Photoresponsive Supramolecular Polymers Capable of Intrachain Folding and Interchain Aggregation.

The competition between polymer chain folding and aggregation is a critical structuring process that determines the physical properties of synthetic and biopolymers. However, supramolecular polymer systems that exhibit both processes have not yet been reported. We herein introduce a system in which folded supramolecular polymers spontaneously undergo interchain aggregation due to a rearrangement in internal molecular order, converting them into crystalline aggregates. These folded supramolecular polymers slowly crystallize over the course of half a day, due to their characteristic higher-order structures. However, the photoisomerization of the trans-azobenzene incorporated into the monomer to the cis isomer leads to unfolding of the polymer, accelerating the intrachain and interchain molecular ordering to a few hours. The intermediate structures visualized by AFM demonstrate that the unfolding is coupled with interchain aggregation.

Diarylethene-Powered Light-Induced Folding of Supramolecular Polymers.

Helical folding of randomly coiled linear polymers is an essential organization process not only for biological polypeptides but also for synthetic functional polymers. Realization of this dynamic process in supramolecular polymers (SPs) is, however, a formidable challenge because of their inherent lability of main chains upon changing an external environment that can drive the folding process (e.g., solvent, concentration, and temperature). We herein report a photoinduced reversible folding/unfolding of rosette-based SPs driven by photoisomerization of a diarylethene (DAE). Temperature-controlled supramolecular polymerization of a barbiturate-functionalized DAE (open isomer) in nonpolar solvent results in the formation of intrinsically curved, but randomly coiled, SPs due to the presence of defects. Irradiation of the randomly coiled SPs with UV light causes efficient ring-closure reaction of the DAE moieties, which induces helical folding of the randomly coiled structures into helicoidal ones, as evidenced by atomic force microscopy and small-angle X-ray scattering. The helical folding is driven by internal structure ordering of the SP fiber that repairs the defects and interloop interaction occurring only for the resulting helicoidal structure. In contrast, direct supramolecular polymerization of the ring-closed DAE monomers by temperature control affords linearly extended ribbon-like SPs lacking intrinsic curvature that are thermodynamically less stable compared to the helicoidal SPs. The finding represents an important concept applicable to other SP systems; that is, postpolymerization (photo)reaction of preorganized kinetic structures can lead to more thermodynamically stable structures that are inaccessible directly through temperature-controlled protocols.

Non-uniform Photoinduced Unfolding of Supramolecular Polymers Leading to Topological Block Nanofibers.

Synthesis of one-dimensional nanofibers with distinct topological (higher-order structural) domains in the same main chain is one of the challenging topics in modern supramolecular polymer chemistry. Non-uniform structural transformation of supramolecular polymer chains by external stimuli may enable preparation of such nanofibers. To demonstrate feasibility of this post-polymerization strategy, we prepared a photoresponsive helically folded supramolecular polymers from a barbiturate monomer containing an azobenzene-embedded rigid π-conjugated scaffold. In contrast to previous helically folded supramolecular polymers composed of a more flexible azobenzene monomer, UV-light induced unfolding of the newly prepared helically folded supramolecular polymers occurred nonuniformly, affording topological block copolymers consisting of folded and unfolded domains. The formation of such blocky copolymers indicates that the photoinduced unfolding of the helically folded structures initiates from relatively flexible parts such as termini or defects. Spontaneous refolding of the unfolded domains was observed after visible-light irradiation followed by aging to restore fully folded structures.

Wavy supramolecular polymers formed by hydrogen-bonded rosettes.

A barbiturate-functionalized supramolecular monomer bearing an ester-linked biphenyl and azobenzene π-conjugated core affords wavy supramolecular polymers. The periodic inversion of curvature is due to the conformational rigidity of the monomer and repulsive interactions between rosettes. Photoisomerization of the azobenzene moiety increases the fragility of the main chain without deteriorating its periodic structure.

Predicting key example compounds in competitors' patent applications using structural information alone.

In drug discovery programs, predicting key example compounds in competitors' patent applications is important work for scientists working in the same or in related research areas. In general, medicinal chemists are responsible for this work, and they attempt to guess the identity of key compounds based on information provided in patent applications, such as biological data, scale of reaction, and/or optimization of the salt form for a particular compound. However, this is sometimes made difficult by the lack of such information. This paper describes a method for predicting key compounds in competitors' patent applications by using only structural information of example compounds. Based on the assumption that medicinal chemists usually carry out extensive structure--activity relationship (SAR) studies around key compounds, the method identifies compounds located at the centers of densely populated regions in the patent examples' chemical space, as represented by Extended Connectivity Fingerprints (ECFPs). For the validation of the method, a total of 30 patents containing structures of launched drugs were selected to test whether or not the method is able to predict key compounds (the launched drugs). In 17 out of the 30 patents (57%), the method was able to successfully predict the key compounds. The result indicates that our method could provide an alternative approach to predicting key compounds in cases where the conventional medicinal chemist's approach does not work well. This method could also be used as a complement to the traditional medicinal chemist's approach.