title: NMR Studies of Hetero-Association of Caffeine with di-O-Caffeoylquinic Acid Isomers in Aqueous Solution.
abstract: Caffeine hetero-association with 3,5-di-O-caffeoylquinic acid, 3,4-di-O-caffeoylquinic acid and 4,5-di-O-caffeoylquinic acid in aqueous solution has been investigated by one-dimensional (1D) and two-dimensional (2D) high resolution1H and13C NMR spectroscopy. Self-association of the di-O-caffeoylquinic acid isomers has been studied as well. Caffeine-di-O-caffeoylquinic acid isomers association constants were measured. The value of the association constant of the caffeine-di-O-caffeoylquinic acid complexes is compatible with previous studies and within the typical range of reported association constants for other caffeine-polyphenols complexes. Structural features of the three different complexes have also been investigated by NMR spectroscopy combined with quantum chemical calculations, and the complex conformation is discussed. Our results show that stacking interactions drive the formation of the complexes and that multiple equilibria are present in the interaction of caffeine with 3,4-di-O-caffeoylquinic acid and 4,5-di-O-caffeoylquinic acid while the complex with 3,5-di-O-caffeoylquinic acid seems to be better defined.
authors.affiliation: Department of Structural and Molecular Biology, University College London, Gower Place, WC1E 6BT London, UK.
authors.forename: Nicola
authors.initials: N
authors.lastname: D'Amelio
authors.affiliation: German Research School for Simulation Sciences, GmbH 52425, Jülich, Germany ; International School for Advanced Studies, SISSA via Bonomea, 265, 34136 Trieste, Italy.
authors.forename: George
authors.initials: G
authors.lastname: Papamokos
authors.affiliation: German Research School for Simulation Sciences, GmbH 52425, Jülich, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Dreyer
authors.affiliation: German Research School for Simulation Sciences, GmbH 52425, Jülich, Germany.
authors.forename: Paolo
authors.initials: P
authors.lastname: Carloni
authors.affiliation: illycaffè S.p.A, via Flavia, 110, I-34147 Trieste, Italy.
authors.forename: Luciano
authors.initials: L
authors.lastname: Navarini
keywords: Caffeine; Caffeine heteroassociation; Density functional theory; Di-O-caffeoylquinic acid isomers; NMR