Ciencias Exactas y Ciencias de la Salud
Permanent URI for this collectionhttps://hdl.handle.net/11285/551039
Pertenecen a esta colección Tesis y Trabajos de grado de las Maestrías correspondientes a las Escuelas de Ingeniería y Ciencias así como a Medicina y Ciencias de la Salud.
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- Synthesis, characterization, and structural determination of ferrispinels(Instituto Tecnológico y de Estudios Superiores de Monterrey, 2022-06-14) Murrieta Muñoz, Ana Cecilia; CONTRERAS TORRES, FLAVIO FERNANDO; 132171; Contreras Torres, Flavio Fernando; puelquio/mscuervo, emipsanchez; Medel Cobaxin, Héctor Javier; Rodríguez Macías, Fernando Jaime; Lozano García, Omar; School of Engineering and Sciences; Campus MonterreySpinel (AB2X4) crystalline system is typically characterized by a distribution of cations that can move from tetrahedral (A) to octahedral (B) sites. This movement also involves the X anions rearrangement into the cubic lattice. Accordingly, spinels can exhibit A-sites and B-sites distribution characterized by a partial to total cell inversion degree (x=1). We are interested in Zn-ferrites due to their chemical and thermal stability, ferrimagnetic properties, and earth abundance. ZnFe2O4 shows the unitary cell for a typical spinel structure; however, some previous reports suggested that this spinel can be inverted at the nanoscale regime. Hence, it is expected that ZnFe2O4 nanoparticles might show a ferrimagnetic behavior, which is an outstanding property for several applications, including high-density magnetic data storage and water splitting. The structural determination and microstructure properties are of great value in analyzing the cell inversion degree for particles synthesized following a proposed experimental design. In this Thesis, we synthesized nano and sub-micro, beam-like, and amorphous particles using a hydrothermal method varying the proportion of reactants, reaction time, and reagents. The morphology and size of the as-prepared particles were characterized by scanning electron microscopy. Atomic chemical composition and elemental stoichiometry were determined using energy-dispersive X-ray and inductively coupled plasma optical emission spectroscopy. Raman spectroscopy measurements indicate redshifts notably observed for the symmetric mode. Such wavenumber increments suggest that the frequency of phonons interacting with the incident photon is decreasing, probably due to the improved crystallinity during annealing treatments. The crystalline evolution was followed by X-ray diffraction. At the same time, lattice parameters were obtained from Rietveld refinements, and microstructure properties were assessed via Williamson-Hall type fittings. The cell parameter is estimated to be about 8.44 nm. The crystallite sizes range from 9 to 65 nm, and the microstrain is less than 0.2%. Finally, the degree of inversion of the crystalline system was evaluated using the Bertaut method. The cell inversion degree follows as 0.85 (400 °C), 0.67 (600 °C), and 0.38 (800 °C), suggesting that the annealing process helps to restore a standard spinel structure. Our simple synthesis method facilitates the tuning of the size and shape of particles, which appropriately leads to improved crystallinity as observed from structural parameters and cell inversion degrees. In this way, we assisted in evaluating and comparing the synthesis parameters to obtain ZnFe2O4 particles with different cell inversion degrees, sizes, and microstrain. We believe that this analysis could be replicated in other spinel structures and might help evaluate the relationship between their structure and magnetic properties.
