With the advent of reversible covalent chemistry the study of the interplay between covalent bond formation and noncovalent interactions has become increasingly relevant. Here we report that the interplay between reversible disulfide chemistry and self-assembly can give rise either to molecular diversity, i.e., the emergence of a unprecedentedly large range of macrocycles or to molecular specificity, i.e., the autocatalytic emergence of a single species. The two phenomena are the result of two different modes of self-assembly, demonstrating that control over self-assembly pathways can enable control over covalent bond formation.

Photoisomerization provides a clean and efficient way of reversibly altering physical properties of chemical systems and injecting energy into them. These effects have been applied in development of systems such as photoresponsive materials, molecular motors, and photoactivated drugs. Typically, switching from more to less stable isomer(s) is performed by irradiation with UV or visible light, while the reverse process proceeds thermally or by irradiation using another wavelength. In this work we developed a method of rapid and tunable Z→E isomerization of C=N bond in acyl hydrazones, using aromatic thiols as nucleophilic catalysts. As thiols can be oxidized into catalytically inactive disulfides, the isomerization rates can be controlled via the oxidation state of the catalyst, which, together with the UV irradiation, provides orthogonal means to control the E/Z state of the system. As a proof of this concept, we have applied this method to control the diversity of acyl hydrazone based dynamic combinatorial libraries.

Self-assembly features prominently in fields ranging from materials science to biophysical chemistry. Assembly pathways, often passing through transient intermediates, can control the outcome of assembly processes. Yet, the mechanisms of self-assembly remain largely obscure due to a lack of experimental tools for probing these pathways at the molecular level. Here, the self-assembly of self-replicators into fibers is visualized in real-time by high-speed atomic force microscopy (HS-AFM). Fiber growth requires the conversion of precursor molecules into six-membered macrocycles, which constitute the fibers. HS-AFM experiments, supported by molecular dynamics simulations, revealed that aggregates of precursor molecules accumulate at the sides of the fibers, which then diffuse to the fiber ends where growth takes place. This mechanism of precursor reservoir formation, followed by one-dimensional diffusion, which guides the precursor molecules to the sites of growth, reduces the entropic penalty associated with colocalizing precursors and growth sites and constitutes a new mechanism for supramolecular polymerization.

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Keratin is one of the most abundant biopolymers, produced on a scale of millions of tons per year but often simply discarded as waste. Due to its abundance, biocompatibility, and excellent mechanical properties, there is an extremely high interest in developing protocols for the recycling of keratin and its conversion into protein-based materials. In this work, we describe a novel protocol for the conversion of keratin from wool into hybrid fibers. Our protocol uses a synthetic polyanion, which undergoes complex coacervation with keratin, leading to a viscous liquid phase that can be used directly as a dope for dry-spinning. The use of polyelectrolyte complexation allows us to use all of the extracted keratin, unlike previous works that were limited to the fraction with the highest molecular weight. The fibers prepared by this protocol show excellent mechanical properties, humidity responsiveness, and ion conductivity, which makes them promising candidates for applications as a strain sensor.