Neighboring Chains Research Articles

Enhanced damping and bandwidth in roton-like dispersion of a beyond nearest neighbor periodic chain

This paper investigates the intriguing roton-like phenomenon occurring in systems with non-local interactions, wherein a single dispersion curve exhibits positive and negative group velocities. Previous research has predominantly concentrated on investigating the roton dispersion in undamped metamaterials through steady-state vibration and driven wave methodologies. However, exploring transient wave propagation in damped metamaterials, employing a free wave approach to study damping enhancement (metadamping), has received comparatively little attention. Addressing this research gap, the damping of the system is quantified as the rate of decay of transient vibrations. Results show a significant increase in damping and attenuation bandwidth, coinciding with the presence of the roton-like phenomenon. Unlike previous studies on metadamping, the proposed beyond nearest neighbor (BNN) chain simultaneously enhances both damping and reduction in acoustic bandwidth without sacrificing either property. Spatiotemporal domain simulation evidenced the existence of backward propagating wave packets due to a roton-like phenomenon in the specific frequency range.

Adsorption on a Spherical Colloidal Particle from a Mixture of Nanoparticles with Competing Interactions.

Adsorption of nanoparticles on a spherical colloidal particle is studied by molecular dynamics simulations. We consider a generic model for a mixture of nanoparticles with energetically favored self-assembly into alternating layers of the two components. When both components are attracted to the colloidal particle, the adsorbed nanoparticles self-assemble either into alternating parallel tori and clusters at the two poles of the colloidal particle, or into alternating spirals wrapped around the spherical surface. The long-lived metastable states obtained in simulations follow from the spherical shape of the adsorbing surface and the requirement that the neighboring chains of the nanoparticles are composed of different components. A geometrical construction leading to all such patterns is presented. When the second component particles are repelled from the colloidal particle and the attraction of the first component is strong, the attracted particles form a monolayer at the surface of the colloidal particle that screens the repulsion of the second component. The subsequent adsorbed alternating spherical layers of the two components form together a thick shell. This structure leads to the adsorption that is larger than in the case of the same attraction of the two components to the colloidal particle.

Impact of the nature of the linker on the 2D and 3D organization of lipid-phenalenone conjugates

A series of phenalenone-lipid conjugates (1A, 1B, 1C, 2) have been synthesized to compensate for the poor water solubility of the photosensitizer phenalenone (PN) and promote the formation of nano-assemblies. We show that the organization and structure of monolayers upon compression strongly depend on the nature of the linker connecting PN to the lipid backbone, and the number of C18 chains. Monolayer properties at the air-water interface were analyzed by surface pressure measurements, Brewster angle and atomic force microscopies, grazing incidence X-ray diffraction, and X-ray reflectivity. Whereas conjugate 1C (ester bond) organizes into multilayers upon compression, conjugates 1A, 1B, and 2 form stable monolayers whose structure is controlled by van der Waals (vdW) interactions between C18 chains, intermolecular H-bonding involving the linker, and for 1B, π-π stacking of PN moieties. Conjugate 1A (amide-triazole linker) is structured into a rectangular network of chains with an order that extends only to the molecule of the adjacent cell. Conjugate 1B (amide bond) forms two incommensurate networks, one for the chains and the other for the headgroups. The distance between molecules in the next near neighbor chain lattice and the sufficient degree of freedom of PN groups allow the latter to pile up via π-π interactions below the chains in a rectangular cell. Conjugate 2 with its double chain adopts a similar behavior to that of a saturated phospholipid. Strong vdW interactions predominate and allow, at high surface pressure, hexagonal packing with no chain tilt. The distance between molecules prevents PN stacking. The identified PN derivative structures explain the linker’s impact on the formation and stability of nano-assemblies.

On substituent effect in 1,n–homodisubstituted polyenes

AbstractThe all-trans and all-cis polyenes homodisubstituted at the ends were calculated at the B3LYP/6-31G** level. The disubstitution gives rise to three end-types of the conformers: trans-trans, trans-cis, and cis-cis, denoted as EE, EZ, and ZZ. The symmetry of the EE or ZZ all-cis isomers depended on the double bond parity. Twelve substituents used: H, BeH, BH2, BF2, Br, CH3, Cl, CN, F, NH2, NO2, OH, and SiH3 were chosen to exhibit different σ- and π-electron donating and electron withdrawing properties. For polyenes composed up to ca. 20 C-atoms, the π-electron donating and withdrawing character of the end groups matters and differently acting substituents play significantly different roles. Unexpectedly, the intramolecular interactions between the substituents and the neighboring chain CH groups near appeared more decisive for the compound’s stability than the substituent electron donating/withdrawing properties. The substituent-chain interplay was consonant in the all-trans and all-cis polyenes. Still, they were always more destabilizing in the latter than in all-trans isomers.

