Jing Sun

Due to the polyanionic nature of RNAs, the structural folding of RNAs are sensitive to solution salt conditions, while there is still lack of a deep understanding of the salt effect on the thermodynamics and kinetics of RNAs at a single base-pair level. In this work, the thermodynamic and the kinetic parameters for the base-pair AU closing/opening at different salt concentrations were calculated by 3-µsec all-atom molecular dynamics (MD) simulations at different temperatures. It was found that for the base-pair formation, the enthalpy change is nearly independent of salt concentration, while the entropy change exhibits a linear dependence on the logarithm of salt concentration, verifying the empirical assumption based on thermodynamic experiments. Our analyses revealed that such salt concentration dependence of the entropy change mainly results from the dependence of ion translational entropy change for the base pair closing/opening on salt concentration. Furthermore, the closing rate increases with the increasing of salt concentration, while the opening rate is nearly independent of salt concentration. Additionally, our analyses revealed that the free energy surface for describing the base-pair opening and closing dynamics becomes more rugged with the decrease of salt concentration.

Nature, Published online: 08 April 2020; doi:10.1038/s41586-020-2161-8

Layered nanocomposites fabricated using a continuous and scalable process achieve properties exceeding those of natural nacre, the result of stiffened matrix polymer chains confined between highly aligned nanosheets.

Nature Chemistry, Published online: 09 April 2020; doi:10.1038/s41557-020-0463-y

A balance between order and disorder provides living materials with just the right amount of disorder needed to sustain life. This feature is currently not found in synthetic materials. Now, a route to the production of composite membranes that are simultaneously stiff and reconfigurable upon contact has been developed.

Nature Communications, Published online: 07 April 2020; doi:10.1038/s41467-020-15427-1

Photothermal therapy (PTT) has recently emerged as a promising approach for cancer therapy. Here, the authors report a hyperbranched polymer vesicle with favorable photothermal stability and high photothermal efficiency for PTT through a supramolecular polymerization-enhanced self-assembly strategy.

Nature Chemistry, Published online: 06 April 2020; doi:10.1038/s41557-020-0440-5

Cyclic polymers have a ring-like architecture and one of the most important consequences of this topology is the absence of any chain ends, which typically have a substantial impact on the physical properties of macromolecules. This Review Article discusses advances in the synthesis, purification and characterization of cyclic polymers and the potential applications they may prove useful for.

Systems Chemistry In their Communication on https://doi.org/10.1002/anie.201914893page 5950, T.‐Y. D. Tang et al. report the use of the pH responsiveness of a polycation to drive liquid–liquid phase separation to form coacervate droplets within lipid vesicles to control enzyme activity.

The simple combination of DMPC and DHPC resulted in various lipid nanostructures with distinct structure–function relationships, differing in uptake, drug encapsulation efficacy, and in vivo anti‐tumor therapy.

Abstract

Structural morphology is the key parameter for efficacy of nanomedicine. To date, lipid‐based nanomaterial has been the most widely used material in nanomedicine and many other biomedical applications. However, to the best of our knowledge, there has not been an in‐depth or systematic investigation of the structure–function relationship of lipid‐based nanostructures. In this report, we investigated the formulation of novel lipid‐based nanostructures via simple tuning of lipid combinations. To prove this concept, we used a combination of various ratios of simple and common phospholipids with different chain lengths (14‐carbon chain DMPC: 6‐carbon chain DHPC) to find out whether a myriad of novel lipid nanostructures could be obtained. Interestingly, many combinations resulted in distinct lipid nanostructures. Drug encapsulation tests confirmed that they are able to load large amounts of drugs for biological application. In vivo anti‐tumor efficacy revealed that certain lipid nanostructures possessed superior tumor retardation effects.

The PICSA concept (polymerization‐induced chiral self‐assembly) is demonstrated by constructing hierarchical supramolecular chiral azobenzene‐containing block copolymer (Azo‐BCP) assemblies in a controlled manner. The construction, dynamic reversibility, and morphological effect of supramolecular chirality in azo liquid‐crystalline assemblies are presented.

