Annie Chabin

Photochemical processing of amino acids in Earth orbit

Abstract Space technology in Earth orbit has been used to investigate whether amino acids and peptides required for the emergence of life can be safely transported to Earth vicinity when they are associated with minerals. In the BIOPAN-1 flight experiment, l -amino acids and one dipeptide were exposed to space conditions, free and associated with clays. Six amino acids found in the Murchison meteorite (Gly, Ala, Leu, Val, Asp, Glu) were tested with respect to chemical degradation and racemization. In addition, photosensitive l -tyrosine was used to check possible oligotyrosine formation. The dipeptide l -alanyl- l -alanine was chosen to test the stability of the peptide bond. No detectable traces of d -amino acids could be found after the flight in any of the samples. Aspartic acid and glutamic acid exposed as free samples have been partially decomposed during exposure to solar UV. Decomposition was prevented when the amino acids were embedded in montmorillonite or kaolinite. The other amino acids were unaffected by the flight. Tyrosine did not condense and the dipeptide remained stable.

Exposure of amino acids and derivatives in the Earth orbit

Abstract Amino acids and amino acid derivatives were exposed to space conditions in Earth orbit as part of the ESA BIOPAN-2 mission to test the possible delivery of extraterrestrial biological building blocks to the primitive Earth. During the Biopan-2 mission, four proteinaceous amino acids (glycine, aspartic acid, glutamic acid and tyrosine), some amino acid esters and two peptides were exposed in Earth orbit for 10 days. Samples were exposed to vacuum and to solar radiation down to 120 nm both alone or associated with montmorillonite as dry films deposited on MgF2 windows. The compounds recovered after the flight were analysed in order to assess chemical degradation, racemization and polymerization. The results confirmed the absence of racemization of the exposed molecules and the high sensitivity of acidic amino acids towards UV radiation already observed in the Biopan-1 exposure mission. Reducing the thickness of the films revealed unexpected sensitivities of exposed amino acids and peptides. A slight protecting effect was observed when the samples were embedded in 5 μm thick montmorillonite films. Several amino acid esters were also exposed to study their possible polymerization in space. Their stability and reactivity in space conditions were compared. Significant degradation was observed for exposed unprotected samples implying that some kind of protection is needed to ensure any amino acid survival in space. Montmorillonite provided some protection but is not an ideal shielding material.

The PROCESS experiment: exposure of amino acids in the EXPOSE-E experiment on the international space station and in laboratory simulations.

To understand the chemical behavior of organic molecules in the space environment, amino acids and a dipeptide in pure form and embedded in meteorite powder were exposed in the PROCESS experiment in the EXPOSE-E facility mounted on the European Technology Exposure Facility (EuTEF) platform on board the International Space Station (ISS). After exposure to space conditions for 18 months, the samples were returned to Earth and analyzed in the laboratory for reactions caused by solar UV and cosmic radiation. Chemical degradation and possible racemization and oligomerization, the main reactions caused by photochemistry in the vacuum ultraviolet domain (VUV, wavelength range 100-200 nm for photon energy from 6.2 to 12.4 eV) were examined in particular. The molecules were extracted and derivatized by silylation and analyzed by gas chromatograph coupled to a mass spectrometer (GC-MS) to quantify the rate of the degradation of the compounds. Laboratory exposure in several wavelength ranges from UV to VUV was carried out in parallel in the Cologne Deutsches Zentrum für Luft- und Raumfahrt (DLR) Center and Centre de biophysique moléculaire (CBM) laboratories. The results show that resistance to irradiation is a function of the chemical nature of the exposed molecules and the wavelengths of the UV light. The most altered compounds were the dipeptide, aspartic acid, and aminobutyric acid. The most resistant were alanine, valine, glycine, and aminoisobutyric acid. Our results also demonstrate the protective effect of meteorite powder, which reemphasizes the importance of exogenic contribution to the inventory of prebiotic organics on early Earth.

The PROCESS experiment: an astrochemistry laboratory for solid and gaseous organic samples in low-earth orbit.

