Directional supramolecular interactions can form non-covalent bonds, which play an important role in many biomimetic materials. Accordingly, an improved understanding of these interactions and the influence of different stimuli is desirable. Metal-ligand (ML) complexes are of particular interest, because their interaction strength and dynamic nature can be tuned by simple variation of the metal ions, ligands, or counter-ions. To explore the response of ML complexes to mechanical force, single molecule force spectroscopy (SMFS) can be employed. This approach is expected to provide insights into the mechanically-induced scission and reversible formation of the ML complexes. Our studies are based on the use of single chain polymeric nanoparticles (SCPNs) that are prepared from methylbenzimidazolyl pyridine side-chain functionalized polymers by formation of intramolecular ML complexes with Fe2+, Zn2+, and Eu3+ ions. The successful formation of nanoparticles was demonstrated by means of dynamic light scattering, Taylor dispersion measurements, and atomic force microscopy imaging. The forced unfolding of these SCPNs by means of SMFS was used to investigate the complex scission events under mechanical stress at the molecular level. The dissociation of intramolecular ML complexes was reflected by discrete transitions in the recorded extension profiles (Figure 1c,d). Fitting of the profiles to the worm like chain (WLC) model of elasticity yielded the persistence length of the polymers and their force constant. More importantly, the rupture force of the intramolecular complexes for the different SCPNs could be successfully determined. This permits for an analysis of the binding parameters of these dynamic bi- and trifold coordinated ML complexes. The results serve to advance our understanding of the mechanical properties of these ML complexes on a molecular level, which is an important step towards the development of novel biomimetic- and mechanoresponsive materials.

Mechanically unravelling metallosupramolecular polymers

254th National Meeting (2017)

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