Solution (i) Many drugs need to pass through one or more cell membranes to reach

Question

Solution (i)

Many drugs need to pass through one or more cell membranes to reach their site of action. The most common method for drugs to cross the cell membrane is by Passive Diffusion. Drug molecules will diffuse down its concentration gradient without the expenditure of energy by the cell. However, the membranes are selectively permeable, so it has different effects on the rate of diffusion of different drug molecules.

Solution (ii)

The partition coefficient abbreviated P, is defined as a particular ratio of the concentrations of a solute between the two solvents (a biphase of liquid phases), specifically for un-ionized solutes, and the logarithm of the ratio is thus log P. When one of the solvents is water and the other is a non-polar solvent, then the log P value is a measure of lipophilicity or hydrophobicity.

A drug's distribution coefficient strongly affects how easily the drug can reach its intended target in the body, how strong an effect it will have once it reaches its target, and how long it will remain in the body in an active form.

Solution (iii)

p-Dichlorobenzene has log P=3.37 at 25 degrees Celsius. Introducing a ring deactivating group (like a nitro group) will lower the log P value.

Explanation / Answer

Most drugs have to pass through one or more membranes in order to reach their target organ; i. (e) Through which mechanism do most drugs pass through membranes and what is the driving force? log P is a parameter that is measured or calculated for molecules in drug development. How is it defined and what property does it describe? ii. ii. Give an example of a molecule with a log P value>2, what substituent would you introduce into this molecule to lower the logP value.

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