rna at -40 to -80 ?

Jim Owens jow at helix.nih.gov
Tue Jun 8 16:41:30 EST 1993

In article <1993Jun8.185521.3689 at gserv1.dl.ac.uk> ,
suter at VAX.MPIZ-KOELN.mpg.d400.de writes:
>why is it that everybody wants to store there rna at -80 ? in my opinion,
>diffusion is reduced to zero at -20, and therefore rnases won't be very
active at
>that temperature. 
>i store all nucleic acids at -20: i have never noticed any drop in
>repeated freezing and thawing will damage nucleic acids much more; that
>is because of the presence of nucleases, but also because of the physical
>forces and chemically instability during these two processes.

I suppose if you use a NON-frost free freezer that no one opens for more
than 10-15 seconds at a time, samples will remain entirely frozen.  In
our lab people frequently leave the door open for a minute or two at a
time while searching for tubes that had been moved around.  Not
everything is kept in insulated containers, and so samples may begin to
thaw when the door is kept open for a long time.

For nor additional charge here is something else to think about:

There was an article in, I think, the J. of Physical Chemistry around
1970.  The authors were examining the properties of aqueous solutions as
they were frozen by different methods.  They found that, except for one
method, pH dropped in the remaining liquid phase.  The interpretation was
that hydronium ions diffuse faster than ice formed from the surface to
the center.  The drop in pH was the same when frozen in cold air (just
put in freezer) or in dry ice.  Drop in pH was less pronounced when
frozen in acetone with dry ice in it.  There was no detectable drop in pH
when frozen in liquid nitrogen.  My advisor felt this vindicated his
method of storing his enzyme (phosphoglucomutase) by freezing dropwise in
liquid nitrogen.  It had the advantage that he only had to thaw out
enough beads for the experiment without having to thaw the whole

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