A Rational Design of Metal–Organic Framework Nanozyme with High‑Performance Copper Active Centers for Alleviating Chemical Corneal Burns

Metal–organic frameworks(MOFs)have attracted significant research interest in biomimetic catalysis.However,the modulation of the activity of MOFs by precisely tuning the coordination of metal nodes is still a significant challenge.Inspired by metalloenzymes with well-defined coordination structures,a series of MOFs containing halogen-coordinated copper nodes(Cu-X MOFs,X=Cl,Br,I)are employed to elucidate their structure–activity relationship.Intriguingly,experimental and theoretical results strongly support that precisely tuning the coordination of halogen atoms directly regulates the enzyme-like activities of Cu-X MOFs by influencing the spatial configuration and electronic structure of the Cu active center.The optimal Cu–Cl MOF exhibits excellent superoxide dismutase-like activity with a specific activity one order of magnitude higher than the reported Cu-based nanozymes.More importantly,by performing enzyme-mimicking catalysis,the Cu–Cl MOF nanozyme can significantly scavenge reactive oxygen species and alleviate oxidative stress,thus effectively relieving ocular chemical burns.Mechanistically,the antioxidant and antiapoptotic properties of Cu–Cl MOF are achieved by regulating the NRF2 and JNK or P38 MAPK pathways.Our work provides a novel way to refine MOF nanozymes by directly engineering the coordination microenvironment and,more significantly,demonstrating their potential therapeutic effect in ophthalmic disease.

A robust Janus bilayer with tailored ionic conductivity and interface stability for stable Li metal anodes

The formation and growth of Li-dendrites caused by inhomogeneous Li deposition severely hinder the commercial applications of Li metal batteries due to the consequence of short-circuiting.Herein,we propose a Janus bilayer composed of black phosphorus(BP)and graphene oxide(GO)as an artificial interface with chemical/mechanical stability and well-regulated Li-ion flux distribution for Li metal anode protection.Owing to the synergy between the fast Li-ion transport of BP in the inner layer and the high mechanical and chemical stability of GO in the outer layer,the GO/BP with good electrolyte wettability acts as a Li-ion regulator that can induce homogeneous growth of Li to suppress the Li dendrites growth.Accordingly,long-term stability(500 h at 1 mA cm^(-2))with a low overpotential of 30 mV is achieved in the symmetric cell with GO/BP-Li anode.Furthermore,the Li–S cell with GO/BP-Li exhibits enhanced cycling performance with a high capacity retention rate of 76.2%over 500 cycles at 1 C.

Different potential of mean force of two-state protein GB1 and downhill protein gpW revealed by molecular dynamics simulation

Two-state folding and down-hill folding are two kinds of protein folding dynamics for small single domain proteins.Here we apply molecular dynamics(MD)simulation to the two-state protein GB1 and down-hill folding protein gpW to reveal the relationship of their free energy landscape and folding/unfolding dynamics.Results from the steered MD simulations show that gpW is much less mechanical resistant than GB1,and the unfolding process of gpW has more variability than that of GB1 according to their force-extension curves.The potential of mean force(PMF)of GB1 and gpW obtained by the umbrella sampling simulations shows apparent difference:PMF of GB1 along the coordinate of extension exhibits a kink transition point where the slope of PMF drops suddenly,while PMF of gpW increases with extension smoothly,which are consistent with two-state folding dynamics of GB1 and downhill folding dynamics of gpW,respectively.Our results provide insight to understand the fundamental mechanism of different folding dynamics of twostate proteins and downhill folding proteins.

Force-dependent unfolding and folding dynamics of protein alpha-catenin modulation domains

α-catenin is an adhesion protein located at the cadherin-based cell-cell adherens junction.α-catenin cross-linksβ-catenin and actin fiber in the adhesion protein complex,and plays an important role in the formation and modulation of cell-cell adhesion.The central modulation domains can be unfolded to expose binding site of vinculin when stretching force is applied.Here,we studied the force-induced unfolding dynamics ofα-catenin modulation domains under different loading rates from which the unfolding distance of M2 and M3 domains is determined to be 5-7 nm,and an unfolding intermediate state is identified.We also found that the folding process of M1-M3 domains goes through different pathways with cooperativity.

