Conjugação verde de ácido gálico a Polissacarídeos (quitosana e dextranas): avaliação química e potencialização de atividades antioxidantes
Oxidative stress occurs in cells when there is an imbalance between the amount of antioxidants and oxidants in favor of the latter, which therefore can cause more than 100 diseases. In order to combat this situation, exogenous antioxidants can be used. For this reason, there is a search for diffe...
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Formato: | doctoralThesis |
Idioma: | pt_BR |
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Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/28203 |
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Resumo: | Oxidative stress occurs in cells when there is an imbalance between the amount
of antioxidants and oxidants in favor of the latter, which therefore can cause more than
100 diseases. In order to combat this situation, exogenous antioxidants can be used.
For this reason, there is a search for different sources of antioxidant molecules,
including semi-synthetic or synthetic compounds. Polysaccharides are natural
molecules whose antioxidant capacity varies according to the polysaccharide type and
can be modified with polysaccharide conjugation with different groups such as gallic
acid (GA). Chitosan and dextran are two of the most abundant polysaccharide families
in the nature and have several applications. However, they have a low antioxidant
potential, which restricts their use. In this work, using a green conjugation method, it
was possible to conjugate GA to chitosan and dextran and the conjugation was
confirmed by the phenolic contend dosage, infrared and nuclear magnetic resonance
spectrometries. It was possible to incorporate 10.2 ± 1.5 mg GA/chitosan g, which
resulted in a 2-fold increase in total antioxidant capacity (TAC), 5-fold increase in
reducting power, and the occurrence of a ferric chelation activity (about 60%) not
observed with native chitosan. In addition, the conjugate was also able to prevent the
exacerbated formation of calcium oxalate crystals in vitro, which was observed with
the native chitosan. As regards to dextran, it is worth noting that this is the first report
of GA conjugation to this polysaccharide, which in this case was 36.8 ± 1.4 mg
GA/dextran g. Due to its novelty, the process of conjugation of dextran with GA was
subjected to a factorial design in order to understand how the variables (amount of
peroxide and amount of GA) influenced the synthesis of conjugated dextran; in its
antioxidant activities; and to obtain an ideal conjugation condition of GA to dextran. It
was verified that the amount of GA in the conjugation process is inversely proportional
to the antioxidant activities, and that the ideal condition for production of a molecule
with maximum antioxidant potential is that produced with 1.2M of hydrogen peroxide
and a 1:1 ration of GA to dextran. The ideal molecule had CAT of 60 mg AA/dextran g,
copper chelation of about 50%, and a reducing power close to 90%. In short, the GA
green conjugation method was efficient for both chitosan and dextran and in both cases
it was possible to increase the antioxidant potential of these polysaccharides,
indicating a feasible use of these derivatives as substituents of their native molecules
in key applications. |
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