title: Effect of β-Cyclodextrin on the Multistate Species Distribution of 3-Methoxy-4',7-dihydroxyflavylium. Discrimination of the Two Hemiketal Enantiomers.
abstract: The effect of β-cyclodextrin on the mole fraction distribution of the multistate species of the anthocyanin model compound, 3-methoxy-4',7-dihydroxyflavylium, was studied by NMR, stopped flow, circular dichroism, and UV-visible absorption spectroscopy. The formation of inclusion complexes with hemiketal and trans-chalcone, possessing transition dipole moments in a parallel orientation to the cyclodextrin n-fold axis, was unequivocally proved by means of the positive-induced circular dichroism signal. The discrimination of the two hemiketal enantiomers was achieved by the splitting of1H NMR peaks in the presence β-cyclodextrin. The spectroscopic data shows that the β-cyclodextrin has only moderate enantioselectivity, slightly favoring one of the optical isomers. The observed binding affinity of β-cyclodextrin for the 3-methoxy-4',7-dihydroxyflavylium multistate species increases in the order flavylium cation < quinoidal base < hemiketal < trans-chalcone < cis-chalcone. As a result of this selectivity and the dynamic nature of the network, the equilibrium is displaced toward the formation of the chalcone species.
authors.affiliation: REQUIMTE, Departamento de Quı́mica, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , 2829-516 Monte de Caparica, Portugal.
authors.forename: Sandra
authors.initials: S
authors.lastname: Gago
authors.affiliation: REQUIMTE, Departamento de Quı́mica, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , 2829-516 Monte de Caparica, Portugal.
authors.forename: Nuno
authors.identifier: http://orcid.org/0000-0002-0121-3695
authors.initials: N
authors.lastname: Basílio
authors.affiliation: Instituto Superior de Ciencias da Saude Egas Moniz, Centro de Investigação Interdisciplinar Egas Moniz , P-2829511 Monte de Caparica, Portugal.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Quintas
authors.affiliation: REQUIMTE, Departamento de Quı́mica, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , 2829-516 Monte de Caparica, Portugal.
authors.forename: Fernando
authors.identifier: http://orcid.org/0000-0001-8529-6848
authors.initials: F
authors.lastname: Pina
mesh_terms: D000872:Anthocyanins / Q000737:chemistry; D002599:Chalcone / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011809:Quinones / Q000737:chemistry*; D013237:Stereoisomerism; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: C494947:4',7-dihydroxyflavylium; D000872:Anthocyanins; D011809:Quinones; D047392:beta-Cyclodextrins; D002599:Chalcone
keywords: anthocyanins; cis−trans isomerization; flavylium; induced circular dichroism; photochemistry hemiketal; β-cyclodextrin