The role of topology and thermal backbone fluctuations on sacrificial bond efficacy in mechanical metalloproteins

Abstract

Sacrificial bonding is a ubiquitous cross-linking strategy for increasing toughness that is found throughout nature in various biological materials such as bone, wood, silk and mussel byssal threads. However, the molecular mechanism of sacrificial bonding remains only poorly understood. Molecular modeling possesses a strong potential to provide insights into the behavior of these crosslinks. Here we use Monte Carlo simulations to investigate the effect of reversible sacrificial binding sites on the mechanical properties of single linear polymer chains based on load-bearing metalloproteins found in the mussel byssus. It is shown that the topology of the bonds determines the position and spacing of sacrificial force peaks, while the height of these peaks is intimately tied to the magnitude of thermal fluctuations in the chain that are dependent on effective chain length. These results bear important implications for understanding natural systems and for the generation of strong and ductile biomimetic polymers.

Influence of reversible cross-link coordination on the mechanical behavior of a linear polymer chain

“…The ordered arrangement shows a higher stiffness than the random arrangement for both the trimer and dimer system. Similar observations were made in [62].…”

“…the effective strength becomes considerably smaller than the theoretical strength of the trimer and dimer given by 0.47 eV R −1 and 0.41 eV R −1 , respectively. As was already shown for systems crosslinked by bis-complexes only, this means that entropic effects play a dominant role in the deformation behavior of such systems [62]. In particular, the load-displacement curve obtained at ambient temperature cannot be directly taken to correspond to the molecular enthalpic energetics given by the configurational potential.…”

“…Previous investigations identified the number and the distribution of sticky sites as a major factor determining the mechanical behavior of a polymer cross-linked with dimers [62][63][64]. Therefore, the influence of the same parameters on the mechanical performance is also investigated in the current study and shown in figure 5.…”

“…Furthermore, the figure clearly shows that the theoretical strength is by far not achieved by any of the systems. As worked out in [62], temperature and entropy reduce the effective strength of the systems. As the figure shows, the strength increases with increasing sticky site density for all systems.…”

Energy dissipation and recovery in a simple model with reversible cross-links

“…The model is inspired by the fascinating class of metalloproteins and was already presented in [49]. Thus, in the following only a short description is given focusing on the new concepts used in this paper.…”