I'm not convinced that you need a conventional buffer at pH 2 or 3. At pH 2, the hydrogen ion concentration is 10 mM. If you want to use something else, the second pKa for sulfuric acid is around 2. The first pKa for phosphoric acid is slightly higher than 2. Lactic acid has a pKa close to 3. Formic acid has a pKa just under 4. Most of these numbers were in an appendix in the first chemistry text you ever used. <wink> These numbers imply pretty strongly that most crystallization screens emphasizing common salts will require determined modification to hit these low pH values, because many stabilizing anions in the Hoffmeister series will be partially or completely protonated at these pH values. PEG and organic screens will require a smaller hammer to retrofit.
On Nov 6, 2011, at 11:19 PM, Sam Arnosti wrote: > Hi everyone > > I have a protein that is extraordinarily stable at PH=3.0 or even 2.0. > > I want to crystallize it in the low PH and compare the differences between > the crystals in regular PH and low PH. > > I was wondering how people set up the boxes in low PH, as usual buffers are > mostly less acidic. > > Regards > > Sam
