Jing Sun

Nature, Published online: 19 November 2019; doi:10.1038/d41586-019-03570-9

Writer’s secret? Shut the door and no interruptions till you’re done

Nature Nanotechnology, Published online: 18 November 2019; doi:10.1038/s41565-019-0578-8

Enzyme-coated liposomal motors show either positive or negative chemotaxis depending on the interplay between enzyme catalysis and solute–phospholipid interactions.

A rotatable “Rubik's Cube” hydrogel (RC) is macroscopically assembled via controllable dynamic covalent interactions by Jonathan L. Sessler, Ben Zhong Tang, and co‐workers in article number https://doi.org/10.1002/adma.2019023651902365. Overly strong or overly weak interactions between the constituent hydrogel building blocks are avoided as they will preclude formation of the RC or rotation of the constituent blocks. Thus, transient differences in hydrogel binding strength are exploited to create an ensemble endowed with both rotational flexibility and structural integrity. The name and representations of the Rubik's Cube used by permission of Rubik's Brand Ltd.

Stereoselective polymerization of chiral or prochiral monomers is a powerful method to produce high-performance stereoregular crystalline polymeric materials. However, for monomers with two stereogenic centers, it is generally necessary to separate diastereomers before polymerization, resulting in substantial material loss and added energy cost associated with the separation and purification process. Here we report a diastereoselective polymerization methodology enabled by catalysts that directly polymerize mixtures of eight-membered diolide (8DL) monomers with varying starting ratios of chiral racemic (rac) and achiral meso diastereomers into stereosequenced crystalline polyhydroxyalkanoates with isotactic and syndiotactic stereodiblock or stereotapered block microstructures. These polymers show enhanced ductility and toughness relative to polymers of pure rac-8DL, subject to tuning by variation of the diastereomeric ratio and structure of the 8DL monomers.

New research on an enzyme that is essential for photosynthesis and all life on earth has uncovered a key finding in its structure which reveals how light can interact with matter to make an essential pigment for life.

A general synthetic route was developed for the preparation of the first example of a new series of modified C‐nucleoside phosphonate analogues bearing a l‐threose sugar moiety and pyrrolo[2,1‐f][1,2,4]triazin‐4‐amine as nucleobase.

A general synthetic route for the preparation of the first analogue of a new series of sugar‐modified C‐nucleoside phosphonates is detailed. Such derivative contains a four‐carbon l‐threose sugar moiety substituted with a phosphonomethoxy group at the 3′‐position and pyrrolo[2,1‐f][1,2,4]triazin‐4‐amine as nucleobase. A C‐nucleoside was initially prepared by coupling a benzyl protected l‐threono‐1,4‐lactone intermediate with the corresponding aglycon moiety. The choice of a tert‐butyldiphenylsilyl group was found to be crucial to achieve the regioselective protection of the hydroxyl group at the 3′‐position. Moreover, it allowed to smoothly perform further synthetic manipulations, including the introduction of a benzyl protected phosphonate synthon under basic conditions, which eventually led to the desired compound after final deprotection.

Coordination isomerism can be used to control the morphology of a supramolecular polymer, as G. Fernández et al. show in their Communication on https://doi.org/10.1002/anie.201908002page 15626. Tuning the coordination isomerism of a Pt^II complex leads to tunable coordination isomerism, which in turn allows fully reversible switching between two distinct aggregate species (1D fibers↔2D lamellae) with different photoresponsive behavior. These observations pave the way for novel stimuli‐responsive materials and offer a new approach for size control in self‐assembled systems.

We present a novel enzymatic method for the preparation of Rib‐p and dRib‐p starting from 7‐Me‐Guo and 7‐Me‐dGuo. Practically irreversible phosphorolysis of 7‐Me‐Guo and 7‐Me‐dGuo in the presence of PNP ensures the quantitative transformation of starting nucleosides to anomerically pure α‐Rib‐p and α‐dRib‐p. Rib‐p and dRib‐p are obtained with 74–96 % yields after isolation and purification.

α‐Ribose‐1‐phosphate (Rib‐p) and 2‐deoxy‐α‐ribose‐1‐phosphate (dRib‐p) are key intermediates in nucleoside metabolism and are important starting compounds for the enzymatic synthesis of various modified nucleosides. To date, chemical and enzymatic methods allowed the preparation of these compounds in rather low yields (11–37 %). This prevents their widespread use for the enzymatic synthesis of biologically active and practically important nucleosides. Here we propose to use 7‐methyl‐2′‐deoxyguanosine (7‐Me‐dGuo) and 7‐methylguanosine (7‐Me‐Guo) for the preparation of dRib‐p and Rib‐p. In this paper, we present the effective preparation of Rib‐p and dRib‐p starting from readily prepared 7‐methylguanosine derivatives via their irreversible enzymatic phosphorolysis in the presence of purine nucleoside phosphorylase. Rib‐p and dRib‐P are obtained in nearly quantitative yields (HPLC analysis) and 74–96 % yields after their isolation and purification, which is much higher than previously reported.

