This reminded me of a haunted beamline that removed crystals from
the loop.
You'd loop the crystals up nicely, block the stream, transfer the
crystal fast to the goniometer head, unblock the stream then look
in the microscope - no crystal! After a few tries (and head
scratching) the culprit was discovered to be a Hampton strong
Magnetic Base that flipped the crystals out of the loops when you
were mounting the pin. It was so strong that the pin 'clicked'
onto the magnet. Interestingly, looking below the goniometer head,
there was a whole graveyard of dead crystals lying there - many
other users had the same problem. The magnet was replaced with a
Hampton light magnetic base and the problem went away completely.
With the concurrence of the beamline scientist the light base
remained with the beamline for many years until a recent upgrade
when they replaced the user with a guy called Sam.
Of course, no names and no synchrotrons will be revealed ;)
Seriously though, 10 to 20 minutes until the sample stops moving
sounds very ominous. I may have misunderstood, but it sounds like
you are warming the crystals for data collection after
cryomounting them? Once cooled they should remain that way.
Cheers,
Eddie
Edward Snell Ph.D.
Assistant Prof. Department of Structural Biology, SUNY Buffalo,
Hauptman-Woodward Medical Research Institute
700 Ellicott Street, Buffalo, NY 14203-1102
Phone: (716) 898 8631 Fax: (716) 898 8660
Email: [EMAIL PROTECTED] Telepathy: 42.2 GHz
Heisenberg was probably here!
-----Original Message-----
From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf
Of Kevin Jude
Sent: Monday, July 21, 2008 2:20 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] Spooky, moving crystals
I've seen haunted crystals before - the culprit was indeed with the
mounting of the pins in their bases (I was re-using some pins and
apparently the adhesive had cracked or otherwise failed).
Fortunately I
never leave home without a tube of Duco cement and was able to
correct
the problem in situ.
kmj
Mark J. van Raaij wrote:
Dear all,
in a recent synchrotron trip we had a problem with our crystals
moving
after mounting them onto the goniometer, in some cases they moved
out of
the beam and even out of the zoomed camera picture - it seemed
the pins,
upon equilibrating to room temperature, extended. It happened with
pre-mounted litho-loops only, not with pre-mounted mitegen loops
on the
same trip, so one possible cause is different metal allows used
in the
pins, somehow the mitegen ones being more suitable.
We used two-component glue to stick the pins into the metal bases
(Spine), so that might be another possible culprit. Perhaps we
did not
allow sufficient time for the glue to react before freezing into
liquid
N2 and it continued its reaction upon thawing, somehow pushing
the pin a
bit out of the base. In this case the difference between
litholoops and
mitegen loops may have been the thickness of the pins, the latter
somehow allowing expansion of the glue along the sides, the
former not.
In any case, I am wondering if any of you has seen this before,
so we
know how to avoid it in the future.
In some cases, it took 10-20 min. for the crystal to stop moving,
which,
with the current data collection speed and robotic mounting, is
significant. Fortunately, it did not affect our trip too much, as
we has
sufficient time in the end.
Greetings,
Mark
Mark J. van Raaij
Dpto de Bioquímica, Facultad de Farmacia
Universidad de Santiago
15782 Santiago de Compostela
Spain
http://web.usc.es/~vanraaij/