The PROCESS (PRebiotic Organic ChEmistry on the Space Station) experiment was part of the EXPOSE-E payload outside the European Columbus module of the International Space Station from February 2008 to August 2009. During this interval, organic samples were exposed to space conditions to simulate their evolution in various astrophysical environments. The samples used represent organic species related to the evolution of organic matter on the small bodies of the Solar System (carbonaceous asteroids and comets), the photolysis of methane in the atmosphere of Titan, and the search for organic matter at the surface of Mars. This paper describes the hardware developed for this experiment as well as the results for the glycine solid-phase samples and the gas-phase samples that were used with regard to the atmosphere of Titan. Lessons learned from this experiment are also presented for future low-Earth orbit astrochemistry investigations.

The Fate of Amino Acids During Simulated Meteoritic Impact

Delivery of prebiotic molecules, such as amino acids and peptides, in meteoritic/micrometeoritic materials to early Earth during the first 500 million years is considered to be one of the main processes by which the building blocks of life arrived on Earth. In this context, we present a study in which the effects of impact shock on amino acids and a peptide in artificial meteorites composed of saponite clay were investigated. The samples were subjected to pressures ranging from 12-28.9 GPa, which simulated impact velocities of 2.4-5.8 km/s for typical silicate-silicate impacts on Earth. Volatilization was determined by weight loss measurement, and the amino acid and peptide response was analyzed by gas chromatography-mass spectrometry. For all compounds, degradation increased with peak pressure. At the highest shock pressures, amino acids with an alkyl side chain were more resistant than those with functional side chains. The peptide cleaved into its two primary amino acids. Some chiral amino acids experienced partial racemization during the course of the experiment. Our data indicate that impact shock may act as a selective filter to the delivery of extraterrestrial amino acids via carbonaceous chondrites.

The AMINO experiment: exposure of amino acids in the EXPOSE-R experiment on the International Space Station and in laboratory

In order to confirm the results of previous experiments concerning the chemical behaviour of organic molecules in the space environment, organic molecules (amino acids and a dipeptide) in pure form and embedded in meteorite powder were exposed in the AMINO experiment in the EXPOSE-R facility onboard the International Space Station. After exposure to space conditions for 24 months (2843 h of irradiation), the samples were returned to the Earth and analysed in the laboratory for reactions caused by solar ultraviolet (UV) and other electromagnetic radiation. Laboratory UV exposure was carried out in parallel in the Cologne DLR Center (Deutsches Zentrum fur Luft und Raumfahrt). The molecules were extracted from the sample holder and then (1) derivatized by silylation and analysed by gas chromatography coupled to a mass spectrometer (GC–MS) in order to quantify the rate of degradation of the compounds and (2) analysed by high-resolution mass spectrometry (HRMS) in order to understand the chemical reactions that occurred. The GC–MS results confirm that resistance to irradiation is a function of the chemical nature of the exposed molecules and of the wavelengths of the UV light. They also confirm the protective effect of a coating of meteorite powder. The most altered compounds were the dipeptides and aspartic acid while the most robust were compounds with a hydrocarbon chain. The MS analyses document the products of reactions, such as decarboxylation and decarbonylation of aspartic acid, taking place after UV exposure. Given the universality of chemistry in space, our results have a broader implication for the fate of organic molecules that seeded the planets as soon as they became habitable as well as for the effects of UV radiation on exposed molecules at the surface of Mars, for example.

The AMINO experiment: a laboratory for astrochemistry and astrobiology on the EXPOSE-R facility of the International Space Station

The study of the evolution of organic matter subjected to space conditions, and more specifically to Solar photons in the vacuum ultraviolet range (120–200 nm) has been undertaken in low-Earth orbit since the 1990s, and implemented on various space platforms. This paper describes a photochemistry experiment called AMINO, conducted during 22 months between 2009 and 2011 on the EXPOSE-R ESA facility, outside the International Space Station. Samples with relevance to astrobiology (connected to comets, carbonaceous meteorites and micrometeorites, the atmosphere of Titan and RNA world hypothesis) have been selected and exposed to space environment. They have been analysed after return to the Earth. This paper is not discussing the results of the experiment, but rather gives a general overview of the project, the details of the hardware used, its configuration and recent developments to enable long-duration exposure of gaseous samples in tight closed cells enabling for the first time to derive quantitative results from gaseous phase samples exposed in space.

Astrochemistry on the EXPOSE/ISS and BIOPAN/Foton experiments

We describe three space experiments designed to expose to space conditions, and more specifically to solar UV radiation, selected samples of organic and mineral material.