Banca de DEFESA: NEUBI FRANCISCO XAVIER JUNIOR

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : NEUBI FRANCISCO XAVIER JUNIOR
DATA : 19/02/2018
HORA: 13:00
LOCAL: PQ sala 50
TÍTULO:

CONFORMATIONAL ANALYSIS AND UNIMOLECULAR REACTIONS OF GLYCINE AND ITS RADICAL CATION

PALAVRAS-CHAVES:

amino acids, astrochemistry, chemical kinetics, theoretical chemistry

PÁGINAS: 89
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Físico-Química
ESPECIALIDADE: Química Teórica
RESUMO:

The origin of life is one of humanity’s most ancient questions. Studies about the source of the first biologicals molecules have a possibility to bring some answers. Hence, the behavior of biologicals molecules in the ISM (interstellar medium) have great importance because space has hostile conditions similar with Primitive Earth`s atmosphere. Glycine is the smallest amino acid and one of the responsible for the first peptidic bonds in the planet. Despite low temperature and vacuum conditions, solid phase glycine is predominant in ISM. High energy phenomenons, like photons and electrons impact, is one of the mechanisms that promote, in ISM, the transport of a glycine fraction to gas phase. Therefore, the glycine structure and reactivity understanding, in a isolated system, become an important contribution to science. This work showed a conformational analysis and gas phase decomposition description for glycine, while in a isolated system. Those high energy phenomenons can also make desorption to occur accompanied with ionization, hence, calculations about possible conformers and decomposition reaction for glycine cation radical also were made. Theoretical calculations using the B3LYP functional 6-31++(d,p) and 6-311++(2d,2p) basis set, together with single-point calculations in CCSD(T) level of theory, for a better description of electronic energy. Rate constants for reactions have been made in different temperatures, since near to absolute zero, until ambient temperature (300K), adopting the canonical variational transition state theory. In order to still mitigate the ISM conditions, microcanonical variational rate constants have been made. Glycine conformational analysis were studied throughout a thermodynamic and kinetic interconversion scheme, making possible that the conformer that most likely will be most present in the decomposition channels. Interconversion barriers, starting from the lower energy conformer, were bigger than RT value on studied temperatures. Calculated rate coefficients, at 300K, showed a value in 10^-34 s^-1 order of magnitude for decarboxylation and 10^-17 s^-1 for deamination. Most favorable decomposition channel, including dissociations, is the deamination. The integrated kinetic study for interconversion and unimolecular reactions showed that reactions does not start from most stable conformer and there is a low probability that reactions occur at low temperatures. In cation radical form, it was characterized a smaller number of of conformers, once that, in cation radical, the NH₂ group showed planar. Only the decarboxylation saddle point were characterized for the ionized form, with a barrier height of 56 kcal/mol, while among the dissociations, the channel with HOCO and (CH₂NH₂)⁺ products showed a lower dissociation channel, of 53,04 kcal/mol. Beside that, this study suggests that cation radical is the most possible intermediate for this amino acid decomposition in ISM conditions.

MEMBROS DA BANCA:
Interno - 1716351 - GLAUCO FAVILLA BAUERFELDT
Interno - 1115883 - ANTONIO MARQUES DA SILVA JUNIOR
Externo ao Programa - 1714151 - ROBERTO BARBOSA DE CASTILHO
Externo à Instituição - LEONARDO BAPTISTA - UERJ
Externo à Instituição - GRACIELA ARBILLA DE KLACHQUIN - UFRJ
Externo à Instituição - Enio Frota da Silveira - PUC - RJ