Exposure of amino acids and derivatives in the Earth orbit

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 pm 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. (C) 2002 Elsevier Science Ltd. All rights reserved.