A nice review of "cryosalts" is available here:
http://dx.doi.org/10.1107/S0907444900007587
For crystals that "don't seem to survive paratone-N", I recommend using
a microscope equipped with a polarizer. The refractive index of
paratone-N is much closer to that of protein crystals than that of
water, so one can easily be fooled into thinking the crystal "dissolved"
when what you are actually seeing is the "disappearing pyrex effect":
https://sites.google.com/site/rooseveltphysics/pyrexandveggieoil.jpg
A nice example of the "disappearing crystal" due to refractive index
matching is also apparent in figure 1d of:
http://dx.doi.org/10.1107/S0021889809023553
Sadly, I think many crystallographers have abandoned my favorite oil
because they didn't know there crystal was actually still intact and happy!
As for salt crystals growing while you are trying to harvest: yes, this
is annoying. This is why I usually bury my drops in paratone-N oil
immediately after opening them. It slows down evaporation
tremendously. If you don't like working through oil, then you must
either work very quickly or find a way to humidify the atmosphere around
your drop after you open it. You can spend an arbitrary amount of money
on "wet air machines" these days, but if you happen to know what your
reservoir contains (you should), and you don't mind making up a liter or
two of it, then all you need to do is bubble air or N2 through a big vat
of your "reservoir solution" and then direct that bubbled-off gas
through a pipe at your drop. I imagine this would be a great way to
deal with alcohol-based conditions as well (provided you had adequate
ventilation).
-James Holton
MAD Scientist
On 7/10/2012 9:28 AM, m zhang wrote:
regaentDear All,
I am sure this question was discussed before. But I am wondering if
anyone got the same experience as I do.
I got a crystal out of condition with 1M KCl, 1.4M Ammonium sulfate at
pH7. I tried to use glycerol, ethylene glycol, 25% sucrose, paraton-N
oil, or ammonium sulfate itself: The problem is that all the cryo plus
original reagents in the reservoir precipitate the salts out. And more
serious problem is because of high salt in the condition, while I am
trying to loop the crystal, both the drop and cryoprotectant drop form
salt crystals (not sure it is KCl or ammonia sulfate) significantly
and very quickly, that cause my crystal dissolved. My crystal doesn't
seem to survive paraton-N oil. Does anyone here have similiar case?
any suggestion will be appreciated.
Thanks,
Min
