In what respect do prontosil and salvarsan resemble. Is there any resemblance between azo dye and prontosil? Explain.
Prontosil, also called sulfamido chrysoidine, trade name of the first synthetic drug used in the treatment of general bacterial infections in humans.
Prontosil resulted from research, directed by German chemist and pathologist Gerhard Domagk, on the antibacterial action of azo dyes. A red azo dye of low toxicity, prontosil was shown by Domagk to prevent mortality in mice infected with Streptococcus bacteria.
The dye was also effective in controlling staphylococcus infections in rabbits. Within a relatively short period, it was demonstrated that prontosil was effective not only in combating experimental infections in animals but also against Streptococcal disease in humans, including meningitis and puerperal sepsis. Structural formula of prontosil is
From the structure of prontosil, it is very clear that it has $-\mathrm{N}=\mathrm{N}$ - linkage. It was discovered that the part of the structure of prontosil molecule shown in box, i.e., p -aminobenzenesulphonamide has antibacterial activity.
Salvarsan is also known as arsphenamine. It was introduced at the beginning of 1910s as the first effective treatment for syphilis. It is an organoarsenic molecule and has $-$As $=$ As$-$ double bond.
Salvarsan and prontosil show similarity in their structure. Both of these drugs are antimicrobials. Salvarsan contains $-\mathrm{As}=\mathrm{As}$ — linkage whereas prontosil has $-\mathrm{N}=\mathrm{N}$ linkage.
Prontosil (a red azo dye) and azo dye both have $-\mathrm{N}=\mathrm{N}-$ linkage.
How do enzymes catalyse a chemical reaction in the living system? Explain drug target interaction taking the example of enzyme as target.
In the catalytic activity, enzymes perform the following two major functions
(i) The first function of an enzyme is to hold the substrate molecule for a chemical reaction. the active sites of the enzymes hold the substrate molecule in a suitable position, so that it can be attacked by the reagent effectively.
The substrate molecules bind to the amino acid residues of the protein present the active site of the enzyme through a variety of interactions such as hydrogen bonding, dipole-dipole interactions, van der Waals' interactions and ionic bonding.
These binding forces should be strong enough to hold the substrate long enough so that the enzyme can catalyse the reaction, but weak enough to allow the products to depart after their formation.
(ii) The second function of the enzyme is to provide functional groups which will attack the substrate to carry out the chemical reaction. This function is carried out by some other amino acid residues of protein present on the active site of the enzyme.
These provide free amino groups to attack the substrate and bring about the chemical reaction. If the amino acid serine is present nearby the substrate held on the active site, then its -OH group is free to act as a nucleophile in the enzyme catalysed reaction.
The part of the amino acid which lies outside the box act as a nucleophile in enzyme catalysed reactions, but the part of the amino acid which is enclosed in the box is involved in the formation of peptide bond in protein molecule.
Sythetic detergents have advantage over usual soaps as far as cleansing power is concerned. But use of synthetic detergents over a long time creates environmental pollution. How can the pollution caused by synthetic detergents be minimised? Classify the detergents according to their chemical nature.
Synthetic detergents are cleansing agents which have all the properties of soaps, but which actually do not contain any soap. These can be used in soft as well as in hard water.
They are mainly classified into three categories
(1) Anionic Detergents
Anionic detergents are sodium salts of sulphonated long chain alcohols or hydrocarbons. Alkyl hydrogen sulphates formed by treating long chain alcohols with conc. $\mathrm{H}_2 \mathrm{SO}_4$ are neutralised with alkali to form anionic detergents. Similarly alkyl benzene sulphonates are obtained by neutralising alkyl benzene sulphonic acids with alkali.
In these detergents, the anionic part of the molecule is involved in the cleansing action. They are mostly used for house hold work. They are also used in toothpaste.
(2) Cationic Detergents
They are quarternary ammonium salts of amines with acetates, chlorides or bromides as anions. Cationic part possess a long hydrocarbon chain and a positive charge on nitrogen atom. Cetyltrimethylammonium bromide is a popular cationic detergent and is used in hair conditioners.
Cationic detergents have germicidal properties and are expensive, therefore, these are of limited use.
(3) Non-ionic Detergents
Non-ionic detergents do not contain any ion in their constitution. One such detergent is formed when stearic acid reacts with polyethylene glycol.
$\underset{\text { Stearic acid }}{\mathrm{H}_3 \mathrm{C}-\left(\mathrm{CH}_2\right)_{16} \mathrm{COOH}} + \underset{\text { Polyethyleneglycol }}{\mathrm{HO(CH_2CH_2O)_n CH_2CH_2OH}} \xrightarrow{\mathrm{H}_2 \mathrm{O}} \underset{\text { Polyethyleneglycol stearate}}{\mathrm{CH_3(CH_2)_{16}COO(CH_2CH_2O)_n CH_2CH_2OH}}$
Liquid dishwashing detergents are non-ionic type
Advantages of Synthetic Detergents over Soaps
(i) Synthetic detergents can be used in hard water without any wastage while some of the soaps gets wasted.
(ii) Synthetic detergents can be used in acidic medium while soaps get precipitated.
(iii) Synthetic detergents are more soluble in water and hence produce lather more easily than soaps. Some synthetic detergents produce lather even in ice cold water.
(iv) Synthetic detergents decrease the surface tension of water to greater extent and hence have a stronger cleansing action than soap.
Synthetic detergents have advantages over usual soaps but use of synthetic detergents over a long time creates environmental pollution because some detergents have highly branched hydrocarbon chains.
These branches or side chains stop bacteria from attacking and breaking the chains. This result in slow degradation of detergent molecule leading to their accumulation. Effluents containing these detergents reach the rivers, ponds etc. These persist in water even after sewage treatment and thus water gets polluted.
Since, unbranched (i.e., straight) chains are more prone to attack by bacteria, therefore, in most of the detergents used these days, the branching is kept to a minimum, so that the detergents become easily biodegradable and hence pollution is prevented.
What are enzyme inhibitors ? Classify them on the basis of their mode of attachments on the active site of enzymes. With the help of diagrams explain how do inhibitors inhibit the enzymatic activity.
Enzymes are responsible to hold the substrate molecule for a chemical reaction and they provide functional groups which will attack the substrate to carry out the chemical reaction. Drugs which inhibit any of the two activities of enzymes are called enzyme inhibitors.
Enzyme inhibitors can block the binding site thereby preventing the binding of the substrate to the active site and hence inhibiting the catalytic activity of the enzyme.
Drugs inhibit the attachment of natural substrate on the active site of enzymes in two different ways as explained below
(i) Drugs which compete with natural substrate for their attachment on the active sites of enzymes are called competitive inhibitors.
(ii) Some drugs, however, do not bind to the active site but bind to a different site of the enzyme which is called allosteric site. This binding of the drug at allosteric site changes the shape of the active site of the enzyme in such a way that the natural substrate cannot recognise it. Such enzymes are called non-competitive inhibitors.