Abstract

Hierarchical supramolecular chiral liquid‐crystalline (LC) polymer assemblies are challenging to construct in situ in a controlled manner. Now, polymerization‐induced chiral self‐assembly (PICSA) is reported. Hierarchical supramolecular chiral azobenzene‐containing block copolymer (Azo‐BCP) assemblies were constructed with π–π stacking interactions occurring in the layered structure of Azo smectic phases. The evolution of chirality from terminal alkyl chain to Azo mesogen building blocks and further induction of supramolecular chirality in LC BCP assemblies during PICSA is achieved. Morphologies such as spheres, worms, helical fibers, lamellae, and vesicles were observed. The morphological transition had a crucial effect on the chiral expression of Azo‐BCP assemblies. The supramolecular chirality of Azo‐BCP assemblies destroyed by 365 nm UV irradiation can be recovered by heating–cooling treatment; this dynamic reversible achiral–chiral switching can be repeated at least five times.

Nature Chemistry, Published online: 27 March 2020; doi:10.1038/s41557-020-0444-1

Responsive hydrogels are of interest for a range of potential applications, including microscale soft robotic and biomedical devices. Now, a versatile fabrication approach has been developed to prepare patterned, multi-material and multi-responsive hydrogels. Pre-gel droplets are connected through lipid bilayers in predetermined architectures and photopolymerized to yield continuous hydrogel structures that respond to a variety of stimuli.

A 2,6‐anthrylene‐linked bis(m‐terphenylcarboxylic acid) strand forms a one‐handed homo double helix induced by chiral amines, thereby producing the chiral anti‐photodimer with up to 98 % enantiomeric excess upon photoirradiation. The chirality of the anti‐photodimer can be readily controlled by the chirality of the chiral amines.

Abstract

A novel 2,6‐anthrylene‐linked bis(m‐terphenylcarboxylic acid) strand (1) self‐associates into a racemic double‐helix. In the presence of chiral mono‐ and diamines, either a right‐ or left‐handed double‐helix was predominantly induced by chiral amines sandwiched between the carboxylic acid strands with accompanying stacking of the two prochiral anthracene linker units in an enantiotopic face‐selective way, as revealed by circular dichroism and NMR spectral analyses. The photoirradiation of the optically active double helices complexed with chiral amines proceeded in a diastereo‐ (anti or syn) and enantiodifferentiating way to afford the chiral anti‐photodimer with up to 98 % enantiomeric excess when (R)‐phenylethylamine was used as a chiral double‐helix inducer. The resulting optically active anti‐photodimer can recognize the chirality of amines and diastereoselectively complex with chiral amines.

The structural and functional complexity of multicellular biological systems, such as the brain, are beyond the reach of human design or assembly capabilities. Cells in living organisms may be recruited to construct synthetic materials or structures if treated as anatomically defined compartments for specific chemistry, harnessing biology for the assembly of complex functional structures. By integrating engineered-enzyme targeting and polymer chemistry, we genetically instructed specific living neurons to guide chemical synthesis of electrically functional (conductive or insulating) polymers at the plasma membrane. Electrophysiological and behavioral analyses confirmed that rationally designed, genetically targeted assembly of functional polymers not only preserved neuronal viability but also achieved remodeling of membrane properties and modulated cell type–specific behaviors in freely moving animals. This approach may enable the creation of diverse, complex, and functional structures and materials within living systems.

Crown‐ether based recognition can be used as an effective tool to improve efficiency and selectivity in supramolecular catalysis. This Minireview highlights examples in which this strategy has been employed and remarks that its application can open still unexplored ways in the field.

In its minimal expression, a supramolecular catalyst that acts on a single bound substrate consists of (i) a binding unit that is complementary to a non‐reacting part of the substrate, (ii) a reactive unit capable of catalyzing the reaction of the bound substrate, and (iii) a spacer connecting the two units in a geometry suitable for productive binding. When binding of two or more species is wanted, the number of binding units increases accordingly. This minireview deals with supramolecular catalysts that use crown ether units for the recognition of one or two reactants involved in a variety of reactions, including cleavage of esters and amides, hydride transfer from dihydropyridine to pyridinium, pyruvate decarboxylation, enolate allylation, radical addition to sodium metacrylate, reduction of NO₂ ^– anion to NO, C–H oxidation of aliphatic chains, and Diels‐Alder reactions.