Mechanical enhancement and weakening in Mo_(6)S_(6)nanowire by twisting

The torsional,bending and tensile mechanical properties of Mo_(6)S_(6)nanowire are examined by molecular dynamics(MD)simulations with a first-principles-based reactive force field(ReaxFF).It is found that Mo_(6)S_(6)nanowire shows unique mechanical properties such as high torsional and bending flexibility,high Young's modulus and strength,and negative Poisson's ratio.The Mo_(6)S_(6)nanowire can be strengthened or weakened via twisting,depending on the twist angle.The Mo_(6)S_(6)nanowire with a slight twist angle shows brittle failure,whereas it with a large twist angle exhibits ductile failure and necking behavior.Twisted Mo_(6)S_(6)nanowires show a crossover in the negative Poisson's ratio at critical strains,that is,Poisson's ratio first decreases but then increases,with a minimum value down to around-0.8 at the strain of 0.01 as the twist angle is 21.0°/nm.The negative Poisson's ratio and the crossover are explained by the bond transform that makes zero angles to the wire cross-section.

Adhesion strength of tetrahydrofuran hydrates is dictated by substrate stiffness

Understanding the hydrate adhesion is important to tackling hydrate accretion in petro-pipelines.Herein,the relationship between the Tetrahydrofuran(THF)hydrate adhesion strength(AS)and surface stiffness on elastic coatings is systemically examined by experimental shear force measurements and theoretical methods.The mechanical factor-elastic modulus of the coatings greatly dictates the hydrate AS,which is explained by the adhesion mechanics theory,beyond the usual factors such as wettability and structural roughness.Moreover,the hydrate AS increases with reducing the thickness of the elastic coatings,resulted from the decrease of the apparent surface elastic modulus.The effect of critical thickness for the elastic materials with variable elastic modulus on the hydrate AS is also revealed.This study provides deep perspectives on the regulation of the hydrate AS by the elastic modulus of elastic materials,which is of significance to design anti-hydrate surfaces for mitigation of hydrate accretion in petro-pipelines.

Reduced Ti-MOFs encapsulated black phosphorus with high stability and enhanced photocatalytic activity

The generation of green hydrogen(H_2) energy is of great significance to solve worldwide energy and environmental issues. Reduced Ti based photocatalyst has recently attracted intensive attention due to its excellent photocatalytic activity, while the synthesis of reduced Ti based photocatalysts with high stability is still a great challenge. Here, we report a facile method for synthesis of reduced Ti metal organic frameworks(small amounts of Pt incorporated) encapsulated BP(BP/R-Ti-MOFs/Pt) hybrid nanomaterial with enhanced photocatalytic activity. The strong interaction between Ti and P reduces the valence state of the binding Ti^(4+)on the BP surface, forming abundant reduced Ti^(4+)within R-Ti-MOFs/BP. Such reduced Ti^(4+)render R-Ti-MOFs/BP efficient charge transfer and excellent light absorption capability, thus promote the photocatalytic H_2 production efficiency. Furthermore, the Ti-P interaction stabilizes both reduced Ti^(4+)and BP during the photocatalytic reaction, which greatly enhanced the stability of the obtained BP/R-TiMOFs/Pt photocatalyst.

Derivation of persistent time for anisotropic migration of cells

Cell migration plays an essential role in a wide variety of physiological and pathological processes. In this paper we numerically discuss the properties of an anisotropic persistent random walk （APRW） model, in which two different and independent persistent times are assumed for cell migrations in the x-and y-axis directions. An intrinsic orthogonal coordinates with the primary and non-primary directions can be defined for each migration trajectory based on the singular vector decomposition method. Our simulation results show that the decay time of single exponential distribution of velocity auto-correlation function （VACF） in the primary direction is actually the large persistent time of the APRW model, and the small decay time of double exponential VACF in the non-primary direction equals the small persistent time of the APRW model. Thus, we propose that the two persistent times of anisotropic migration of cells can be properly estimated by discussing the VACFs of trajectory projected to the primary and non-primary directions.

