Experimental investigation of the formation of dipeptides in the ices of Kuiper Belt Objects

• Applicant: Dr. Marko Förstel
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Astrophysics and Astronomy ; Biophysics
• Term: from 2014 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 250929795

• Final Report Year: 2016

Final Report Abstract

The main goal of this project was to investigate the possible extraterrestrial formation of dipeptides in ices of Kuiper belt objects (KBOs). KBOs are icy objects in the solar system beyond the orbit of Neptune. They consist of ice covered rocks and are considered to be the primary source of short period comets. This means that chemicals that formed on these bodies are brought into the inner solar system and can be delivered to the planets. It is possible that this delivery of organic material plays a role in the development of life on early Earth. The chemistry on KBOs can be different from the chemistry in an aqueous environment because the molecules are immobilized in an ice matrix. Therefore reactions may take place between two neighboring molecules that would be highly unlikely in an aqueous environment, in which they could move and come into contact with more suitable reaction partners. To understand these processes, we used a space simulation chamber to create conditions like those found on KBOs. In this chamber, we achieved pressures of about 10,000,000,000,000 times less than those on Earth. We then created ices of our molecules of interest at temperatures as low as 4 K. To simulate radiation in space, we irradiated the ices with electrons. With a variety of tools, we then probed the ices during irradiation to observe if and how new molecules form. Then we carefully heated the ices and detected signals from the molecules that sublimed into the gas phase. Thanks to our unique setup we were able to detect molecules with very high sensitivity and can even distinguish isomers of the same molecule. The ices of KBOs can be complex and are mostly made of inorganic molecules like NH3, CO, CO2, CH4 and H2O. If we were to irradiate an ice that contained all these molecules, we would be able to observe a large variety of new molecules, but their signals would be too complex and numerous to decipher. We therefore started by irradiating simple ices made up purely of one kind of molecule, before moving on to more complex ices. Our first experiment focused on NH3 ice. The –NH– or amide bond is an essential part of all peptides, which are key buildings blocks in all living things. We believe that the nitrogen atom in that –NH– bond can initially come from NH3. After irradiation of the NH3 ice, we observed several molecules which have N-N and N=N bonds. We also observed two new molecules, N3H3 and N3H5, and described their structures. Our discovery was featured on the cover of the journal ChemPhysChem. We also irradiated another pure ice, carbon monoxide (CO) and found another novel molecule (C5O2). This molecule could one day help explain the history of our solar system because it can now be used as an indicator: wherever it is found, we will know (thanks to this experiment) that CO was likely very abundant there in the past. The main discoveries of my research involved ices containing both of the compounds above, NH3 and CO. By irradiating these ices in our space simulation chamber, we showed that urea, a molecule important to the formation of life, forms from simple inorganic starting materials and under conditions found in outer space. We also showed that formamide, a molecule that has already been found in the interstellar medium, is a likely precursor in the formation of urea. Furthermore, we demonstrated that organic molecules even more complex than urea formed in the irradiated ices. These molecules carry more than one –NH–(C=O)– group and in this way are similar to polypeptides, which are important for life on Earth. In summary, our findings underline that very complex organic molecules can form in the harsh conditions found in outer space, even with only very simple inorganic starting material. With the discovery of three new molecules formed by irradiating ices similar to those in outer space, we also show that exotic molecules that do not form in an aqueous environment could have been delivered to early Earth and should be considered when trying to understand the chemical reactions that eventually led to life.

Publications

• "Detection of the Elusive Triazane Molecule (N3H5) in the Gas Phase." ChemPhysChem 16, no. 15 (2015)
  Förstel M., Maksyutenko P., Jones B. M., Sun B.-J., Chen S.-H., Chang A. H. H. and Kaiser R. I.
  
• "On the Formation of Amide Polymers Via Carbonyl - Amino Group Linkages in Energetically Processed Ices of Astrophysical Relevance." The Astrophysical Journal 820, no. 2 (2016)
  Förstel M., Maksyutenko P., Jones B. M., Sun B.-J., Lee H. C., Chang A. H. H. and Kaiser R. I.
  
• "Pentacarbon Dioxide (C5O2) Formation and Its Role as a Tracer of Solar System Evolution." The Astrophysical Journal Letters 818, no. 2 (2016)
  Förstel M., Maksyutenko P., Mebel A. M. and Kaiser R. I.
  
• "Synthesis of Urea in Cometary Model Ices and Implications for Comet 67P/Churyumov–Gerasimenko." Chemical Communications (2016) Vol 52 Issue 4, 741-744
  Förstel M., Maksyutenko P., Jones B. M., Sun B.-J., Chang A. H. H. and Kaiser R. I.