title: Establishment of the chemical equilibria of different types of pyranoanthocyanins in aqueous solutions: evidence for the formation of aggregation in pyranomalvidin-3-O-coumaroylglucoside-(+)-catechin.
abstract: The chemical equilibria of the pyranomalvidin-3-glucosides linked to (+)-catechin, (-)-epicatechin, and catechol moieties (and the respective coumaroylglucoside compounds) were established by means of UV-vis spectroscopy. The conjugated double bonds among pyranic rings C and D provide a higher electronic delocalization that prevents the nucleophilic attack of water at position 2. Consequently, besides flavylium cation (AH(+)), the bases A, A(-), and A(2-) have been identified by increasing pH, and the respective acidity constants were determined by spectrophotometry. The formation of dimers at higher concentration was observed for pyranomalvidin-3-O-coumaroylglucoside-(+)-catechin, and the respective data treated by the exciton model suggests the formation of a dimer where the monomers form J-type aggregates with the dipolar moments in opposite directions and rotated by 174° at a distance of 5.2 Å (from the center).
authors.affiliation: Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.
authors.forename: Luís
authors.initials: L
authors.lastname: Cruz
authors.forename: Vesselin
authors.initials: V
authors.lastname: Petrov
authors.forename: Natércia
authors.initials: N
authors.lastname: Teixeira
authors.forename: Nuno
authors.initials: N
authors.lastname: Mateus
authors.forename: Fernando
authors.initials: F
authors.lastname: Pina
authors.forename: Victor
authors.initials: V
authors.lastname: de Freitas
mesh_terms: D000872:Anthocyanins / Q000138:chemical synthesis / Q000737:chemistry*; D002392:Catechin / Q000737:chemistry*; D005960:Glucosides / Q000737:chemistry; D011714:Pyrans / Q000138:chemical synthesis / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D000872:Anthocyanins; D005960:Glucosides; D011714:Pyrans; D014867:Water; D002392:Catechin