State of matter and properties of matter (Part-8)�(Physicochemical properties of drug molecule: Determination and Application 1. Refractive Index 2. Optical Rotation)�

REFRACTIVE INDEX: Definition, Snell’s law, Determination: Abbe’s refractometer. Application.
OPTICAL ROTATION: Definition, Determination: Polarimeter, Application

1. IIIrd Semesester B. pharmacy Physical Pharmaceutics-I Unit-II State of matter and properties of matter (Part-8) ( P hysicochemical properties of drug molecule: Determination and Application 1. Refractive Index 2. Optical Rotation ) Miss. Pooja D. Bhandare (Assistant professor) Kandhar college of pharmacy

2. PHYSICOCHEMICAL PROPERTIES OF DRUG MOLECULES: Physicochemical properties of any drug greatly affect their biological action by altering their absorption, protein binding, solubility and stability. Refractive Index Optical Rotation Dielectric Constant Dipole Moment Dissociation Constant

3. REFRACTIVE INDEX When a ray of light passes from one medium to another, its direction is changed. This change of direction is called as refraction. If the light ray passes from a less dense medium ( eg. Air) to a denser medium ( eg. Water), it refracts towards the normal. It is a characteristics of of a liquid. It is equal to the velocity of light of a given wavelength in the empty space or the vacuum divided by its velocity in the selected medium . It is expressed as: n= Where, C = velocity of light of a given wavelength in a vacuum V = velocity of light of a given wavelength in a selected medium The refractive index is a dimensionless physical quantity specific to a certain medium.  

4. Snell’s law : Describe the relation between the angle of incidence and refraction. States that the refractive index of the liquid as a constant ratio of the sine of the incidence to that of the refraction. It may be written as: n = Where, i = angle of incidence and r = angle of refraction  

5. DETERMINATION

6. Abbe’s refractometer Most practical and widely used. First refractometer to be commercially applicable. Principle: based on measurement of critical angle. Working: Liquid sample is placed in a thin layer(͠ 0.1 mm) between an illuminating prism and a refracting prism. A sodium lamp is projected through the illuminating prism. The radiation is refracted at the interface of the sample and smooth surface of the upper prism.

7. After that it passes into the fixed telescope. The refractive index is read through the eyepiece at the upper end. APPLICATION To identify a substance. To measure the purity of a substance ( Pharmacopoeial standards) To determine the concentration of substance. To determine the molar refraction without conducting the experiment. To determine dielectric constant. To determine molar polarizability of a substance.

8. OPTICAL ROTATION Ordinary light transmits its rays in all direction , i.e. in all planes. When light is allowed to pass through a polarizing prism, light vibrations in only one plane are transmitted. Such a light beam is know as plane-polarized light. Optical rotation: Certain liquids and solutions possess the inherent property to rotate the plane of incident polarized light through a certain angle i.e. angle of rotation ( α ). The rotation of the plane of polarization of plane polarized light by an optically active substance.

9. Optical activity: ability of certain substances to rotate the plane of polarized light. Optically active substances: can rotate the plane of polarized light either to right side or to left side. Dextrorotatory Levorotatory When the rotation of plane polarized light take place in clock-wise direction (towards the right) When the rotation of plane polarized light take place in anticlock -wise direction (towards the left) Prefixed with the symbol (+) Prefixed with the symbol (-)

10. Optical rotation is normally expressed as specific rotation and mathematically expressed in IP as Specific rotation=  

11. Polarimeter Light source (sodium vapour lamp) Unpolarized light (ordinary light) Polarized light Sample tube containing organic molecules Optical rotation Movable analyzer ( nicol prism) Observer DETERMINATION

12. PRICEDURE When light is passes through a polarizer only light oscillating in one plane will leave the polarizer. The plane polarized light is introduced to a tube containing a solution with the substance to be measured. If the substance is optically inactive, the plane of polarized light will not change in orientation. If the compound in the polarimetry cell is optically active, the plane of the light would be rotated on its way through the tube either clockwise or anticlockwise direction depending on the nature of the compound.

13. APPLICATION To identify substance. To measure the purity of a substance ( Pharmacopial standards) To determine the concentration of a substance dissolved in a liquid (quality control test, assy.)

14. THANK YOU!