State of matter and properties of matter (Part-9)�(Physicochemical properties of drug molecule: Determination and Application 3. Dielectric constant 4. Dipole moment

DIELECTRIC CONSTANT: Definition, Determination and Application.
DIPOLE MOMENT: Definition, Determination and Application.

1. IIIrd Semesester B. pharmacy Physical Pharmaceutics-I Unit-II State of matter and properties of matter (Part-9) ( P hysicochemical properties of drug molecule: Determination and Application 3. Dielectric constant 4 . Dipole moment ) Miss. Pooja D. Bhandare (Assistant professor) Kandhar college of pharmacy

2. DIELECTRIC CONSTANT Definition: Physicochemical property of a solvent relating to the amount of energy required to separate two opposite charged region in the solvent as compared with the energy required to separate the same in vacuum. Or, “dielectric constant of a substance is a measure of its efficiency to induce dipole in another molecule.” A quantity measuring the ability of a substance to store electrical energy in the electric field.

3. The relative permittivity, or dielectric constant, of a material is its permittivity expressed as a ratio relative to the vacuum permittivity. Permittivity is a material property that affects the Coulombs force between two point charges in the material. Expressed as ε r = Where, ε r = relative permittivity, ε = Permittivity of material ε 0 = Permittivity of vacuum  

4. DETERMINATION An electrical condenser (capacitor) is considered to understand the concept of dielectric constant. Condenser is one that can store energy. A simple condenser consists of two parallel plates separated by an insulting medium

5. Dielectric constant is measured by measuring the effect of the intervening solvent on the electric field between two opposite charged particles. The capacitance between the two plates for holding the test solution between the plates is measured. After that, measure the capacitance by maintaining the vacuum between the plates. Then, the dielectric constant is obtained which is the ratio of the capacitance of a capacitor completely filled with the dielectric to the capacitance of the capacitor filled with space or vacuum.

6. Formula ε = , C 0 = Where, C = capacitance using material as the dielectric capacitor Co = capacitance using vacuum as the dielectric. ε o = Permittivity of free space A= Area pf a plate/ sample cross section area T = Thickness of the sample Units: dimensionless because it is a ratio  

7. APPLICATION To measure polarity of solvent: higher the magnitude of the dielectric constant, the greater the polarity of solvent. Solubilization of drugs: The higher the magnitude of the dielectric constant, the greater the solvation energy to the solvent, hence greater is solubility Selection of solvents or solvents blends for the solubility of drug

8. DIPOLE MOMENT In the chemical structure of a polar molecule, the poles are separated. Dipolar molecule is defined as the one in which the region of positive and negative charges are well separated due to uneven distribution of electrons in the molecule. Water, hydrochloric acid etc.

9. The magnitude of charge separation is expressed as dipole moment. Dipole moment is define as the vector equal in magnitude to the product of electric charge and distance, having the direction of the joining the positive and negative centers Dipole moment has a magnitude and direction. Mathematically, dipole moment expressed as μ = qr Where, μ= Dipole moment r = distance chargeq q = charges Units: SI Coulomb matre , cgs: debye

10. Polarizability is defined as the ease with which an ion or a molecule can be polarized by any external force. In the influence of external force, dipole can also have induced dipoles which facilitated further alignment of negatively charged centres close to positively charge centres. Similarly, chlorine molecule gets polarized and develops charges. This is called induced dipole moment.

11. DETERMINATION When a solution of polar molecule is placed between two plates having opposite charge, they align themselves along the direction of the field. This process consumes energy that is returned to the electric circuit when the field is switched off, an effect know as electrical capacitance. The measurement of capacitance of a gas or a solution serves to determine the magnitude of the dipole moment of a substance .

12. APPLICATION Solubilization of drugs. By hydrating solute molecules and ions. By inducing in nonpolar molecules. Crystalline nature of solids: eg. Oice crystals are organized through their dipole forces Dipole forces are believed to contribute for drug-receptor interaction. Therapeutic activity of drugs: permanent dipole moment can be correlated with biological activity.

13. 5 . Chemical structure of compounds Deciding nature of a bond Identifying shape of molecules Identifying the shape and bond angle Deciding the arrangement of groups Identifying geometric isomers.

14. Thank you!