Banca de DEFESA: NEUBI FRANCISCO XAVIER JUNIOR

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : NEUBI FRANCISCO XAVIER JUNIOR
DATE: 24/03/2022
TIME: 08:00
LOCAL: Plataforma RNP
TITLE:

Computational Investigations of Glycine Polymorphism in Interstellar Medium: Phase Equilibrium and Surface Reactions.

KEY WORDS:

Polymorphism; Glycine; Theoretical Calculations; Periodic Boundary Conditions; Density Functional Theory

PAGES: 106
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Físico-Química
SPECIALTY: Química Teórica
SUMMARY:

Glycine, the simplest amino acid, has already been detected in meteoritic and cometary samples. The understanding of its existence in the solid state, in the interstellar medium (ISM) is limited, due the lack of studies concerning its reactivity in this environment. Therefore, this work was developed aiming to investigate, by means of computational
methodologies, the thermodynamic equilibrium of the alpha-, beta- and gamma-glycine polymorphs and their reactivity in the solid-gas interface, in ISM analogous conditions. Computational methodologies were applied adopting the Density Functional Theory, accordingly to the periodic boundary conditions formalism. The PBE functional was adopting with the dispersion correction, D3. The inner electrons were treated with the Vanderbilt Ultrasoft pseudopotentials. Kinetic cutoff energy values were tested and converged to 80 Ry. A k-points sample of the reciprocal lattice of 4 x 2 x 4, 4 x 3 x 4 e 3 x 3 x 4 were assumed for the alpha-, beta- and gamma-glycine, respectively. Vibrational properties were obtained by means of the Density Functional Perturbation Theory. The quasi-harmonic approximation was adopted for the estimation of solid-state thermodynamic properties. Calculated entropy values were slightly lower than experimental findings, with absolute deviations of 5.27, 0.13 and 5.42 J mol -1 K -1 , for the alpha-, beta- and gamma-glycine, respectively, at 298.15 K. The obtained Salpha - Sgamma difference value was of 0.44 J mol -1 K -1 , in good agreement with the experimental value of 0.35 J mol -1 K -1 , at 298.15 K. Gibbs free energy values were obtained in the range between 50 K and 500 K and at ambient pressure, being possible to suggest the correct stability order among the crystalline phase: gamma > alpha > beta. The gamma→alpha phase transition was suggested at 442.55 K, in excellent agreement with the experimental value of 440 K. Sublimation properties were investigated taking in consideration the gas-phase transformations between the zwitterionic glycine, present in the crystalline phase and the gas-phase most stable conformer. These energetic terms were obtained at the CCSD(T)/CBS level. Sublimation temperature values were estimated by means of the Clausius-Clapeyron equation, with a maximum deviation of -5.31 K for the alpha-glycine, in the pressure range between 0.1 and 1 Pa, in comparison with experimental findings. Glycine gas-phase decomposition reactions, forming CO2 and CH3NH2, catalyzed by a (010) alpha-glycine surface, were investigated. For this reason, a
3 x 3 expansion containin 4 glycine layers was considered. A k-point sample of 2 x 2 x 1 was adopted. Decarboxylation reaction proceeded through a 4 steps mechanism, with barrier heights of 30.01, 112.10 and 108.83 kJ mol -1 , respectively. Therefore, the good agreement between computational investigations, reported here, and experimental findings, it is possible to suggest that the solid-solid and solid-gas reactivity model of glycine, proposed here, can be adopted for future investigations of the amino acids reactivity in the ISM.

BANKING MEMBERS:
Presidente - 1716351 - GLAUCO FAVILLA BAUERFELDT
Interno - 1220404 - CARLOS MAURICIO RABELLO DE SANT ANNA
Externo ao Programa - 1808284 - MARCIO SOARES PEREIRA
Externo à Instituição - ALEXANDRE AMARAL LEITÃO - UFJF
Externo à Instituição - RICARDO RODRIGUES DE OLIVEIRA JUNIOR - UFRJ
Externo à Instituição - IVAN GUILHON MITOSO ROCHA - ITA
Externo à Instituição - LEONARDO BAPTISTA - UERJ