As per Modified noyes whitney equation (dc/dt = DAKo/w (Cs-Cb)/Vh), rate of dissolution is directly propertional to Partition coefficient. But we have studied partitiion coefficient means lipophilicity and increase in partition coeffecient leads to decrease in solubility. Then how modified Noyes whitney equation is correct.
The modified Noyes-Whitney equation states that the rate of dissolution (dc/dt) is directly proportional to the partition coefficient (K) multiplied by the driving force for dissolution (Cs-Cb)/Vh. The driving force for dissolution is the difference between the concentration of the solute in the solid phase (Cs) and the concentration of the solute in the liquid phase (Cb), divided by the volume of the liquid phase (Vh).
The partition coefficient represents the equilibrium distribution of the solute between the solid and liquid phases and is defined as the ratio of the concentration of the solute in the liquid phase to the concentration of the solute in the solid phase. A high partition coefficient means that the solute is preferentially partitioned into the liquid phase and is more soluble, while a low partition coefficient means that the solute is preferentially partitioned into the solid phase and is less soluble.
Therefore, the rate of dissolution is directly proportional to the partition coefficient because a high partition coefficient means that the solute is more soluble and has a higher driving force for dissolution, which results in a higher rate of dissolution. On the other hand, a low partition coefficient means that the solute is less soluble and has a lower driving force for dissolution, which results in a lower rate of dissolution.
Partition coefficient means distrubtion of drug in water phase and organic liquid phase. If a drug has high partition coefficient then it means drug has high lipophilicity or if lipophilicity is high then solubility will low
Different partition coefficients can be defined depending on the particular distribution processes you may consider.
The partition coefficient you mention governs the equilibrium distribution of a molecule between two phases with different polarity and, therefore, it will characterize the hydrophobicity/hydrophilicity of the molecule.
The partition coefficient for dissolution relates the equilibrium concentrations in two phases, bulk solution and diffusion layer surrounding the solid. Thus, the rate of dissolution is proportional to the tendency of the molecules to be hydrated.
For hydrophobic molecules, the first partition coefficient is large and the second partition coefficient is small.
- Badges
- Science topic
- Similar topics
- Biological Science
- Biochemistry
- Biochemical Techniques
- Analytical Chemistry
- pH