Improving physical properties of poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels via the Hofmeister effect

Hydrogel is a kind of three-dimensional crosslinked polymer material with high moisture content.However,due to the network defects of polymer gels,traditional hydrogels are usually brittle and fragile,which limits their practical applications.Herein,we present a Hofmeister effect-aided facile strategy to prepare high-performance poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels.Layered montmorillonite nanosheets can not only serve as crosslinking agents to enhance the mechanical properties of the hydrogel but also promote the ion conduction.More importantly,based on the Hofmeister effect,the presence of(NH_(4))_(2)SO_(4)can endow nanocomposite hydrogels with excellent mechanical properties by affecting PVA chains'aggregation state and crystallinity.As a result,the as-prepared nanocomposite hydrogels possess unique physical properties,including robust mechanical and electrical properties.The as-prepared hydrogels can be further assembled into a high-performance flexible sensor,which can sensitively detect large-scale and small-scale human activities.The simple design concept of this work is believed to provide a new prospect for developing robust nanocomposite hydrogels and flexible devices in the future.

Bioinspired nanofluidic iontronics for brain-like computing

The human brain performs computations via a highly interconnected network of neurons.Taking inspiration from the information delivery and processing mechanism of the human brain in central nervous systems,bioinspired nanofluidic iontronics has been proposed and gradually engineered to overcome the limitations of the conventional electron-based von Neumann architecture,which shows the promising potential to enable efficient brain-like computing.Anomalous and tunable nanofluidic ion transport behaviors and spatial confinement show promising controllability of charge carriers,and a wide range of structural and chemical modification paves new ways for realizing brain-like functions.Herein,a comprehensive framework of mechanisms and design strategy is summarized to enable the rational design of nanofluidic systems and facilitate the further development of bioinspired nanofluidic iontronics.This review provides recent advances and prospects of the bioinspired nanofluidic iontronics,including ion-based brain computing,comprehension of intrinsic mechanisms,design of artificial nanochannels,and the latest artificial neuromorphic functions devices.Furthermore,the challenges and opportunities of bioinspired nanofluidic iontronics in the pioneering and interdisciplinary research fields are proposed,including brain–computer interfaces and artificial neurons.

Pressure-driven membrane inflation through nanopores on the cell wall

Walled cells,such as in plants and fungi,compose an important part of the model systems in biology.The cell wall primarily prevents the cell from over-expansion when exposed to water,and is a porous material distributed with nanosized pores on it.In this paper,we study the deformation of a membrane patch by an osmotic pressure through a nanopore on the cell wall.We find that there exists a critical pore size or a critical pressure beyond which the membrane cannot stand against the pressure and would inflate out through the pore and further expand.The critical pore size scales linearly with the membrane tension and quadratically with the spontaneous curvature.The critical pressure is inversely proportional to the pore radius.Our results also show that the fluid membrane expansion by pressure is mechanically different from the solid balloon expansion,and predict that the bending rigidity of the membrane in walled cells should be much larger than that of the mammalian cells so as to prevent membrane inflation through the pores on the cell wall.

Hydrogen diffusion in C′_(1) phase clathrate hydrate

Recently,a new phase C'_(1) H_(2) hydrate was experimentally identified.In this work,the diffusive behaviors of H_(2) in C'_(1)phase clathrate hydrate are explored using classic molecular dynamics(MD)simulations.It reveals that the cage occupancy by H_(2) molecule negligibly influences the C'_(1) phase clathrate structure but greatly dictates the diffusion coefficient of H_(2)molecule.Due to the small cage size and small windows connecting the neighboring cages in C'_(1) phase clathrate,nonoccupancy of the neighboring cages is demanded to enable the diffusion of H_(2) molecule that is primarily dominated by hopping mechanism.Moreover,the analysis of diffusive free energy landscape reveals lower energy barrier of H_(2) molecule in C'_(1) phase clathrate hydrate than that of other gases in conventional clathrate hydrates,and that H_(2) molecule travels through the windows between neighboring cages with preferential molecular orientation.This study provides critical physical insights into the diffusion behaviors of H_(2) in the C'_(1) phase clathrate hydrate,and implies that the C'_(1) clathrate hydrate is a promising solid structure for the next-generation H_(2) storage.

