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Author(s): Frederico Nave
Vesselin Petrov
Fernando Pina
Natercia Teixeira
Nuno Mateus
Victor de Freitas
Title: Thermodynamic and Kinetic Properties of a Red Wine Pigment: Catechin-(4,8)-malvidin-3-O-glucoside
Issue Date: 2010
Abstract: Catechin-(4,8)-malvidin-3-glucoside, a red pigment adduct (at acid pH) found in red wine and resulting from the reaction between malvidin-3-glucoside and flavan-3-ols during wine aging, was synthesized. The thermodynamic and kinetic constants of the network of chemical reactions were fully determined by stopped flow: (i) Direct pH jumps, from thermal equilibrated solutions at pH = 1.0 (flavylium cation, AH(+)), show three kinetic processes. The first one occurs within the mixing time of the stopped flow and leads to the formation of quinoidal bases A and/or A(-) depending on the final pH; the second one takes place with a rate constant equal to 0.075 + 33[H(+)] and was attributed to the hydration reaction that forms the pseudobases (hemiketals), B/B(-). The third process is much slower, 2 x 10(-4) s(-1), and is due to the cis-trans isomerization giving rise to a small fraction of truns-chalcones, Ct/Ct(-). (ii) Reverse pH jumps from the thermally equilibrated solution at moderate to neutral pH values back to a sufficiently acidic medium clearly distinguish three kinetic processes: the first one takes place within the dead time and is due to the protonation of the bases; the second process occurs with the same rate constant of the hydration reaction monitored by direct pH jumps and is attributed to the formation of flavylium cation from the B; the last process occurs with a rate constant of 1.8 s(-1) and results from the formation of AH(+) from Ct through B, reflecting the rate of the ring closure (tautomerization). The separation of the hydration from the tautomerization upon a reverse pH jump is only possible because at pH < 1 the former reaction is faster than the last. An identical situation was observed for malvidin-3-glucoside (oenin) for pH < 2.
Subject: Química
Chemical sciences
Scientific areas: Ciências exactas e naturais::Química
Natural sciences::Chemical sciences
Document Type: Artigo em Revista Científica Internacional
Rights: restrictedAccess
Appears in Collections:FCUP - Artigo em Revista Científica Internacional

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