From: jeff davis (jrd1415@yahoo.com)
Date: Mon May 27 2002 - 21:43:34 MDT
Extropes,
--- "Robert J. Bradbury" <bradbury@aeiveos.com> wrote:
>
> This Nature article (subscription required):
>
> Berglund, G. I., et al
> "The catalytic pathway of horseradish peroxidase at
> high resolution"
> Nature 417:463-468 (2002)
>
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v417/n6887/full/417463a_fs.html
>
> contains the following statement:
>
> "Electron transfer reactions and proton-coupled
> electron transfer
> processes readily occur at cryogenic temperatures
> in protein
> crystals along with small-scale movements of
> ligands and side chains."
>
> I was under the impression that when frozen to LN2
> temperatures
> all chemistry came ceased. Is this inaccurate?
>
> Any feelings about what impact this might have on
> cryonic suspendees?
>
> Robert
All chemistry, yes, almost. Standard Arhennius
slowdown. But all motion? No, of course not. And in
particular, motion of the sub-atomic constituents of
atoms, very of course not.
Exactly what is meant by "electron transfer reactions"
and "proton-coupled electron transfer"? Electrons are
in motion at all temperatures. For them to jump from
one molecule to another, or from one region of the
same molecule to another seems plausible. They are in
some sense--because of their inherent mobility and
'orbital' motion something akin to a gas (a charged
gas; a plasma). But what does that mean for the
chemical stability or thermal stiffness of whole
molecules or bulk assemblages of molecules at LN2
temperatures? Very little, I think.
Similarly, constituent atoms of any molecule are also
in constant motion--in solids that would be in-place
vibration--at any temperature above absolute zero. So
how is this vibrational motion different from the
'small-scale movements of ligands and side chains'
mentioned above? Such movements--and I have to guess
a bit here, because I don't have access to the full
paper--could be slight shifts in position or shape due
to altered charge distribution, and not a chemical
change at all.
Barring magic physics, you can't get around
thermodynamics, I reckon.
Then, of course, there's the repair that cryonic
suspendees will require in any case. So what's a
teeny tiny little bit more.
Best, Jeff Davis
"My guess is that people don't yet realize how
"handy" an indefinite lifespan will be."
J Corbally
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