Catenanes from catenanes: quantitative assessment of cooperativity in dynamic combinatorial catenation

Abstract

A new azobenzene-based dithiol building block was developed which, upon oxidation, forms predominantly a [2]catenane consisting of two interlocked trimers. In the presence of cyclodextrin templates a series of [2] and [3]catenanes was formed instead. We developed a method that enabled estimating the equilibrium constants for catenation in all of these systems. The formation of the [3]catenanes is either cooperative or anticooperative, depending on the nature of the cyclodextrin. Using molecular dynamics simulations, we linked positive and negative cooperativity to, respectively, burying and exposure of hydrophobic surfaces upon catenation. Our results underline the importance of directly quantifying noncovalent interactions within catenanes, as the corresponding pseudo-rotaxane model systems were found to be poor predictors of binding interactions in the actual catenane.