Available online at www.sciencedirect.com Planetary and Space Science 52 (2004) 613–621 www.elsevier.com/locate/pss Pyrolisis of phosphorylated molecules and survivability limits during the atmospheric passage in earth-like planets Vicente Marcano a , Pedro Benitez a , Javier Campins a , Paula Matheus a , Cesyen Cede˜ no b , Nelson Falcon c , Ernesto Palacios-Pr u a ; * a Evolutionary Biology and Chemistry Laboratory, Electron Microscopy Center, University of the Andes, P.O. Box 163, M erida, Venezuela b Crystalography Laboratory, Faculty of Sciences, University of the Andes, M erida, Venezuela c Department of Physics, Faculty of Science and Technology, University of Carabobo, Valencia, Venezuela Received 8 April 2003; received in revised form 11 November 2003; accepted 20 November 2003 Abstract There is evidence that space energy sources could give place to the appearance of phosphorylated nucleosides outside of Earth. These compounds may have been delivered mainly by interplanetary dust particles due to the lower temperatures experienced during atmospheric deceleration and impacts to the terrestrial surface. In this report, we communicate the results of pyrolytic studies to simulate atmospheric survivability of adenosine-5 ′ -diphosphates (ADP) (and adenosine-5 ′ -monophosphate, adenosine and adenine as degradation products) at temperatures ¡ 500 ◦ C and at various time intervals. Our results revealed that phosphorylated and non- phosphorylated nucleosides transported by IDPs having sizes of 10 -6 –10 -5 m could resist temperatures up to 500 ◦ C generated during atmospheric entry. However, atmospheric passage should not exceed a time ¿ 150 s due to the thermal lability of these molecules. Because of the high half-life showed by ADP in the presence of meteoritic powder, it is thought that extraterrestrial delivery of very complex biomolecules is more suitable under such protected conditions. These data indicate that the formation of a Fe 2+ - and/or Ca 2+ - complex could increase the stability of the molecules in the presence of meteoritic matter. Therefore, if the synthesis of nucleosides, nucleotides or oligonucleotides could take place in icy bodies, then micron-sized dust could have contributed signicantly to the availability of phosphorylated nucleosides in the early Earth or in extrasolar early Earth-like planets, and thereby could have allowed the arising of an early biological activity. ? 2003 Elsevier Ltd. All rights reserved. Keywords: Pyrolisis; Interplanetary dust; Organic delivery; Atmospheric survivability; Phosphorylated and non-phosphorylated nucleosides 1. Introduction Livingorganismsneedimportantamountsofadenosine-5 ′ - diphosphate (ADP) or ATP to carry out energetic bio- chemical processes. If the earliest organisms used ADP or ATP acquired from the environment as a source of energy, they would have to assimilate appropriate amounts of them (Keefe and Miller, 1995; Monnard and Deamer, 2001). Pre- sumably there were no enzymes and no template in the prim- itive Earth to facilitate the synthesis of the rst nucleotides so another form of chemical evolution must have been involved (Zubay and Mui, 2001). Several reviews of prebi- otic phosphorylations assayed under conditions of the early Earth have not given robust synthesis of nucleotideswith few exceptions (Rabinowitz et al., 1968; Schwartz ∗ Corresponding author. Fax: +58-74-403156. E-mail addresses: prupal@ula.ve, cme@ula.ve (E. Palacios-Pr u). and Ponnamperuma, 1968; Bishop et al., 1972; Lohrman and Orgel, 1968, 1973; Yamagata et al., 1979; Reimann and Zubay, 1999). These reactions, however, have several problems: (1) dihydrogen phosphate minerals utilized are not known in nature today (Keefe and Miller, 1995, 1996); (2) high temperatures (65–200 ◦ C) during prolonged times would have destroyed organic compounds such as bases, sugars, phosphates and nucleosides on the early Earth (White, 1984; Larralde et al., 1995; Keefe and Miller, 1995, 1996; Levy and Miller, 1998), and (3) in most of these phosphorylation experiments high concentrations of reagents were used, and such high concentrations of those reagents could not have occurred on the early Earth (Maci a et al., 1997). It is also well known that the synthesis of purine nucleosides yields very small amounts in simu- lated prebiotic conditions (Fuller et al., 1972) whereas the synthesis of pyrimidine nucleosides is more dicult to ob- tain under those experimental prebiotic conditions because 0032-0633/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.pss.2003.12.006