Re: [ccp4bb] Twinning: P43 apparently P42212

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Subject: Re: Twinning: P43 apparently P42212
From: Roberto Steiner roberto {- dot -} steiner {- at -} KCL {- dot -} AC {- dot -} UK
Date: 2007-10-04

Hi Charlie,

Maybe it is not P43.
What about your real symmetry being lower than tetragonal? (For
example, twinning in an orthorhombic space group with a more or less
equal to b)
What about the h00 reflections? Any trend there?
Signs of pseudo-translation?

Roberto

On 4 Oct 2007, at 04:40, Charlie Bond wrote:

> Hi All,
> I'm trying to understand what's going on in one of our crystals:
> Merging and sysabs clearly indicate P42212. Looking at the
> intensities, 00l=2n are absolutely clearly present and are not
> systematically weaker than 004n.
>
> Intensity stats show clear signs of twinning. The structure can be
> solved and refined in P43212 (and not in any P4,P41,P42
> spacegroup), although refining in P43 with twice as many molecules
> and a h,-k,-l twin fraction of 0.48 produces a better R-factor
> (0.24 vs 0.30 - still high as I'd expect 0.1-0.15 based on other
> crystal forms).
>
> What I cannot understand is how we see 00l=2n reflections for a
> structure that is apparently P43.
>
> Any explanation of this phenomenon and why it may contribute to the
> R-factor not going down despite excellent, informative, atomic
> electron density would be gratefully received.
>
> Cheers,
> Charlie
> --
> Charlie Bond
> Professorial Fellow
> University of Western Australia
> School of Biomedical, Biomolecular and Chemical Sciences
> M310
> 35 Stirling Highway
> Crawley WA 6009
> Australia
> Charles.Bond@uwa.edu.au
> +61 8 6488 4406

---
Dr. Roberto Steiner
Randall Division of Cell and Molecular Biophysics
New Hunt's House
King's College London
Guy's Campus
London, SE1 1UL
Phone +44 (0)20-7848-8216
Fax +44 (0)20-7848-6435
e-mail roberto.steiner@kcl.ac.uk

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CCP4bb <-- 2007 <-- October 2007 <-- 04 October 2007

Previous message:
Subject: Open position at the Institute for Biochemistry (Advt. Nr. 07/B51)
From: Rajesh Kumar Singh singhrk {- at -} UNI-GREIFSWALD {- dot -} DE
Date: 2007-10-04