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Advisor(s)
Abstract(s)
A peroxidação lipídica, além de causar sérios danos no corpo humano, é a principal
causa da deterioração dos alimentos afectando a sua cor, aroma e valor nutricional, o
que conduz a uma diminuição do seu ciclo de vida. O fenómeno de oxidação pode ser
retardado com recurso a antioxidantes, de origem natural ou sintética, que inibam a
formação de espécies reactivas, ou que reajam com estas, formando posteriormente
radicais com menor grau de reactividade.
Nesta dissertação procedeu-se à síntese e elucidação estrutural de novos antioxidantes,
derivados dos ácidos 3,4-diidroxibenzóico (PCA) e 3,4-diidroxifenilacético (DOPAC), e à
avaliação da sua actividade anti-radicalar e antioxidante. Os novos antioxidantes
sintetizados foram caracterizados usando RMN de 1H e de 13C, FTIR e EM-IE. A
avaliação da actividade antioxidante foi realizada com base no método do radical 2,2-
difenil-1-picrilhidrazilo (DPPH·) e por técnicas electroquímicas (voltametria de impulso
diferencial e voltametria cíclica).
Os resultados obtidos permitiram concluir que a eficácia anti-radicalar (AE) é determinada
por aspectos da estrutura molecular dos compostos, nomeadamente pela presença de
grupos hidroxilo no anel aromático e também de grupos extensores relativamente à
posição do grupo carboxílico. Os resultados permitiram verificar que o DOPAC apresenta
a mais elevada eficiência anti-radicalar dos compostos em estudo, incluindo o trolox e o
ácido gálhico (compostos de referência).
Com base nos resultados obtidos concluiu-se que, um menor potencial de oxidação
conduz a uma melhor actividade anti-radicalar dos compostos. De facto, verificou-se para
o PCA e respectivos ésteres o maior potencial de oxidação e também a menor eficiência
anti-radicalar. Em contrapartida, os antioxidantes com maior eficiência anti-radicalar,
DOPAC, trolox e ácido gálhico, apresentaram menor potencial de oxidação.
The lipid peroxidation, besides causing serious damage to the human body, is the main cause of deterioration of food affecting its colour, flavour and nutritional value, leading to a decrease in its life cycle. The phenomenon of oxidation can be delayed using antioxidants of natural or synthetic origin, which inhibit the formation of reactive species, or that subsequently react with these leading to less reactive radicals. In this dissertation we proceeded to the synthesis and structural elucidation of new antioxidants, esters derived from 3,4-dihydroxybenzoic acid (PCA) and 3,4- dihydroxyphenylacetic acid (DOPAC), and the evaluation of its anti-radical and antioxidant properties. The new synthesized antioxidants were characterized using 1H and 13C NMR, FTIR and MS-IE. The evaluation of the antioxidant activity was based on the method of 2,2-diphenyl-1-picryl hydrazyl radical (DPPH) and electrochemical techniques (differential pulse voltammetry and cyclic voltammetry). The results showed that the anti-radical efficiency (AE) is determined by aspects of the molecular structure of compounds, particularly the presence of hydroxyl groups on aromatic ring and also of spacer groups towards the position of carboxylic acid group. The results have shown that DOPAC presents the highest anti-radical efficiency of the compounds under study, including trolox and gallic acid (reference compounds). Based on the results it was concluded that, a smaller potential for oxidation is generally associated to highest anti-radical activity of the compounds. In fact, PCA and its esters presented the greatest potential for oxidation and also the lesser anti-radical efficiency. In contrast, the antioxidants with more anti-radical efficiency, DOPAC, trolox and gallic acid, showed the lowest potential of oxidation.
The lipid peroxidation, besides causing serious damage to the human body, is the main cause of deterioration of food affecting its colour, flavour and nutritional value, leading to a decrease in its life cycle. The phenomenon of oxidation can be delayed using antioxidants of natural or synthetic origin, which inhibit the formation of reactive species, or that subsequently react with these leading to less reactive radicals. In this dissertation we proceeded to the synthesis and structural elucidation of new antioxidants, esters derived from 3,4-dihydroxybenzoic acid (PCA) and 3,4- dihydroxyphenylacetic acid (DOPAC), and the evaluation of its anti-radical and antioxidant properties. The new synthesized antioxidants were characterized using 1H and 13C NMR, FTIR and MS-IE. The evaluation of the antioxidant activity was based on the method of 2,2-diphenyl-1-picryl hydrazyl radical (DPPH) and electrochemical techniques (differential pulse voltammetry and cyclic voltammetry). The results showed that the anti-radical efficiency (AE) is determined by aspects of the molecular structure of compounds, particularly the presence of hydroxyl groups on aromatic ring and also of spacer groups towards the position of carboxylic acid group. The results have shown that DOPAC presents the highest anti-radical efficiency of the compounds under study, including trolox and gallic acid (reference compounds). Based on the results it was concluded that, a smaller potential for oxidation is generally associated to highest anti-radical activity of the compounds. In fact, PCA and its esters presented the greatest potential for oxidation and also the lesser anti-radical efficiency. In contrast, the antioxidants with more anti-radical efficiency, DOPAC, trolox and gallic acid, showed the lowest potential of oxidation.
Description
Keywords
Antioxidantes Ácido 3,4-diidroxibenzóico Ácido 3,4-diidroxifenilacético Benzoatos Fenilacetatos DPPH Voltametria Antioxidants 3,4-dihydroxybenzoic acid 3,4-dihydroxyphenylacetic acid Protocatechuate Phenylacetate Voltammetry
Citation
Publisher
Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto