effects of salt on twinned crystals

From: Peter Hsu
Date: 22 February 2012 07:03

Hi all,

Thanks to all those who responded to my query about indexing my dataset. I'm beginning to suspect that the crystals are twinned. the crystals initially started as fused plates which were then optimized to single crystals that diffracted poorly (3.5-4). I then set up an additive screen, found an additive that changed crystal form (looked more like the plates from earlier), went through much optimization and got what appeared to be single rods, that diffracted much more strongly (2.5-3), although some crystals in the same drop looked like fused crystals, despite having single rods.

The initial condition used LiCl as the salt, which during the optimization I changed to NaCl. I'm now looking for ideas to see how much more I can optimize this condition since I haven't found crystals in any other conditions (even did a seed screen). Does anyone have any experience with varying the different salts to get untwinned crystals? KCl better than NaCl? Ammonium chloride better than the others? Been looking at the Hofmeister series to get ideas.

Long post I realize, but many thanks for any previous experiences with salts.

Peter

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From: Peter Hsu


Forgot to mention, that this 2.5-3A diffracting crystal was the same one that I have been unable to index and suspect are twinned due to the presence of these other fused crystals in the same drop.

Thanks for any input.

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From: Francis E Reyes

I read your description of the crystals and Figure 4 of the following paper came to mind. Post-crystallization treatment in lower PEG eventually allowed them to tease the bundles apart.



1.      MacRae, I. J. & Doudna, J. A. An unusual case of pseudo-merohedral twinning in orthorhombic crystals of Dicer. urn:issn:0907-4449 63, 993–999 (2007).


F

On Feb 22, 2012, at 10:59 AM, Peter Hsu wrote:

> Forgot to mention, that this 2.5-3A diffracting crystal was the same one that I have been unable to index and suspect are twinned due to the presence of these other fused crystals in the same drop.
>
> Thanks for any input.

---------------------------------------------
Francis E. Reyes M.Sc.

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From: Ms Chiung-Wen Chang

hi
did u have other crystals grew in different conditions in your additive screen ?
in my case, i did the additve screen for the condition i got twinned crystals
i got crystals grew in few conditions
one of them is salt but it still gave me twinned crystals
then i tried NDSB-221 and the crystals turned out non-twin

hope it helps
by the way, even though its twinned crystal
should be ok to solve the structure

Mary