Introduction of solubilty, solubility expression, solute solvent interaction.pdf
1. SOLUBILITY OF DRUGS
SOLUBILITY EXPRESSION, MECHANISM OF SOLUTE-SOLVENT
Presented by – Mr Shubhrat Maheshwari
Assistant Professor, Faculty of
Pharmaceutical Sciences, Rama University
2. Solubility of Drugs
• Solubility is defined as the concentration of a
substance (solute) that dissolves in a given volume of
solution (solvent) at a certain temperature to form a
spontaneous solution of solute in the solvent.
• Solubility can also be defined as the spontaneous
interaction of two or more substances to form a
homogenous molecular dispersion.(Qualitative)
• Solubility of a substance in a particular solvent is
defined as the concentration of the substance in
saturated solution at certain temperature.
3. Solubility of Drugs
• Solubility is an intrinsic material properties -> can be
altered By chemical modification of the molecules.
• Dissolution →→ is an extrinsic material property,
influenced by various chemical, physical, and
crystallographic means like complexations, particle
size. surface properties.
• Solubility of a compound depends on:
Physical, Chemical properties of the solvent and
Temperature, pressure and pH of solution.
4. SOLUBILITY OF DRUGS
Terms used in Solubility
It is mixture of components which are physically and chemically
The components which are present in the solution is called as solute
that dissolves in solvent.
The medium in which components are dissolved is known as solvent.
The ability of substance to dissolve in a solvent is called solubility.
5. SOLUBILITY OF DRUGS
Terms used in Solubility
• SATURATED SOLUTION
The solution containing maximum number of solute at a constant
temperature is called saturated solution.
• SUPER SATURATED SOLUTION
A solution that contains more of the dissolved material then could
be dissolved by the solvent under normal circumstances.
• UNSATURATED SOLUTION
A solution where the solute concentration is lower than its
7. Solubility of Drugs
SOLUBILITY EXPRESSION- Quantitative expression
• PERCENTAGE TERM USED IN SOLUBILITY
1. % W/W = Percent Weight by Weight → No. of gram of solute
dissolved in 100 gram of solution.
2. % V/V = Percent volume by volume → No. of gram of solute
dissolved in 100 gram of solution.
3. % W/V = Percent Weight by volume → No. of gram of solute
dissolved in 100 ml of solution.
8. Solubility of Drugs
• It is defined as the number of moles (or gram molecular weight) of solute
dissolved in 1 litre of solution.
• It is defined as the moles of solute dissolved in 1000 g of solvent.
• It is defined as the number of gram or mole equivalents of solute
present in one litre of a solution.
• Mole fraction is the number of moles of a specific component in the
solution divided by the total number of moles in the given solution.
9. Solvent-Solute Interactions
• Binding forces between molecules Cohesive
and adhesive forces are manifestation of
• When molecule interact both repulsion force
and attraction forces act.
• To cohere attraction forces are necessary and
to prevent interpenetration repulsion forces are
10. Solvent-Solute Interactions
Types of attraction forces
• Van der Waals Force
Dipole-dipole interaction (Keesom interactions)
Dipole-induced dipole interaction (Debye interactions)
Induced-dipole -Induced-dipole interaction (London dispersion
• Ion-Dipole and ion-Induced Dipole Force
• Ion-ion Interaction
• Hydrogen Bonds
Selection of solvent is based on 'like dissolve like’
11. Solvent Solutes Interactions
• Water is good solvent for –salt and Sugar&
• Mineral oils dissolve - normally only slightly
water soluble substances
• So “like dissolves like”
12. Solvent Solutes Interactions
• Solubility of drug is due to polarity of solvent
that is dipole moment.
• Polar solvents dissolves
• Water mixes in all proportions with
Other polyhydroxy compounds.
13. Solvent Solutes Interactions
• Hildebrand showed that a consideration of dipole
moments, alone is not adequate to explain solubility of,
polar substances in water
• The ability of the solute to form hydrogen bonds is
more significant factor.
• Water dissolves → phenols, alcohols. aldehydes,
ketones, amines, and other. oxygen and nitrogen
containing compounds that can form hydrogen bonds.
• Difference in acid- base character of constituents (in the
Lewis electron donor-acceptor sense) also contributes
to specific interaction in solutions.
14. Solvent Solutes Interactions
• Nonpolar solvents unable to reduce attraction
b/w ions of strong and weak electrolytes
because solvent low dielectric constants.
• Non polar solvent dissolve non polar solute
with similar internal pressure.
15. Solvent Solutes Interactions
• The solute molecules are kept in solution by
weak van der Waals, London types of forces.
• Oil and fats dissolved in carbon tetrachloride
benzene and mineral oils.
• Alkaloids bases and fatty acids dissolves in
non polar solvents.
16. Solvent Solutes Interactions
• Semipolar solvents → ketones and alcohols.
induce certain degree of polarity in non polar
• Example-benzene (readily polarizable) become
soluble in alcohol.
• Semipolar compounds can act as intermediate
solvents - bring miscibility of polar and
17. Mechanism of Solute-Solvent
• If the solvent is A & the solute is B. and the
forces of attraction are represented by A-A, B-
B and A-B.
• If A-A >> A-B The solvent molecules will be
attracted to each other.
• Example: Benzene & water, where benzene
molecules are unable to penetrate the closely
bound water aggregates.
18. Mechanism of Solute-Solvent
• If B-B >> A-A The solvent will not be able to break the
binding forces between solute molecules.
• Example NaCl in benzene, where the NaCl crystal is
held by strong electrovalent forces which cannot be
broken by benzene.
• If A-B >> A-A or B-B, or the three forces are equal.
Formation of solution takes place.
• Example: NaCl in water.
• Solution is formed when Solvent-solvent interaction <
Solvent -solute interaction > Solute -solute interaction.