Longa vida útil, alta densidade de energia, segurança ambiental, baixo custo, por-tabilidade e confiabilidade são requisitos exigidos pela moderna sociedade na produção das baterias. As baterias recarregáveis de lítio usando soluções eletrolíticas com solventes apróticos atendem, em princípio, estes requisitos. Ao se usar uma solução eletrolítica for-mada por LiPF6, etilenocarbonato (EC) e dietilcarbonato (DEC) a separação de fase começa em cerca de –220C. Se o DEC for substituído pelo metiletilcarbonato (MEC) o início da separação de fase cai para –400C. Este é um bom resultado para aplicações tecnológicas, especialmente em baterias de lítio. A presente tese relata, do ponto de vista teórico, a formação do par iônico LiPF6, a estrutura de solvatação do cátion lítio pelo MEC e a coordenação competitiva do cátion lítio em um mistura formada pelos solventes EC e MEC. Todos os cálculos foram feitos a nível MP2, Hartree-Fock e DFT usando o programa Gaussian 98. As estruturas geométricas dos complexos Li+MEC, Li+(MEC)2, Li+(MEC)3, Li+(MEC)4, e Li+(MEC)5 foram obtidas usan-do vários níveis de teoria. Os espectros de infravermelho e Raman e seus respectivos assi-nalamentos foram obtidos para os compostos PF6¯, LiPF6 (nas simetrias C4V, C3V e C2V), MEC, Li+MEC, Li+(MEC)2. O número máximo de coordenação do cátion lítio pelo MEC obtidos nos cálculos de DFT situa-se entre 3 e 4. Os resultados dos cálculos mecânico-quânticos apontam para uma coordenação seletiva do Li+ em uma mistura de EC e MEC. Na formação do par iônico, a estrutura energeticamente mais favorável encontrada nos cál-culos foi a C3V(tridentada). As ftalocianinas (Pc) constituem outro grupo de moléculas com grandes possibili-dades para aplicações tecnológicas. Algumas ftalocianinas exibem fotossensibilidade no infravermelho próximo e podem ser usadas em conjunto com os diodos de laser nas impres-soras de alta velocidade. Outras ftalocianinas estão sendo testadas para aplicações em tera-pia fotodinâmica contra alguns tipos de câncer. A segunda parte da presente tese relata os resultados realizados sobre as proprie-dades geométricas e eletrônicas das ftalocianinas de alumínio (AlPc+1, OAlPc-1, FAlPc, ClAlPc, BrAlPc, IAlPc, F2AlPc, Cl2AlPc, (CO)AlPc+1, (CO)2AlPc+1, N2AlPc+1, (N2)2AlPc+1), ftalocianinas de silício (SiPc+2, OSiPc, FSiPc+1, ClSiPc+1, F2SiPc, Cl2SiPc, COSiPc+2) e as metal-ftalocianinas, com o metal pertencente à primeira fila dos elementos de transição. Os espectros vibracionais de infravermelho para as ftalocianinas acima men-cionadas também foram investigados. O ligante axial apresenta influência na posição da banda Q (banda de mais baixa energia) no espectro de UV/visível dos derivados ftalocianí-nicos. As geometrias e os espectros de infravermelho foram obtidos usando a teoria do fun-cional da densidade com o método híbrido B3LYP. Os espectros das transições eletrônicas foram obtidos usando o programa ZINDO/S.

Highly correlated quantum chemical methods have been appliedto study the photophysical properties of substituted benzenes.With the inclusion of spin-orbit coupling, the phosphorescencesof these molecules have been calculated usingMulti-CongurationalSelf- Consistent Field (MCSCF) quadraticresponse theory. The Herzberg-Teller approximation has beenadopted to evaluate the vibronic contributions tophosphorescence. The performance of hybrid density functional theory (DFT) atthe B3LYP level is examined in comparison to the MP2, CCSD andCCSD(T) methods for the geometry and permanent dipole moment ofp-aminobenzoic acid. The time-dependent DFT/B3LYP method isapplied to calculate the two-photon absorption of a series ofZinc-porphyrin derivatives in combination with a two-statemodel. The transitions between excited singlet and tripletstates of Zinc and Platinum based organometallic compounds havebeen computed using DFT quadratic response theory. The resultsare used to simulate the non-linear propagation of laser pulsesthrough these materials utilizing a dynamical wave propagationmethod.

