Proteinstrukturen aus dem Chemie‐Baukasten. Definierte Peptidarchitekturen

This review summarizes some of the various efforts to synthesize defined secondary structures with unnatural building blocks. These molecules are intended to mimic the molecular architecture of naturally occurring biopolymers while displaying (or even improving) biological function. After a general introduction into the principles of protein structure including the concepts of hierarchy and cooperativity, several examples of the synthesis of defined secondary structures are given. In particular, β‐peptides have received considerable attention as a class of molecules with defined structural elements, such as helices and sheets. Finally, preliminary studies towards tertiary structure and biological applications of β‐peptides and semisynthetic enzymes are presented and the increased stability of β‐peptides over their α‐analogues is discussed.     

Instant Locking of Molecular Ordering in Liquid Crystal Elastomers by Oxygen‐Mediated Thiol–Acrylate Click Reactions

Liquid crystal elastomers (LCEs) with intrinsic anisotropic strains are reversible shape‐memory polymers of interest in sensor, actuator, and soft robotics applications. Rapid gelation of LCEs is required to fix molecular ordering within the elastomer network, which is essential for directed shape transformation. A highly efficient photo‐cross‐linking chemistry, based on two‐step oxygen‐mediated thiol–acrylate click reactions, allows for nearly instant gelation of the main‐chain LCE network upon exposure to UV light. Molecular orientation from the pre‐aligned liquid crystal oligomers can be faithfully transferred to the LCE films, allowing for preprogrammed shape morphing from two to three dimensions by origami‐ (folding‐only) and kirigami‐like (folding with cutting) mechanisms. The new LCE chemistry also enables widely tunable physical properties, including nematic‐to‐ isotropic phase‐transition temperatures (T_N‐I), glassy transition temperatures (T_g), and mechanical strains, without disrupting the LC ordering.