Every which way and loose: A single amphiphilic thermoresponsive diblock copolymer can reversibly form spheres, worms or vesicles in aqueous solution. Self‐consistent mean field theory indicates that this rich self‐assembly behavior arises from the temperature‐dependent degree of hydration of the structure‐directing hydrophobic poly(2‐hydroxypropyl methacrylate) block.

Abstract

It is well‐known that the self‐assembly of AB diblock copolymers in solution can produce various morphologies depending on the relative volume fraction of each block. Recently, polymerization‐induced self‐assembly (PISA) has become widely recognized as a powerful platform technology for the rational design and efficient synthesis of a wide range of block copolymer nano‐objects. In this study, PISA is used to prepare a new thermoresponsive poly(N‐(2‐hydroxypropyl) methacrylamide)‐poly(2‐hydroxypropyl methacrylate) [PHPMAC‐PHPMA] diblock copolymer. Remarkably, TEM, rheology and SAXS studies indicate that a single copolymer composition can form well‐defined spheres (4 °C), worms (22 °C) or vesicles (50 °C) in aqueous solution. Given that the two monomer repeat units have almost identical chemical structures, this system is particularly well‐suited to theoretical analysis. Self‐consistent mean field theory suggests this rich self‐assembly behavior is the result of the greater degree of hydration of the PHPMA block at lower temperature, which is in agreement with variable temperature ¹H NMR studies.

The milling ball is the catalyst: In a mechanochemical Suzuki polymerization of 4‐bromo‐ or 4‐iodophenylboronic acid yielding poly(para‐phenylene) the classical Pd catalysts could be replaced by solid Pd milling balls, enabling outstanding degrees of polymerization.

Abstract

The milling ball is the catalyst. We introduce a palladium‐catalyzed reaction inside a ball mill, which makes catalyst powders, ligands, and solvents obsolete. We present a facile and highly sustainable synthesis concept for palladium‐catalyzed C−C coupling reactions, exemplarily showcased for the Suzuki polymerization of 4‐bromo or 4‐iodophenylboronic acid giving poly(para‐phenylene). Surprisingly, we observe one of the highest degrees of polymerization (199) reported so far.

Naturally occurring aza‐spiro scaffolds are synthesized in aqueous micellar solutions of a cationic surfactant without metal catalysis. Dynamic light scattering and cryogenic transmission electron microscopy monitoring revealed the incorporation of the substrate and the presence of the reaction products in the micelles.

Micellar solutions of cetyltrimethylammonium bromide (CTAB) surfactant allow the spirocyclization of keto‐ynamides in an aqueous medium without recourse to transition‐metal catalysis, enabling access in water to naturally occurring aza‐spiro compounds with potential in drug discovery. The reaction was monitored by dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo‐TEM), which determined the morphology and change in size of the micelles before and after incorporation of the substrate and achievement of 5‐endo‐dig cyclization inside the micelles.

A DNA nanopump is produced with azobenzene‐functionalized DNA strands for efficient and controllable drug release through the photoisomerization of azobenzene fueled by the simultaneous UV and visible‐light emissions of upconversion nanoparticles (UCNPs) under NIR irradiation. This triggers the release of an anticancer drug and enhances anticancer therapy.

Abstract

Stimulus‐responsive drug release possesses considerable significance in cancer therapy. This work reports an upconversion‐luminescence‐fueled DNA–azobenzene nanopump for rapid and efficient drug release. The nanopump is constructed by assembling the azobenzene‐functionalized DNA strands on upconversion nanoparticles (UCNPs). Doxorubicin (DOX) is loaded in the nanopump by intercalation in the DNA helix. Under NIR light, the UCNPs emit both UV and visible photons to fuel the continuous photoisomerization of azo, which acts as an impeller pump to trigger cyclic DNA hybridization and dehybridization for controllable DOX release. In a relatively short period, this system demonstrates 86.7 % DOX release. By assembling HIV‐1 TAT peptide and hyaluronic acid on the system, targeting of the cancer‐cell nucleus is achieved for perinuclear aggregation of DOX and enhanced anticancer therapy. This highly effective drug delivery nanopump could contribute to chemotherapy development.

A light touch: The use of carboxy‐functionalized dithienylethene photochromes as initiators in controlled cationic polymerizations of vinyl ethers enables the photocontrol of polymer dispersity. Reversible photoisomerization of these initiators induces changes in their acidities by up to an order of magnitude, and the degree of light‐induced acidity change correlates with the degree of dispersity change.

Abstract

Deterministic methods for tuning polymer dispersity are rare, especially for nonradical polymerizations. Reported here is the first example of photomodulating dispersity in controlled cationic polymerizations of vinyl ethers using carboxy‐functionalized dithienylethene initiators. Reversible photoisomerization of these initiators induces changes in their acidities by up to an order of magnitude. Using the more acidic, ring‐closed isomers as initiators results in polymers with lower dispersities. The degree of light‐induced pK _a change in the initiators correlates with the degree of dispersity change in polymers derived from the isomeric initiators. The polymerizations are controlled, and dynamic photoswitching of dispersity during the polymerization reaction was demonstrated. This work provides a framework for photomodulating dispersity in other controlled polymerizations and developing one‐pot block copolymerization reactions in which the dispersities of component blocks can be controlled using light.

