Periodic Reporting for period 1 - MolecularEVOLUTION (Molecular Evolution of the Primary Structure of Single Chain Polymer Nanoparticles via Dynamic Covalent Chemistry)
Reporting period: 2016-03-01 to 2018-02-28
The primary objective of this project was to develop new fundamental chemistry to control the high order structure of SCPNs. We sought to design SCPNs with reversible connections so that the sequence could be “shuffled” in conjunction with the dynamic aggregation of the “sticky” pendant units to “molecularly evolve” the SCPN primary structure. This strategy allows for individual SCPNs to thermodynamically optimize their structure to achieve a lower energy state, leading to a better defined core for performing catalytic reactions. We have developed new chemistry that allows us to “shuffle” the sequences of SCPNs and track the changes of this process by nuclear magnetic resonance spectroscopy. Additionally, in response to challenges in achieving later project milestones, we pursued an alternative line of research to improve SCPN folding. We investigated “stickier” aggregation units, envisioning that they could be used to more efficiently fold SCPNs, and discovered a new class of “stickier” units that form one-dimensional stacks. Remarkably, these stacks change their helicity as a function of temperature, and we ultimately discovered that these transitions are caused by water molecules binding to the stacks. A manuscript that describes these discoveries was recently accepted for publication in Nature and give researchers better insight into fundamentals of hydrophobic effects. We believe that this technology will be key in developing SCPNs with better folding and temperature responsiveness.
In the second component of this project, we aimed to explore new hydrogen bond-based “sticky” groups used to fold polymers into SCPNs; we envisioned that the efficiency of the folding could be increased by using a “stickier” unit. We targeted a biphenyl tetracarboxamide (BPTA), predicting that it would be stronger. Our experiments with a model BPTA compound confirmed that these units bind more strongly than our older design, forming one-dimensional helical fibers. Intriguingly, these fibers change their helicity as a function of temperature; we ultimately discovered that the binding of water molecules is responsible for this change in structure. These insights are unprecedented in the field of supramolecular chemistry and resulted in a manuscript that was recently accepted for publication in Nature. This project has also been orally presented at the 2016 and 2017 American Chemical Society National Meetings as well as 2016 CHAINS and the 2018 Dutch Polymer Days. As soon as the Nature manuscript is published online, we will further promote this work through a university news article, social media announcements, and a blog post on the Nature Research Chemistry Community website. Additionally, as part of a collaboration with the Voets group at the Eindhoven University of Technology, we developed a new super-resolution fluorescence microscopy technique for visualizing these fibers. A manuscript detailing this technique was just accepted for publication in ACS Nano.