[ccp4bb] Twinning: P43 apparently P42212

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

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Subject: Beam Time Available @X6A
From: "Stojanoff, Vivian" stojanof {- at -} BNL {- dot -} GOV
Date: 2007-10-03

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From: Eckhard Hofmann eckhard {- dot -} hofmann {- at -} BPH {- dot -} RUHR-UNI-BOCHUM {- dot -} DE
Date: 2007-10-04

Subject: Twinning: P43 apparently P42212
From: Charlie Bond Charles {- dot -} Bond {- at -} UWA {- dot -} EDU {- dot -} AU
Date: 2007-10-03

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

CCP4bb navigation

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

Previous message:
Subject: Beam Time Available @X6A
From: "Stojanoff, Vivian" stojanof {- at -} BNL {- dot -} GOV
Date: 2007-10-03

Next message:
Subject: Summary torsion restraints in refmac
From: Eckhard Hofmann eckhard {- dot -} hofmann {- at -} BPH {- dot -} RUHR-UNI-BOCHUM {- dot -} DE
Date: 2007-10-04