3D lipid vesicles are converted to 2D lipid nanosheets by addition of anionic amphiphilic peptides and cationic copolymers that act as peptide chaperones. 2D–3D reconversion is triggered by stimuli such as enzymatic activity or pH change, allowing tuning of lipid bilayer structures and functionalities.

Abstract

Nanosheets have thicknesses on the order of nanometers and planar dimensions in the micrometer range. Nanomaterials that are capable of converting reversibly between 2D nanosheets and 3D structures in response to specific triggers can enable construction of nanodevices. Supra‐molecular lipid nanosheets and their triggered conversions to 3D structures including vesicles and cups are reported. They are produced from lipid vesicles upon addition of amphiphilic peptides and cationic copolymers that act as peptide chaperones. By regulation of the chaperoning activity of the copolymer, 2D to 3D conversions are reversibly triggered, allowing tuning of lipid bilayer structures and functionalities.

Asymmetric click chemistry is used to induce planar stereogenicity in prochiral ferrocenyl diynes, giving products in up to 99.5 % ee. Asymmetric induction and kinetic resolution studies on a novel library of prochiral 1,2,3‐trisubstituted bis‐alkynylferrocenes are reported.

The new asymmetric click CuAAC reaction is used for the first time to induce asymmetry in planar chiral compounds. There are only three classes of stereogenicity (atom‐centred, axial and planar), and these results are therefore of fundamental importance as well as practical significance, providing access to chiral ferrocenes at near enantiopurity. Here, we report asymmetric induction (AI) and kinetic resolution (KR) studies on a novel library of prochiral 1,2,3‐trisubstituted bis‐alkynylferrocenes, obtained by diiodination, derivatisation (including reduction and etherification), double Sonogashira coupling and finally transesterification, azidation or silylation. Desymmetrisation using chiral ligands to modify the CuAAC reaction proceeds in up to 60 % yield and >99.5 % ee, yielding planar chiral ferrocenes. The absolute configuration of two of the preferred products was proved by chemical correlation and related to the entire series by circular dichroism spectroscopy (CD).

A “crystal‐clear” process: Base‐catalyzed thermal decarboxylation of an organic acid controls the temporal crystallization of a cucurbit[8]uril‐based host‐guest complex, preventing the accumulation of chemical wastes and thereby showing minimal dampening in subsequent cycles.

Abstract

Transient self‐assembling systems often suffer from accumulation of chemical wastes that interfere with the formation of pristine self‐assembled products in subsequent cycles. Herein, we report the transient crystallization of a cucurbit[8]uril‐based host‐guest complex, preventing the accumulation of chemical wastes. Base‐catalyzed thermal decarboxylation of trichloroacetic acid that chemically fuels the crystallization process dissolves the crystals, and produces volatile chemical wastes that are spontaneously removed from the solution. With such self‐clearance process, no significant damping in the formation of the crystals was observed. The morphology and structural integrity of the crystals was also maintained in subsequent cycles. The concept may be further extended to obtain other temporally functional materials, quasicrystals, etc., based on stimuli‐responsive guest molecules.

Nature Chemistry, Published online: 16 September 2019; doi:10.1038/s41557-019-0322-x

The emergence of pristine RNA and DNA on the early Earth would have been hindered by a lack of specificity in their prebiotic syntheses. Now, it has been shown that chimeric sequences—with a mixture of RNA and DNA backbones—mediate the template-directed ligation of oligomers present in mixtures of nucleic acids, enabling the simultaneous appearance of RNA and DNA.

Nature Chemistry, Published online: 23 September 2019; doi:10.1038/s41557-019-0327-5

It is difficult to prepare 2D polymers that are crystalline over large areas. Now, few-layer 2D polyimides and polyamides with good crystallinity on the micrometre scale have been synthesized on a water surface. A surfactant monolayer is used to organize amine monomers before their polymerization with anhydride moieties.

Carbon allotropes built from rings of two-coordinate atoms, known as cyclo[n]carbons, have fascinated chemists for many years, but until now they could not be isolated or structurally characterized because of their high reactivity. We generated cyclo[18]carbon (C₁₈) using atom manipulation on bilayer NaCl on Cu(111) at 5 kelvin by eliminating carbon monoxide from a cyclocarbon oxide molecule, C₂₄O₆. Characterization of cyclo[18]carbon by high-resolution atomic force microscopy revealed a polyynic structure with defined positions of alternating triple and single bonds. The high reactivity of cyclocarbon and cyclocarbon oxides allows covalent coupling between molecules to be induced by atom manipulation, opening an avenue for the synthesis of other carbon allotropes and carbon-rich materials from the coalescence of cyclocarbon molecules.