Temperature-regulation liquid gating membrane with controllable gas/liquid separation

Membrane separation technology with the ability to regulate gas/liquid transport and separation is critical for environmental fields, such as sewerage treatment, multiphase separation, and desalination. Although numerous membranes can dynamically control liquid-phase fluids transport via external stimuli, the transport and separation of gas-phase fluids remains a challenge. Here, we show a temperature-regulation liquid gating membrane that allows in-situ dynamically controllable gas/liquid transfer and multiphase separation by integrating a thermo-wettability responsive porous membrane with functional gating liquid. Experiments and theoretical analysis have demonstrated the temperature-regulation mechanism of this liquid gating system, which is based on thermo-responsive changes of porous membrane surface polarity, leading to changes in affinity between the porous membrane and the gating liquid. In addition, the sandwich configuration with dense Au-coated surfaces and heterogeneous internal components by a bistable interface design enables the liquid gating system to enhance response sensitivity and maintain working stability. This temperature-regulation gas/liquid transfer strategy expands the application range of liquid gating membranes,which are promising in environmental governance, water treatment and multiphase separation.

Highly stretchable and reliable graphene oxide- reinforced liquid gating membranes for tunable gas/liquid transport

The ability of membrane technologies to dynamically tune the transport behavior for gases and liquids is critical for their applications.Although various methods have been developed to improve membrane success,tradeoffs still exist among their properties,such as permeability,selectivity,fouling resistance,and stability,which can greatly affect the performance of membranes.Existing elastomeric membrane designs can provide antifracture properties and flexibility;however,these designs still face certain challenges,such as low tensile strength and reliability.Additionally,researchers have not yet thoroughly developed membranes that can avoid fouling issues while realizing precise dynamic control over the transport substances.In this study,we show a versatile strategy for preparing graphene oxide-reinforced elastomeric liquid gating membranes that can finely modulate and dynamically tune the sorting of a wide range of gases and liquids under constant applied pressures.Moreover,the produced membranes exhibit antifouling properties and are adaptable to different length scales,pressures,and environments.The filling of graphene oxide in the thermoplastic polyurethane matrix enhances the composites through hydrogen bonds.Experiments and theoretical calculations are carried out to demonstrate the stability of our system.Our membrane exhibits good stretchability,recovery,and durability due to the elastic nature of the solid matrix and dynamic nature of the gating liquid.Dynamic control over the transport of gases and liquids is achieved through our optimized interfacial design and controllable pore deformation,which is induced by mechanical stimuli.Our strategy will create new opportunities for many applications,such as gas-involved chemical reactions,multiphase separation,microfluidics,multiphase microreactors,and particulate material synthesis.

The kinetics of force-dependent hybridization and strand-peeling of short DNA fragments

Deoxyribonucleic acid(DNA) carries the genetic information in all living organisms. It consists of two interwound single-stranded(ss) strands, forming a double-stranded(ds) DNA with a right-handed double-helical conformation. The two strands are held together by highly specific basepairing interactions and are further stabilized by stacking between adjacent basepairs. A transition from a dsDNA to two separated ssDNA is called melting and the reverse transition is called hybridization. Applying a tensile force to a dsDNA can result in a particular type of DNA melting, during which one ssDNA strand is peeled away from the other. In this work, we studied the kinetics of strand-peeling and hybridization of short DNA under tensile forces. Our results show that the force-dependent strand-peeling and hybridization can be described with a simple two-state model. Importantly, detailed analysis of the force-dependent transition rates revealed that the transition state consists of several basepairs dsDNA.

Graphene-supported biomimetic catalysts with synergistic effect of adsorption and degradation for efficient dye capture and removal

Design and development of iron porphyrin-based artificial enzymes system have been attracting a lot of attention.Herein,without any toxic reductant and harsh processing,we present a facile one-pot method to fabricate bifunctional catalytic nanocomposites consisting of graphene and hemin by using vitamin C as a mild reduction reagent.The presence of graphene helps the formation of a high degree of highly active and stable hemin on the graphene surface in a monomeric form through theirπ-πstacking interaction.As a result,such nanocomposites possess a superior adsorption capacity and intrinsic peroxidase-like catalytic activity.Moreover,by the combination of their dye adsorption ability,RGOhemin nanocomposites can serve as a suitable candidate for efficient capture and removal of dyes via a synergistic effect.Our findings may pave the way to apply graphene-supported artificial enzymes in a variety of fields,such as environmental chemistry,bionics,medicine,and biotechnology.

