title: Thermodynamics, kinetics, and photochromism of oaklins: a recent family of deoxyanthocyanidins.
abstract: Two oaklins guaiacylcatechinpyrylium (GCP) and syringylcatechinpyrylium (SCP) and a model compound deoxypeonidin (DOP) were synthesized, and the rate and equilibrium constants of the respective pH dependent network of chemical reactions were calculated. In contrast to anthocyanins, the three compounds possess a small cis-trans isomerization barrier and hence the rate of the trans-chalcone formation follows a bell-shaped curve as a function of pH. The three compounds exhibit photochromism obtained by irradiation of the trans-chalcone, which, depending on pH, leads to the colored species flavylium cation and quinoidal base. The flash photolysis together with pH jumps followed by UV-vis absorption and stopped flow is a very useful tool to achieve the rate and equilibrium constants of the network of chemical reactions followed by these molecules. Oaklin compounds which are formed in wine aged in oak barrels present physical-chemical properties more similar to simpler deoxyanthocyanidins rather than anthocyanins and may play a significant role in color changes observed in wine aging. Given their higher stability, they may be regarded as potential food colorants.
authors: Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.
authors: André
authors: A
authors: Sousa
authors: Vesselin
authors: V
authors: Petrov
authors: Paula
authors: P
authors: Araújo
authors: Nuno
authors: N
authors: Mateus
authors: Fernando
authors: F
authors: Pina
authors: Victor
authors: V
authors: de Freitas
mesh_terms: D000872:Anthocyanins / Q000138:chemical synthesis / Q000737:chemistry*; D002599:Chalcone / Q000737:chemistry; D002839:Chromans / Q000138:chemical synthesis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D007700:Kinetics; D013816:Thermodynamics
chemical_list: D000872:Anthocyanins; D002839:Chromans; C582987:deoxypeonidin; C582985:guaiacylcatechinpyrylium; C582986:syringylcatechinpyrylium; D002599:Chalcone