Mechanically interlocked calix[4]arene dimers display reversible bond breakage under force

The physics of nanoscopic systems is strongly governed by thermal fluctuations that produce significant deviations from the behaviour of large ensembles(1,2). Stretching experiments of single molecules offer a unique way to study fundamental theories of statistical mechanics, as recently shown for the unzipping of RNA hairpins'. Here, we report a molecular design based on oligo calix[4]arene catenanes-calixarene dimers held together by 16 hydrogen bridges-in which loops within the molecules limit how far the calixarene nanocapsules can be separated. This mechanically locked structure tunes the energy landscape of dimers, thus permitting the reversible rupture and rejoining of the individual nanocapsules. Experimental evidence, supported by molecular dynamics simulations, reveals the presence of an intermediate state involving the concerted rupture of the 16 hydrogen bridges. Stochastic modelling using a three-well potential under external load allows reconstruction of the energy landscape.