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Master's Dissertation
DOI
10.11606/D.46.2012.tde-28032012-092644
Document
Author
Full name
Luis Eduardo Ossandón Caiconte
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2012
Supervisor
Committee
Quina, Frank Herbert (President)
Bastos, Erick Leite
Rettori, Daniel
Title in Portuguese
Especiação e atividade anti-oxidante de íons hidroxiflavílio
Keywords in Portuguese
Antioxidantes (Capacidade)
Antocianinas
Íons flavílios
Método ABTS
TEAC
Abstract in Portuguese
As antocianinas compreendem o maior conjunto de pigmentos solúveis em água do reino vegetal. Responsáveis pelas cores vermelha, azul e roxa da maioria das frutas e flores, estas pertencem ao grupo dos flavonóides (polifenois). A cor apresentada por uma determinada antocianina depende do padrão de substituição, presença ou não de íons metálicos ou de outras moléculas capazes de estabilizar a cor, co-pigmentos, do pH local do meio e da natureza do microambiente em que a antocianina se encontra. Neste projeto, realizou-se um estudo de especiação e das propriedades antioxidantes de uma série de compostos análogos às antocianinas: os sais de 3' -hidroxiflavílio (3'-HF), 4'- hidroxiflavílio (4'-HF), 7,4-dihidroxiflavílio (7,4'-DHF), 3',4'-dihidroxiflavílio (3',4'-DHF), 5,7-dihidroxi-4-metilflavílio (5,7-DH-4-MF), 7-hidroxi-4-metilflavílio (7-H-4-MF) e 7- metoxi-4-metilflavílio (7-metox-4-MF). No estudo de especiação, foram determinados o pK imediatamente após a preparação da amostra e o pKfinal após 1 dia. Para 3'-HF, os valores do pK e pKfinal foram 2,88±0,05 e 1,94±0,15; para 4'-HF, 4,56±0,10 e 4,23±0,20. Para os flavílios com dois grupos hidroxila ionizáveis, as constantes pK1, pK2, pK1final e pK2final para 7,4'-DHF foram 4,12±0,07, 7,85±0,01, 3,29±0,01 e 7,40±0,03; para 3',4'-DHF, 3,98±0,10, 8,80±0,40, 3,70±0,01 e 7,01±0,22. Para o 5,7-DH-4-MF, que não sofre hidratação devido à presença do grupo metílico na posição 4, o pK1 e pK2 foram 4,87±0,01 e 7,97±0,01. Para a determinação da atividade antioxidante, foi utilizado o método de ABTS em que o poder antioxidante é obtida comparando-se a descoloração do radical 2,2'-azino-bis(3- etilbenzoiltiazolina-6-sulfônico) (ABTS+), a 734 nm, pela amostra com a do composto padrão Trolox (ácido 6-hidroxi-2,5,7,8-tetrametilcroman-2-carboxílico), sendo expressa como a TEAC (Trolox Equivalent Antioxidant Capacity). A cinética da reação com os flavílios é bifásica, com uma fase lenta devido à atividade antioxidante residual dos subprodutos da reação. Utilizou-se a primeira derivada das curvas cinéticas para identificar o fim da fase rápida e, portanto, o tempo ótimo para a determinação do valor da TEAC. Os monohidroxiflavílios (3'-HF e 4'-HF) e o 7,4'-DHF não apresentaram poder antioxidante em solução aquosa a pH 2,1 (H3PO4/H2PO4-). Por outro lado, o grupo catecol presente no anel B do 3',4'-DHF e o grupo resorcinol no anel A do 5,7-DH-4-MF conferem propriedades antioxidantes, mesmo em pH baixo. Também apresentaram atividade antioxidante a pH 2,1 o 7-H-4-MF e o 7-metox-4-MF. Em pHs acima do pK, a formação de cis- e trans-chalconas, devido à hidratação, tautomerização e isomerização dos flavílios, resultou num aumento do valor da TEAC.
Title in English
Speciation and antioxidant activity of hydroxyflavylium ions
Keywords in English
ABTS method
Anthocyanins
Antioxidant (Capacity)
Flavylium ions
TEAC
Abstract in English
Anthocyanins are the major water-soluble pigments of the plant kingdom. Responsible of the red, blue and purple colors of the majority of fruit and flowers, they belong to the group of flavonoids (polyphenols). The color presented by an anthocyanin depends on the pattern of substitution, the presence or not of metal ions or other molecules capable to stabilize the color (co-pigments), the local pH of the solution and the nature of the microenvironment of the anthocyanin. In this project, a study was made of the speciation and the antioxidant properties of a series of compounds analogous to anthocyanins: 3'-hydroxyflavylium (3'-HF), 4'- hydroxyflavylium (4'-HF), 7,4'-dihydroxyflavylium (7,4'-DHF), 3',4'-dihydroxyflavylium (3',4'-DHF), 5,7-dihydroxy-4-methylflavylium (5,7-DH-4-MF), 7-hydroxy-4- methylflavylium (7-H-4-MF) and 7-methoxy-4-methylflavylium (7-Methox-4-MF). In the study of the speciation, the pK is determined immediately after preparation of the samples and the pKfinal after 1 day. For 3'-HF, the values of pK and pKfinal were 2.88±0.05 and 1.94±0.15; for 4'-HF, 4.56±0.10 and 4.23±0.20. For the flavyliums with two ionizable hydroxyl groups, the constants pK1, pK2, pK1final and pK2final for 7,4'-DHF were 4.12±0.07, 7.85±0.01, 3.29±0.01 and 7.40±0.03; for 3',4'-DHF, they were 3.98±0.10, 8.80±0.40, 3.70±0.01 and 7.01±0.22. For 5,7-DH-4-MF, which does not hydrate due to the presence of the methyl group at position 4, pK1 and pK2 were 4.87±0.01 and 7.97±0.01. For the determination of the antioxidant activity, the ABTS method was employed, in which the antioxidant power is obtained by comparing the rate of bleaching of the 2,2'-azinobis( 3-ethylbenzothiazoline-6-sulfonate) radical (ABTS+), at 734 nm, by the sample with that of the standard compound Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), the result being expressed as the TEAC (Trolox Equivalent Antioxidant Capacity). The reaction kinetics with the flavyliums are biphasic, with the slower phase due to the residual antioxidant activity of the reaction subproducts. The first derivative of the kinetic curves was employed to determine the end of the faster phase and thus the optimum time for measuring the TEAC value. The monohydroxyflavyliums (3'-HF and 4'-HF) and 7,4'DHF showed no antioxidant power in aqueous solution at pH 2.1 (H3PO4/H2PO4-). However, the catechol group in ring B of 3',4'-DHF and the resorcinol group in ring A of 5,7-DH-4-MF conferred antioxidant properties even at low pH. In addition, 7-H-4-MF and 7-Methox-4-MF also showed antioxidant activity at pH 2.1. At pH above the pK, the formation of the cis- and trans-chalcones via hydration, tautomerization and isomerization resulted in an increase in the value of the TEAC.
 
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Publishing Date
2012-06-06
 
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