Quadruple Helix Formation of a Photoresponsive Peptide Amphiphile and Its Light-Triggered Dissociation into Single Fibers

Abstract

Building well-defined higher-order architectures through supramolecular chemistry is one of the challenges in nanotechnology and is critical for our understanding of biological self-assembly. Secondary structures, such as R-helices and β-sheets in proteins and the double-helix of nucleic acids, generate stable tertiary and quaternary structures with critical roles in the three-dimensional architectures in biology. Furthermore, conformational changes of proteins can switch functional states such as enzymatic activities. 1 Inspired by these switchable structures seen in biomolecules, we have investigated here the synthesis of photoresponsive peptide amphiphiles (PAs), well-known to self-assemble into supramolecular nanofibers. 2 The single-handed helical structure has always been an attractive target, and more recently, there is also interest in multiple helices. [3][4][5] Here we report the discovery of a quadruple helical fiber formed by photoresponsive PA 1 and its conversion into single fibers upon photochemical cleavage of the 2-nitrobenzyl group in 1.

Single‐Chain Polymeric Nanoparticles by Stepwise Folding

“…The magnitude (À16 mdeg at l = 223 nm), sign, and shape of the CD spectrum is similar to those found in other chiral BTAs dissolved in MCH at a similar concentration and temperature. [47] This result indicates that o-nitrosobenzaldehyde, which is released during the reaction, [39] does not interfere with the self-assembly process and that supramolecular polymers with a preferred helicity are formed upon deprotection.…”

“…The photolabile o-nitrobenzyl protecting group is used to avoid solubility issues and allows controlled BTA self-assembly. [39,40] The design of the system and the polymers we studied in this investigation are given in Scheme 1.…”

Light‐Responsive Block Copolymers

“…[19] A peculiar example of irreversible light-induced disruption of nano-objects has been reported by Stupp and coworkers ( Figure 4) on photosensitive peptide oligomers containing an o-nitrobenzyl group. [20,21] Although those oligomers are not strictly speaking LRBCs, their unique photo-responsive behavior merits to be mentioned here. Those molecules were found to self-assemble into supramolecular quadruple helical nanofibers as observed by transmission electronic microscopy (TEM) [ Figure 4(a)].…”

Rapid self-healing and anion selectivity in metallosupramolecular gels assisted by fluorine–fluorine interactions

“…Non-covalent interactions such as hydrogen bonding, p-p stacking, charge transfer interactions, and hydrophobic effects have been extensively utilized towards rational design of low molecular mass organo-and hydrogelators with new functional properties. [17][18][19][20] Peptides, 21 carbohydrates, 22 steroids, 23 ureaderivatives, 24 and simple fatty acids, 25 have been shown to exhibit remarkable ability to self-assemble into highly entangled fibrillar networks thereby able to encapsulate and immobilize solvent molecules. While a majority of the gelators have been discovered serendipitously, 26,27 continuing efforts have been made towards rational design of gelators with tunable properties as for example thermotropic polymorphism 28 or stimuli-responsiveness 29 including anion dependent gels 30 with interesting applications in molecular sensing.…”