Self-Assembly of Chiral Supramolecular Ureido-Pyrimidinone-Based Poly(ethylene glycol) Polymers via Multiple Pathways

The recently developed supramolecular hydrogelator system based on poly­(ethylene glycols) end-functionalized with ureido-pyrimidinone (UPy) units has been shown to be eminently suitable as a drug delivery vehicle in soft tissues such as the heart and kidney. To understand the assembly behavior of this system in more detail, we here report on the introduction of a stereogenic center. This allowed for the investigation of the self-assembly mechanism of this system by circular dichroism, which showed the presence of helical fibers. Additionally, fluorescence spectroscopy and scattering techniques in combination with cryoTEM showed elongated rod-like structures as the major species, next to spherical micelles. Interestingly, different self-assembly pathways occurred when using two aggregate preparation methods based on different cooling rates. Both positive and negative bisignate Cotton effects were observed only by changing the method of preparation, indicating that the UPy-polymer constructs self-assemble via multiple pathways. A similar phenomenon is observed in biology, which illustrates the versatility of the system. This versatility is key to the optimization of material properties for biomedical applications