Radiolysis and radioracemization of 20 amino acids from the beginning of the Solar System

Abstract

A series of chiral amino acids in the levo form used in the current terrestrial biochemistry were irradiated in the solid and dry state with c-radiation to a dose of 3.2 MGy which is the dose equivalent to that derived by radionuclide decay in comets and asteroids in 1.05 9 10 9 years at a depth [20 m. For each amino acids, the radiolysis degree and the radioracemization degree was measured, respectively by differential scanning calorimetry (DSC) and by optical rotatory dispersion (ORD) spectroscopy. From

Unusual nonterrestrial l‐proteinogenic amino acid excesses in the Tagish Lake meteorite

“…1979). Although it has been argued that racemization in an asteroid would not have completely erased any initial enantiomeric biases present in the α‐H amino acids (Cohen and Chyba 2000; Cataldo et al. 2011), some racemization of the α‐H amino acids will occur during parent body aqueous alteration and exposure to ionizing radiation.…”

Stability toward High Energy Radiation of Non-Proteinogenic Amino Acids: Implications for the Origins of Life

“…After having studied the radiolysis stability of all proteinogenic amino acids in an astrochemical perspective [ 30 , 32 , 33 , 34 , 35 ], we are focusing our attention to non-proteinogenic or non-proteinaceous amino acids which are abundant in carbonaceous chondrites exceeding by far the concentration and the variety of proteinogenic amino acids [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. Here we report briefly the list of the selected amino acids for the present work explaining the reason for their selection.…”

“…About amino acids radiolysis, there are available also the very important and classical works of Bonner and colleagues [ 21 , 56 , 57 , 58 , 59 , 60 ], which were specifically designed to test the Wester-Ulbricht hypothesis that parity violation in the β-decay may have originated the enantiomeric excess in the biochemical world, and the work of Kminek and Bada [ 61 ]. However, with the exclusion of Cataldo and colleagues [ 30 , 32 , 33 , 34 , 35 , 36 ], no systematic studies on the effects of high energy radiation on amino acids have been made. This paper represents a continuation of the work.…”

“…However, in our study, we will not consider the effect of water. The problem of radiation processing of organic molecules embedded in asteroids and comets was addressed for the first time by the Nobel laureate Harold Urey more than 60 years ago [ 26 , 27 , 28 ], but the result of his calculation is still valid today [ 29 , 30 ]. Urey stated that organic molecules buried at a depth of 20 m are completely shielded by cosmic ray radiation and can be preserved unchanged for billions years.…”

“…The delivery of such energy is not linear but is very high in the first billion of years of the solar system due to the decay of the radionuclide 26 A1 which is characterized by a short half-life in comparison to the other aforementioned radionuclides characterized by much longer half-lives [ 31 ]. In order to assess the radiolysis resistance of amino acids and their preservation of chirality to high energy radiation, we have started a systematic study on the radiolysis of all proteinogenic amino acids to a radiation dose of 3.2 MGy, which corresponds to 22.8% of the total dose they should have taken inside asteroids, comets and other bodies of the solar system [ 30 , 32 , 33 , 34 , 35 ]. The results were extrapolated to 14 MGy of radiation dose, showing that practically all the proteinogenic amino acids could partially “survive” such an enormous radiation dose with preservation of the chiral excess [ 35 ].…”