Is there a buffer at acidic pH? (pH 1 and 2) - (Sep/04/2013 )
mdfenko on Fri Sep 27 12:30:51 2013 said:
as for literature regarding commonly used biological buffers, i already posted some. on the other hand, it is unusual to work at such a low pH in biological systems (unless you are working with acidophiles).
Actually, acidophiles wouldn't be very happy with that buffer. In general they are pretty sensitive to anions other than sulfate (or selenate due similarity), being chloride quite toxic.
mdfenko on Mon Oct 7 13:45:17 2013 said:
on the other hand, using straight hcl with proteins (if that's the purpose of the medium) may endanger the peptide bonds and certain amino acids (hcl is used to hydrolyze peptide bonds for amino acid analysis, albeit at higher concentrations).
For aa analysis you use really high HCl concentration and under high temperature, nearly as done for mineral analysis.
The buffer is common use to determine stability and activity of enzymes at the buffer pH range (1.0-2.2)
mdfenko on Mon Oct 7 13:45:17 2013 said:
(i learned a little bit more about calculating ionic strength, thanks)
You are welcome :)
i would guess, then, that the primary reason to use a polyprotic buffer salt is that you can maintain pH with a lower molarity than with a monoprotic "buffer" (buffering capacity).
Now that I think about it - lower osmolality for sure. Still, if that's what you want, you don't need a salt, you can use just a strong polyprotic acid. Comparing pH 1.00 solutions of hydrochloric acid and sulfuric acid:
HCl H2SO4
molarity 0.155 0.135
ionic strength 0.155 0.197
buffering capacity 0.402 0.461
osmolality 0.200 0.171
(these are calculated using Davies equation, I can give more details if someone wants to reproduce these results).
on the other hand, using straight hcl with proteins (if that's the purpose of the medium) may endanger the peptide bonds and certain amino acids (hcl is used to hydrolyze peptide bonds for amino acid analysis, albeit at higher concentrations).
El Crazy Xabi on Tue Oct 8 03:38:39 2013 said:
mdfenko on Fri Sep 27 12:30:51 2013 said:
as for literature regarding commonly used biological buffers, i already posted some. on the other hand, it is unusual to work at such a low pH in biological systems (unless you are working with acidophiles).
Actually, acidophiles wouldn't be very happy with that buffer. In general they are pretty sensitive to anions other than sulfate (or selenate due similarity), being chloride quite toxic.
As I already wrote earlier - while HCl has its obvious advantages, I used it only as an example in calculations, I never suggested it is the best possible acid to use. Just sulfuric acid would work as well - it would even have slightly higher buffering capacity due to the presence of HSO4-/SO42- system (at pH 1.0 ratio of concentrations HSO4-/SO42- is about 3:1).
I guess that when it comes to peptide bonds hydrolysis HCl is just a perfect source of H+ that do the job, counterion is most likely not that important. I doubt peptide bonds would be much safer in any other solution with comparable pH.
at a pH of 1 the buffer "salt" would be mostly (if not completely) acid. there may be some counterion to fine tune the pH, if necessary.
chlorine ion will attack certain amino acids, so choice of counterion (or, in this case, buffering ion) is important.