Radiolysis and Thermolysis of Cytosine: Importance in Chemical Evolution

An important aspect of chemical evolution is the study of the stability of organic molecules with biological significance in primitive conditions, especially in the presence of constant energy sources. An example of sets of biologically important organic compounds is nitrogenous bases. The presence of these compounds in prebiotic environments is very important in forming more complex systems, such as nucleic acids, in which nitrogenous bases are an essential component. The aim of the present work is to study the stability of cytosine, a pyrimidine base, in high-radiation fields or at high temperature and to evaluate its recovery. Our results show that the cytosine (1x10-4 M aqueous solution, oxygen-free) decomposed completely at a dose of 22 kGy, and 25% recovery was obtained with a dose of 7.4 kGy. The analysis of irradiated samples was followed by HPLC, HPLC-mass spectrometry and UV-VIS spectroscopy. The main product in both thermolysis and radiolysis was uracil, formed via a deamination reaction. Uracil is another nitrogenous base with biological significance

Study of Solid-State Radiolysis of Behenic, Fumaric, and Sebacic Acids for their Possible Use as Gamma Dosimeters Measured Via ATR-FT-IR Spectroscopy

The intensive use of ionizing radiation has promoted the constant investigation of adequate dosimetric systems in the measurement of doses applied in irradiated products. The objective of this work is to propose gamma dosimetric systems, using carboxylic acids in a solid state and measuring the change via infrared spectroscopy (carboxylic acid/ ATR-FT-IR1). We worked with three systems: (1) behenic acid/ATR-FT-IR, (2) sebacic acid/ATR-FT-IR, and (3) fumaric acid/ATR-FT-IR. The change in absorbance corresponding to the stretching vibration frequency of the carbonyl group to the absorbed dose (in the range of kGy) was measured. The results showed that the acid/ATR-FT-IR systems have a linear response with respect to the absorbed dose, for behenic acid/ATR-FT-IR from 0 to 122 kGy, for ATR-FT-IR sebacic acid from 0 to 61 kGy, and for fumaric acid/ATR-FT-IR from 0 to 34 kGy. The results indicated that the linear response of the absorbance dose in the three systems allows us to continue studying other variables to be able to propose them as chemical dosimeters

Radiolysis of Nucleosides: Study of Sedimentary Microenvironment Models for the Protection of Bio-Organic Molecules on Early Earth

Nucleic acid bases and their derivatives are important compounds in biological systems. Many efforts have been made to demonstrate the possible prebiotic origin of these molecules, but the abiotic synthesis of these compounds has proved to be very difficult in that conditions. So, if their synthesis actually took place, a study of their stability in prebiotic conditions is quite relevant in chemical evolution studies. In this work, it has been examined and compared the influence of Sodium Montmorillonite on the chemical transformations undergone by two nucleosides (guanosine –purinic– and uridine, –pyrimidinic–) when subjected to conditions simulating the primitive Earth during the period of chemical evolution. The experiments prove the concentration capacity and protective role against external sources of ionizing radiation (specifically γ-ray) that clays can provide to these specific compounds adsorbed on them. By using X-ray diffraction, UV-vis spectrophotometry and HPLC for the analysis, it was found that purinic nucleosides (more than pyrimidinic) are quickly adsorbed on clay at low pH values, and the temperature of mineral desiccation applied after adsorption promotes their decomposition into their corresponding nitrogenous bases. In both, purinic and pyrimidinic, desorption occurs in neutral or slightly basic aqueous solutions, and both are protected by clay. Pyrimidinic nucleosides show more resistance to heat, but less resistance towards ionizing radiation, even when adsorbed in clay

Agent-based Model of Oxidation Reactions of Ferrous Ions

Molecules in comets are formed through chemical oxidation reactions induced by radiation. Thesereactions can be simulated in laboratory experiments applying gamma radiation to samples at low temperatures. The kinetics of the induced reactions can be modeled by a system of coupled non-linear ordinary differential equations describing the mass balance of all of the species involved. However, finding a traditional solution to this system is difficult because of the large number of reactions involved, the need to solve all of the equations simultaneously, and the strong dependence on the initial conditions due to the non-linear character of the equations. For each species, the mass-balance equation includes all of the reaction rates leading to production (source terms) and to destruction (sink terms). In this sense, each equation is analogous to the prey-predator model, with the sink terms consider to be the “prey” and the source terms as the “predators”. Due to this, we can use an agent-based model to follow the kinetics of the chemical reactions. In this paper, we present a code in Python for an agent-based model of the chemical oxidation of ferrous ions (Fe2+) induced by gamma radiation and in the presence of molecular oxygen. We compare the results that this code produces for molar concentrations of Fe3+over time with those obtained in the laboratory

Stability of Aspartic Acid at 77°K under Gamma Radiation in a Comet Cores Simulation: Implications for Chemical Evolution Studies

