[doctorsmonsters]

Can someone please explain or share a link about the relation between PH and PKa of substances like amino acids and how amino acids have different charges at different PH levels. I really don't get it. :toosad:

 

[drahmednawaz]

Pka of a substance is the PH at which half of it is charged and half uncharged.
water has a pka of 7. Anything below it is acidic and above it is alkaline.
if an acidic amino acid has a pka of 3; below 3, it will be acidic for that amino acid and in a PH of 2 it will be uncharged. An acid in acidic medium is uncharged. Mnemonic for that is a male doesn't get charged in the presence of the males; it has to be in the opposite medium. Above a PH of 3 it will be alkaline for that amino acid and it will be charged. Do the vice versa for basic amino acids until ur head starts spinning.

 

[Mondoshawan]

Exactly - and the next part of it, for pharmacokinetics/bioavailability, is that a drug will distribute through membranes better in its uncharged state, and it will remain mostly unabsorbed in its charged state.