De Novo Designed Peptide and Protein Hairpins Self‐Assemble into Sheets and Nanoparticles

The design and assembly of peptide‐based materials has advanced considerably, leading to a variety of fibrous, sheet, and nanoparticle structures. A remaining challenge is to account for and control different possible supramolecular outcomes accessible to the same or similar peptide building blocks. Here a de novo peptide system is presented that forms nanoparticles or sheets depending on the strategic placement of a “disulfide pin” between two elements of secondary structure that drive self‐assembly. Specifically, homodimerizing and homotrimerizing de novo coiled‐coil α‐helices are joined with a flexible linker to generate a series of linear peptides. The helices are pinned back‐to‐back, constraining them as hairpins by a disulfide bond placed either proximal or distal to the linker. Computational modeling indicates, and advanced microscopy shows, that the proximally pinned hairpins self‐assemble into nanoparticles, whereas the distally pinned constructs form sheets. These peptides can be made synthetically or recombinantly to allow both chemical modifications and the introduction of whole protein cargoes as required

Regenerated cellulose and willow lignin blends as potential renewable precursors for carbon fibers

We report on the extraction of lignin from willow and its use to manufacture cellulose-lignin fibers as potential precursors for the manufacture of carbon fibers. The lignin from willow was extracted using triethylammonium hydrogen sulfate [Et3NH][HSO4]. The lignin extracted by this process was characterized by ATR-IR and elemental analysis, which indicated a high carbon yield. 1-Ethyl-3-methylimidazolium acetate [C2C1im][OAc] was then used as a common solvent to dissolve cellulose and lignin to manufacture lignin-cellulose fiber blends. The Young’s modulus of a 75:25 lignin/cellulose fiber was found to be 3.0 ± 0.5 GPa, which increased to 5.9 ± 0.6 GPa for a 25:75 lignin/cellulose blend. From a characterization of the surface morphology, using scanning electron microscopy (SEM) and atomic force microscopy (AFM), it was observed that higher lignin content in the fiber blend increased the surface roughness. FT-IR analysis confirmed the presence of aromatic groups related to lignin in the obtained fibers from the presence of peaks located at ∼1505 cm–1 and ∼1607 cm–1. The presence of lignin improves the thermal stability of the fiber blends by allowing them to degrade over a wider temperature range. The presence of lignin also improved the carbon yield during carbonization. Therefore, the lignin-cellulose fibers developed in this work can offer an excellent alternative to pure cellulose or lignin filaments