title: Conformational equilibria in selected A-type trimeric procyanidins.
abstract: A-type procyanidin trimers cinnamtannin B-1, cinnamtannin D-1, lindetannin, and aesculitannin B were studied in terms of their conformation and interaction with four solvents: methanol, acetone, DMSO and pyridine. The experiments demonstrated that for each trimer there are two principal conformers observable in the NMR. The ratio of the conformers (rotamers) depends on the structure of a given trimer as well as on the solvent used for NMR measurements. The DFT calculations (B3LYP/6-31G(d,p)) proved the presence of two main conformers to be the result of a steric hindrance that prevents free rotation along the B-type interflavan bond. An analysis of the solvent-procyanidin interactions showed that the strong electron donating solvents, pyridine and DMSO, favor different conformers from methanol and acetone, which prefer the lowest-energy gas phase conformer. These findings are in line with predictions of DFT/M06-2X calculations with the inclusion of the thermal corrections. The variations in the rotamer ratios in the studied solvents correlate with the solvent's capacity to induce local changes in the electron density of the particular procyanidin trimer.
authors.affiliation: Physical Chemistry Department, Faculty of Pharmacy, Medical University of Warsaw, 1 Banacha Street, 02097 Warsaw, Poland. marta.dudek@wum.edu.pl.
authors.forename: Marta K
authors.initials: MK
authors.lastname: Dudek Jamróz
authors.forename: Sławomir
authors.initials: S
authors.lastname: Kaźmierski
authors.forename: Kamil
authors.initials: K
authors.lastname: Stefaniak
authors.forename: Vitold B
authors.initials: VB
authors.lastname: Gliński
authors.forename: Jan A
authors.initials: JA
authors.lastname: Gliński
mesh_terms: D008968:Molecular Conformation; D044945:Proanthocyanidins / Q000138:chemical synthesis* / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D044945:Proanthocyanidins