Improved data analysis method of single-molecule experiments based on probability optimization

To extract the dynamic parameters from single molecule manipulation experiments, usually lots of data at different forces need to be recorded. But the measuring time of a single molecule is limited due to breakage of the tether or degradation of the molecule. Here we propose a data analysis method based on probability maximizalion of the recorded time trace to extract the dynamic parameters from a single measurement. The feasibility of this method was verified by dealing with the simulation data of a two-state system. We also applied this method to estimate the parameters of DNA hairpin folding and unfolding dynamics measured by a magnetic tweezers experiment.

Biexponential distribution of open times of a toy channel model

The biexponential distributions of open times are observed in various types of ion channels. In this paper, by discussing a simple channel model, we show that there are two different schemes to understand the biexponential distribution of open times. One scheme is mathematically strict based on generator matrix theory, while the other one has a clear physical explanation according to an approximation process with numerical simulation of Markovian channel dynamics. Our comparison results suggest that even for biologically complex channels, in addition to carrying out a stochastic simulation, the strict theoretical analysis should be considered to understand the multiple exponential distributions of open times.

A common rule for the intermediate state caused by DNA mismatch in single-molecule experiments

Defective structures,such as DNA mismatches,occur in DNA with a high frequency in some biological processes.They are difficult to identify and have recently become the focus of singlemolecule investigations.Three single-molecule experiments were successively conducted to detect the effects of DNA mismatch on the stability of DNA hairpins.However,there was no consensus regarding the results of the intermediate state caused by DNA mismatch.Based on the extended ox-DNA model,DNA mismatch was introduced to the stem of DNA hairpins with different stem lengths(12-20 bps)and 4T in hairpin loops.The intermediate state and its dependence on the position of the DNA mismatch in the stem from the hairpin loop were systematically studied.The results indicated that DNA mismatch definitely reduced the critical forces of DNA hairpins.At the same time,a common rule about the dependence of the intermediate state on the position of DNA mismatch was generalized in a phase diagram constructed in a phase space of a scaled position of DNA mismatch.Three segments on its diagonal line corresponded to the ranges of the scaled position of DNA mismatch[0,0.55),[0.55,0.85),and[0.85,1],respectively.In the[0.55,0.85)range,the extension probability distribution of DNA hairpins had unfolded,intermediate,and folded states.In contrast,in the other ranges[0,0.55)and[0.85,1],the extension probability distributions had unfolded and folded states.The scaled positions of DNA mismatch for the DNA hairpins used in the three single-molecule experiments(0.65,0.4736,and 0.5)fell in the ranges[0.55,0.85)and[0,0.55).Obviously,the common rule generalized in the phase diagram not only clarifies the nonconsensus between the three single-molecule experiments but also highlights the design of single-molecule experiments in the future.

Using silk-derived magnetic carbon nanocomposites as highly efficient Nanozymes and electromagnetic absorbing agents

Functional carbon nanomaterials have become the stars of many active research fields,such as electronics,energy,catalysis,imaging,sensing and biomedicine.Herein,a facile and one-pot strategy for generating ferromagnetic nanoparticles loaded on N-doped carbon nanosheets(Fe-N-CNS)is presented by salt-assisted high-temperature carbonization of natural silk proteins.Due to their graphitic structures,N-doping and ferromagnetic nanoparticles(FeN_(x),FeO_(y),FeC_(z)),the silk-derived Fe-N-CNS can act as excellent mimics of both peroxidase and oxidase.Benefiting from the combined character of the graphene-like structures and enzyme-like activities,Fe-N-CNS can be further applied to highly efficient dye removal via synergistic adsorption and degradation.Meanwhile,the as-prepared Fe-N-CNS with intrinsic magnetism and electrical conductivity can also serve as an efficient electromagnetic wave absorption agent.The broadest effective absorption bandwidth(EAB)of as-obtained absorbing material yields a 6.73 GHz with 1 mm thickness,with a maximum reflection loss of-37.33 dB(11.41 GHz).The EAB can cover2~18 GHz with a tunable absorber thickness from 1.0 mm to 5.0 mm.Collectively,Fe-N-CNS,as a dualfunctional material,can tackle the aggravating environmental pollution issues of both dyes and electromagnetic waves.