Evolução molecular: como os blocos construtores da vida podem se formar no espaço

quinta-feira, abril 26, 2018

Glycine formation in CO2:CH4:NH3 ices induced by 0-70 eV electrons featured

The Journal of Chemical Physics 148, 164702 (2018); https://doi.org/10.1063/1.5021596

Sasan Esmaili, Andrew D. Bass, Pierre Cloutier, Léon Sanche, and Michael A. Huelsa)


Département de Médecine Nucléaire et Radiobiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Quebec J1H5N4, Canada

a)Author to whom correspondence should be addressed: Michael.Huels@usherbrooke.ca and huels@kth.se. Tel.: 1-819-821-8000 (74776).

Source/Fonte: Science Daily


Glycine (Gly), the simplest amino-acid building-block of proteins, has been identified on icy dust grains in the interstellar medium, icy comets, and ice covered meteorites. These astrophysical ices contain simple molecules (e.g., CO2, H2O, CH4, HCN, and NH3) and are exposed to complex radiation fields, e.g., UV, γ, or X-rays, stellar/solar wind particles, or cosmic rays. While much current effort is focused on understanding the radiochemistry induced in these ices by high energy radiation, the effects of the abundant secondary low energy electrons (LEEs) it produces have been mostly assumed rather than studied. Here we present the results for the exposure of multilayer CO2:CH4:NH3 ice mixtures to 0-70 eV electrons under simulated astrophysical conditions. Mass selected temperature programmed desorption (TPD) of our electron irradiated films reveals multiple products, most notably intactglycine, which is supported by control measurements of both irradiated or un-irradiated binary mixture films, and un-irradiated CO2:CH4:NH3ices spiked with Gly. The threshold of Gly formation by LEEs is near 9 eV, while the TPD analysis of Gly film growth allows us to determine the “quantum” yield for 70 eV electrons to be about 0.004 Gly per incident electron. Our results show that simple amino acids can be formed directly from simple molecular ingredients, none of which possess preformed C—C or C—N bonds, by the copious secondary LEEs that are generated by ionizing radiation in astrophysical ices.