Uracila (U), timina (T) e citosina (C) sÃo bases nitrogenadas do tipo pirimidÃnicas. Essas juntamente com as outras duas bases pÃricas adenina (A) e guanina (G), formam as bases essenciais da molÃcula do Ãcido ribonucleico (ARN) e Ãcido desoxirribonucleico (ADN), que contÃm as informaÃÃes genÃticas usadas pelas cÃlulas vivas. Os cristais de ADN e ARN apresentam caracterÃsticas semicondutoras bastantes atrativas na Ãrea de eletrÃnica orgÃnica, e por este motivo sÃo fortes candidatos na fabricaÃÃo de nanodispositivos moleculares. No entanto, os avanÃos nessa Ãrea ainda sÃo prematuros. Nesse trabalho sÃo apresentadas as propriedades estruturais, eletrÃnicas e Ãpticas dos cristais anidros das bases nucleotÃdicas pirimidÃnicas. Os resultados teÃricos foram obtidos apÃs cÃlculos baseados na teoria do funcional da densidade DFT, sob uma energia de corte de 830 eV, utilizando a aproximaÃÃes da densidade local (LDA) e do gradiente generalizado (GGA), nessa Ãltima foi incluindo correÃÃes empÃricas para interaÃÃes dispersivas (PBE+TS) disponÃveis no pacote CASTEP. Os resultados computacionais foram comparados entÃo com os experimentos de absorÃÃo Ãtica e de absorÃÃo UV para os cristais. Estudos teÃricos aplicados a cristais de citosina, timina, adenina e guanina jà estÃo disponÃveis na literatura. No entanto, faltava ainda uma descriÃÃo utilizando funcionais mais sofisticado como o adotado neste trabalho. Os valores de absorÃÃo apresentados para os cristais de uracila, timina e citosina mostra que estes possuem, respectivamente, gaps indireto, direto e indireto com valores obtidos de 4,03 eV, 3,80 eV e 4,20 eV. Como esperado, os resultados GGA+TS mostraram gaps de energia menores dos que os valores experimentais: 3,45 eV (U), 3,47 eV (C) e 3,50 eV (T). CÃlculos de massa efetiva confirmam os dados da literatura de que as bases, em geral, sÃo semicondutores de gaps largos. Por fim, os resultados obtidos por DFT sugerem um razoÃvel grau de anisotropia Ãptica para a absorÃÃo e funÃÃo dielÃtrica complexa, especialmente na uracila e timina / Uracil (U), thymine (T) and cytosine (C) are nitrogenous bases of the pyrimidine type. These along with the other two bases purines adenine (A) and guanine (G), form the essential basis of the ribonucleic acid molecule (RNA) and acid deoxyribonucleic (DNA), which contains the genetic information used by living cells. DNA and RNA crystals have enough attractive semiconductor characteristics in the field of organic electronics, and for this reason are strong candidates in the manufacture of molecular nanodevices. However, advancements in this area are still premature. This work presents the structural, electronic and optical of the anhydrous crystals of pyrimidine nucleotide bases. The theoretical results were obtained after calculations based on density functional theory (DFT), with an energy cut of 830 eV, using the approximations of local density (LDA) and generalized gradient (GGA), this last one including empirical corrections to dispersive interactions (PBE + TS) available at CASTEP package. The computational results were then compared with the crystals experiments of optical absorption and UV absorption. Theoretical studies applied to the crystals cytosine, thymine, adenine and guanine are already available in the literature. However, it is still missing a description using a more sophisticated functional as was used in this work. The absorption values obtained for the uracil, thymine and cytosine crystals shows that these have, respectively, indirect, direct and indirect gaps with values of 4.03 eV, 3.80 eV and 4.20 eV. As expected, the theoretical results exhibited energy gaps lower than the experimental values: 3.45 eV (U), 3.47 eV (C) and 3.50 eV (T). Effective mass calculations confirm literature data that the bases are generally wide gap semiconductor. Finally, the results obtained by DFT suggest a reasonable degree of optical anisotropy for the absorption and complex dielectric function, especially in uracil and thymine. As expected, the theoretical results exhibited energy gaps lower than the experimental values: 3.45 eV (U), 3.47 eV (C) and 3.50 eV. (T). Effective mass calculations confirm the literature data that the bases are semiconductor with wide gaps. Finally, the results obtained by DFT suggest a reasonable degree of optical anisotropy for the absorption and complex dielectric function, especially in the uracil and thymine cases.
| Identifer | oai:union.ndltd.org:IBICT/oai:www.teses.ufc.br:10569 |
| Date | 29 January 2016 |
| Creators | Mauricelio Bezerra da Silva |
| Contributors | Valder Nogueira Freire |
| Publisher | Universidade Federal do CearÃ, Programa de PÃs-GraduaÃÃo em FÃsica, UFC, BR |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da UFC, instname:Universidade Federal do Ceará, instacron:UFC |
| Rights | info:eu-repo/semantics/openAccess |
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