Despite the growing applications of silver nanoparticles, toxicity information on this nanomaterial is still deficient. Conclusions on the toxicity of silver nanoparticles vary and atomic level toxicity mechanisms are not yet achieved. Consequently, our group conducted combined computational and experimental toxicity studies of silver nanoparticles (AgNPs). Toxicity of 10 nm citrate stabilized AgNPs on HepG2 cells were investigated. Experimental results show that the 10 nm citrate stabilized AgNPs begin to be toxic to HepG2 cells at a dosage that exceeds 1 ppm and LD50 was observed at 3 ppm. Elevated reactive oxygen species levels were seen upon exposure to AgNPs with the maximum at the LD50 concentration of 3 ppm. Normal protein regulation of HepG2 cells were affected by exposure to AgNPs. TEM images of HepG2 cells exposed to AgNPs reveal that AgNPs can penetrate and agglomerate inside the cells. Our preliminary computational study was guided by one of the widely accepted toxicity mechanism of AgNPs in which the nanoparticles dissolute to Ag+. The computational model was composed of a 1:1 ratio of silver and phospholipid head. The silver employed are in atomic and anionic form while the phospholipid head are the phosphocholine (PC) and phosphoethanolamine (PE), which are abundant in HepG2 cells. Computational study shows that the presence of Ag+ results in partial oxidation of both the phospholipid heads. Our preliminary experimental and computational studies lead us to develop new computational methods that can accurately predict oxidation potentials (HOMO), reduction potentials (LUMO), and absorption spectra that can be used in studying toxicity mechanism of AgNPs through the oxidation pathway. Thus, computational methods for cyclic voltammetry and absorption spectroscopy that use DFT and TD-DFT, respectively, were improved to provide more accurate electronic and optical properties. Cyclopenta-fused polycyclic hydrocarbons (CP-PAHs) with available experimental data for HOMO, LUMO, ΔEgap and absorption spectra and have potential application as AgNP stabilizers were used in developing the improved computational methods for cyclic voltammetry and absorption spectroscopy. The improved computational method for cyclic voltammetry was developed by accounting for the anion species that occur experimentally and by using B3LYP the best density functional in predicting the HOMO, LUMO and ΔEgap of CP-PAHs with overall MAE of 014 eV. The best absorption spectra otef CP-PAHs were predicted using B3LYP for geometry optimizations followed by TD-CAMB3LYP with MAE of 29 nm. All calculations of CP-PAHs were implemented using the 6-311g (d,p) basis set and tetrahydrofuran (THF) as solvent. These two developed computational methods were tested on a group of methyl triphenyl amine (MTPA) derivatives with available experimental data for HOMO, LUMO, ΔEgap and absorption spectra and have potential application as AgNP stabilizers. The new computational methods for cyclic voltammetry and absorption spectroscopy also provided the most accurate predicted electronic and optical properties of MTPA derivatives. Among the ten density functionals employed, prediction of HOMO, LUMO and ΔEgap were most accurate using B3LYP and B3PW91 with overall MAE of 0.31 eV and 0.27 eV, respectively. Absorption spectra of MTPA derivatives were still best predicted using the B3LYP/TD-CAMB3LYP method with MAE of 13 nm. All calculations of MTPA were implemented using the 6-31+g (d,p) basis set and dichloromethane as solvent.