- Adsorption mechanisms of glycine onto graphene oxide models: a computational approach from DFT and AIMD simulations(Instituto Tecnológico y de Estudios Superiores de Monterrey, 2021-11-20) Abril Martinez, Fausto Guilherme; CONTRERAS TORRES, FLAVIO FERNANDO; 132171; Contreras Torres, Flavio Fernando; emipsanchez; Cholula Díaz, Jorge Luis; López Aguayo, Servando; Medel Cobaxin, Héctor Javier; Escuela de Ingeniería y Ciencias; Campus MonterreyNanomedicine is a nanotechnology application based on the engineering of nanomaterials to develop tools for diagnosis, prevention, imaging, and treatment of diseases. Understanding the interaction mechanisms between nanomaterials and biomolecules is essential in creating novel sensing platforms such as electrochemical devices, drug delivery systems, and biosensors. Carbon has become the most widely used nanomaterial in the 21st century. Graphene (G) is the most important allotrope because of its intrinsic properties, such as a zero bandgap. However, due to the sophisticated synthesis procedures, several related G materials are proposed to be used in applications. Graphene oxide (GO) contains oxidized functional groups on the surface, which can serve to functionalize with other molecules and thus enhance the chemical and physical properties as compared to graphene. Moreover, structural defects can appear in both G and GO materials which are also influenced by the properties of these materials. G and GO can have a perfect lattice or contain Stone-Wales structural defects that are formed by rotating a C-C bond 90º, which creates a 5-7 ring pair. The investigation of interactions of important biomolecules with carbon-based nanomaterials (CNMs) has emerged in an explosion of research since CNMs are extensively proposed for biological assays to detect biomarkers facilitating their detection and optical imaging in biological systems. In this way, amino acids (AAs) are the critical chemical structures in organisms. AAs are known as the building blocks of proteins. AAs can manifest the common physical-chemical properties of more significant biomolecules. Glycine (GLY) is the simplest amino acid; therefore can serve as a simple novel to evaluate this amino acid's adsorption process in CNMs. A first approximation of the interaction mechanism between G (or GO) with GLY can be studied at a fundamental level using theoretical approaches. Density functional theory (DFT) and Ab-initio molecular dynamics (AIMD) are modern tools to gain insights into the interaction mechanisms and microscopic details of chemical processes in both gas-phase and solvent medium (e.g., water). DFT is a set of quantum mechanical approaches to investigate the electronic structure of a system at its ground state. However, DFT is not accurate for accounting for noncovalent intermolecular interactions, and they can be described using semi-empirical approaches. Atom-pairwise specific dispersion coefficients (–C6/R6) and cutoff radii that are both computed from time-dependent first principles have proved to be a valuable alternative to capture dispersion interactions in the G∙∙∙GLY complexes adequately. On the other hand, AIMD resolves the classical dynamics of the nuclei numerically, and at each time step, the forces are computed to minimize the Kohn-Sham DFT energy functional at a current nuclear configuration. AIMD can allow both equilibrium thermodynamic and dynamical properties of G∙∙∙GLY interactions at finite temperature to be computed. The objective is to analyze the adsorption mechanisms of neutral glycine onto graphene oxide models using dispersion-corrected DFT and AIMD approaches and compare their stability when including Stone-Wales structural defects. DFT studies were computed to study the adsorption sites of GLY on G and GO flakes models. A molecular system of C42 atoms (including 16 H atoms saturating dangling bonds) was used to model the graphene flakes. These graphene structures were varied with hydroxyl groups, glycine moieties, and structural defects on the surface. In particular, Stone-Wales (SW) sites containing 5 and 7 member rings at the center of the graphene flake were used to mimic structural detects. Interactions of GLY neutral molecules with the perfect lattice and SW sites were investigated in both the gas-phase (vacuum) and dissolvent medium (water). AIMD simulations at room-temperature and total relaxation of atomic positions are performed to study adsorption sites on the perfect lattice and SW defects for G and GO models. Interactions of GLY neutral molecules with both models are investigated. DFT and AIMD simulations were carried out using the ORCA quantum chemistry package. It was found that the GLY molecule interacts with the perfect graphene lattice through noncovalent bonds, and the interaction energy was computed in about −16 kcal/mol. Hydrogen bridges between the hydroxyl groups of GOs models and the –NH2 from GLY lead to total interaction energy of about −24 kcal/mol. However, the –COOH moiety of GLY binds to the hydroxyl groups of GOs with interaction energy of about −33 kcal/mol. The respective interaction energy amounts to about −44.53 kcal/mol for a configuration with Stone-Wales defects. AIMD simulations showed that GLY could stay bonded to the graphene surface to reach a thermodynamic equilibrium (>25 fs) and form simultaneous hydrogen bonds. The molecular dynamics simulations indicate that the complexes and the reservoir tend to thermal equilibrium when the temperature is lowered by about 100 K. The AIMD simulations suggested that after 25 fs, the configuration for the complexes is not different from 0 K. It was suggested that GLY form mainly noncovalent complexes depending on the G (or GO) model. G and GLY can interact from –16 kcal/mol to -34 kcal/mol. This energy value is about 3 to 9 times the average noncovalent interaction energy. Furthermore, it was shown that Stone-Wales defects cause minor changes in the complex configurations, interaction energies, and thermodynamic stability. AIMD results indicate that after 25 fs, the initial structure at 0 K will not differ after the relaxation of atomic positions at room temperature. In summary, we studied and discussed the interaction mechanisms between neutral glycine and graphene, graphene oxide models to gain insights into the adsorption interaction, potential energies, and their thermodynamic stability based on DFT and AIMD approaches. As future work, it is proposed to study the noncovalent interaction for these proposed graphene oxide models with other AAs to gain a complete understanding of the adsorptive properties for these critical biomolecules. It is proposed to increase the time frame for AIMD simulations because biochemical events of interest, such as structural changes in proteins, take place on timescales in the nano or microseconds order. Finally, the basis set level might have an impact on the accuracy of the obtained energies, and thus it is recommendable to extend to a triple-zeta basis set.
