Detailed analytical study of radiolysis products of simple organic compounds as a methodological approach to investigate prebiotic chemistry—Part 1 D. Dondi a,n , D. Merli a , L. Pretali b , A. Buttafava a , A. Faucitano a a Department of General Chemistry, University of Pavia, Via Taramelli 12, Pavia 27100, Italy b Department of Organic Chemistry, University of Pavia, Via Taramelli 10, Pavia 27100, Italy article info Article history: Received 21 July 2010 Accepted 20 September 2010 Keywords: Prebiotic chemistry Gamma irradiation Analytical chemistry Reaction mechanisms abstract Aqueous solutions of simple organic C1 compounds (methanol and acetonitrile) and ammonia, presumably present on primordial Earth, were subjected to 60 Co gamma irradiation (total dose 800 kGy). The irradiation gave a complex mixture of organic compounds leading interestingly to a positive balance of synthesis vs. degradation reactions. In particular, if acetonitrile was used, nucleobase analogues could be detected among products. Highly sensitive and powerful analytical techniques (e.g. GC–MS, HPLC-MS) made this investigation feasible at a reasonable cost in terms of time and results. Plausible reaction pathways leading to major compounds were proposed, supported by literature data. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction Prebiotic chemical evolution encompasses the sequence of events on primitive Earth that led to the formation of complex organic compounds from simple organic and inorganic building blocks, the so called Oparin–Haldane hypothesis (Miller et al., 1997). According to this theory, the synthesis of organic compounds on primitive Earth, their transformation into more complex molecules and generation of replicating systems were the steps, which ultimately led to the appearance of life. Different energy sources were implicated in synthesis of organic molecules of biological interest from simple compounds, and it is generally admitted that ionizing radiation was among the most important energy sources in the prebiotic environment (Albarra´n et al., 1988) due to the abundance of radionuclides in primitive Earth’s crust, the lack of Earth’s magnetic field shielding and the presence of natural nuclear reactors (Draganic et al., 1983). However, poor attention has been paid to it (see, e.g., Colin-Garcia et al., 2007; Draganic, 2005; Negron-Mendoza et al., 1995) and, in addition, the radiation chemistry and reaction mechanisms of complex mixtures are, at the best of our knowledge, poorly known. In fact, forecasting the effect of intense radiolysis of aqueous solutions of organic compounds is a hard task, as more concentration of highly reactive species can generate complex chemical networks leading to unpredictable reaction products (Sole´ and Munteanu, 2004); nowadays, due to the availability of highly sensitive and powerful analytical techniques (e.g. GC–MS, HPLC-MS) this investigation is made feasible at a reasonable cost in terms of time and results. In this work we take into account the mechanisms and reaction products arising from gamma irradiation of simple compounds of prebiotic interest in an oxygen-free environment, mimicking terrestrial Hadean conditions, during which life supposedly arised (Daniel et al., 2006; Morrison, 2006). In particular we used binary and ternary aqueous solutions of C 1–3 carbon sources (alcohols, ketones, nitriles) and nitrogen containing compounds (ammonia and amines). The molar ratio between carbon and oxygen was kept near 1:5 for all the mixtures considered, but since all oxygen is present in the reduced form, the simulated environment is considered to be redox-neutral. Solutions were irradiated by a 60 Co gamma source (800 kGy total dose) and products were analyzed by chromatographic techniques (GC–MS, HPLC). The total dose given mimes the natural irradiation that would be absorbed over several thousand years in the Hadean period (considering the higher amount of different unstable isotopes and the lack of Earth’s magnetic field) (Draganic, 2005; Bedini et al., 2004) or shorter time periods in natural nuclear reactors (Draganic et al., 1983). The dose rate was kept relatively low (about 0.45 kGy/h) in order to avoid secondary dose rate depending effects. We find it appropriate to divide the paper into two parts: the former dealing with the radiolysis of mixtures containing methanol and acetonitrile, of greater prebiotic interest, and the latter related to the radiolysis of mixtures containing acetone, having a more complex mechanism and thus interesting also for basic radiation chemistry. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/radphyschem Radiation Physics and Chemistry 0969-806X/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2010.09.010 n Corresponding author. Tel.: + 39 0382 987344; fax: + 39 0382 528544. E-mail address: dondi@unipv.it (D. Dondi). Radiation Physics and Chemistry 80 (2011) 403–407