Jing Sun

Nature Chemistry, Published online: 26 June 2020; doi:10.1038/s41557-020-0494-4

The integration of replication with metabolism represents a key step in the transition of chemistry into biology. Now, it has been shown that a self-replicator can recruit and activate two different photocatalytic cofactors, which then catalyse the synthesis of the precursors for the replicator.

Nature Materials, Published online: 22 June 2020; doi:10.1038/s41563-020-0707-7

Peptide amphiphile supramolecular polymers with a crosslinked spiropyran network respond to light by expelling water, enabling the fabrication of soft actuators or light-driven crawlers.

One hand makes light work: The crystallization‐driven asymmetric self‐assembly (CDASA) of the block copolymers leads to the formation of single‐handed helical nanofibers with controlled length, narrow dispersity, and well‐defined helicity. The helical assembly of the block copolymer induced white‐light emission and intense circularly polarized luminescence (CPL).

Abstract

Controlling the self‐assembly morphology of π‐conjugated block copolymer is of great interesting. Herein, amphiphilic poly(3‐hexylthiophene)‐block‐poly(phenyl isocyanide)s (P3HT‐b‐PPI) copolymers composed of π‐conjugated P3HT and optically active helical PPI segments were readily prepared. Taking advantage of the crystallizable nature of P3HT and the chirality of the helical PPI segment, crystallization‐driven asymmetric self‐assembly (CDASA) of the block copolymers lead to the formation of single‐handed helical nanofibers with controlled length, narrow dispersity, and well‐defined helicity. During the self‐assembly process, the chirality of helical PPI was transferred to the supramolecular assemblies, giving the helical assemblies large optical activity. The single‐handed helical assemblies of the block copolymers exhibited interesting white‐light emission and circularly polarized luminescence (CPL). The handedness and dissymmetric factor of the induced CPL can be finely tuned through the variation on the helicity and length of the helical nanofibers.

Delivery driver: Photo‐activated polymersome nanomotors (PNMs) composed of a biodegradable polymersome system coated with a hemisphere gold layer were utilized for intracellular delivery of molecular cargo via the assistance of a NIR laser. The active penetration of the cell membrane by the nanomotors allowed both encapsulated payloads and surrounding cargo to be delivered into cells.

Abstract

Synthetic nanomotors are appealing delivery vehicles for the dynamic transport of functional cargo. Their translation toward biological applications is limited owing to the use of non‐degradable components. Furthermore, size has been an impediment owing to the importance of achieving nanoscale (ca. 100 nm) dimensions, as opposed to microscale examples that are prevalent. Herein, we present a hybrid nanomotor that can be activated by near‐infrared (NIR)‐irradiation for the triggered delivery of internal cargo and facilitated transport of external agents to the cell. Utilizing biodegradable poly(ethylene glycol)‐b‐poly(d,l‐lactide) (PEG‐PDLLA) block copolymers, with the two blocks connected via a pH sensitive imine bond, we generate nanoscopic polymersomes that are then modified with a hemispherical gold nanocoat. This Janus morphology allows such hybrid polymersomes to undergoing photothermal motility in response to thermal gradients generated by plasmonic absorbance of NIR irradiation, with velocities ranging up to 6.2±1.10 μm s⁻¹. These polymersome nanomotors (PNMs) are capable of traversing cellular membranes allowing intracellular delivery of molecular and macromolecular cargo.

Time‐programmable, transient supramolecular naphthalimide‐dipeptide nanofibers were reported, the lifetimes of which are predictably variable, demonstrated through variation of the self‐assembly propensity of their amino acid precursors. Thus, the work shows that a thermodynamic parameter dictates kinetic lifetimes in transient fibers formed by competing biocatalytic self‐assembly and disassembly of aromatic peptide amphiphiles.

Abstract

Transient self‐assembly of dipeptide nanofibers with lifetimes that are predictably variable through dipeptide sequence design are presented. This was achieved using 1,8‐naphthalimide ( NI ) amino acid methyl‐esters (Phe, Tyr, Leu) that are biocatalytically coupled to amino acid‐amides (Phe, Tyr, Leu, Val, Ala, Ser) to form self‐assembling NI ‐dipeptides. However, competing hydrolysis of the dipeptides results in disassembly. It was demonstrated that the kinetic parameters like lifetimes of these nanofibers can be predictably regulated by the thermodynamic parameter, namely the self‐assembly propensity of the constituent dipeptide sequence. These lifetimes could vary from minutes, to hours, to permanent gels that do not degrade. Moreover, the in‐built NI fluorophore was utilized to image the transient nanostructures in solution with stimulated emission depletion (STED) based super‐resolution fluorescence microscopy.

