Volume 457, Number 3, October III 2006
|Page(s)||741 - 751|
|Published online||12 September 2006|
The effects of circularly polarized light on amino acid enantiomers produced by the UV irradiation of interstellar ice analogs
Institut d'Astrophysique Spatiale (IAS), Bât. 121, Université Paris-Sud, 91405 Orsay Cedex, France
2 Graduate Institute of Astronomy, National Central University, No. 300, Jhongda Rd, Jhongli City, Taoyuan County 32049, Taiwan e-mail: firstname.lastname@example.org
3 Universität Bremen, Physikalische Chemie NW2, FB02, Leobener Str., 28359 Bremen, Germany
4 Laboratoire de Chimie Bioorganique, UMR 6001 CNRS, Université de Nice-Sophia Antipolis, Faculté des Sciences, Parc Valrose, 06108 Nice Cedex 2, France
5 Centro de Astrobiología, INTA-CSIC, carretera de Ajalvir, km 4, Torrejón de Ardoz, 28850 Madrid, Spain
6 Institut de Biochimie et de Biophysique Moléculaire et Cellulaire, Bât. 430, Université Paris-Sud, 91405 Orsay Cedex, France
7 Laboratoire pour l'Utilisation du Rayonnement Electromagnétique (LURE), Bât. 209D, Université Paris-Sud, 91405 Orsay Cedex, France
8 CEA/DRECAM/SPAM and LFP/CNRS URA 2453, Bât. 522, CE de Saclay, 91191 Gif-sur-Yvette Cedex, France
9 SOLEIL, L'Orme des Merisiers, St Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France
Accepted: 24 May 2006
Aims.Two irradiation experiments on interstellar ice analogs at 80 K under interstellar-like conditions were performed with the LURE SU5 synchrotron beamline to assess, for the first time, the photochemical effect of circularly polarized ultraviolet light (UV CPL) at 167 nm (7.45 eV) with right and left polarizations on such ice mixtures.
Methods.This effect was measured by determining the enantiomeric excesses (e.e.s) for two amino acids formed in the solid organic residues produced during the subsequent warm-up of the irradiated samples to room temperature: alanine, the most abundant chiral proteinaceous amino acid produced (both polarizations) and 2,3-diaminopropanoic acid (DAP), a non-proteinaceous amino acid (right-polarization experiment). These excesses were compared to those measured for the same amino acids produced after unpolarized UV irradiation of the same ice mixtures (expected to be zero), in order to determine the contribution of CPL only. A careful estimate of all the associated uncertainties (statistical and systematic errors) was also developed.
Results.It appears that the enantiomeric photochemical effect at this wavelength is weak, since both alanine and DAP e.e.s were found to be small, at most of the order of 1% in absolute values, and tends to be inconclusive since the effects obtained for both amino acids and both polarizations are not those expected. In light of these results, the hypothesis that CPL may be one source responsible for the e.e.s measured for such amino acids in some meteorites and, more generally, that CPL may be directly related to the origin of biomolecular homochirality on Earth is discussed.
Key words: molecular processes / polarization / methods: data analysis / methods: laboratory / ISM: molecules / infrared: ISM
© ESO, 2006
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