Nature, Published online: 04 March 2020; doi:10.1038/s41586-020-2042-1

A method of growing crystals that does not require undisturbed solutions involves adding polyelectrolytes to the starter solution and shearing (that is, stirring).

A photoresponsive hydrogel was constructed by using a supramolecular design strategy. A red‐shifted anthracene group furnishes the system with fast photo‐actuation. Hydrogen bonding, π–π interactions, and anthracene photodimerization results in an actuator with high mechanical strength, fast self‐healing, and recyclability.

Abstract

The most pressing challenges for light‐driven hydrogel actuators include reliance on UV light, slow response, poor mechanical properties, and limited functionalities. Now, a supramolecular design strategy is used to address these issues. Key is the use of a benzylimine‐functionalized anthracene group, which red‐shifts the absorption into the visible region and also stabilizes the supramolecular network through π–π interactions. Acid–ether hydrogen bonds are incorporated for energy dissipation under mechanical deformation and maintaining hydrophilicity of the network. This double‐crosslinked supramolecular hydrogel developed via a simple synthesis exhibits a unique combination of high strength, rapid self‐healing, and fast visible‐light‐driven shape morphing both in the wet and dry state. As all of the interactions are dynamic, the design enables the structures to be recycled and reprogrammed into different 3D objects.

Nature Chemistry, Published online: 09 March 2020; doi:10.1038/s41557-020-0426-3

A programmable polymer library that responds to external and internal stimuli has been developed and used to fabricate a series of nanocarriers for drug release. The carriers respond to disease biomarkers, triggering self-immolative motifs and leading to the site-specific release of therapeutics both in vitro and in vivo.

A new class of near‐infrared fluorescent protein nanoassemblies is developed by genetic engineering. Stable and specific vivo tumor imaging is realized via simple exogenous injection of the robust protein nanomaterials. Hydrophobic anti‐tumor antibiotic of thiostrepton can be efficiently loaded in the protein nanoaggregates and effective tumor therapy is achieved.

Abstract

Fluorescent proteins are investigated extensively as markers for the imaging of cells and tissues that are treated by gene transfection. However, limited transfection efficiency and lack of targeting restrict the clinical application of this method rooted in the challenging development of robust fluorescent proteins for in vivo bioimaging. To address this, a new type of near‐infrared (NIR) fluorescent protein assemblies manufactured by genetic engineering is presented. Due to the formation of well‐defined nanoparticles and spectral operation within the phototherapeutic window, the NIR protein aggregates allow stable and specific tumor imaging via simple exogenous injection. Importantly, in vivo tumor metastases are tracked and this overcomes the limitations of in vivo imaging that can only be implemented relying on the gene transfection of fluorescent proteins. Concomitantly, the efficient loading of hydrophobic drugs into the protein nanoparticles is demonstrated facilitating the therapy of tumors in a mouse model. It is believed that these theranostic NIR fluorescent protein assemblies, hence, show great potential for the in vivo detection and therapy of cancer.

Macromolecular gear: Long‐range chiral induction is produced in poly(phenylacetylene)s (PPAs) that bear achiral Aib oligomers capped at the N‐termini with a chiral acid (Mosher's reagent). The chiral residue induces screw sense preferences in the different Aib oligomers, which are harvested by the PPAs adopting an excess of a single‐handed helical structure.

Abstract

Herein, macromolecular gears composed of helical poly(phenylacetylenes) (PPAs) bearing short oligopeptides as pendant groups are described, in which the two structural motifs (framework and substituents) are combined. These gears are obtained by polymerization of the acetylene groups introduced at the C‐terminus of short oligopeptides formed by achiral (Aib) _n units (n=1–3) derivatized at the N‐terminus by a single enantiomer (R or S) of α‐methoxy‐α‐trifluoromethylphenylacetic acid (MTPA, Mosher's reagent). The chiral information of the MTPA is transmitted to the achiral Aib fragments and, through either chiral tele‐induction and/or chiral harvesting mechanisms, is further transferred to the polyene backbones, which adopt preferentially P or M helical senses. Moreover, these materials also show dynamic behavior and respond to the action of external stimuli by either inverting the P/M sense and/or modifying the elongation in fully reversible processes.

