Study of the inclusion of the (R)- and (S)-camphor enantiomers in alpha-cyclodextrin by X-ray crystallography and molecular dynamics.

The inclusion of (R)- and (S)-camphor compounds in alpha-cyclodextrin has been studied by X-ray crystallography. The crystal structures of the complexes reveal that one guest molecule is accommodated inside the cavity formed by a head-to-head cyclodextrin dimer. In the crystal lattice, the dimers form layers which are successively shifted by half a dimer. In both (R)- and (S)-cases, the camphor molecule exhibits disorder and occupies three major sites with orientations that can be described as either 'polar' or 'equatorial'. Molecular dynamics simulations performed for the observed complexes indicate that although the carbonyl oxygen of both (R)- and (S)-camphor switches between different hydrogen bonding partners, it maintains the observed mode of 'polar' or 'equatorial' alignment.