Mechanically interlocked molecules are likely candidates for the design and synthesis of artificial molecular machines. Although polyrotaxanes have already found niche applications in exotic materials with specialized mechanical properties, efficient synthetic protocols to produce them with precise numbers of rings encircling their polymer dumbbells are still lacking. We report the assembly line–like emergence of poly[n]rotaxanes with increasingly higher energies by harnessing artificial molecular pumps to deliver rings in pairs by cyclical redox-driven processes. This programmable strategy leads to the precise incorporation of two, four, six, eight, and 10 rings carrying 8+, 16+, 24+, 32+, and 40+ charges, respectively, onto hexacationic polymer dumbbells. This strategy depends precisely on the number of redox cycles applied chemically or electrochemically, in both stepwise and one-pot manners.

Cool down: Depending on the cooling rate, a monomeric perylene bisimide equipped with four acyloxy bay substituents self‐assembles into two distinct polymorphs that exhibit distinctive optical properties and packing arrangements. The interchromophoric arrangement was elucidated in the liquid‐crystalline state, demonstrating the effect of homo‐ versus heterochiral self‐sorting, directing self‐assembly into one‐ or two‐dimensional structures, respectively.

Abstract

A new perylene bisimide (PBI), with a fluorescence quantum yield up to unity, self‐assembles into two polymorphic supramolecular polymers. This PBI bears four solubilizing acyloxy substituents at the bay positions and is unsubstituted at the imide position, thereby allowing hydrogen‐bond‐directed self‐assembly in nonpolar solvents. The formation of the polymorphs is controlled by the cooling rate of hot monomer solutions. They show distinctive absorption profiles and morphologies and can be isolated in different polymorphic liquid‐crystalline states. The interchromophoric arrangement causing the spectral features was elucidated, revealing the formation of columnar and lamellar phases, which are formed by either homo‐ or heterochiral self‐assembly, respectively, of the atropoenantiomeric PBIs. Kinetic studies reveal a narcissistic self‐sorting process upon fast cooling, and that the transformation into the heterochiral (racemic) sheetlike self‐assemblies proceeds by dissociation via the monomeric state.

This Perspective looks at the advances and future challenges in the field of anion receptor chemistry, including new strategies for achieving selective anion recognition in water.

The discovery of the phenomenon of aggregation-induced emission (AIE) has overwritten the conventional wisdom that molecular aggregation is detrimental to solid-state light emission. Since then, the AIE concept has guided numerous exciting advancements in luminogen research. This Catalysis article highlights the progress of AIE research over the last two decades and discusses several milestones defining the field, ranging from the rise of the AIE concept and identification of AIE applications to the expansion of AIE research to practical technological applications.

Fluorescence imaging facilitated by NIR‐II emissive aggregation‐induced emission luminogens (AIEgens) is an emerging research field. This minireview summarizes recent efforts on developing novel NIR‐II AIEgens in terms of molecular design strategies and bioapplications, and discusses current challenges and future prospects.

Abstract

Fluorescence imaging in the second near‐infrared (NIR‐II) window facilitated by aggregation‐induced emission luminogens (AIEgens) is an emerging research field. NIR‐II AIEgens overcome limitations imposed by penetration depth and fluorescence efficiency, offering high‐performance imaging with enhanced precision. Some reported NIR‐II AIEgens demonstrate capabilities for fluorescence and photoacoustic bimodal imaging, and fluorescence imaging guided photothermal therapy, which not only improves diagnosis accuracy but provides an efficient theranostic platform to accelerate preclinical translation as well. This minireview summarizes recent efforts on exploiting NIR‐II AIEgens with regard to molecular design strategies and bioapplications, and puts forward current challenges and promising prospects. This timely sketch should benefit the further exploitation of diverse and multifunctional NIR‐II AIEgens for a wide array of applications.

The addition of chain stoppers significantly improves carbon nanotube (CNT) sorting with an H‐bonding supramolecular polymer. In‐depth characterization reveals that this supramolecular polymer exhibits ring–chain equilibrium, and that stoppers skew the distribution toward chains, which can wrap CNTs more effectively. Careful selection of the stopper–monomer ratio results in doubling of the sorting yield without compromising the purity or properties of sorted CNTs.

Abstract

Supramolecular polymer sorting is a promising approach to separating single‐walled carbon nanotubes (CNTs) by electronic type. Unlike conjugated polymers, they can be easily removed from the CNTs after sorting by breaking the supramolecular bonds, allowing for isolation of electronically pristine CNTs as well as facile recycling of the sorting polymer. However, little is understood about how supramolecular polymer properties affect CNT sorting. Herein, chain stoppers are used to engineer the conformation of a supramolecular sorting polymer, thereby elucidating the relationship between sorting efficacy and polymer conformation. Through NMR and UV–vis spectroscopy, small‐angle X‐ray scattering (SAXS), and thermodynamic modeling, it is shown that this supramolecular polymer exhibits ring–chain equilibrium, and that this equilibrium can be skewed toward chains by the addition of chain stoppers. Furthermore, by controlling the stopper–monomer ratio, the sorting yield can be doubled from 7% to 14% without compromising the semiconducting purity (>99%) or properties of sorted CNTs.