Crystallization-Induced Self-Assembly of Poly(ethylene glycol) Side Chains in Dithiol-yne-Based Comb Polymers: Side Chain Spacing and Molecular Weight Effects.

The chain architecture and topology of macromolecules impact their physical properties and final performance, including their crystallization process. In this work, comb polymers constituted by poly(ethylene glycol), PEG, side chains, and a dithiol-yne-based ring polymer backbone have been studied, focusing on the micro- and nanostructures of the system, thermal behavior, and crystallization kinetics. The designed comb system allows us to investigate the role of a ring backbone, the impact of varying the distance between two neighboring side chains, and the effect of the molecular weight of the side chain. The results reflect that the governing factor in the crystalline properties is the molar mass of the side chains and that the tethering of PEG chains to the ring backbone brings important constraints to the crystallization process, reducing the crystallinity degree and slowing down the crystallization kinetics in comparison to analogue PEG homopolymers. We demonstrate that the effect of spatial hindrance in the comb-like PEG polymers drives the morphology toward highly ordered, self-assembled, semicrystalline superstructures with either extended interdigitated chain crystals or novel (for comb polymers) interdigitated folded chain lamellar crystals. These structures depend on PEG molecular weight, the distance between neighboring tethered PEG chains, and the crystallization conditions (nonisothermal versus isothermal). This work sheds light on the role of chain architecture and topology in the structure of comb-like semicrystalline polymers.

Synthesis and structure of a manganese(II) coordination polymer assembled with 5-(tert-butyl)isophthalic acid and 1,3-dimethyl-2-imidazolidinone

Abstract A manganese(II) coordination polymer [Mn(tbip)(DMI)] n (1), (tbipH2 = 5-(tert-butyl)isophthalic acid, DMI = 1,3-dimethyl-2-imidazolidinone), has been synthesized under “urea-thermal conditions” (i.e. in an excess of urea). Its structure has been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis and IR spectra. Complex 1 crystallizes in the monoclinic space group P21/c with Z = 4. In 1, the [tbip]2− ligand bridges the Mn(II) cations to form infinite chains, and the neighbouring chains are connected through [tbip]2− ligands into layers.

Dehydroxylation and structural transition in α-GaOOH investigated by in situ X-ray diffraction

Ga2O3 is an ultra-wide-bandgap semiconductor that is receiving considerable attention due to its promising applications in high-frequency, high-power and high-temperature settings. It can be prepared by calcinating the α-GaOOH phase at high temperatures. Understanding the significance of hydroxyl groups in α-GaOOH, dehydroxylation and the structural transition at high temperatures has become a key aspect of preparing high-quality α-Ga2O3 crystals, but the underlying mechanism remains unknown. In this research, α-GaOOH nanorods were hydrothermally synthesized and the structural evolution of α-GaOOH investigated at high temperatures by in situ X-ray diffraction. The hydroxyl group in α-GaOOH squeezes Ga3+ from the center of the [GaO6] octahedron, resulting in deformed [GaO6] octahedra and significant microstrain in α-GaOOH. The hydroxyl groups are peeled off from α-GaOOH when the temperature exceeds 200°C, resulting in contraction along the c-axis direction and expansion along the a-axis direction of α-GaOOH. When the temperature exceeds 300°C, the Ga—O bond inside the double chains preferentially breaks to generate square-wave-like octahedron chains, and the neighboring chains repack to form hexagonal-like octahedron layers. The octahedron layers are packed up and down by electrostatic interaction to generate the α-Ga2O3 structure. This work highlights the role of hydroxyl groups in α-GaOOH, dehydroxylation and the structural transition on the atomic scale, providing valuable guidelines for the fabrication of high-quality α-Ga2O3 crystals.

