If you find yourself in the situation where the buffer you started with is out 
of range of the pH you would 
like to attain, there are sets of buffers you can use that contain most of the 
standard buffers that will give 
you a fairly linear response across ~4-10, as described by Newman, Acta Cryst 
D, 2004, v60, pp 610-612. 

cheers, tom
From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] On Behalf Of Xiaodi Yu 
Sent: Wednesday, February 08, 2012 8:06 PM
Subject: Re: [ccp4bb] pH optimisation for crystallisation

Hello Sreetama:

I think for crystallization, everything is hard to say. But if you find your 
crystal is sensitive to the pH, you certainly can optimize the pH value but it 
is better not to deviate a lot. For example you can make 0.2 unit interval (for 
example: pH value 4.5, 4.7, 4.9...etc which are closed to your original pH 
value ).
For the buffer, you can change or not.  Another thing is that, you can also 
incorporate bis-tris in your last purification, since you find your crystal in 
this buffer.
When you do additive screen, the drops which is clear, also can give you 
important information. You might find a compont which can "inhibit" crystal 
formation. You can use it to slow down the crystal formation to get a big or 
single crystal.
However, you see, sometimes, this optimization is time consuming. I suggest you 
to try seeding. It can give you a big surprise, sometimes.

Yu Xiaodi

Date: Wed, 8 Feb 2012 11:56:30 +0530
From: somon_...@yahoo.co.in
Subject: [ccp4bb] pH optimisation for crystallisation

Dear all,
           I have a 17 KDa protein that gives crystals in a condition that has 
0.1M bis-tris pH 6.5. The crystals are thin needle clusters and do not 
diffract. I have tried additives, but they haven't improved the crystals. I 
intend to vary the pH of the condition.
           My questions are-
1. should the buffer be kept the same or can it also be changed (as long as the 
desired pH is within the range of both the buffers)?
2. in case of a different buffer, should its molarity be the same as that of 
the original one in the crystallization condition?


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