I have crystallized in PEG with citrate at pH 3. If you want to go lower
I would suggest maleate:
effective pH range pKa 25°C buffer
1.2-2.6 1.97 maleate (pK1)
2.2-6.5 3.13 citrate (pK1)
Enrico.
On Mon, 07 Nov 2011 14:15:02 +0100, Craig A. Bingman
<[log in to unmask]> wrote:
> 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
--
Enrico A. Stura D.Phil. (Oxon) , Tel: 33 (0)1 69 08 4302 Office
Room 19, Bat.152, Tel: 33 (0)1 69 08 9449 Lab
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