Sunlight is the best disinfectant : A benzothiadiazole‐ and tetraphenylethene‐containing conjugated polymer (PTB‐APFB) with high ROS‐generation ability and selectivity for pathogenic microorganisms over mammalian cells was developed. In vitro and in vivo results show that PTB‐APFB inhibits growth of bacteria efficiently, leading to recovery from infection 3 days faster than cefalotin.

Abstract

New, biocompatible materials with favorable antibacterial activity are highly desirable. In this work, we develop a unique conjugated polymer featuring aggregation‐induced emission (AIE) for reliable bacterial eradication. Thanks to the AIE and donor‐π‐acceptor structure, this polymer shows a high reactive oxygen species (ROS)‐generation ability compared to a low‐mass model compound and the common photosensitizer Chlorin E6. Moreover, the selective binding of pathogenic microorganisms over mammalian cells was found, demonstrating its biocompatibility. The effective growth inhibition of bacteria upon polymer treatment under light irradiation was validated in vitro and in vivo. Notably, the recovery from infection after treatment with our polymer is faster than that with cefalotin. Thus, this polymer holds great promise in fighting against bacteria‐related infections in practical applications.

Strong links : Polymers containing luminophores or sub‐luminophores may display enhanced emission upon crosslinking by covalent, supramolecular, and ionic bonding, and by through‐space interactions in confined domains. In this Minireview the theoretical background is discussed and numerous examples are provided, which may guide researchers in crosslinkage techniques to improve luminescent systems.

Abstract

The crosslink‐enhanced emission effect was first proposed to explore the strong luminescence of nonconjugated polymer dots possessing only either non‐emissive or weakly emissive sub‐luminophores. Interesting phenomena in recent research indicate such enhancement caused by extensive crosslinking appears in diverse luminescent polymers with sub‐luminophores (electron‐rich heteroatomic moieties) or luminophores (conjugated π domains). This enhancement can promote the emission from nonluminous to luminous, from weakly luminous to strongly luminous, and even convert the pathway of radiative transitions. The concept of the crosslink‐enhanced emission effect should be updated and extended to an in‐depth spatial effect, such as electron overlap and energy splitting in confined domains by effective crosslinking, more than initial immobilization. This Minireview outlines the development of the crosslink‐enhanced emission effect from the perspective of the detailed classification, inherent mechanism and applicable systems. An outlook on the further exploration and application of this theory are also proposed.

Planar luminophores with excellent aggregation‐induced emission and reactive oxygen species (ROS) generation properties that are based on intermolecular hydrogen‐bonding interactions can serve as photosensitizers in the photodynamic therapy of bacterial infections.

Abstract

Planar luminogens have encountered difficulties in overcoming intrinsic aggregation‐caused emission quenching by intermolecular π‐π stacking interactions. Although excited‐state double‐bond reorganization (ESDBR) can guide us on designing planar aggregation‐induced emission (AIE) luminogens (AIEgens), its mechanism has yet been elucidated. Major challenges in the field include methods to efficiently restrict ESDBR and enhance AIE performance without using bulky substituents (e.g., tetraphenylethylene and triphenylamine). In this study, we rationally developed fluoro‐substituent AIEgens with stronger intermolecular H‐bonding interaction for restricted molecular motions and increased crystal density, leading to decreased nonradiative decay rate by one order of magnitude. The adjusted ESDBR properties also show a corresponding response to variation in viscosity. Furthermore, their aggregation‐induced reactive oxygen species (ROS) generations have been discovered. The application of such planar AIEgen in treating multidrug‐resistant bacteria has been demonstrated in a mouse model. The relationship between ROS generation and distinct E /Z ‐configurational stacking behaviors have been further understood, providing a design principle for synthesizing planar AIEgen‐based photosensitizers.

Nature, Published online: 03 June 2020; doi:10.1038/s41586-020-2330-9

A prebiotic synthesis of the purine DNA nucleosides (deoxyadenosine and deoxyinosine) in which the pyrimidine RNA nucleosides (cytidine and uridine) persist has implications for the coexistence of DNA and RNA at the dawn of life.

Photoprogrammable mesogenic helical soft materials with both photosensitive and mesogenic moieties in molecules possess typical chiro‐optical properties, showing handedness dependency on the transmission, reflection, and absorption of an incident circularly polarized light (photonic bandgap and circular dichroism). This can be modulated readily by light irradiation, thus paving the way toward future chiro‐optical devices and systems.

