Solubility
Science
- Drug discovery
The overall desirable properties of a drug molecule affects the adsorption and distribution of drug is best describe by the lipinski rule of 5. Three out of the Lipinski rule of five describes the solubility.Lipinski’s “Rules of Five” [1]
– Molecular weight ≤ 500 Da (optimal ~350)
– Number of H bond acceptors ≤ 10 (optimal ~5)
– Number of H bond donors ≤ 5 (optimal ~2)
– Number of rotatable bonds ≤ 10
– -2 < Log P < 5 (optimal ~0.5 – ~3)- Adsorption – For oral drugs, in order to be able to be absorb by the small intestine and distributed to other parts of body, it has to strike a balance between hydrophobic and hydrophillic (Log P) value – a ratio of the concentration of solute being soluble in 1-octanol and water. Drugs that are too hydrophillic cannot pass through the intestinal membrane and it will be excreted as solid waste or broken down by bacteria in the colon.
- Distribution – In order to get to the intended site from the intestine to other parts of the body, the drug has to interact with either the blood or proteins found in the plasma depending on the solubility. After reaching the site, the drug has to exit the blood stream and enter the extracellular fluid. The process of exiting the blood vessel and extracellular fluid will favor the drugs that are hydrophobic and small [2].
- Metabolism & Excretion – Drugs are usually metabolized in the liver by adding functional groups and making them more hydrophillic or soluble in water so that they can get excreted. Hydrophobic drugs, on the other hand, tends to stay in body for a long time and may cause toxic effects [2,3].
- Adsorption – For oral drugs, in order to be able to be absorb by the small intestine and distributed to other parts of body, it has to strike a balance between hydrophobic and hydrophillic (Log P) value – a ratio of the concentration of solute being soluble in 1-octanol and water. Drugs that are too hydrophillic cannot pass through the intestinal membrane and it will be excreted as solid waste or broken down by bacteria in the colon.
Impact on environment
- The mechanism of action of pollutant causing pollution
- Oil spill – water and oil do not mix as the force of attraction between the oil molecules/ water molecules are stronger than the force of attraction between oil and water molecules. There is no interaction between the 2 molecules and hence form two distinct layers. Aside from toxicity, having a oil layer prevents oxygen exchange application in daily life. (add some oil to stagnant water to prevent breeding of mosquito)
Solution: The concept of solubility can be applied to how oil spill is resolved. Oil dispersants are used during oil spills that helps to break up the oil layer into droplets by using surfactants and solvents to speed up the biodegradation of oil and protect coastal life. The surfactants must be hydrophobic in oil and hydrophilic in water to ensure successful dispersion of oil slicks.
- Heavy metal pollution – metals such as lead, iron are oxidized to produce metal ions that are dissolve in the water and reduce overall water quality and are toxic to consume. It may lead to lead poisoning which is harmful to the human’s nervous system.
References
- Oil spill – water and oil do not mix as the force of attraction between the oil molecules/ water molecules are stronger than the force of attraction between oil and water molecules. There is no interaction between the 2 molecules and hence form two distinct layers. Aside from toxicity, having a oil layer prevents oxygen exchange application in daily life. (add some oil to stagnant water to prevent breeding of mosquito)
- C. Lipinski, et al. Adv. Drug Rev. 23, 3-25 (1997)
- C.F.Liu Drug discovery and Development Biotechnology Lecture slides
- Richard A. Harvey, et al. Lippincott’s illustrated review pharmacology 3rd edition
- ITOF, retrieved from online website http://www.itopf.com/knowledge-resources/documents-guides/clean-up-techniques/dispersants/