DFT studies of cation binding by β-cyclodextrin

Interactions of the β-cyclodextrin (β-CD) ligand with Na+, Cu+, Mg2+, Zn2+, and Al3+ cations were investigated using density functional theory modeling. The objective of this study was to give insight into the mechanism of cation complexation. Two groups of conformers were found. The first group preserved the initial orientation of glucopyranose residues inside the β-CD ligand. The mutual orientation of glucopyranose residues was strongly affected by the cation in the second group of conformers. The system interaction energy was decomposed into electrostatic (ES), Pauli and orbital contributions using the Ziegler–Rauk energy partitioning scheme. The total electrostatic energy, i.e., the sum of ES energy and polarization energy, is the dominating term in the interaction energy. In vacuum, the complexes formed with Al3+ were found to be more stable than with di- and monocations. The vacuum stability sequence was changed in aqueous solution.