- Toxicological evaluation of the TiO2 anatase and rutile crystalline phases in H9c2 cardiac cells(Instituto Tecnológico y de Estudios Superiores de Monterrey, 2020-12-05) Santos Aguilar, Pamela; CONTRERAS TORRES, FLAVIO FERNANDO; 132171; Contreras Torres, Flavio Fernando; emipsanchez; Lozano García, Omar; Silva Platas, Christian Iván; Salas Treviño, Daniel; School of Engineering and Sciences; Campus Monterrey; García Rivas, Gerardo de JesúsAlthough TiO2 particles constitute a highly used material in consumer products, including food and pharmaceutical industries, considerable experimental evidence suggests that TiO2 particle exposure could be harmful and cause adverse health effects. Generally, the most studied factor for toxicity is size as nano, and fine particles are considered more toxic than bulk forms. The second structural factor most studied is the crystalline phase. The TiO2 rutile phase is considered a more inert phase than the highly active, high-refractive-index anatase phase. The cytotoxicity of TiO2-anatase has been related to that these particles can induce higher production of reactive oxygen species (ROS), which is a trigger of apoptosis pathway and alteration of mitochondrial membrane potential in cells. However, such a toxicological susceptibility to the TiO2-anatase phase may differ from the one initiated by the TiO2-rutile phase, suggesting a different cell death mechanism, which is not known at the detail. In this thesis, a series of experimental measurements were carried out to analyze TiO2-anatase and TiO2-rutile submicron-sized particles' physical properties. The TiO2 particles in anatase phase were transformed to rutile phase through a heating process, and then both were analyzed by Raman spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), and zeta potential. The evaluation of the toxicity of TiO2 particles in H9c2 cardiac cells to identify the role of the crystalline phase that may pose a health risk in a dose-dependent manner is the main objective of this study. The TiO2-anatase and TiO2-rutile particles' toxicity assessment was conducted in vitro, evaluating the metabolic activity, the plasma membrane integrity, mitochondrial superoxide production, and intracellular redox state. The particles' characterization by XRD and Raman spectroscopy confirmed the successful transformation of anatase particles to the rutile phase through a heating process. By DLS, it was confirmed that the hydrodynamic particle diameter was 166 nm and 468 nm for anatase and rutile, respectively. At the same time, further analysis by XLPA methods: Williamson-Hall and Warren Averbach showed that the apparent crystallite size of anatase is larger than for rutile. SEM microscopy identified that anatase particles had a spheric-like shape while for rutile were slightly more elongated. H9c2 cells show metabolic activity inhibition of 50% at an approximate value of 30 μg/mL when exposed to either anatase or rutile particles for 24 h. However, the dose-dependent inhibition at lower or higher values of the IC50 is dependent on the crystalline structure. Neither anatase phase nor rutile phase reduces the number of viable cells through necrosis; however, cell death has been categorized as early or late apoptosis for both particles. No significant alteration of the intracellular redox state at any particle exposure concentration between 0.3 μg/mL – 30 μg/mL was observed. On the other hand, for anatase, a 3-fold increase in mitochondrial superoxide production at 30 μg/mL was found, indicating that the intrinsic mitochondrial apoptotic pathway might mediate the apoptosis. However, for rutile, there is no increase in mitochondrial ROS production, suggesting that the cell death mechanism is dependent on a different metabolic pathway independent of the mitochondria.