The complexation behavior of 1-naphthyl-1-ethanol (1-NpOH) and 2-naphthyl-1-ethanol (2-NpOH) with β-cyclodextrin (β-CD) was studied by employing several spectroscopic techniques. In the case of 1-NpOH, only a complex with 1:1 stoichiometry is formed with β-CD, which has an equilibrium constant that is smaller than that observed for the 1:1 complex between β-CD and 2-NpOH. Excimer emission was observed in the presence of β-CD for solutions containing high 2-NpOH concentrations. This excimer emission was ascribed to a complex with 2:2 β-CD/2-NpOH stoichiometry. In addition, 1H NMR data suggest that 2-NpOH is axially incorporated into the β-CD cavity. Only in the case of 2-NpOH was a broadening of the signals corresponding to the aromatic protons observed in the presence of β-CD. This broadening was attributed to the formation of the 2:2 complex. The dynamics of NpOH complexation was investigated by using the quenching methodology for triplet states. The entry rate constants for the 1:1 complex of 1-NpOH and 2-NpOH are (4.7 ± 1.9) × 108 M-1 s-1 and (2.9 ± 1.6) × 108 M-1 s-1, respectively, whereas the exit rate constants for the two compounds are (4.8 ± 1.8) × 105 s-1 and (1.8 ± 0.7) × 105 s-1. In the case of 2-NpOH, we were able for the first time to estimate the rate constant for the dissociation of a β-CD 2:2 complex ((0.2−2.5) × 103 s-1), showing that the dynamics for complexes including more than one cyclodextrin are remarkably slower than the dynamics observed for 1:1 complexes.

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.