Polymers possessing helical conformation in the solid state are in high demand. We report a helical peptide-polymer via the topochemical ene-azide cycloaddition (TEAC) polymerization. The molecules of the designed Gly-Phe–based dipeptide, decorated with ene and azide, assemble in its crystals as β-sheets and as supramolecular helices in two mutually perpendicular directions. While the NH…O H-bonding facilitates β-sheet–like stacking along one direction, weak CH…N H-bonding between the azide-nitrogen and vinylic-hydrogen of molecules belonging to the adjacent stacks arranges them in a head-to-tail manner as supramolecular helices. In the crystal lattice, the azide and alkene of adjacent molecules in the supramolecular helix are suitably preorganized for their TEAC reaction. The dipeptide underwent regio- and stereospecific polymerization upon mild heating in a single-crystal-to-single-crystal fashion, yielding a triazoline-linked helical covalent polymer that could be characterized by single-crystal X-ray diffraction studies. Upon heating, the triazoline-linked polymer undergoes denitrogenation to aziridine-linked polymer, as evidenced by differential scanning calorimetry, thermogravimetric analysis, and solid-state NMR analyses.

Topochemical reactions, high‐yielding solid‐state reactions arising from the proximal alignment of reacting partners in the crystal lattice, do not require solvents, catalysts, and additives, are of high demand in the context of green processes and environmental safety. However, the bottleneck is the limited number of reactions that can be done in the crystal medium. We present the topochemical ene–azide cycloaddition (TEAC) reaction, wherein alkene and azide groups undergo lattice‐controlled cycloaddition reaction giving triazoline in crystals. A designed monomer that arranges in a head‐to‐tail manner in its crystals pre‐organizing the reacting groups of adjacent molecules in proximity undergoes spontaneous cycloaddition reaction in a single‐crystal‐to‐single‐crystal fashion, yielding the triazoline‐linked polymer. A unique advantage of this reaction is that the triazoline can be converted to aziridine by simple heating, which we exploited for the otherwise challenging post‐synthetic backbone modification of the polymer. This reaction may revolutionize the field of polymer science.

Topochemical reactions, high-yielding solid-state reactions arising from the proximal alignment of reacting partners in the crystal lattice, do not require solvents, catalysts, and additives, are of high demand in the context of green processes and environmental safety. However, the bottleneck is the limited number of reactions that can be done in the crystal medium. We present the topochemical ene-azide cycloaddition (TEAC) reaction, wherein alkene and azide groups undergo lattice-controlled cycloaddition reaction giving triazoline in crystals. A designed monomer that arranges in a head-to-tail manner in its crystals pre-organizing the reacting groups of adjacent molecules in proximity undergoes spontaneous cycloaddition reaction in a single-crystal-to-single-crystal fashion, yielding the triazoline-linked polymer. A unique advantage of this reaction is that the triazoline can be converted to aziridine by simple heating, which we exploited for the otherwise challenging post-synthetic backbone modification of the polymer. This reaction may revolutionize the field of polymer science.

Packing a polymer in different ways can give polymorphs of the polymer having different properties. β-turn forming peptides such as 2-aminoisobutyric acid (Aib)-rich peptides adopt several conformations by varying dihedral...

Topochemische Reaktionen sind kristallgittergesteuerte Reaktionen, die in Kristallen oder anderen sterisch starren Medien ablaufen. Bislang sind jedoch nur eine Handvoll topochemischer Reaktionen bekannt. In ihrem Forschungsartikel auf S. 25079 berichten K. M. Sureshan und R. Khazeber über eine neue topochemische Reaktion: die topochemische En‐Azid‐Cycloaddition, bei der ein proximal angeordnetes Azid und ein Alken eine Einkristall‐zu‐Einkristall‐Cycloaddition zu Triazolin durchlaufen.