RESUMO
Researchers have suggested that the condensation of low-molecular-weight aldehydes under basic conditions (e.g., pH > 11) is the prebiotic reaction responsible for the abiotic formation of carbohydrates. It has also been suggested that surface hydrothermal systems were ubiquitous during the early Archean period. Therefore, the catalysis of prebiotic carbohydrate synthesis by metallic oxide minerals under acidic conditions in these environments seems considerably more probable than the more widely hypothesized reaction routes. This study investigates the stability of DL-glyceraldehyde and its reaction products under the simulated conditions of an Archean surface hydrothermal system. The Hveradalur geothermal area in Iceland was selected as an analog of such a system. HPLC-ESIMS, UV−Vis spectroscopy, Raman spectroscopy and XPS spectroscopy were used to analyze the reaction products. In hot (323 K) and acidic (pH 2) solutions under the presence of suspended iron(III) oxide hydroxide powder, DL-glyceraldehyde readily decomposes into low-molecular-weight compounds and transforms into sugar-like molecules via condensation reactions.
RESUMO
On ancient Earth, environmental conditions favored prebiotic chemical reactions. In the Archean, some molecules with conjugated rings might have been synthesized, displaying structural stability in the Archean in the presence of ionizing radiation and hydration-dehydration events. Additionally, it is suggested that on ancient Earth, calcite was a common mineral promoting organic compound synthesis. In the present work a study of the interaction of amino acid mixtures with the (104) surface of calcite is presented. Our preliminary results show the abiotic synthesis of alloxazine (a flavin with relevant photochemical properties). Computer simulations were performed in HyperChem 8.0.1. by means of MM+ molecular mechanics and PM3 semi-empirical methods, in 27 possible amino acid trimers of alanine, glycine and lysine. Alloxazine formation is possible by the gamma irradiation of amino acids. The computer simulations show that trimers GGG and GGA promote the further transformation from diketopiperazines (DKP's) and KGK to alloxazine. The computer simulations with free radicals are not stable when alloxazine is interacting with the calcite surface. Experiments in anoxygenic environments with hydration-dehydration events in gamma irradiated samples allow the abiotic formation of flavins, DKP's and a heterocycle compound with possible relevance in prebiotic chemistry.
Assuntos
Aminoácidos/efeitos da radiação , Evolução Química , Flavinas/síntese química , Raios gama , Aminoácidos/química , Simulação por Computador , Planeta Terra , Islândia , Modelos Químicos , Origem da VidaRESUMO
Most adsorption and radiolysis experiments related to prebiotic chemistry studies are performed in distilled water or sodium chloride solutions. However, distilled water and sodium chloride solutions do not represent the composition of the primitive seas of Earth. In this work, an artificial seawater with ion abundances Mg2+ > Ca2+ >> Na+ ≈ K+ and SO42- >> Cl- was used, one that is different from the average composition of seawater today. This artificial seawater is named seawater 4.0 Ga, since it better represents the composition of the major constituents of seawater of primitive Earth. The radiolysis of adenine adsorbed onto montmorillonite was studied. The most important result is that adenine is adsorbed onto montmorillonite, when it is dissolved in artificial seawater 4.0 Ga, and the clay protects adenine against gamma radiation decomposition. However, desorption of adenine from montmorillonite was possible only with 0.10 mol L-1 of KOH. This result indicates that adenine was strongly bonded to montmorillonite. Fourier transform infrared spectroscopy showed that NH2 group and electrostatic interactions, between negatively charged montmorillonite and positively charged adenine, are responsible for adsorption of adenine onto montmorillonite. In addition, X-ray diffractograms showed that adenine enters in the interlayer space of montmorillonite.
Assuntos
Adenina/química , Bentonita/química , Radiação Ionizante , Adsorção , Liofilização , Espectroscopia de Infravermelho com Transformada de Fourier , Difração de Raios XRESUMO
Solids of adenine obtained from distilled water and seawater lyophilized solutions were γ irradiated at a 94.52 kGy dose. Results indicate that pure solid adenine had a low degradation rate, likewise the solid containing seawater salts. However, EPR spectroscopy analysis suggests a high interaction of the radiation with seawater salts, by radical formation in sulfate ions. These outcomes are of interest for prebiotic chemistry, since ions could have played important roles in chemical evolution. In addition, Martian soil is rich in sulphate salts, thus these salts could protected organic molecules being degraded by γ-radiation.