|MadSci Network: Biochemistry|
I am a little unclear about exactly what you are trying to calculate, but I will answer with a speculation about what you mean.... In your first sentence you ask how to figure out the concentrations of amino acid species at different pHs. I am assuming by "species" you mean you want to know at a given pH what concentration of the amino acid is +1 charged, and how much is +2 charged, etc?
The Henderson-Hasselbalch equation relates pH, pKa and the concentrations of the two species on either side of the pKa value (i.e. the concentrations of the 0 and +1 species, or the concentrations of the +1 and +2 species, etc). The equation is:
pH = pKa + log([HA]/[A])
Of course, you will have to look up the pKa of the various ionizable groups in the amino acid of interest, but that information is easy to find.
Hope this helps!
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