Possible survival of simple amino acids to X-ray irradiation in ice: the case of glycine

Abstract

Context. Glycine, the simplest of amino acids, has been found in several carbonaceous meteorites collected on Earth, though its presence in the interstellar medium (ISM) has never been confirmed as of today. It is now considered that its synthesis took place in the icy mantles of interstellar grains, but it remains unclear how glycine, once synthesized and trapped in interplanetary particles, survives during the transfer to the Earth. Aims. Assuming that glycine was effectively formed in the ice, we address the question of its resistance to a solar-like radiation field and look for the possible molecular remnants that would be useful tracers of its former existence. Methods. The search was conducted using an interdisciplinary approach that mixes, on the one hand, irradiations in ultra high vacuum at 30 K on the TEMPO beam line of the synchrotron SOLEIL, simultaneously with near-edge X-ray absorption spectroscopy (NEXAFS) measurements, and on the other hand, quantum calculations to determine the energetics of the fragmentations and the relative stability of the different byproducts. The last points were addressed by means of density functional theory (DFT) simulations followed by high-level post Hartree-Fock calculations when more accurate relative energies were necessary. The constraints of an icy environment deserved special attention and the ice was modeled by a polarizable continuum medium that relies on the dielectric constant of water ice at 10-50 K. Results. Destruction of glycine is observed in the first seconds of irradiation, and carbon dioxide (CO 2 ) and methylamine (CH 3 NH 2 ) are formed. Carbon monoxide (CO), methanimine (CH 2 NH) and hydrogen cyanide (HCN) are also produced in secondary reactions. The amino acid destruction is the same for pure glycine and glycine in ice, indicating that the OH radicals released by the water matrix is barely involved in the photolytic process; however, these radicals are involved in the production of the secondary byproducts through dehydrogenation reactions as shown by ab initio quantum chemical simulation presented in this article along with the experimental results. Conclusions. The experiments show that glycine is only partially destroyed. Its abundance is found to stay at a level of ∼30% of the initial concentration, for an irradiation dose equivalent to three years of solar radiation (at a distance of one astronomical unit). This result supports the hypothesis that, if trapped in protected icy environments and/or in the interior of interplanetary particles and meteorites, glycine may partly resist the radiation field to which it is submitted and, accordingly, survives its journey to the Earth.

Ultraviolet irradiation of glycine in presence of pyrite as a model of chemical evolution: an experimental and molecular modelling approach

“…The bands at ~1131 cm −1 were assigned as rocking vibrations of NH + 3 groups, and were clearly identified over all of the samples. For glycine irradiated in the UV, however, no clear changes were noticed, which is consistent with the chemical stability of glycine against the exposure to ionizing radiation; this is in agreement with earlier observations (Pernet et al 2013). Other fingerprint bands that were absent in all spectra were those of amide I at ~1650 cm −1 and amide II at ~1550 cm −1 (black arrow in Fig.…”

STABILITY OF EXTRATERRESTRIAL GLYCINE UNDER ENERGETIC PARTICLE RADIATION ESTIMATED FROM 2 keV ELECTRON BOMBARDMENT EXPERIMENTS

“…Irreversible first order kinetics was also assumed in previous studies, where a monotonic decline of the glycine concentration was observed upon irradiation of UV photons (ten Kate et al 2005;Poch et al 2013), soft X rays (Pilling et al 2011), or energetic ions in the MeV range (Pilling et al 2013;Portugal et al 2014). In other experiments, however, protons (Gerakines et al 2012), X ray (Pernet et al 2013) and UV photon (Johnson et al 2012;Maté et al 2014) processing lead to a stationary state, where a fraction of the amino acid is not decomposed. In the latter case it was generally assumed that reversible reactions within the solid sample can re-generate part of the glycine destroyed by the energetic irradiation.…”

“…Laboratory studies on the survival of glycine under irradiation by UV photons (Ehrenfreund et al 2001;Bernstein et al 2004;ten Kate et al 2005;Orzechowska et al 2007;Ferreira-Rodrigues et al 2011;Johnson et al 2012), X-rays (Pilling et al 2011;Pernet et al 2013), and high energy ions (Huang et al 1998;Gerakines et al 2012;Gerakines & Hudson 2013;Pilling et al 2013;Portugal et al 2014) have been reported by several groups during the last 15 years. The results of these works indicate that the amino acid would be readily destroyed, largely by short wavelength UV irradiation, in the diffuse ISM and in unshielded surfaces within the solar system (Ehrenfreund et al 2001;ten Kate et al 2005;Orzechowska et al 2007;Johnson et al 2012).…”

A nature-inspired hydrogen-bonded supramolecular complex for selective copper ion removal from water

“…Both features are lower in energy than the corresponding 1 s →1π* transition of the pyridinic nitrogen in the imidazole ring of the ZIF-8 structure (~400.5 eV). As the imino group typically shows a transition at 398–399 eV 39 , 40 , the peak at 399 eV for ZIOS and ZIOS-Cu likely stems from the N 1 s →1π* transition of the oximate nitrogen (C=N–O) or the imidazolate pyridinic nitrogen 41 . After copper(II) ion adsorption in ZIOS, this peak for the 1 s →1π* transition intensifies significantly compared with the broad peaks at 403.2, 406.3, and 410.5 eV, which correspond to the ionization of aromatic N–H and transitions from N 1 s →σ* N–H and σ* C–N , respectively 42 .…”