Active Template Synthesis of Protein Heterocatenanes

Covalent‐bond‐forming protein domains can be versatile tools for creating unconventional protein topologies. In this study, through rewiring the SpyTag–SpyCatcher complex to induce rationally designed chain entanglement, we developed a biologically enabled active template for the concise, modular, and programmable synthesis of protein heterocatenanes both in vitro and in vivo. It is a general and good‐yielding reaction for forming heterocatenanes with precisely controlled ring sizes and broad structural diversity. More importantly, such heterocatenation not only provides an efficient means of bioconjugation for integrating multiple native functions, but also enhances the stability of the component proteins against proteolytic digestion, thermal unfolding, and freeze/thaw‐induced mechanical denaturation, thus opening up a versatile path in the nascent field of protein‐topology engineering.     

Topological Transformation of π‐Conjugated Molecules Reduces Resistance to Crystallization

Two electronically delocalized molecules were designed as models to understand how molecular shape impacts the tradeoff between solubility and crystallization tendencies in molecular semiconductors. The more soluble compound TT contains a non‐planar bithiophene central fragment, whereas CT has a planar cyclopentadithiophene unit. Calorimetry studies show that CT can crystallize more easily than TT . However, absorption spectroscopy shows that the initially amorphous TT film can eventually form crystals in which the molecular shape is significantly more planar. Two thermally reversible polymorphs for TT were observed by XRD and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) measurements. These findings are relevant within the context of designing soft semiconductors that exhibit high solubility and a tendency to provide stable organized structures with desirable electronic properties.     

Photoresponsive Circular Supramolecular Polymers: A Topological Trap and Photoinduced Ring‐Opening Elongation

Topological features of one‐dimensional macromolecular chains govern the properties and functionality of natural and synthetic polymers. To address this issue in supramolecular polymers, we synthesized two topologically distinct supramolecular polymers with intrinsic curvature, circular and helically folded nanofibers, from azobenzene‐functionalized supramolecular rosettes. When a mixture of circular and helically folded nanofibers was exposed to UV light, selective unfolding of the latter open‐ended supramolecular polymers was observed as a result of the curvature‐impairing internal force produced by the trans‐to‐cis photoisomerization of the azobenzene. This distinct sensitivity suggests that the topological features of supramolecular polymers define their mechanical stability. Furthermore, the exposure of circular supramolecular polymers in more polar media to UV irradiation resulted in ring opening followed by chain elongation, thus demonstrating that the circular supramolecular polymer can function as a topological kinetic trap.