biochemistry

1. Astringents
Definition:
 The word "astringent" derives from Latin “adstringere”, meaning "to bind fast".
 Astringents are protein precipitants of limited penetrative power, i.e., they are
able to coagulate protein primarily on the surface of cells ( an action that does
not result in the death of the cell).
 An astringent is a chemical compound that tends to shrink or constrict tissues
and precipitate the protein and form protective layer on the surface.
 Due to their mild protein precipitant action, astringents are able to reduce the
cell permeability. This reduces local edema, exudation and inflammation.
 They decrease sweating and possess deodorant properties.
 They are usually applied to damaged skin topically or to the mucous membrane
of GIT including the mouth.
 Mild astringent solutions are used in the relief of such minor skin irritations as
those resulting from superficial cuts, allergies, insect bites, or fungal infections
such as athlete's foot.
Characteristics:
 Affect only the superficial layer. Reduce cellular permeability.
 Make the surface mechanically strong, decrease exudation.
 Protect from external irritation.
 Possess local styptic and local antiseptic action.
 May interfere with the function of pain receptors. The pain relieving action is
mild.
 Constrict the blood vessels to stop bleeding.
Some of the uses:
i. Styptic: to stop bleeding from small cuts by promoting coagulation of blood and
constricting small capillaries.
ii. Antiperspirant: to decrease secretion of perspiration by constricting pores at the
surface of the skin.

2. iii. Restriction of the supply of blood to the surface of mucous membranes as a
means of reducing inflammation.
iv. Direct action on skin to remove unwanted tissue. This requires a higher
concentration or a stronger protein precipitant, sometimes termed a corrosive.
v. Internally used as anti-diarrheal.
Types of Astringents:
1) Vegetable astringents: Tannic acid, Gallic acid
2) Metallic Astringents:
i. Aluminium salts: Alum [KAl(SO4)2•12H2O], Aluminium chloride (AlCl3),
Auminium acetate.
ii. Zinc salts: Zinc chloride (ZnCl2), Zinc sulfate (ZnSO4)
iii. Ferric chloride (FeCl3)
iv. Strontium chloride
v. Silver nitrate (AgNO3)
vi. Copper sulfate (CuSO4)
vii. Miscellaneous: Very cold water, Alcohol
ZINC SULFATE
Molecular formula: ZnSO4.7H2O
Synonym: White vitriol
Properties:
Appearance: White powder or White granular in nature
Odor: Odorless
Taste: Astringents and metallic taste
Solubility in water: Soluble in water
When heated over 680 ⁰C, zinc sulfate decomposes into sulfur dioxide gas and zinc
oxide fume, both of which are hazardous: ZnSO4 → SO2 + ZnO

3. Dehydration of Zinc sulfate heptahydrate:
Preparation:
It can be prepared by the reaction of the metal with aqueous sulfuric acid
Zn + H2SO4 + 7H2O → ZnSO4.7H2O + H2
Pharmaceutical grade zinc sulfate is produced by treating high purity zinc oxide with
sulfuric acid.
ZnO + H2SO4 + 6H2O → ZnSO4.7H2O
Zinc sulfate also obtained by heating Zinc sulphide in presence of air
ZnS + 2O2 → ZnSO4
Uses:
 Zinc sulfate is an inorganic compound and dietary supplement. As a supplement
it is used to treat zinc deficiency.
 0.25% Zinc sulfate used for ophthalmic astringent.
 It is used internally as emetics.
 It has mild germicidal, styptic and astringent action depending on the
concentration of salt used. This is due to slow release of zinc ions from its salt
or solution.
 It is used as in electrolytes for zinc plating, as a mordant in dyeing, as a
preservative for skins and leather.

4. ALUM
 Alum can be either the Aluminium potassium sulfate KAl (SO4)2·12H2O Potash
alum (potassium salt) or Aluminum ammonium sulfate NH4Al (SO4)2·12H2O
(Ammonium salt).
 The official compound exists as large, colorless crystals, or as a white powder.
Odorless & has a sweetish, strongly astringent taste.
 Solution is acidic to litmus.
 Freely soluble in water, freely but slowly soluble in glycerin, insoluble in alcohol.
Preparation:
 It is prepared by adding a concentration solution of potassium sulphate to a hot
solution of an equimolar proportion of aluminium sulphate. On cooling, crystals
are separated.
K2SO4 + Al2(SO4)3 + 24H2O → 2 KAl (SO4)2·12H2O
Uses:
i. Alum is used as a source of aluminium ion, making it useful as topical astringent.
ii. It can be used in footbaths as means of toughening the skin.
iii. As styptic to stop bleeding from small cuts.
iv. The protein precipitant properties of Alum are utilized in the preparation of
precipitated diphtheria & tetanus toxoids.
v. is used as an adjuvant in many subunit vaccines, such as include hepatitis A,
hepatitis B, and Diphtheria.
vi. Alum in rock form is used as an aftershave. If it is rubbed on a freshly shaved
face, its astringent property helps to prevent and reduce bleeding in minor cuts
and abrasions.
vii. Alum has a strong antibacterial property and so it is useful as a natural
deodorant by inhibiting the growth of the bacteria responsible for body odor.
viii. It is also used as an emetic agent to induce vomiting when a person has
swallowed poison.