The effects of circularly polarized light on amino acid enantiomers produced by the UV irradiation of interstellar ice analogs

Abstract

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 (rightpolarization 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.

The Photochemistry of Pyrimidine in Realistic Astrophysical Ices and the Production of Nucleobases

“…Its formation mechanism requires the presence of [(XCOO − )(NH 4 + )] salts at room temperature (Muñoz Caro & Schutte 2003), where XCOO − denotes the anionic (carboxylate) form of a carboxylic acid. Any or all of the carboxylic acids identified in our residues could play the role of the carboxylate XCOO − , while the ammonium cation NH 4 + is known to be present in residues resulting from the photoprocessing of NH 3 -containing ices (Bernstein et al 1995;Muñoz Caro & Schutte 2003;Nuevo et al 2006). This suggests that HMT may be formed from several precursors.…”

Irradiation of nitrogen-rich ices by swift heavy ions

“…However, residues both obtained at room temperature (e.g. Muñoz Caro et al 2004;Nuevo et al 2006) and exposed directly to cosmic radiation in space (e.g. EURECA experiment, Greenberg et al 1995) do not match the residues of the IOM from meteorites.…”

Photochirogenesis: Photochemical Models on the Origin of Biomolecular Homochirality

“…After the hydrolysis of the residues several amino acids could be detected using reversed-phase liquid chromatography; for example, glycine, alanine, serine, aspartic acid, α-aminobutyric acid, valine, and β-alanine. For one chiral amino acid-alanine-an enantiomeric excess of +0.44% by r-CPSR and -0.65% by l-CPSR was reported with a standard deviation of ±0.31 and ±0.23 (1 respectively A second irradiation experiment of interstellar ice analogs with VUV-CPSR was reported by Nuevo et al [113,114]. The two interstellar gaseous mixtures containing water, methanol, and ammonia were directly irradiated with either left-or right-circularly polarized synchrotron light, for 56 h and 43 h, respectively.…”