Made available in DSpace on 2017-07-24T19:37:53Z (GMT). No. of bitstreams: 1 Renan Augusto Ribeiro.pdf: 3827899 bytes, checksum: 9440ed4880cbb0fbf9997c789341ea92 (MD5) Previous issue date: 2015-03-12 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The development of spintronic has motivated the research for new half-metallic magnetic materials due to multifunctionality of these compounds and the spin-based devices fabrication with increased performance as compared to the usual electronic devices. From this perspective, we propose a theoretical investigation of FeBO3 (B = Ti, Zr, Hf, Si, Ge, Sn) ilmenite materials based on Density Functional Theory (DFT) within B3LYP hybrid functional to investigate the B-site cation replacement effect on the structural, elastic, magnetic and electronic properties of ilmenite materials. Calculated structural parameters are in agreement with experimental results and shown that the unit cell volume can be controlled by ionic radius of the B-site metals. The bond distances for FeO6 and BO6 octahedral clarify the Jahn-Teller distortion and Fe-O-B-O-Fe intermetallic connection. The elastic behavior was investigated from bulk modulus and showed that such results were influenced by different material densities. Furthermore, these quantities can be used for analyzing the thermodynamic stability of solids, proving that FeSnO3 and FeHfO3 are unstable due to the negative values for bulk modulus. The B-site radius effect is also evidenced on the magnetic property, where Fe(Ti, Si, Ge)O3 are antiferromagnetic, while Fe(Zr, Hf, Sn)O3 are ferromagnetic. The Mulliken population analysis and charge density maps show the charge corridor formation in the [001] direction due to the intermetallic connection with the B-site metals and electronegativity affecting the stability of ilmenite materials. The Density of States and Band Structure profiles show that antiferromagnetics materials and FeZrO3 are convectional semiconductors, whereas FeHfO3 and FeSnO3 exhibit intrinsic half-metallic behavior, making them promising candidates for spintronic devices. / O desenvolvimento da spintrônica tem motivado a busca por novos materiais magnéticos com comportamento meio-metálico devido à multifuncionalidade desses compostos e ao desenvolvimento de dispositivos baseados no spin do elétron, proporcionando um aumento do desempenho em relação aos dispositivos eletrônicos usuais. Nesse trabalho, propomos a investigação teórica, baseada na Teoria do Funcional de Densidade utilizando o funcional híbrido B3LYP, dos materiais FeBO3 (B = Ti, Zr, Hf, Si, Ge, Sn) na estrutura ilmenita com objetivo de esclarecer o efeito da substituição do cátion B sobre as propriedades estruturais, elásticas, magnéticas e eletrônicas. Os parâmetros estruturais calculados se mostraram em concordância com resultados experimentais e teóricos, revelando que o volume da célula unitária é controlado pelo raio iônico do cátion B. As distâncias de ligação calculadas para os octaedros FeO6 e BO6 indicam a existência do efeito de distorção Jahn-Teller e da conexão intermetálica Fe-O-B-O-Fe. O comportamento elástico foi investigado a partir do bulk modulus, indicando que tal entidade é dependente da densidade dos materiais e discute-se a possibilidade de utilizar esse fator para análise da estabilidade termodinâmica de sólidos, sugerindo a instabilidade dos materiais FeSnO3 e FeHfO3 devido aos valores negativos de bulk modulus. O efeito do tamanho dos cátions B é evidenciado sobre as propriedades magnéticas dos materiais, sendo que Fe(Ti, Si, Ge)O3 são antiferromagnéticos; enquanto que, Fe(Zr, Hf, Sn)O3 são ferromagnéticos. A análise populacional de Mulliken e os mapas de densidade de carga mostraram a formação de um corredor de carga nas conexões intermetálicas observadas na direção [001] e que a eletronegatividade dos cátions B afeta a estabilidade dos materiais com estrutura ilmenita. Os perfis de Densidade de Estados e Estrutura de Bandas mostram que os materiais antiferromagnéticos e o FeZrO3 são semicondutores convencionais, entretanto, FeHfO3 e FeSnO3 exibem comportamento meiometálico intrínseco, tornando-os promissores candidatos para dispositivos spintrônicos, porém, com outra estrutura.

No description available.

The prediction of detonation properties of the new generation of high-nitrogen energetic materials (HNEM) is based on knowledge of their heats of formation, which are sum of values of particular nitrogen heterocyclic fragments. The diploma thesis describes theoretical calculations of heats of formation in gas phase ?f H°(298,g) for series of azines (number of N atoms 2-6) and azoles (number of N atoms 2-5) by means of quantum chemical methods. The semiempirical methods as PM3, DFT methods utilizing isodesmic approach and finally thermochemical G-recipes were used. All calculated values of heats of formation were scrutinized and for future application to HNEM materials the DFT B3LYP/cc-pVTZ method and thermochemical recipe T1 were recommended.

The main goal of the presented thesis is a theoretical study of heat of formation for high-nitrogen energetic materials. A modification of the classical approach to the isodesmic reactions is realized with the intent that molecules on both sides of the corresponding equation have not only the same number of atoms but also approximately the same size and skeletal similarity. This approach is designated as a method "Alternative Isodesmic Reaction (AIR method)". At its base, using the DFT B3LYP / cc-pVTZ and B3PW91 / cc-pVTZ, for the high nitrogen heterocycles, which are selected from the group of triazoles, triazines, tetrazines, the enthalpy of formation values the gaseous phase f H°(298,g), were obtained whose values are close to the published f H°(298,g). Their application in the calculation of the relevant characteristics of these heterocycles detonation gave real values.

