Mechanochemistry is the study of the activation of chemical bonds through force. Despite recent advances in the mechanochemistry of organic molecules, little is known about how metal-ligand bonds respond to this exact, vectorial stimulus. Mechanical activation, one form of which is bond scission, occurs stochastically due to thermal fluctuations in already strained bonds. Single-molecule force spectroscopy (SMFS) represents the only method developed to date that can apply sufficient force for bond activation while simultaneously quantifying molecular-level response. By analyzing polymer chains containing a high monomer fraction of non-integral mechanically active species, we can continue to load remaining mechanophores after some units have already been activated. Probing many connected coordination complex-based mechanophores allows us to obtain an ensemble average value of the force necessary for their activation.<br/>We hope to drive dissociation of chelated metal centers from metallopolymers using force. High molecular weight polymers incorporating a nitrogenous tridentate ligand and a coblock to promote microscope tip adhesion have been synthesized by entropy-driven ring opening metathesis polymerization through a novel procedure. The repeating, unspecific metal-binding motif permits facile synthesis of thermally stable metallopolymers from a wide range of transition metals. Current work focuses on probing the mechanochemical properties of these resulting species by SMFS. These data could better enable our field to draw upon the rich array of transition metals and the unique reactivity they exhibit as we develop compounds that selectively release small molecules in response to the diverse mechanics found in many human pathologies, nanoscale force probes to explicate material failure or cellular mechanotransduction, or catalysts that are only active following an exquisite mechanical activation event.

Chelating polymers to investigate coordination complex mechanochemistry

254th National Meeting (2017)

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