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Old January 21st 18, 04:43 PM posted to sci.astro.research
Martin Brown[_3_]
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Default Astronomy and Biology

[[Mod. note -- My apologies for the delay in processing this article;
which arrived in my moderation inbox on 2018-01-19. -- jt]]

On 17/01/2018 22:59, Steve Willner wrote:
In article ,
Martin Brown writes:
I thought there was a project underway to send a small stable isotope
mass spectrometer to look for any variation of deltaC13 or deltaS34 in
the rocks that would be indicative of life. Life preferentially
concentrates the lighter isotopes making inorganic materials have a
higher concentration of the heavier isotopes. eg.

https://ntrs.nasa.gov/archive/nasa/c...9890016972.pdf


Distinguishing between life and abiotic chemistry is the reason for
doing _chiral_ labeled release. Life should prefer one enantiomer
over the other, while abiotic processes should show little or no
preference.


Not sure you need to use chiral labelled reagents.

You could feed the critters a racemic mixture and then measure any
change in the angle of rotation of plane polarised light if there was
any difference in the rate of reaction for the two forms.

I suspect there may well be some abiotic reactions on clay surfaces that
do show a preference for handedness if that is how life got started.

Anybody know when or why 'stereoisomers' became 'enantiomers'?

They were called D and L optical isomers first because of the effect
their solutions had on rotating plane polarised light. Essentially
materials with the same chemistry but different effect on light.

Some crystals, sugars and naturally occurring amino acids solutions
first observed to do this in 1813 by Biot and explained in 1874 by Hoff
as being due to an asymmetric tetrahedral carbon atom in the molecule.

I think the preferred names are down to IUPAC.

Enantiomers are strictly non superposable mirror images of each other
whilst (dia)stereoisomers can include other things as well.

http://goldbook.iupac.org/html/D/D01679.html

Still chiral molecules but not related as exact mirror images.

--
Regards,
Martin Brown