Covalent functionalization significantly enhances the utility of carbon nanomaterials for many applications. In this study, we investigated the functionalization of double nitrogen doped graphene by the addition of different alkyl and phenyl functional groups at N atoms in syn and anti-configurations. Density functional theory calculations at the B3LYP/def-SV(P) level were employed to understand the syn versus anti preference on functionalization. The bond lengths, bond angles, relative energies, deformation energies and HOMO-LUMO energy gaps, of the syn and anti-configurations of the functionalized 2N-doped graphenes, have been compared. Functionalization with two groups leads to considerable deformation of 2N-doped graphene, which is confirmed by the change in C–N bond lengths by attachment of the functional groups. The attachment of larger functional groups deforms 2N-doped graphene to a greater extent than smaller functional groups. The HOMO-LUMO energy gap values are the least for the alkyl functionalized products, indicating that these structures are kinetically less stable than the phenyl functionalized products.

Computer modeling of enzymes is a valuable complement to experiments. Quantum chemical studies of enzymatic reactions can provide a detailed description of the reaction mechanism and elucidate the roles of various residues in the active site. Different reaction pathways can be analyzed, and their feasibility be established based on calculated energy barriers. In the present thesis, density functional theory has been used to study the active sites and reaction mechanisms of three different enzymes, cytosine deaminase (CDA) from Escherichia coli, ω-transaminase from Chromobacterium violaceum (Cv-ωTA) and dinitrogenase reductase-activating glycohydrolase (DraG) from Rhodospirillum rubrum. The cluster approach has been employed to design models of the active sites based on available crystal structures. The geometries and energies of transition states and intermediates along various reaction pathways have been calculated, and used to construct the energy graphs of the reactions. In the study of CDA (Paper I), two different tautomers of a histidine residue were considered. The obtained reaction mechanism was found to support the main features of the previously proposed mechanism. The sequence of the events was established, and the residues needed for the proton transfer steps were elucidated. In the study of Cv-ωTA (Paper II and Paper III), two active site models were employed to study the conversion of two different substrates, a hydrophobic amine and an amino acid. Differences and similarities in the reaction mechanisms of the two substrates were established, and the role of an arginine residue in the dual substrate recognition was confirmed. In the study of DraG (Paper IV), two different substrate-binding modes and two different protonation states of an aspartate residue were considered. The coordination of the first-shell ligands and the substrate to the two manganese ions in the active site was characterized, and a possible proton donor in the first step of the proposed reaction mechanism was identified. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Ce travail présente une étude théorique des spectres RMN de molécules biologiques. Dans la première partie, les calculs DFT des paramètres RMN (déplacements chimiques et constantes de couplage spin-spin) pour les protons liés à des atomes de carbone ont été réalisés pour quatre métabolites de la prostate: la putrescine, la spermidine, la spermine, et la sarcosine, et trois métabolites du cerveau: l'acétate, l'alanine et la sérine. Une étude théorique systématique, dans l'approche DFT, des paramètres de RMN des métabolites a montré que la méthode B3LYP/6- 311++G** est un bon compromis entre la précision et les coûts. Les contributions du solvant ont été évaluées en utilisant le modèle PCM, les effets des isomères, pondérés dans l'approximation de Boltzmann, ont été pris en compte, et les corrections de vibration de point zéro ont été estimées en utilisant une approche perturbative au second ordre. La comparaison avec l'expérience a démontré que tous ces effets sont nécessaires pour améliorer l'accord entre les données calculées et expérimentales, aboutissant à des résultats de grande précision. Dans la deuxième partie, nous avons développé un nouveau modèle, BioShift, qui permet la prédiction des déplacements chimiques des différents noyaux (H, N, C ...) pour des molécules biologiques (protéines, ADN, ARN, polyamine ...). Il est simple, rapide, et comporte un nombre limité de paramètres. La comparaison avec des modèles sophistiqués conçus spécialement pour la prédiction des déplacements chimiques des protéines a montré que Bioshift est concurrentiel avec de tels modèles.