3555 2006 2006 eng 241 246 April 54 article 0 2020-01-28 -- -- Geometries, stabilities, electronic properties and NMR-shielding of cucurbit[6]uril–spermine host-ligand complexes are investigated with DFT calculations and compared to experimental results. Cucurbit[6]uril and spermine can form complexes with two different minimum energy geometries and corresponding characteristic differences in NMR shielding. The energetically preferred complex geometry has a perfect inversion symmetry and its proton NMR shielding agrees very well with experimental results. The cucurbit[6]uril host molecule shows a distinct geometrical flexibility in ligand binding which allows an induced fit of the spermine ligand. The energetic barrier for the rotation of spermine in the favourable complex is approximated to be in the order of a few kilocalories per mole. Journal of inclusion phenomena and macrocyclic chemistry 10.1007/s10847-005-8140-8 0923-0750 © Alle Rechte vorbehalten Hans-Jürgen Buschmann Andreas Wego Achim Zielesny Eckhard Schollmeyer Westfälisches Institut für Gesundheit Westfälische Hochschule Gelsenkirchen Bocholt Recklinghausen