Heterogeneous radiolysis of urea. Implications in astrobiology and prebiotic chemistry

Abstract

Abstract:Urea is an organic molecule present in most living organisms. Historically, it was the first organic molecule synthesized in the laboratory. In prebiotic chemistry, urea readily forms in different laboratory simulations using different energy sources. Furthermore, the role of solid surfaces, particularly minerals, might have been crucial to increase the complexity of the organic matter which may have led to the subsequent emergence of life on Earth.In this work, the radiolysis of urea in presence of a clay is studied to determine to what extent the mineral surfaces influence the decomposition of organics. The results indicate that urea is relatively stable to ionizing radiation in aqueous solutions and up to 20 kGy no decomposition is observed. Moreover, the presence of sodium montmorillonite, by a mechanism until now unknown, affects the radiolytic behavior and urea remains in the heterogeneous solution without a change in concentration even at very high doses (140 kGy). These results indicate that solids could have protected some organics, like urea, from degradation enabling them to remain in the environment on the primitive Earth.

High‐Energy Proton‐Beam‐Induced Polymerization/Oxygenation of Hydroxynaphthalenes on Meteorites and Nitrogen Transfer from Urea: Modeling Insoluble Organic Matter?

“…The presence of urea increased the conversion of the substrate in the case of NWA 4482 and Al‐Haggunia. Unconverted urea (50–90 % with respect to the initial amount) was also detected in the reaction mixture, in accordance with the relative stability shown by this compound toward ionizing radiation once adsorbed on the surface of minerals [49] . Regarding the chemoselectivity of the reaction, the presence of urea decreased significantly the total yield of monomeric derivatives in the case of Al‐Haggunia (Table 2, entry 6 versus entry 3).…”

Particle size effect of silica gel on the ɤ-radiation induced electrical conductivity of urea aqueous solutions

“…Seino et al, noted that radiolytic yield of hydrogen depends on gamma radiation dose absorbed and metal oxide particle size [9,10]. Radiolysis of urea aqueous solutions was studied before in different workers [11][12][13][14][15][16]. Urea is relatively stable to ionizing radiation in aqueous solutions up to 20 kGy [11].…”

“…Radiolysis of urea aqueous solutions was studied before in different workers [11][12][13][14][15][16]. Urea is relatively stable to ionizing radiation in aqueous solutions up to 20 kGy [11]. Moreover, it was reported that the RIC of urea aqueous solutions significantly increases upon radiolysis [12,13].…”