β-cyclodextrin (β-CD) is an oligosaccharide made up of 7 glucose units bound together in a ring. The β-CD geometry is roughly that of a truncated cone, with hydrophilic exterior and a hydrophobic pore. β-CD is known to act as a catalyst in biphasic systems, enhancing the rate of S<sub>N</sub>2 reaction between 1-bromooctane and anionic nucleophiles present in an adjacent, immiscible aqueous phase. Molecular dynamics simulations are used to quantify the energetic advantages provided by β-CD as catalyst in this inverse phase transfer system. The 1-bromooctane reactant may form a host/guest complex with the surface-active β-CD and be transported to the aqueous phase to react. Potential of mean force curves for the formation/separation of this complex in different solvent environments reveal the energetic barriers to guest exchange in bulk 1-bromooctane versus bulk water. These simulations also locate the preferred position of the guest molecule’s S<sub>N</sub>2 reactive site relative to the β-CD host. With this knowledge, we use the empirical valence bond (EVB) model to probe the host molecule’s impact on the energetic barrier to reaction. These studies provide molecular insight into the β-CD catalyst’s role in both the mass transport and chemical reaction in a simulated phase transfer reaction.

Quantifying the catalyst’s role in inverse phase transfer catalysis with computer simulations

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.