beta-cyclodextrin at the water/1-bromobutane interface: Molecular insight into reverse phase transfer catalysis

Molecular insight into the role of beta-cyclodextrin (betaCD) as a phase transfer catalyst at the liquid/liquid interface is obtained by molecular dynamics simulations of the structure and dynamics of beta-cyclodextrin (betaCD) adsorbed at the interface between water and 1-bromobutane. In particular, we consider the structure and dynamics of the water and bromobutane molecules inside the betaCD cavity and compare them with the behavior when betaCD is dissolved in bulk water. betaCD is preferentially oriented at the interface, with the cavity opening along the interface normal. While in bulk water the cavity includes 6-8 water molecules that are relatively mobile with short residence time, at the interface the cavity is mostly dehydrated and includes a single bromobutane molecule. This inclusion complex is stable in bulk water. The implication of this behavior for reverse phase transfer catalysis is discussed.