6533b7d6fe1ef96bd1265d59

RESEARCH PRODUCT

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

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The physics of nanoscopic systems is strongly governed by thermal fluctuations that produce significant deviations from the behaviour of large ensembles1,2. Stretching experiments of single molecules offer a unique way to study fundamental theories of statistical mechanics, as recently shown for the unzipping of RNA hairpins3. 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. Stretching experiments on single molecules offer a unique way to study the fundamental theories of statistical mechanics. Researchers have now shown that entangled calix[4]arene dimers can be used in such experiments as a tuneable model system for investigating the strength of hydrogen bonds on a single-molecule level.