Phase Transitions of Non-Racemic Mixtures of Enantiomers: A Path towards Homochirality? Доклады на конференциях
Язык | Английский | ||||
---|---|---|---|---|---|
Тип доклада | Стендовый | ||||
Url доклада | http://www.origins2011.univ-montp2.fr/PublSchedAbstr/P6.html | ||||
Конференция |
ISSOL and Bioastronomy Joint International Conference 03-08 июл. 2011 , Montpellier |
||||
Авторы |
|
||||
Организации |
|
Реферат:
Homochirality of biologically important molecules such as amino acids and sugars is a prerequisite for the
origin of life. There are different forces or mechanisms in the Universe to trigger off the primary imbalance
in the enantiomer ratio: circular polarized light, magnetic field in the combination with linear polarized
irradiation, influence of parity violation forces or chiral symmetry breaking via asymmetric autocatalysis
(Guijarro and Yus 2009). However we do not know how the presumably racemic prebiotic world has
evolved to the present life which is homochiral.
Recently an astrophysically-relevant mechanism for amino acid enantiomer enrichment via sublimation has
been proposed (Fletcher et al. 2007). In addition to asymmetric autocatalysis (Frank’s model) and after the
works of Blackmond (Blackmond 2010 and references herein), it seems that the phase transitions of nonracemic
mixtures of enantiomers are one of the most likely mechanism for the homochirogenesis.
Nevertheless, the enantioenrichment via sublimation known over then 50 years lacks of systematic studies
and the proposed sublimation of a mixture with a eutectic composition cannot give answer to many
experiments maybe because any equilibrium is reached in most of the experimental conditions.
Several discrepant explanations have been discussed in the literature like the different speeds of sublimation
of a racemate and an enantiopure compound (Han et al. 2011 and reference herein) or the distinction in
homo/hetero-chiral interaction and “magic number” clusters (octamers) of amino acids (Perry et al. 2007).
We have investigated studies on the partial sublimation of enantioenriched mixtures of natural amino acids
(leucine, alanine, valine) with a continuous condensation of the gas phase in a standard sublimation
apparatus. Since the theory on the formation of a eutectic is independent on the composition of the starting
mixture, our experiments show different results (Bellec and Guillemin 2010a,b):
- with racemate and enantiopure mixtures, the ee values of sublimate are relatively identical that shows a
control of the sublimation in the gas phase independently of the ee of the starting material.
- on the contrary, in the absence of DL solid phase (L + D mixtures), weak ee values of sublimates were
obtained.
- moreover, in the case of independent sublimations of DL and L solids, the joined sublimates give a ee
similar to the one obtained starting from the mixed sample. This results shows that the formation of a
eutectic in the gas phase is not demonstrated even when similar ee are obtained independently of the ee of
the starting mixtures.
Some explanations of this behavior will be proposed and the relevance of these studies to the Prebiotic Earth
will be discussed.
References
Bellec A, Guillemin JC (2010a) A simple explanation of the enhancement or depletion of the enantiomeric excess in the
partial sublimation of enantiomerically enriched amino acids, Chem Commun, 46:1482–1484.
Bellec A, Guillemin JC (2010b) Attempts to explain the self-disproportionation observed in the partial sublimation of
enantiomerically enriched carboxylic acids, J Fluor Chem, 131:545–548.
Blackmond DG (2010) The Origin of Biological Homochirality, Cold Spring Harb Perspect Biol, 2:a002147.
Fletcher SP, Jagt RBC, Feringa BL (2007) An austrophysiclly-relevant mechanism for amino acid enantiomer
enrichment, Chem Commun, 2578–2580.
Guijarro A, Yus M (2009) The Origin of Chirality in the Molecules of Life: A Revision from Awareness to the Current
Theories and Perspectives of this Unsolved Problem, RSC Publishing, Cambridge.
Han J, Shan Z, Sorochinsky E, Soloshonok VA (2011) Self-Disproportionation of Enantiomers via Sublimation; New
and Truly Green Dimension in Optical Purification, Cur Org Synth, in print.
Perry RH, Wu C, Neufliu M, Cooks RG (2007) Serine sublimes with spontaneous chiral amplification, Chem Commun,
1071–1073.
Библиографическая ссылка:
Tarasevych A.V.
, Bellec A.
, Guillemin J.
Phase Transitions of Non-Racemic Mixtures of Enantiomers: A Path towards Homochirality?
ISSOL and Bioastronomy Joint International Conference 03-08 Jul 2011
Phase Transitions of Non-Racemic Mixtures of Enantiomers: A Path towards Homochirality?
ISSOL and Bioastronomy Joint International Conference 03-08 Jul 2011