Richard
A paper from some time back which describes this is
Increased resolution data from a large unit cell crystal collected at a
third-generation synchrotron X-ray source Authors: W R Wikoff, W
Schildkamp, J E Johnson Acta crystallographica. Section D, 56(Pt
7):890-3.
By focusing the bending
Hi
Yes good data with a micron size beam but, in this case, the path length
was 20- 30 micron.
I presume one would like a complete data set rather than a single or a
few processable images. If the latter, then in principle anything is
possible provided background is minimised and a low dose
I'm not sure where this rumor got started that the intensity reflected
from a mosaic block or otherwise perfect lattice is proportional to the
square of the number of unit cells
Of course it is proportional to the square of the number of unit cells. With
more cells, more photons are scattered.
and undulator parameters to confirm this
impression. Perhaps James Holton will chime in again?
Ethan
From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of Nave,
C (Colin)
Sent: Thursday, January 29, 2009 10:14 AM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb
Hi
Nice of Jacob to mention the paper below but I don't think it is
relevant to these patterns (well it might not be relevant to anything!).
I think James has given the most likely explanation. The AB type
stacking disorder he mentioned is similar to the type in the paper I
referenced. I think
Bernard
I guess this came from
Aren't detwinning methods appropriate only in the case of true twin
domains which are larger than the X-ray photon correlation length in
order for the assumption to be valid that |F|^2 from each domain can be
summed? This wouldn't give rise to the apparent 'diffuse
Margriet
This looks like stacking or shift disorder which can occur when perfect
3 dimensional order breaks down. For example one can have a situation
where the lattice is preserved in 2 dimensions but the planes can slide
with respect to one another destroying the order in the 3rd dimension,
Jacob
Traditional mosaic spread (ordered mosaic blocks imperfectly aligned with
respect to one another) gives spherical caps in reciprocal space. These would
appear as arcs on a single crystal rotation photograph. If anisotropic, the
arcs would be more extensive in some directions. The
Yes - reading early articles is always illuminating. Over the past few
years I have looked at Charles Galton Darwin's (yes a relation) 1914
paper and Arthur Compton's in order to understand what is really happens
to these x-rays. However, as Bayes work is being highlighted, I can't
resist giving
Harry
Can you clarify why you get a substantially better structure at cryo
temperatures
e.g higher intensity at high resolution due to reduction in B factors,
reduction in radiation damage, anything else?
Colin
-Original Message-
From: CCP4 bulletin board
Richard
Not sure about chains but mutual hydrogen bonded networks (you mention
networks) between protein, water (and ligand) surely occur. I think most
self respecting waters would try and form more then two hydrogen bonds
(rather then just be part of a chain) though one might not see all the
Andy
I guess it all depends on what temperature you mean by cryocooling. I
was not aware at the Low et. al. paper - interesting early work. Low
et. al. did not study reduction in radiation damage below -130C as they
noticed a large increase in mosaicity occurring so abandoned this
method. They
Hi
Just for completeness (seeing as we are discussing scattering factors
and radiation damage) there is an increased susceptibility to primary
damage for sulphur due to the increased absorption which follows f'',
tabulated for example in
http://henke.lbl.gov/optical_constants/asf.html. The x-ray
Dear all
If you simply want to see if Ca and Mn are in your sample, you could
also use x-ray fluorescence excited by the x-rays on the beamline used
to collect the diffraction data. It doesn't need the energy set to be at
each absorption edge, it just has to be above the edges. One then sets
the
The latest Acta D shows the social consensus is sometimes lacking even (or
especially) among very experienced and able crystallographers.
Experimental determination of optimal root-mean-square deviations of
macromolecular bond lengths and angles from their restrained ideal values
Ian J.
Fifth International Workshop on X-ray Radiation Damage to Biological
Crystalline Samples :
Registration and Abstract submission is now open at:
http://user.web.psi.ch/rd5/
for the Fifth International Workshop on X-ray Radiation Damage to
Biological Crystalline Samples which will be held at
Richard
I think the sharp spot is just small angle scattering (e.g. from domain
boundaries) resulting from the beam hitting one of the defining
apertures in your collimation system. If you ray trace the beam from the
last defining aperture, through the guard aperture then to the detector
you
To bathers and non bathers
This is an interesting discussion with several relevant points. I agree
that, if small beams can pick up the best bits of the crystal that is a
very good reason for using them. The background arguments can be
relevant and having the beam size at the detector matched
Note the density of air is approximately 1000 times less than a protein
crystal. The total scatter for a beam going through a 50 micron thick
crystal will be similar to that from 50mm air. Most beamlines will have
a path length less than this but nevertheless the air scatter will be
significant
The Fifth International Workshop on X-ray Radiation Damage to Biological
Crystalline Samples will be held at the Swiss Light Source from 13:00
March 3rd to 13:00 March 5th 2008.
This series of workshops was originally concerned with the effects of
radiation damage during investigation of protein
Good summary as expected from James.
Have you ever heard of photon-photon scattering?
Well yes! See for example
http://2physics.blogspot.com/2006/03/photon-photon-scattering.html
which says according to Quantum Electrodynamics (QED), particles can still be
created in this emptiness of vacuum
Apologies for the late posting (been away). Interesting question from James and
an interesting answer from Ian!
There should be a radiation pressure effect here resulting in a transfer of
energy and momentum to the sample. The effect is very small (the term includes
flux density divided by
Seems to be a general issue.
Read the editorial in Nature 10 May 2007 Volume 447 Number 7141, pp116.
Under the microscope - The use of 'black box' techniques carries risks.
Colin
-Original Message-
From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] Behalf Of Flip Hoedemaeker
Sent: 10 May
Alejandro,
As others have said, the most likely explanation is the attenuation of the air
scatter by the sample holder. There is no sharp edge to the shadow which
indicates the source of scatter is along an extended path. Ed Berry pointed out
that he didn't see spots in the shadow. This might
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