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Possible orginis of amino-acid homochirality

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posted on Oct, 3 2006 @ 10:27 AM
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I found this one in a french magazine (Science et Vie) but I also search for the orginal papers. I've found only one of them, the other being around 30 or 40$....
But lets see what they are saying:
This first one is in english


An international science team lead by Franco-German researchers [...] traced the
homochirality of life back to space from where elementary bricks of life such as amino-acids are thought to be coming from.

Uwe Meierhenrich [...], Laurent Nahon [...], and André Brack [...] propose that the origin of life homochirality would be due to irradiation of symmetric (racemic) amino acids in space, leading to an asymmetric mixture of amino-acids. In order to test this hypothesis, a racemic mixture of a simple amino acid, leucine – encountered for instance in human body or in corn - was irradiated with circularly-polarized radiation in the far UV range. For the first time, a solid state amino acid was exposed in the laboratory to left- or right-circularly polarized synchrotron radiation, to simulate astrophysical conditions.

The application of a new analytical technique enabled the authors to identify a selective deg-radation of left-handed leucine exposed to right-handed circularly polarized radiation, leading to a 2.6% enantiomeric excess of the amino acid leucine, starting form a racemic mixture.


The second one is in french but I'll translate the basic ideeas. (you could go to altavista's babelfish for a translator)
delage.presse.fre... e.fr/wordpress/wp-content/homochiralit_SV.pdf#search=%22robert%20pascal%20auguste%20commeyras%22



...fait, un tel rayonnement asymétrique a été repéré en 1998 par le télescope anglo-australien AAT en provenance de la nébuleuse d’Orion, véritable pouponnière d’étoiles: sa lumière est polarisée circulairement.

In 1998, the AAT telescope discovered that light from Orion nebula is polarised ....If the initial light from stars is not polarised, complex interstellar processes of diffusion or reflection are capable of transforming it into a circular polarised one.



Si un rayonnement polarisé est bien à l’origine de l’asymétrie moléculaire, une amplification du phénomène a également été nécessaire.

Although the polarised light is the origin of the molecular asymetry, an amplification process is needed.



“Durant les phases sèches, à marée descendante, l’atmosphère encourage la formation d’acides aminés prêts à se combiner [...]Mais cette transformation acidifie le milieu, ce qui empêche les acides aminés de se lier entre eux. Il faut attendre la marée montante pour que l’acidité chute et favorise la synthèse des peptides.”

During the dry phases at low tide, the atmosphere encourages the formation of amino acids ready to combine themselves [...], but this transformation increases the acidity of the mediun wich in turn prohibits the formation of amino-acid chains. We have to wait for the high tide so as the acidity to fall and allow again peptide syntesis.



Tout d’abord, lors de la formation d’une petite chaîne d’acides aminés, le dernier maillon a tendance à réagir de préférence avec une molécule de même configuration, formant ainsi des chaînes composées exclusivement soit de molécules G, soit de molécules D. Mais, lorsque le réservoir de molécules n’est plus capable de fournir la configuration qui convient, ce sont deux acides aminés de type différent qui se lient. Ce qui enclenche un nouveau type de réaction chimique: “Le dernier acide aminé qui s’accroche peut changer sa configuration en fonction de l’acide aminé précédent”

During the formation of a amino-acid chain the last piece in the chain has a tendency to react with a molecule of the same type, forming in this way chains exclusively of the same molecular type (L or R). When the source of the molecules can no longer provide the right configuration, the chain continues with the combination of the two types. This leads to a new reaction: The amino-acid that attached last can change its configuration according to the preceding amino-acid



“Des systèmes prébiotiques réels formés de dérivés d’acides aminés sont capables d’atteindre spontanément en quelques siècles un état stable énantiomériquement
pur, c’est-à-dire formé d’acides aminés de même configuration”

Real prebiotic systems formed from derived amino-acids can acheive spontaneously in a few hundred years a steady state (I don't know how to translate in english "énantiomériquement pur"), that is formed only of amino-acids of the same configuration.

So the ideea is that molecular asymetry originates in space (because of the polarised light) and then the tides amplify this asymmetry (this means that we need our moon)




posted on Oct, 3 2006 @ 11:32 AM
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Hi Apass,

There's actually a decent amount of stuff about this already out there. Here[/ur l]
is an interesting paper that discusses cyclical patterns of polymerization, epimerization, and hydrolysis.

Another popular theory is stereoselective adsorption onto surfaces. For a decent description, see Klabunowskii, E. and Thiemann, W.: 2000, The Role of Quartz in the Origin of Optical Activity on Earth, Origins Life Evol. Biosphere 30, 431–434.

For a decent overall review see this ref

For a description of mechanism involving spontaneous crystallization of a single enantiomer, see this paper

Lucas et al. have a decent description of a mechanism that assumes the formation of an enantiomeric excess by polarized light.

But in any case... I just wanted to point out that a lot of the basics of what you've posted here have been floating around in one form or another for quite sometime... more-or-less since the discovery of Optical Activity.


[edit on 3-10-2006 by mattison0922]



posted on Oct, 3 2006 @ 03:19 PM
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Yes, they have been floating for a while, but it's cool to see that there are natural processes that can produce that (and quite rapidly), and no need for a supernatural being to create them



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