title: Extending the Study of the 6,8 Rearrangement in Flavylium Compounds to Higher pH Values: Interconversion between 6-Bromo and 8-Bromo-apigeninidin.
abstract: The rearrangement between isomers 6- and 8-bromo-apigeninidin (6and8) was studied by pH jumps using stopped flow, UV/Vis, NMR, and HPLC analysis. The system constitutes a pH-dependent network of chemical reactions involving up to 18 different species. The dynamic network is equivalent to a single diprotic acid exhibiting two pKas, 2.55 and 5.4. Similar to other flavylium derivatives, the mole fraction of the species hemiketal andcis-chalcone in both multistate isomers are negligible at the equilibrium. At pH 1, the pure isomers are slowly converted in a mixture containing about 50 % of isomers6and8, while at pH 4, the system evolves to mixture of 10 %trans-chalcone and 90 % of quinoidal bases. A series of pH jumps from pure isomer6at pH 1 to pH 6 and back to pH 1 leads to the same initial absorption spectra of the pure isomer6. The same occurs for pure isomer8, showing the lack of communication between thecis-chalcones, at least in the time scale of few minutes. A pH jump from the equilibrated mixture of the isomers at pH 1.0 to 5.8 permits to follow a very slow isomerization.
authors.affiliation: Laboratório Associado para a Química Verde (LAQV), Rede de Química e Tecnologia (REQUIMTE) Departamento de Química e Bioquímica Faculdade de Ciências Universidade do Porto Rua do Campo Alegre, 687 4169-007 Porto Portugal.
authors.forename: Luís M
authors.identifier: 0000-0003-2226-0404
authors.initials: LM
authors.lastname: Cruz
authors.affiliation: Laboratório Associado para a Química Verde (LAQV), Rede de Química e Tecnologia (REQUIMTE) Departamento de Química Faculdade de Ciências e Tecnologia Universidade Nova de Lisboa 2829-516 Caparica Portugal.
authors.forename: Nuno M
authors.identifier: 0000-0002-0121-3695
authors.initials: NM
authors.lastname: Basílio
authors.affiliation: Laboratório Associado para a Química Verde (LAQV), Rede de Química e Tecnologia (REQUIMTE) Departamento de Química e Bioquímica Faculdade de Ciências Universidade do Porto Rua do Campo Alegre, 687 4169-007 Porto Portugal.
authors.forename: Victor A
authors.identifier: 0000-0003-0586-2278
authors.initials: VA
authors.lastname: de Freitas
authors.affiliation: Laboratório Associado para a Química Verde (LAQV), Rede de Química e Tecnologia (REQUIMTE) Departamento de Química Faculdade de Ciências e Tecnologia Universidade Nova de Lisboa 2829-516 Caparica Portugal.
authors.forename: João C
authors.identifier: 0000-0003-0528-1967
authors.initials: JC
authors.lastname: Lima
authors.affiliation: Laboratório Associado para a Química Verde (LAQV), Rede de Química e Tecnologia (REQUIMTE) Departamento de Química Faculdade de Ciências e Tecnologia Universidade Nova de Lisboa 2829-516 Caparica Portugal.
authors.forename: Fernando J
authors.identifier: 0000-0001-8529-6848
authors.initials: FJ
authors.lastname: Pina
keywords: 6,8 flavylium rearrangement; 6-bromo-apigeninidin; 8-bromo-apigeninidin; UV/Vis; anthocyanins