Be careful with electron diffraction and apparent absence violations. It
is possible these weak spots are simply due to multiple scattering. If
so, you would see them relatively stronger with larger crystals,but much
weaker relative to the strong reflections when the crystal is smaller.
Do you?
-James Holton
MAD Scientist
On 5/27/2020 6:49 PM, Jessica Bruhn wrote:
Hello,
I am wondering if pseudosymmetry can cause weak reflections that mimic
the doubling of one unit cell axis' length. Has anyone seen something
like this before?
I am processing data from a small molecule sample collected with
electron diffraction from multiple crystals. For the b axis, it is not
clear if the length should be 10A or 20A. There are spots
with the correct spacing for b=20A, but every other spot seems weaker
than the spots along k if I choose b=10A (this extends beyond
(0,k,0)). I am unable to phase the b=20 data. I have solved this
structure in P1 with b=10 and found four molecules in the ASU and in
P212121 with b=10 resulting in one molecule in the ASU. In P1, three
of the four molecules adopt the same conformation, but the fourth
molecule is in an alternate conformation that causes only ~1/2 of the
molecule to be consistent with the first three. In P212121 I see
density for part of this alternative conformation, but the full
molecule in this alternate conformation cannot pack properly in
P212121. Based on these results and some orthogonal data, I think I
should refine the solution in P1 with b=10. Does it seem reasonable
that pseudosymmetry is causing these weak reflections along k hinting
at a doubling of the b axis?
Thanks in advance!
Best,
Jessica
--
Jessica Bruhn, Ph.D
Principal Scientist
NanoImaging Services, Inc.
4940 Carroll Canyon Road, Suite 115
San Diego, CA 92121
Phone #: (888) 675-8261
www.nanoimagingservices.com <http://www.nanoimagingservices.com>
------------------------------------------------------------------------
To unsubscribe from the CCP4BB list, click the following link:
https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1
########################################################################
To unsubscribe from the CCP4BB list, click the following link:
https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1
This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list
hosted by www.jiscmail.ac.uk, terms & conditions are available at
https://www.jiscmail.ac.uk/policyandsecurity/
