Syntheses and polymerizations of alpha-amino acid N-carboxyanhydrides (NCAs) were reported for the first time by Hermann Leuchs in 1906. Since that time, these cyclic and highly reactive amino acid derivatives were used for stepwise peptide syntheses but mainly for the formation of polypeptides by ring-opening polymerizations. This review summarizes the literature after 1985 and reports on new aspects of the polymerization processes, such as the formation of cyclic polypeptides or novel organometal catalysts. Polypeptides with various architectures, such as diblock, triblock, and multiblock sequences, and star-shaped or dendritic structures are also mentioned. Furthermore, lyotropic and thermotropic liquid-crystalline polypeptides will be discussed and the role of polypeptides as drugs or drug carriers are reviewed. Finally, the hypothetical role of NCAs in molecular evolution on the prebiotic Earth is discussed.

Polypeptides and 100 years of chemistry of alpha-amino acid N-carboxyanhydrides.

A spider can spin major ampullate silk (drag line) at rates that differ by more than an order of magnitude, and yet obtain consistently reliable tensile properties. Silk samples collected at different rates and stained by infiltration with tin were studied by transmission electron microscopy. The stained microstructures indicate the presence of nonperiodic lattice crystals, the average size of which depends on the silking rate. A simple statistical point model demonstrates that the ordered regions in major ampullate silk can originate from statistical matches between adjacent chains. The minimum size of the ordered regions is dictated by the fixed monomer sequence in the chains and not by processing kinetics. Inductively coupled plasma—mass spectroscopy shows that the concentration of multivalent protein-binding cations in the unstained fibre is significantly reduced at the higher rates of silking, compared with their concentration at the lowest rates. Qualitatively, this result is consistent with the ions being used to maintain the shear sensitivity of silk secretion over the range of processing rates studied.

Spider major ampullate silk (drag line): smart composite processing based on imperfect crystals

Arthropods face several key challenges in processing concentrated feedstocks of proteins (silk dope) into solid, semi-crystalline silk fibres. Strikingly, independently evolved lineages of silk-producing organisms have converged on the use of liquid crystal intermediates (mesophases) to reduce the viscosity of silk dope and assist the formation of supramolecular structure. However, the exact nature of the liquid-crystal-forming-units (mesogens) in silk dope, and the relationship between liquid crystallinity, protein structure and silk processing is yet to be fully elucidated. In this review, we focus on emerging differences in this area between the canonical silks containing extended-β-sheets made by silkworms and spiders, and ‘non-canonical’ silks made by other insect taxa in which the final crystallites are coiled-coils, collagen helices or cross-β-sheets. We compared the amino acid sequences and processing of natural, regenerated and recombinant silk proteins, finding that canonical and non-canonical silk proteins show marked differences in length, architecture, amino acid content and protein folding. Canonical silk proteins are long, flexible in solution and amphipathic; these features allow them both to form large, micelle-like mesogens in solution, and to transition to a crystallite-containing form due to mechanical deformation near the liquid–solid transition. By contrast, non-canonical silk proteins are short and have rod or lath-like structures that are well suited to act both as mesogens and as crystallites without a major intervening phase transition. Given many non-canonical silk proteins can be produced at high yield in E. coli, and that mesophase formation is a versatile way to direct numerous kinds of supramolecular structure, further elucidation of the natural processing of non-canonical silk proteins may to lead to new developments in the production of advanced protein materials.

/pdf/more-than-one-way-to-spin-a-crystallite-multiple-2rg0l7du56.pdf

More than one way to spin a crystallite: multiple trajectories through liquid crystallinity to solid silk

Synthese und Polymerisation von α-Aminosaure-N-carboxyanhydriden (NCAs) wurden erstmals im Jahre 1906 von Herrmann Leuchs beschrieben. Seit dieser Zeit wurden diese cyclischen, sehr reaktiven α-Aminosaurederivate mehrfach zur schrittweisen Peptidsynthese eingesetzt, sie wurden aber vor allem zur Herstellung von Polypeptiden durch ringoffnende Polymerisation (ROP) verwendet. Es werden nun neue Aspekte der ringoffnenden Polymerisation diskutiert, z. B. die Verwendung neuartiger metallorganischer Initiatoren oder die Entstehung cyclischer Polypeptide. Des Weiteren werden Architekturen wie Diblock-, Triblock- und Multiblockcopolymere sowie sternformige oder hochverzweigte Polypeptide vorgestellt. Ferner werden lyotrope und thermotrope Polypeptide sowie die Verwendung von Polypeptiden als Pharmaka oder Pharmakatrager besprochen. Schlieslich wird die Rolle von NCAs im Konzept der molekularen Evolution diskutiert.

Polypeptide und 100 Jahre Chemie der α‐Aminosäure‐N‐carboxyanhydride

Nature offers useful lessons on how fibres with controlled properties can be produced from sustainable starting materials under environmentally friendly conditions. As we begin to learn these lessons, the advantages that they offer have to be weighed against Nature's limitations: the same molecular features that make biomolecular fibres initially processable in water are also reflected in the fibres having water-sensitive properties, which may not be attractive in an engineering material. Particular attention is given to recent findings that the short-term impressive tensile properties of spider dragline silk as recorded in conventional tests performed at constant strain rate are compromised by creep and stress relaxation, especially in humid environments. Some practical steps towards applying Nature's lessons while addressing the constraints of these lessons are suggested.

Inspiration versus duplication with biomolecular fibrous materials: learning nature's lessons without copying nature's limitations

The aptly-named liquid crystalline state behaves in some respects like an ordinary fluid, while also exhibiting properties that would usually be associated with crystalline solids. For example, the low viscosity of many liquid crystals enables them to readily adopt the shape of their container; yet, transmitted polarized light microscopy performed on thin undisturbed specimens of the same materials may reveal a high degree of local structural anisotropy on a greater-than-micrometer scale.

Liquid Crystalline Phase Behavior of Proteins and Polypeptides

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Liquid Crystalline Phase Behavior of Proteins and Polypeptides