Estudo teórico dos caminhos para formação de aminas precursoras de aminoácidos no meio interestelar

Abstract

Amino acids have been detected in meteorites since the 1970s (Shivani, et al., 2017). To understand the formation of these amino acids in the interstellar medium and in astronomical bodies, it is necessary to understand the formation and development of their possible precursors. In this work, we want to analyze the possible paths for successive reactions of hydrogen dissociation of ethylamine and dimethylamine in gas phase, using a retrosynthetic analysis strategy, through theoretical calculations, at CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ level. These calculations aimed at geometry optimizations, determination of vibrational frequencies and reaction paths. Reaction paths were obtained with the hypothesis that they are dissociation associated with barrierless recombination reactions, therefor, saddle points were not located. Dissociation energies were found in the range from 14 – 123 kcal/mol. The lowest energy path, starting from ethylamine, was identified in the sequence of steps: CH3CH2NH2 → CH3CHNH2 → CH3CHNH → CH3CHN → CH3CN → CH2CN → CHCN → CCN. Similarly, the lowest energy path, starting from dimethylamine, comprises the steps: CH3NH2CH3 → CH3NHCH2 → CH3NCH2 → CH3NCH → CH3NC → CH2NC → CHNC → CNC. Velocity coefficients were calculated by the canonical variational model, for the temperature range from 10 K to 300 K, typical for astrophysical environment, showing a tendency for the constant to increase with increasing temperature. The nitriles and some radicals presented were observed in the interstellar medium, corroborating the reaction pathways proposed as possible routes for the formation of amine precursors of amino acids.