The recent advances in accelerated polymerization of N-carboxyanhydrides (NCAs) enriched the toolbox to prepare well-defined polypeptide materials. Herein we report the use of crown ether (CE) to catalyze the polymerization of NCA initiated by conventional primary amine initiators in solvents with low polarity and low hydrogen-bonding ability. The cyclic structure of the CE played a crucial role in the catalysis, with 18-crown-6 enabling the fastest polymerization kinetics. The fast polymerization kinetics outpaced common side reactions, enabling the preparation of well-defined polypeptides using an α-helical macroinitiator. Experimental results as well as the simulation methods suggested that CE changed the binding geometry between NCA and propagating amino chain-end, which promoted the molecular interactions and lowered the activation energy for ring-opening reactions of NCAs. This work not only provides an efficient strategy to prepare well-defined polypeptides with functionalized C-termini, but also guides the design of catalysts for NCA polymerization.

Polypeptide micelles are widely used as biocompatible nanoplatforms but often suffer from their poor structural stability. Unimolecular polypeptide micelles can effectively address the structure instability issue, but their synthesis with uniform structure and well-controlled and desired sizes remains challenging. Herein we report the convenient preparation of spherical unimolecular micelles through dendritic polyamine-initiated ultrafast ring-opening polymerization of N-carboxyanhydrides (NCAs). Synthetic polypeptides with exceptionally high molecular weights (up to 85 MDa) and low dispersity (Đ < 1.05) can be readily obtained, which are the biggest synthetic polypeptides ever reported. The degree of polymerization was controlled in a vast range (25–3200), giving access to nearly monodisperse unimolecular micelles with predictable sizes. Many NCA monomers can be polymerized using this ultrafast polymerization method, which enables the incorporation of various structural and functional moieties into the unimolecular micelles. Because of the simplicity of the synthesis and superior control over the structure, the unimolecular polypeptide micelles may find applications in nanomedicine, supermolecular chemistry, and bionanotechnology.

The Early Cambrian (Ϸ540 million years old) Meishucun fossil assemblage of Ningqiang County (Shaanxi Province), China, contains the oldest complex skeletonized organisms known in the geological record. We here report the finding in this assemblage of an exquisitely preserved late-stage embryo of a ctenophore (''comb jelly''), its fine structure documented by confocal laser scanning microscopy and shown by Raman spectroscopy to be composed of carbonaceous kerogen permineralized in apatite. In its spheroidal morphology, the presence of eight comb rows and the absence of tentacles, this embryo resembles an adult ctenophore (Maotianoascus octonarius) known from the immediately younger Chengjiang fauna of Yunnan, China. The oldest ctenophore and the only embryonic comb jelly known from the fossil record, this exceptionally well preserved specimen provides important clues about the early evolution of the phylum Ctenophora and of metazoans in general.comb jelly ͉ confocal laser scanning microscopy ͉ Meishucun fossil assemblage ͉ Ningqiang fossil fauna

Developing recyclable, self-healable, and highly malleable thermosets is one of the keys to relieve environmental pollution and meet our increasing demand for "greener" materials. Hindered urea bonds (HUBs) have been successfully incorporated in preparing dynamic covalent networks with those desirable properties. However, one key drawback is the low thermal stability and poor mechanical performance of previously reported systems.In this work, we demonstrated that the incorporation of aromatic moiety-containing diamine-based HUBs can greatly improve the thermal and mechanical performance of the poly(urethane-urea)s (PUUs) while still maintaining the desirable recycling, self-healing, and reprocessing properties. Studies on model compounds revealed the origin of the thermal stability and demonstrated the dynamic property. The aromatic-containing diamine-based HUBs were then used to prepare a series of catalyst-free PUUs with improved thermal and mechanical properties. The dynamic HUBs significantly reduced the relaxation timescale and allowed the PUU networks to be recycled multiple times. The healed and recycled PUUs regained most of the mechanical strength and integrity of the original material. Therefore, this unique and simple approach is expected to open up new avenues to design PUUs with optimal performance for various applications.