The synthesis of organic matter in a simulated primitive environment (terrestrial or extraterrestrial) has been widely studied. The stability of organic matter of biological significance, exposed to energy fields in primitive conditions, is equally important in the context of chemical evolution. We present a detailed analysis of the stability of prebiotic organic molecules under the effect of ionizing radiation at a low temperature, simulating a comet core. The laboratory simulation consists of icy phases of prototype organic matter and a mineral in a physical mixture. This chemical system was irradiated with gamma radiation at 77°K. The icy phases are methanol, formic acid, and aspartic acid in aqueous solution, in the presence of sodium montmorillonite as silicates surface.Our results show the stability of aspartic acid in this comet core simulation. We have been identified some radiolytic products of this mixture: ethylene glycol, glycolaldehyde, formamide, alanine, glycine and succinic acid. The products were identified by Gas Chromatography (GC) and High Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry (HPLC-ESI-MS). The protection role of the clay in the radiolysis of aspartic acid was observed in this mixture. This result may be due to an energy transfer from the clay. At pH=4, aspartic acid is adsorbed onto the clay at the interlayer channel as is shown in the X-ray diffractograms (XRD)

Stability of Pyruvic Acid Adsorbed Onto Clays and Exposed to Ionizing Radiation: Relevance in Chemical Evolution

Chemical evolution studies focus on the synthesis and stability of organic molecules during various transformative physicochemical processes. Gaining insight into the possible mechanisms behind these processes requires the use of various energy sources and catalysts that can produce such transformations. In this work, ionizing radiation (60Co) was used as a source of energy, and two clays with different exchangeable cations-sodium and iron (III)-were combined with pyruvic acid, a key alpha keto acid in metabolism. The samples of pyruvic acid were prepared at a concentration of 0.01 M; then, adsorption experiments were carried out by combining sodium or iron montmorillonite at different times. The amount that adsorbed onto iron montmorillonite was greater than the amount that adsorbed onto sodium montmorillonite. Samples of alpha keto acid at the same concentration were irradiated-in the absence of clay-at 0 to 146.1 kGy and at two pHs (6.7 and 2.0). The suspended samples with sodium and iron clay were then irradiated at the same doses. The results show that keto acid decomposes more quickly at more acidic pHs. The main reaction to irradiation without clay involves the dimerization of pyruvic acid, and 2,3-dimethyltartaric acid is the majority product. When irradiated in the presence of clay, the main reaction is decarboxylation, and acetic acid is the majority product. The exchangeable cation type modifies the interactions between the organic molecule and the solid phase. The percentage of recovered pyruvic acid is higher for iron montmorillonite than for sodium montmorillonite

Agent Based Model of the Cytosine Radiation Induced Reaction

The stability of cytosine in aqueous solution was studied in the laboratory, simulating prebiotic conditions and using gamma radiation as an energy source, to describe cytosine behavior under radiation. For a better understanding of the radiation-induced processes, we proposed a mathematical model that considers chemical reactions as nonlinear ordinary differential equations. The radiolysis can be computationally simulated by an agent-based model, wherein each chemical species involved is considered to be an agent that can interact with other species with known reaction rates. The radiation is contemplated as a factor that promotes product formation/destruction, and the temperature determines the diffusion speed of the agents. With this model, we reproduce the changes in cytosine concentration obtained in the laboratory under different irradiation conditions

Radiolysis of the Glycolaldehyde-Na+Montmor- illonite and Glycolaldehyde-Fe3+Montmorillonite Systems in Aqueous Suspension under Gamma Radiation Fields: Implications in Chemical Evolution

The stability and reactivity of organic molecules with biological and pre-biological significance in primitive conditions are of paramount importance in chemical evolution studies. Sugars are an essential component in biological systems for the different roles that they play in living beings. The objective of the present work is to study the gamma radiolysis of aqueous solutions of glycolaldehyde, the simplest sugar and aqueous suspensions of glycolaldehyde-Na+-montmorillonite and glycolaldehyde-Fe3+Montmorillonite. Our results indicate that the radiolysis of the aqueous solutions of glycolaldehyde (0.03M), oxygen free, mainly produce the linear dimer known as eritriol (122 g/mol) and a sugar-like compound with six carbon atoms (180 g/mol). The experiments with the clay suspensions show that clays can adsorb glycolaldehyde and protect it from gamma irradiation. Additionally, it was observed that depending on the cation present in the clay, the percentage and the product (monomer or cyclic dimer) adsorption was different. In the case of Fe3+ Montmorillonite, this clay catalyzed the decomposition of glycolaldehyde, forming small amounts non-identified products. The analysis of these systems was performed by ATR-FTIR, UV spectroscopy, liquid chromatography (UHPLC-UV), and HPLC coupled to a mass spectrometry

Study of L-Glutamic Acid in Solid State for its Possible Use as a Gamma Dosimeter at Different Temperatures (77, 195 and 295 K)

The experimental response of the dosimeter as a function of the irradiation temperature plays an important role, and this effect has consequences in the practical applications of dosimetry. In this work, L-glutamic acid (2-aminopentanedioic acid) is proposed to be a good response, easy to handle, and a cheap gamma dosimeter. For this purpose, polycrystalline samples were irradiated with gamma rays at 77, 195, and 295 K and doses in the kiloGray range (43–230 kGy). The potential use of the glutamic acid system as a chemical dosimeter is based on the formation of stable free radicals when the amino acid is exposed to ionizing radiation. The observed species in these experiments were attributed to deamination and decarboxylation reactions that were studied using electron spin resonance (ESR). The results indicate that the analysis generates a linear response as the irradiation dose increases in a reliable range for industrial and research purposes at three different temperatures

Ionizing Radiation, an Instrument in Chemical Evolution Studies: Scope and Perspectives

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