Estudio de la influencia de la estructura del anillo B de flavonoles en sus constantes de acidez y capacidad antioxidante
Four flavonols namely: Quercetin, Morin, Kaempferol and Myricetin were studied using spectrophotometry UV/Vis, in aqueous solution. The study was performed varying the pH to analyze the stability of these compounds, and to estimate their acidity constants. In addition, the deprotonation mechanisms w...
| Autor: | |
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2014 |
| País: | México |
| Institución: | Universidad Autónoma Metropolitana |
| Repositorio: | Repositorio Institucional de la UAM Iztapalapa |
| Idioma: | español |
| OAI Identifier: | oai:bindani.izt.uam.mx:gm80hv44c |
| Acceso en línea: | https://doi.org/10.24275/uami.gm80hv44c |
| Access Level: | acceso abierto |
| Palabra clave: | info:eu-repo/classification/LEM/Free radicals (Chemistry) info:eu-repo/classification/LEM/Oxidation info:eu-repo/classification/LEM/Antioxidants info:eu-repo/classification/LEM/Radicales libres (Química) info:eu-repo/classification/LEM/Antioxidantes info:eu-repo/classification/LEM/Flavonoides -- Efectos fisiológicos info:eu-repo/classification/LEM/Oxidación info:eu-repo/classification/LEM/Chemistry info:eu-repo/classification/LEM/Química info:eu-repo/classification/LEM/Flavonoids -- Physiological effect info:eu-repo/classification/LEM/Polyphenols info:eu-repo/classification/cti/2 |
| Sumario: | Four flavonols namely: Quercetin, Morin, Kaempferol and Myricetin were studied using spectrophotometry UV/Vis, in aqueous solution. The study was performed varying the pH to analyze the stability of these compounds, and to estimate their acidity constants. In addition, the deprotonation mechanisms were studied using computational chemistry, within the Density Functional Theory framework. The calculations were performed in aqueous solution using the SMD continuum model and the results are reported as deprotonation energies. Our results show that both quercetin and myricetin are highly unstable at basic pH. Kaempferol, on the other hand, is much more stable; and morin is the only one, among the studied compounds, that was not affected by pH. In spite of this inconvenience, their acidity constants were estimated through analysis of their decomposition kinetics, correcting the spectra accordingly, and obtaining a correlation of values between the experimentally observed pKa and the calculated ∆G of successive deprotonations. On the other hand cadmium sulfide nanocrystals where synthesized and characterized using TEM. A fluorescence quenching of these nanoparticles was observed in the presence of flavonoids. This allows proposing a high selective method of determination for this kind of compounds. The percentage of inhibition depends on the structure of the compound and might be related to their antioxidant activity. The antioxidant capacity was estimated using the traditional DPPH method. The results indicate that Myricetin is the most reactive among all the studied flavonoids. Furthermore, regeneration of the catechol group in methanol was postulated. In addition computational calculations were also employed to estimate the antioxidant activity, considering different reaction mechanisms and reactions with the OOH radical. For the electron transfer mechanism the obtained trend is similar to that arising from the DPPH assay. However the predominant mechanism for the hydroperoxyl radical scavenging activity of these compounds is the hydrogen transfer. Morin was found to be the most reactive of the studied compounds via H transfer, with rate constant within the diffusion-limited regime. This methodology demonstrates the importance of considering the molar fraction of the chemical species at a fixed pH. |
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