug brompheniramine (Dimetapp) and terfenadine (Seldane) act as antihistamines.
(iii) Neurologically Active Drugs
(i) Tranquilizers : They affect the message transfer mechanism from nerve to receptor. They are class of chemical compounds used for treatment of stress, mild or even severe mental diseases. They form essential component of sleeping pills. They relieve anxiety, stress, irritability or excitement by including sense of well being. Examples, Chlordiazepoxide, meprobamate are mild tranquilizers suitable for relieving tension.
(ii) Analgesics : They reduce or abolish pain without causing impairment of consciousness, mental confusion, incoordination or paralysis or some other disturbances of nervous system. They are classified as :
(a) Non-narcotic (non-addictive) analgesics : Example- Aspirin, Paracetamol.
(b) Narcotic analgesics : Example- Morphine and its homologues like Heroin, Codeine etc.
They destroy or prevent development or inhibit the pathogenic action of microbes such as bacteria (by antibacterial drug), fungi (by antifungal agents), virus (by antiviral agents) or other parasites (antiparasitic drugs) selectively.
Antibiotics : These are drugs used to cure infections because of low toxicity for humans and animals. Initially, they were classified as chemical substances produced by microorganisms, that inhibit the growth or even destroy other microorganisms.
(v) Antiseptic and Disinfectants
They are chemicals which either kill or prevent growth of microorganisms.
They are applied to living tissues such as wounds, cuts, ulcers and diseased skin surfaces. They are not ingested like antibiotics. Examples are :
- Furacine, Soframycin.
- Dettol, which is a mixture of chloroxylenol and terpineol.
- Bithionol, which is added to soaps to impart antiseptic properties.
- Iodine, which a powerful antiseptic, is a 2-3% solution in alcohol-water mixture, also known as tincture of iodine.
- Iodoform, which is also used as antiseptic for wounds.
They are applied to inanimate objects such as floors, instruments, drainage system etc. Same substance can act as antiseptic as well as disinfectant by varying its concentration. For example, 0.2% solution of phenol is an antiseptic but 1% solution of phenol is disinfectant.
(vi) Antifertility Drugs
They are used in direction of birth control and in family planning. Birth control pills essentially contains a mixture of synthetic estrogen and progesterone derivatives. Both of these compounds are hormones. Progesterone suppresses ovulation. Synthetic progesterone derivatives are more potent than progesterone. Example, Norethindrone a synthetic progesterone derivative, has antifertility action.
Chemicals in Food
Chemicals are added to food for (i) their preservation, (ii) enhancing their appeal, and (iii) adding nutritive value in them. Main categories of food additives are as follows:
- Food colours
- Flavours and sweeteners
- Fat emulsifiers and stabilising agents
- Flour improvers- antistalling agents and bleaches
- Antioxidants Preservatives
- Nutritional supplements like minerals, vitamins and amino acids.
(1) Artificial Sweetening Agents
They are as sweet as sugar, but have no or less calories, whereas natural sweeteners e.g., sucrose add to calorie intake. It is used by a diabetic person and those who want to control their intake of calories. Ortho-sulphobenzimide, called saccharin is the first popular artificial sweetening agent, which is about 550 times as sweet as cane sugar. It is excreted from the body in urine unchanged. It is harmless and appears to be entirely inert.Other examples are :
(i) Aspartame: It is the most successful and widely used sweetener. It is roughly 100 times as sweet as cane sugar. It is methyl ester of dipeptide formed from aspartic acid and phenylalanine. As it is unstable at cooking temperature, its use is limited to cold foods and soft drinks.
(ii) Alitame : It is a high potency sweetener, more stable than aspartame. But control of sweetness of food is difficult while using it.
(iii) Sucralose : It is a trichloro derivative of sucrose. Its appearance and taste are like sugar. It is stable at cooking temperature and does not provide calories.
They prevent spoilage of food due to microbial growth. Commonly used preservatives are table salt, sugar, vegetable oils, sodium benzoate (C6H5COONa), salts of sorbic acid and propanoic acid. Sodium benzoate is used in limited quantities and is metabolised in the body.
(2) Cleansing Agents
They improve cleansing properties of water and help in removal of fats which bind other materials to the fabric or skin. They include-
Soaps: Soaps used for cleaning purpose are sodium or potassium salts of long chain fatty acids e.g., stearic, oleic and palmitic acids. Soaps containing sodium salts are formed by heating fat (i.e., glyceryl ester of fatty acid) with aqueous sodium hydroxide solution. This reaction is known as saponification.
In this reaction, esters of fatty acids are hydrolysed and soap obtained remains in colloidal form. It is precipitated from solution by adding sodium chloride. The solution left after removing soap contains glycerol and can be recovered by fractional distillation.
Types of Soaps
(i) Toilet Soaps : They are prepared by using better grades of fats and oils and excess of alkali is removed. Colour and perfumes are added to make these more attractive.
(ii) Transparent Soaps : They are made by dissolving the soap in ethanol and then evaporating the excess solvent.
(iii) Medicated Soaps : Substances of medicinal values are added.
(iv) Shaving Soaps : Contain glycerol to prevent rapid drying. A gum called, rosin is added while making, it forms sodium rosinate which lathers well.
(vi) Laundry Soaps : These contains fillers like sodium rosinate, sodium silicate, borax and sodium carbonate.
Why soaps do not work in hard water?
As we know that hard water contains calcium and magnesium ions which forms insoluble salts with soaps, that gets separated as scum in water.
2C17H35COONa + CaCl2 ⟶ 2NaCl + (C17H35COO)2Ca
In fact, the scum so separated offers hinderance to soap action as the precipitate adheres onto the fabric as gummy mass. Also, the hair washed with hard water looks dull because of this sticky precipitate. Similarly, dyes do not absorb evenly on cloth washed with soap using hard water.
Limitations of Detergents
The problem of using detergents is that if their hydrocarbon chain is highly branched, then bacteria cannot degrade this easily and their slow degradation leads to their accumulation. Effluents containing such detergents reach rivers, ponds etc. and persist in water even after sewage treatment. This cause foaming in rivers, ponds and streams which pollutes the water.
Now a days, the branching of hydrocarbon chain is controlled and kept to the minimum. Unbranched chains can be biodegraded more easily and hence pollution is prevented.
Chemotherapy: Use of chemicals for therapeutic effect.
Antihistamines: Drugs which prevent interaction of histamines with receptors.
Tranquilizers: Chemical compounds used for treatment of anxiety, mental disease, stress etc. by acting on CNS.
Analgesics: Reduce or abolish pain without affecting nervous system.
Antipyretics: Lower down body temperature.
Broad spectrum antibiotics: Antibiotics which kill or inhibit wide range of gram-positive and gram-negative bacteria.
Saponification: Involves preparation of soap by heating fat with aqueous solution of NaOH.
A chemical agent which helps in curing ailment is called drug. They can have side effects if taken in higher dosage than those recommended.
Chemotherapy involves use of chemicals for therapeutic effect. Drugs interact with target molecules such as carbohydrates, proteins, lipids, nucleic acid etc.
Food additive as preservatives (prevent spoilage of food), sweetening agents (no calories), antioxidants, edible colours, nutritional supplements etc. are added to food.
Synthetic detergents are classified as anionic, cationic and non-ionic. They are preferred over soap as work even in hard water.
Detergents with branched hydrocarbon chain as slowly degraded by microorganism, causes pollution. Hence detergents with straight hydrocarbon chain preferred.