In: Chemistry
On amino acid titration curves, using pH, pKa, etc, how do we know which hydrogens to remove at which states? I know it has to do with the acidity, and that at low pH the structure gets protonated and whatnot, but how do I know the order in which to protonate/deprotonate?
amino acids have pKa values, which are mainly:
the pH value at which the specie get protonated
if pKa > pH; then the species will be PROTONATED, that is COO- + H+ = COH and NH2 + H+ = NH3+
if pKa < pH; then the species are NOT protonated, there is not enough H+ in solution to do this, so the sample will doante H+ from its own, COOH = COO- + H+ and NH3+ = NH2 + H+
therefore, knowing the pKa values of the amino acid, we can set the values at which the titration will "shift" and also:
- using buffer equaiton
pH = pKa + log(A-/HA)
relate the protonated vs the deprotoanted state
pH = pKa + log(COO-/COOH)
pH = pKa + log(NH2/NH3+)