Mechanically strong biological fibers have been produced using a novel chimeric protein. In stark contrast to traditional polymer fibers, these fibers combine high strength and high toughness. The fibers exhibit a breaking strength up to about 630 MPa and the toughness is as high as about 130 MJ m⁻³, making them superior to many recombinant spider silks and even comparable to some native counterparts.

Abstract

Silk‐protein‐based fibers have attracted considerable interest due to their low weight and extraordinary mechanical properties. Most studies on fibrous proteins focus on the recombinant spidroins, but these fibers exhibit moderate mechanical performance. Thus, the development of alternative structural proteins for the construction of robust fibers is an attractive goal. Herein, we report a class of biological fibers produced using a designed chimeric protein, which consists of the sequences of a cationic elastin‐like polypeptide and a squid ring teeth protein. Remarkably, the chimeric protein fibers exhibit a breaking strength up to about 630 MPa and a corresponding toughness as high as about 130 MJ m⁻³, making them superior to many recombinant spider silks and even comparable to some native counterparts. Therefore, this strategy is a novel concept for exploring bioinspired ultrastrong protein materials through the development of new types of structural chimeric proteins.

Targeting soft‐matter chemists and beginning structural biologists, this work aims to give a concise background into electron microscopy, including topics like image formation, microscope composition, and processing possibilities. Furthermore, it discusses technical developments that have been implemented in the field of biology and are also of interest to the field of soft‐matter chemistry.

Abstract

With a significant role in material sciences, physics, (soft matter) chemistry, and biology, the transmission electron microscope is one of the most widely applied structural analysis tool to date. It has the power to visualize almost everything from the micrometer to the angstrom scale. Technical developments keep opening doors to new fields of research by improving aspects such as sample preservation, detector performance, computational power, and workflow automation. For more than half a century, and continuing into the future, electron microscopy has been, and is, a cornerstone methodology in science. Herein, the technical considerations of imaging with electrons in terms of optics, technology, samples and processing, and targeted soft materials are summarized. Furthermore, recent advances and their potential for application to soft matter chemistry are highlighted.

Organic conjugated materials for printed electronics are facing the transition from laboratory research to scaled up production. The need for a quantum leap in efficiency and sustainability of synthetic procedures is boosting intense research in alternative protocols. Surfactant enhanced chemistry in water can dramatically improve sustainability, without eroding efficiency.

Organic semiconductors have been at the center of intense investigation for decades. The efficiencies of the most performing candidates, along with the compatibility with solution processing and printing led to relevant technological breakthrough. The development of market applications for Organic Light Emitting Devices (OLEDs), Organic Thin film transistors (OTFTs), and Organic Photovoltaics (OPVs) poses a relevant question regarding to the scaling up and overall sustainability of synthetic protocols employed for the preparation of active compounds. This review summarizes the role that the emerging field of micellar catalysis and surfactant enhanced chemistry can play in dramatically improving the sustainability of established and emerging performing organic semiconductors.

Self‐assembly of an amphiphilic azobenzene dyad was investigated in methylcyclohexane. The dyad formed mechanically fragile nanotubes. UV light irradiation induced dissociation of nanotubes into the molecularly dispersed state through trans/cis photoisomerization. Visible light irradiation did not result in the reconstruction of nanotubes while amorphous films were obtained due to coaggregation of photoisomers.

Azobenzene dyad 1 possessing hydrophobic side chains has previously been reported to assemble into toroidal nanostructures, which can further stack to afford nanotubes in nonpolar media. In this study, amphiphilic dyad 2 was synthesized to obtain nanotubes with the hydrophilic interior. Dyad 2 directly assembled into nanotubes without forming isolatable toroidal nanostructures. UV light irradiation to the nanotubes resulted in monomerization by trans→cis photoisomerization, but following reconstruction by visible light irradiation afforded amorphous films, suggesting a kinetic trap of trans‐2 by residual cis‐2 through co‐aggregation.