Mechanochemical Understanding of Metal-Coordinated Polymers Using Simulation and Experiment
Metal-coordination bonds have the capacity to reform after rupture, thereby enabling dynamic, tunable, and reversible (self-healing) mechanical properties. Several biological organisms, such as marine mussels (Mytilus) and marine worm jaws (Nereis virens), have been found to take advantage of these...
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| Format: | Thesis |
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Massachusetts Institute of Technology
2023
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| Online Access: | https://hdl.handle.net/1721.1/151299 https://orcid.org/0000-0001-8696-9821 |
| Summary: | Metal-coordination bonds have the capacity to reform after rupture, thereby enabling dynamic, tunable, and reversible (self-healing) mechanical properties. Several biological organisms, such as marine mussels (Mytilus) and marine worm jaws (Nereis virens), have been found to take advantage of these unique properties of metal-coordinated complexes to produce loadbearing materials with complex mechanical functions. Inspired by these biological materials, metal-coordination bonds have been incorporated into synthetic materials to produce a range of mechanical properties. However, efforts in engineering such metal-coordinated materials have been highly empirical, limiting the full design potential of these bonds. Developing an understanding between the microscopic metal-coordination bond properties and resulting macroscopic mechanical properties of metal-coordinated materials would enable an a priori prediction for optimized utilization of coordination bonds to build materials with advanced mechanical functions.
This dissertation systematically characterizes metal-coordinated polymers and proteins with the aim of developing a mechanistic understanding of the relationship between microscopic bond chemistry and resulting macroscopic dynamic mechanical properties. We begin with a well-studied model system using an idealized polymer network where individual metal-coordination complexes control the macroscopic relaxation dynamics of the network. We use metadynamics simulations to show that the free energy landscape of metal-coordination bonds can be related to the macroscopic dynamic relaxation of these bonds in ideal polymer hydrogels as measured through experimental rheology. We then expand beyond single coordination complexes and use single molecule force spectroscopy to show that clusters of coordination bonds in model metal-coordinated protein dimers can rupture cooperatively, thereby synergistically increasing the rupture strength of the proteins. We resolve this rupture behavior mechanistically by using steered molecular dynamics simulations to show that metal-coordination bond rupture is highly heterogenous and undergoes several rupture pathways, even with the same initial conditions. This indicates that metal-coordination bonds may have evolved in natural materials for primarily dissipative functions.
The above insights are subsequently evaluated within the context of the Nvjp-1 protein, a major component of the Nereis worm jaw with high amounts of metal coordination. We find that increasing quantity of metal ions makes the protein more compact, whereas increasing the spatial distribution of metal ions is found to increase the protein toughness. We then briefly demonstrate how machine learning methods can be developed for similar systems to predict materials properties. The methodology and insights developed in this thesis have important implications for understanding the molecular mechanisms of metal-coordination bond-based stabilization of proteins and polymers and the a priori design of new metal-coordinated materials with desired mechanical properties. |
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