Chemical Evolution, Keto Acids, Ionizing Radiation.
||August 6, 2018
||The Author(s) 2018. This article is published with open access at www.chitkara.edu.in/publications.
The study of synthesis and stability of molecules in different environments it’s been part of chemistry evolution and origin of life studies for more than 70 years. Various kinds of ionizing radiation have been analyzed as possible sources of energy for the transformations undergone by the first organic molecules. Now experimental and computational simulation approaches continue with different groups of organic molecules, in search for more information that help us to understand and reconstruct somehow the mechanisms that toke place on early Earth and space. In that line, this paper presents first approach of keto acids stability to ionizing radiation, an interesting group of molecules involved in the Krebs cycle and glycolysis. Preliminary results obtained by HPLC/UV analysis of irradiating aqueous solutions of 5 keto acids ranging from 3 to 6 carbons with a 60Co gamma ray source, using doses up to 53 kGy, show different stabilities and a general tendency of shifting the keto-enol equilibrium to the enol tautomer before decomposition.
Space and early Earth are hypothetical scenarios with environmental conditions that represent a challenge for the survival of simple organic molecules and their evolution into more complex ones. Organic molecules diluted into vast oceans and the presence of high radiation fields of ionizing radiation sources, like radioisotopes and cosmic rays, with high penetration capacity, might have made specially complicated for these first organic molecules to survive and react with each other to evolve . Experimentation in this field has been made with different kinds of ionizing radiation. First, due to its ubiquity and abundance, the relevance of UV light was evaluated and its capacity of synthesis and degradation of molecules was experimentally evidenced, including its possible implications in the development of homochirality. Other forms of ionizing radiation were considered, even when they were relatively scarce and sometimes more destructive (due to their higher energies), because they were found to be able to penetrate deeper into matter and lead reactions where others can’t .
Studies in radiation chemistry can provide a deeper insight into chemical processes that may be important for origin of life, such as that related to some relatively labile compounds like keto acids, that are part of apparently ancient and critical metabolic processes . To this end, we investigated the survival of keto acids exposed to a high radiation field in an aqueous solution. Keto acids are organic compounds that contain a carboxylic acid group and a ketone group (that stays in equilibrium with the hydrated form). Depending on structure, they can be typically alpha, beta and gamma keto acids. Keto acid and their derivatives are important compounds in biological systems. Alphaketo acids are especially important in biology, as they are involved in the Krebs citric cycle and in glycolysis. Some other appear in a wide variety of anabolic pathways in metabolism, across living organisms, like the production of some alkaloids in plants, so, their synthesis and stability in environmental conditions is of paramount importance in chemical evolution [3,4].
Studies of their stability in primordial environments are scarce, especially those related to the stability in an aqueous medium at high temperatures or in the presence of high radiation fields. Compounds such as pyruvic acid, oxalacetic acid, citric acid, isocitric acid, alpha-ketoglutaric acid (all members of the citric acid cycle), and others have been just recently identified in extraterrestrial sources (in carbonaceous meteorites) and/or as low temperature (laboratory) reaction products of pyruvic acid [3,5,6], but up to now, the abiotic synthesis of these compounds has not been fully understood, and their synthesis is at least difficult in prebiotic chemistry. Considering these combinations of factors, the detailed study of these kinds of molecules seems to be a promising way to understand the role of each one and reconstruct somehow the mechanisms that toke place in the development of organic molecules that constituted life from the beginning.
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