Relate to Drug Behaviour

Use drugs as an example of the relationship between how much of a species is protonated and how much is non-protonated. This is an equilibrium process. For a carboxylic acid drug, if it’s protonated it’s not ionic, if it’s not protonated it’s anionic. And if it’s going from gut into blood for example, whether or not it goes through the membrane will depend upon the pH of the system. A drug could get caught in a lysosome because it goes through the membrane when it’s at pH 7, but can’t get back out again because there’s been a drop in pH and the molecule is protonated, and so it stays in there. When you’re designing a drug you’ve got to know the route of administration - whether you’re talking about one that’s going in the gut or one that’s being injected. The pH of the system it’s going into will govern its behaviour. If you want to complex something and the lone pair sites are protonated, it’s not going to complex, you’ve got to take it to a pH that will make it available for complexation.