Abstract

Mesogenic soft materials, having single or multiple mesogen moieties per molecule, commonly exhibit typical self‐organization characteristics, which promotes the formation of elegant helical superstructures or supramolecular assemblies in chiral environments. Such helical superstructures play key roles in the propagation of circularly polarized light and display optical properties with prominent handedness, that is, chiro‐optical properties. The leveraging of light to program the chiro‐optical properties of such mesogenic helical soft materials by homogeneously dispersing photosensitive chiral material into an achiral soft system or covalently connecting photochromic moieties to the molecules has attracted considerable attention in terms of materials, properties, and potential applications and has been a thriving topic in both fundamental science and application engineering. State‐of‐the‐art technologies are described in terms of the material design, synthesis, properties, and modulation of photoprogrammable chiro‐optical mesogenic soft helical architectures. Additionally, the scientific issues and technical problems that hinder further development of these materials for use in various fields are outlined and discussed. Such photoprogrammable mesogenic soft helical materials are competitive candidates for use in stimulus‐controllable chiro‐optical devices with high optical efficiency, stable optical properties, and easy miniaturization, facilitating the future integration and systemization of chiro‐optical chips in photonics, photochemistry, biomedical engineering, chemical engineering, and beyond.

Nature Communications, Published online: 03 June 2020; doi:10.1038/s41467-020-16595-w

Sequestration of reactants in lipid vesicles is a strategy prevalent in biological systems to raise the rate and specificity of chemical reactions. Here, the authors show that micelle-assisted reactions facilitate native chemical ligation between a peptide-thioester and a Cys-peptide modified by a lipid-like moiety.

“Aggregation‐induced emission research has brought us to the meso territory, where the synergy and cooperation between many molecules in the aggregate make it different from its elementary components. … Let's enthusiastically embrace the opportunity to develop meso science and to innovate meso technology, and make our planet a brighter place to live !” Read more in the Guest Editorial by B. Liu and B. Z. Tang.

Kinetically controlled DNA nanostructures were generated through purely chemical reactions. In their Research Article on https://doi.org/10.1002/anie.202002180page 13238, F. Ricci et al. describe the transient self‐assembly of DNA‐based nanostructures achieved by reduction/oxidation of disulfide/thiol controllers. Inspired by redox signaling in cells to control cellular processes, redox cycles of DNA‐based disulfide controller strands were employed to kinetically control the reversible assembly and disassembly of DNA tubular nanostructures.

Abstract

Prof. Takuzo Aida is one of the most visible materials chemists thanks to his many creative contributions to the broad field of supramolecular chemistry. Over the past two decades he has ingeniously utilized self‐assembly across scales and between various components to access a breathtaking variety of complex materials with fascinating properties. For example, the Aida Lab has pioneered conducting “bucky gel” by dispersing carbon nanotubes in ionic liquids as well as “aqua materials”, in which a tiny amount of additive renders water mechanically robust. From his personal insight he shares in this Interview, we can learn how his research evolved since his undergraduate studies. Moreover, he shares his vision on the importance of supramolecular polymers (Supra‐Plastics) to realize a sustainable society.

What is essential in the aggregation‐induced emission (AIE) mechanism? This question is addressed by using the photophysical processes associated with 9,10‐bis(N ,N ‐dialkylamino)anthracene as a case study. The AIE phenomenon requires control of the non‐radiative decay (deactivation) pathway, that is, controlling the conical intersection (CI) on the potential energy surface enables the formation of fluorescent molecules (CI high) and non‐fluorescent (CI low) molecules separately.

Abstract

Twenty years ago, the concept of aggregation‐induced emission (AIE) was proposed, and this unique luminescent property has attracted scientific interest ever since. However, AIE denominates only the phenomenon, while the details of its underlying guiding principles remain to be elucidated. This minireview discusses the basic principles of AIE based on our previous mechanistic study of the photophysical behavior of 9,10‐bis(N,N‐dialkylamino)anthracene (BDAA ) and the corresponding mechanistic analysis by quantum chemical calculations. BDAA comprises an anthracene core and small electron donors, which allows the quantum chemical aspects of AIE to be discussed. The key factor for AIE is the control over the non‐radiative decay (deactivation) pathway, which can be visualized by considering the conical intersection (CI) on a potential energy surface. Controlling the conical intersection (CI) on the potential energy surface enables the separate formation of fluorescent (CI:high) and non‐fluorescent (CI:low) molecules [control of conical intersection accessibility (CCIA )]. The novelty and originality of AIE in the field of photochemistry lies in the creation of functionality by design and in the active control over deactivation pathways. Moreover, we provide a new design strategy for AIE luminogens (AIEgens) and discuss selected examples.