Force Probe MD Simulations of Calixarene Catenanes

If one reverses the pulling direction after the system has undergone the transition to the open structure, one observes a rebinding into the closed state for pulling 

Because the rupture event is a stochastic process, the rupture forces are distributed in a certain range. Therefore, as in the experimental studies, we performed a large number of simulations and analyzed the rupture force distributions and the rejoin force distributions. The mean values as a function of the pulling velocity represent the so-called force spectmm. Experimentally, often a logarithmic dependence of the mean rupture force on v is observed, but the data collected by Schlesier et al. [98] allow no definite conclusion regarding this dependence. 

As mentioned above, we also performed simulations on a bis-loop system undergoing two transitions. The first transition is from a compact, closed structure stabilized by a maximum of 16 UU-bonds to an intermediate reminiscent of the open structure of the tetra-loop system. In the second transition, this UE-stabilized structure opens upon further increase of the external force and an open structure 

All simulations discussed so far have been performed using one particular force field, the GROMOS G53A5 force field [99]. Because it is well known that the choice of the force field has a strong impact on the results of MD simulations, we performed force probe MD simulations of the tetra-loop calix[4]arene dimer using three different frequently used force fields [100]. The most important 

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