Not an expert on integration at all, but is this true for mosaic
crystals when spots overlap rather messily?
Eleanor
George M. Sheldrick wrote:
Since processing non-merohedrally twinned crystals became routine in
small-molecule crystallography, the number of such twins has increased
dramatically. The data are often as good as from normal crystals and
there is the advantage of getting a higher redundancy and greater
completeness by collecting data from two or more crystals in different
orientations at the same time! At the moment non-meroderally twinned
protein crystals are often thrown away (e.g. because they don't index
with programs designed for untwinned crystals) or one tries not to
notice that the other components are there. I predict that when
MOSFLM, XDS, HKL2000 etc. are able to index and integrate non-merodedral
twins, they will suddenly become much more common for macromolecules
too. At least there is no problem indexing and integrating merohedral
twins, and some refinement programs can handle them, so most of the
discussion in this list has been about merohedral twins so far.
George
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-2582
On Fri, 31 Aug 2007, Ian Tickle wrote:
In the past twinned crystals must have been much more frequent than
published twinned structures because the traditional reaction of
crystallographers to twinning has been either to find a way of
inhibiting it or chucking the crystals in the bin and finding a
non-twinned form. But I guess that's changing now with better software
and we're becoming more adventurous - maybe that's why we're hearing
about more twinned crystals now.
-- Ian
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Jacob Keller
Sent: 31 August 2007 18:32
To: CCP4BB@JISCMAIL.AC.UK
Subject: How many twinned crystals?
Since I joined this list, I have seen many many issues with
twinned structures, but have never seen
any personally. Granted, problems with twinning induce people
to write to the list, making them
seem more prominent, but does anyone have an idea what
percent of crystals are twinned, or know of
a ref about this? I always thought it was an anomaly, but....
All the best,
Jacob Keller
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