Solvation and association (Solubility of drug Part -3)

Solvation, solvation and solubility, Solvation energy thermodynamic consideration, Association

1. IIIrd Semesester B. pharmacy Physical Pharmaceutics-I Unit-I Solubility of drugs(Part-3) (Solvation and Association) Presented By : Miss. Pooja D. Bhandare (Assistant Professor) Kandhar College of Pharmacy, Nanded

2. SOLVATION According to IUPAC definition, solvation is an interaction of a solute with the solvent, which leads to stabilization of the solute species in the solution. Solvation of solute by water is called as hydration. In the solvated state, an ion or uncharged molecule in a solution is surrounded or complexed by solvent molecule. The strength and nature of this interaction influence many properties of the SOLUTE SOLVENT Solubility Viscosity Reactivity Density Color

3. Solvation and Solubility Solvation or dissolution is a kinetic process and is a quantified by its rate and dissolution rate is mol/s Solubility quantifies the dynamic equilibrium state achieved when the rate of dissolution equals the rate of precipitation Solvents and intermolecular interactions: Hydrogen bonding Ion-dipole interactions Van der Waals forces dipole-dipole dipole-induced dipole induced dipole- induced dipole interactions

4. Solvation energy and thermodynamic consideration: Where = Gibbs energy Change in enthalpy T = Absolute temperature = Change in entropy /degree of randomness  

5. Solvation involves multiple steps with different energy consequences. First, a cavity must from in the solvent to make space for a solute. This is both entropically and enthalpically unfavorable . A particle of solute must separate from the bulk. This is enthalpically unfavorable . The resulting solvent solute interactions are enthalpically favorable

6. ASSOCIATIONS Association of the ion or molecule is the chemical reaction. Opposite electric charge Molecule or ion come together to form new in solution to form distinct chemical entity. The extent of it depends on the dielectric constant of the solvent. Ions- Electrostatic force- Columb’s law: Where, q 1 and q 2 are magnitude of electric charges, F is the force of attraction ε is the dielectric constant r is the distance between the ions

7. Example: Dimerisation of Benzoic acid

8. THANK YOU!