OIA1011 DISTRIBUTION OF SOLUTE BETWEEN INMMISCIBLE SOLVENTS

Q:What is partitioning in chemistry?

A:The distribution of a solute between two immiscible solvents at equilibrium.

Q:State the partition law.

A:C1/C2=K, where C1​ and C2​ are solute concentrations in two solvents, and K is the partition coefficient.

Q:What is the partition coefficient?

A:A ratio that describes the equilibrium distribution of a solute between two immiscible phases.

Q:Name two factors affecting partitioning.

A:Ionic dissociation and molecular association.

Q:Why is partitioning important in pharmaceuticals?

A:It influences drug absorption, distribution, and formulation in oil-water systems.

Q:How does pH affect the partitioning of benzoic acid in oil-water systems?

A:pH changes the degree of ionization, affecting its solubility in each phase.

Q:What is the partition coefficient formula for ionizing substances like benzoic acid?

A:K= Co/Cw = [HA]o/[HA]w+[A−]w.

Q:How does molecular association in benzene affect the partitioning of benzoic acid?

A:Benzoic acid forms dimers in benzene, altering its effective concentration.

Q:What is extraction in chemistry?

A:A technique to separate components of a mixture using two immiscible solvents.

Q:Write the formula for the weight of solute remaining in the original solvent after single extraction.

A:W1=W(KV1+V2) , where K is the partition coefficient, V1​ and V2 are solvent volumes.

Q:What is the principle behind multiple extractions?

A:Repeating extractions with smaller solvent volumes increases overall efficiency.

Q:State the formula for solute remaining after n extractions.

A:Wn = W(KV1/KV1+V2)^n.

Q:How much iodine is extracted from water into CCl44​ if K=0.012,W=0.1g, V1​=50ml, and V2​=10ml?

A:0.0943 g of iodine is extracted.

Q:What is the iodine remaining in water after two 5 ml extractions with CCl44​?

A:0.0011 g.

Q:Why is small solvent volume preferred for multiple extractions?

A:To maximize the extraction efficiency.

Q:How is the partition coefficient K calculated for a drug in octanol and water?

A:K=Co/Cw, where Co​ and Cw​ are the drug concentrations in octanol and water, respectively.

Q:How does partition coefficient affect drug absorption?

A:Drugs with moderate K values (−0.4 to +5.6) can cross cell membranes efficiently.

Q:Define Lipinski’s Rule of Five in drug design.

A:

1. molecular weight: mw < 500 daltons

2. octanol-water partition (log P)

   -log P « 5 (measure lipophilicity)

   - decrease in log P → hinder solubility in aqueous phase

3. H-bond donors

   -no more than 5 H-bond donors (sum of -OH & -NH groups)

4. H-bond acceptors

   -no more than 10 H-bond acceptors (sum of N & O atoms)

5. Rotatable bonds

   -highly Rotatable bond increases conformation flexibility → complete absorption & distribution.

Q:Give an example of a drug with high partition coefficient.

A:DNIB, with log⁡P=2.87.

Q:Why is partitioning studied for drug delivery?

A:To understand drug behavior in biological systems like absorption and distribution.

Q:What does a high logP value indicate about a drug's solubility?

A:It is more lipid-soluble and likely to remain in lipid layers.

Q:What happens to drugs with logP< -0.4?

A:They remain in the aqueous layer and have poor membrane permeability.

Q:What is the physiological partition system used for testing?

A:Octanol and 0.1 M phosphate buffer at pH 7.4.

Q:How does temperature affect partitioning?

A:It can change solute solubility, altering the partition coefficient.

Q:Why is UV spectroscopy used in partition studies?

A:To determine solute concentrations in different phases.

Q:What is the role of partition coefficient in excretion?

A:It predicts drug removal via lipid or aqueous pathways.

Q:How can dimerization affect partition coefficients?

A:It reduces the apparent solute concentration in one phase, altering KK.

Q:Why are immiscible solvents used in partitioning studies?

A:To separate phases clearly for accurate measurements.

Q:What is the significance of partition coefficient in toxicity studies?

A:It helps predict accumulation in biological tissues.