Thank you for correcting my misleading statement, Zbyszek!
Cheers,
Martin
On 21/01/2026 22:59, zbyszek wrote:
Diffraction anisotropy has nothing to do with beam size and its
relationship to the shape of the crystal. Diffraction anisotropy
depends only on microscopic order of the crystal and crystal symmetry.
For example, in cubic symmetries, diffraction is always isotropic.
Microscopic order is mostly a function of the type of packing
molecular contacts, so it could be quite variable even for the same
protein, but in different crystal packing arrangements. In my
experience, I didn't find much correlation between r-factors and
anisotropy, but I use anisotropic informativity cutoff of the data
using HKL3000 automatic corrections option, which some people also
use. Other programs may use a similar procedure but I am not familiar
with them.
Zbyszek Otwinowski
On 2026-01-21 16:02, Martin Malý wrote:
Dear Purity,
One very common reason for diffraction anisotropy is a shape of
crystal, in combination with a beam size. If a crystal is a needle or
a plate, then it's no surprise that data with diffraction anisotropy
are collected. But there are also other reasons.
I would personally say - don't be so unhappy when comparing R-values
of different structures/datasets. The R-values are only well
comparable when they are calculated against the same data range (here
it means the same set of reflections). I guess this criterion is not
met in the cases you are referring to so you can probably relax.
Much more important is whether Rfree and Rfree-Rwork gap are getting
lower and lower when you do your iterations of model building and
refinement against your particular dataset. And it's also important
whether you can see "density good enough" to build your structure
model. Staraniso can help there. You can also try Servalcat
refinement against intensities and carry out map sharpening e.g. in Coot.
Cheers,
Martin
On 21/01/2026 19:49, Ezennubia, Purity wrote:
Thank you, Gerard, for the document recommendation.
/Kelechi Purity Ezennubia/
/Graduate research assistant /
/Department of Chemistry & Biochemistry /
/Baylor University /
/Clinger lab C161R/
/[email protected] <mailto:[email protected]>/
------------------------------------------------------------------------
*From:* Gerard Bricogne <[email protected]>
<mailto:[email protected]>
*Sent:* Wednesday, January 21, 2026 1:29:55 PM
*To:* Ezennubia, Purity <[email protected]>
<mailto:[email protected]>
*Cc:* [email protected] <mailto:[email protected]>
<[email protected]> <mailto:[email protected]>; Star Aniso
<[email protected]> <mailto:[email protected]>
*Subject:* Re: [ccp4bb] Anisotropy diffraction data user discussion
[You don't often get email from [email protected]
<mailto:[email protected]>. Learn why this is important at
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Dear Purity,
A personalised answer will be forthcoming but in the meantime,
since you are asking about the causes of anisotropy in diffraction
data, you would certainly benefit from reading the document at
https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fstaraniso.globalphasing.org%2Fanisotropy_about.html&data=05%7C02%7CPurity_Ezennubia1%40BAYLOR.EDU%7C27c5ce1c69ac44cb2d7108de592377a3%7C22d2fb35256a459bbcf4dc23d42dc0a4%7C0%7C0%7C639046206077920452%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=xuRCFinfgQSFb0Ysfa6tuJsli%2BMFm6PjnANxnYi6Eug%3D&reserved=0
<https://staraniso.globalphasing.org/anisotropy_about.html>
in which all technical terms used are explained in the accompanying
Glossary at
https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fstaraniso.globalphasing.org%2Fstaraniso_glossary.html&data=05%7C02%7CPurity_Ezennubia1%40BAYLOR.EDU%7C27c5ce1c69ac44cb2d7108de592377a3%7C22d2fb35256a459bbcf4dc23d42dc0a4%7C0%7C0%7C639046206077955875%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=JjXzau8KZJ1iSiWGEFN6lC6ZB0pyKu17GE3wiVBDG1s%3D&reserved=0
<https://staraniso.globalphasing.org/staraniso_glossary.html>
With best wishes,
Gerard.
--
On Wed, Jan 21, 2026 at 05:58:42PM +0000, Ezennubia, Purity wrote:
> Hello everyone,
>
> It's becoming almost a regular norm for my crystals to be
anisotropic when I look at the diffraction data. Its really unideal
for me because when the data is anisotropic my R-work and R-free
values are usually high when compared to some lucky data I got that
was not anisotropic.
>
> I would like to hear from other people in this forum what causes a
crystal to diffract anisotropically going to different resolution in
the hkl axis.
>
> Thank you,
> Purity
>
> Kelechi Purity Ezennubia
> Graduate research assistant
> Department of Chemistry & Biochemistry
> Baylor University
> Clinger lab C161R
> [email protected] <mailto:[email protected]>
>
>
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