Re: [ccp4bb] which concentrated salt has lowest vapour pressure?

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

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Subject: Help with Superpose results
From: Mona Rahman rahmanm {- at -} QUEENSU {- dot -} CA
Date: 2008-04-07

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From: "Stojanoff, Vivian" stojanof {- at -} BNL {- dot -} GOV
Date: 2008-04-07

Subject: Re: which concentrated salt has lowest vapour pressure?
From: Bart Hazes bart {- dot -} hazes {- at -} UALBERTA {- dot -} CA
Date: 2008-04-07

George M. Sheldrick wrote:
> Li salts tend to increase the solubility of peptides (Seebach et al.,
> Helv. Chim. Acta 72 (1989) 857-867), which is a pity, because they can
> also be used as cryoprotectants.
>
> George

But that is not an issue if you add the salt only to the reservoir. The
same is not necessarily true for AS, because ammonium is volatile. Janet
Newman was successful with AS in her paper (Acta Cryst D61, 490-3) but
for us it didn't work well (Dunlop & Hazes, Acta Cryst D61, 1041-8, 2005).
We did take some measurements to vapour pressure reduction caused by
various reagents. All PEGS are VERY poor. There is some variation
between salts but the effect is clearly concentration dependent, as it
should, so if you want the maximum dehydrating power, I would still go
with LiCl. However, unless there is already a lot of salt in the
crystallization drops you may dry out the drops completely if you push
it too far.

Bart

> Prof. George M. Sheldrick FRS
> Dept. Structural Chemistry,
> University of Goettingen,
> Tammannstr. 4,
> D37077 Goettingen, Germany
> Tel. +49-551-39-3021 or -3068
> Fax. +49-551-39-2582
>
>
> On Mon, 7 Apr 2008, Kay Diederichs wrote:
>
>
>>Dear all,
>>
>>a protein which we work on is available in low quantity. The only
>>crystallization screen we set up is completely clear, no precipitate, nothing.
>>
>>Now we would like to modify the reservoirs of this screen, by adding LiCl or
>>Ammoniumsulfate or ... , with the goal of reducing the vapour pressure, to at
>>least get the protein concentration in the drop into the range where
>>"something happens".
>>
>>Does anyone have advice as to which salt we should add (to the reservoir
>>only)? AmSO4 is only soluble to 4M, LiCl goes to 10M. But vapour pressure
>>reduction is not the same as molarity.
>>
>>thanks for any insight,
>>
>>Kay
>>--
>>Kay Diederichs http://strucbio.biologie.uni-konstanz.de
>>email: Kay.Diederichs@uni-konstanz.de Tel +49 7531 88 4049 Fax 3183
>>Fachbereich Biologie, Universität Konstanz, Box M647, D-78457 Konstanz
>>

--

==============================================================================

Bart Hazes (Assistant Professor)
Dept. of Medical Microbiology & Immunology
University of Alberta
1-15 Medical Sciences Building
Edmonton, Alberta
Canada, T6G 2H7
phone: 1-780-492-0042
fax: 1-780-492-7521

==============================================================================

CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: Help with Superpose results
From: Mona Rahman rahmanm {- at -} QUEENSU {- dot -} CA
Date: 2008-04-07

Next message:
Subject: Crystallization: focus on memebrane proteins 2008
From: "Stojanoff, Vivian" stojanof {- at -} BNL {- dot -} GOV
Date: 2008-04-07