Hi Len,

a possible theory: your crystals may be macroscopically twinned, i.e. 
consisting of single crystals attached to each other in the way that the twin 
operation describes.
At your home source, you employ a rather big beam that hits more than one 
single crystal. So the data appear twinned. At the synchrotron however, the 
beam is way smaller, and may hit only a single crystal. Hence, untwinned data.

HTH, Kay

On Mon, 25 Mar 2024 19:22:54 +0000, Thomas, Leonard M. <lmtho...@ou.edu> wrote:

>Hello,
>
>I have run into a very odd situation.  Upon collection and data processing on 
>a crystal on my home source all pointers seemed to show twinning.  Was not 
>surprised since previous crystals under different but related conditions have 
>showed significant twinning though the cell dimensions were different but not 
>the resulting apparent space group.
>
>Now the odd thing, I sent the crystal to the synchrotron figuring I might be 
>able to get some data that might help figure out what is going on.  Upon 
>processing of the synchrotron data, SSRL 9-2, magically no twining was 
>detected.  A couple of other crystals of the same compound though not from the 
>same exact condition showed the twinning.  I processed the data using HKL, 
>which I primarily on my home source data and XDS with similar results.
>
>In summary, the exact same crystal shows twinning on Cu home source and no 
>twinning at all at the synchrotron.
>
>Any ideas would be welcomed.
>
>Len
>
>Leonard Thomas, Ph.D.
>Biomolecular Structure Core, Director
>Oklahoma COBRE in Structural Biology
>Price Family Foundation Institute of Structural Biology
>University of Oklahoma
>Department of Chemistry and Biochemistry
>101 Stephenson Parkway
>Norman, OK 73019-5251
>Office: (405)325-1126
>lmtho...@ou.edu<mailto:lmtho...@ou.edu>
>http://www.ou.edu/structuralbiology/cobre-core-facilities/mcl
>
>
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