Synthesis and crystal structure of a cadmium(II) coordination polymer based on 4,4′-(1H-1,2,4-triazole-3,5-diyl)dibenzoate

The asymmetric unit of the title compound, catena-poly[[[aquabis(pyridine-κN)cadmium(II)]-μ2-4,4′-(1H-1,2,4-triazole-3,5-diyl)dibenzoato-κ4 O,O′:O′′,O′′′] 4.5-hydrate], {[Cd(C16H9N3O4)(C5H5N)2(H2O)]·4.5H2O} n or {[Cd(bct)(py)2(H2O)]·4.5H2O} n (I), consists of a Cd2+ cation coordinated to one bct2– carboxylate dianion, two molecules of pyridine and a water molecule as well as four and a half water molecules of crystallization. The metal ion in I possesses a pentagonal–bipyramidal environment with the four O atoms of the two bidentately coordinated carboxylate groups and the N atom of a pyridine molecule forming the O4N equatorial plane, while the N atom of another pyridine ligand and the O atom of the water molecule occupy the axial positions. The bct2– bridging ligand connects two metal ions via its carboxylic groups, resulting in the formation of a parallel linear polymeric chain running along the [1\overline{1}1] direction. The coordinated water molecule of one chain forms a strong O—H...O hydrogen bond with the carboxylate O atom of a neighboring chain, leading to the formation of double chains with a closest distance of 5.425 (7) Å between the cadmium ions belonging to different chains. Aromatic π–π stacking interactions between the benzene fragments of the anions as well as between the coordinated pyridine molecules belonging to different chains results in the formation of sheets oriented parallel to the (\overline{1}01) plane. As a result of hydrogen-bonding interactions involving the water molecules of crystallization, the sheets are joined together in a three-dimensional network.

Study on wall-slipping mechanism of nano-injection polymer under the constant temperature fields

Abstract Polyphenylene sulfide (PPS) and copper (Cu) were used as the polymer and substrate material to simulate the nano-injection molding process by molecular dynamics method. The results show that the PPS chain obeys Einstein’s diffusion law in the early stage of injection molding then deviates from it in the late stage due to the entanglement and limitation of surrounding nanoparticles. In addition, the process of conformational isomerization of polymer chains is accompanied by the twisting and stretching of fixed chains. There are two kinds of adhesion phenomena, one is the macromolecular slides violently in small areas of some sure nanoscale groove to form multiple anchor points. The other case involves multiple nano-grooves along the metal interface, the polymer chain slides and is bolted as multiple anchors in different grooves due to the exerted wall-drag effect on the neighboring chains. These two slipping and anchoring mechanisms are consistent with de Gennes’ slipping theory. Through the quantitative analysis of the influence of pressure on injection filling, it is found that injection pressure should be kept within a certain range to achieve the positive effect of molding.

Structure adaptation in Omicron SARS-CoV-2/hACE2: Biophysical origins of evolutionary driving forces

Since its emergence, the COVID-19 threat has been sustained by a series of transmission waves initiated by new variants of the SARS-CoV-2 virus. Some of these arise with higher transmissivity and/or increased disease severity. Here, we use molecular dynamics simulations to examine the modulation of the fundamental interactions between the receptor binding domain (RBD) of the spike glycoprotein and the host cell receptor (human angiotensin-converting enzyme 2 [hACE2]) arising from Omicron variant mutations (BA.1 and BA.2) relative to the original wild-type strain. Our key findings are that glycans play a vital role at the RBD···hACE2 interface for the Omicrons, and the interplay between glycans and sequence mutations leads to enhanced binding. We find significant structural differences in the complexes, which overall bring the spike protein and its receptor into closer proximity. These are consistent with and attributed to the higher positive charge on the RBD conferred by BA.1 and BA.2 mutations relative to the wild-type. However, further differences between subvariants BA.1 and BA.2 (which have equivalent RBD charges) are also evident: mutations reduce interdomain interactions between the up chain and its clockwise neighbor chain in particular for the latter, resulting in enhanced flexibility for BA.2. Consequently, we see occurrence of additional close contacts in one replica of BA.2, which include binding to hACE2 by a second RBD in addition to the up chain. Although this motif is not seen in BA.1, we find that the Omicrons can directly/indirectly bind a down-RBD to hACE2 through glycans: the role of the glycan on N90 of hACE2 switches from inhibiting to facilitating the binding to Omicron spike protein via glycan-protein lateral interactions. These structural and electrostatic differences offer further insight into the mechanisms by which viral mutations modulate host cell binding and provide a biophysical basis for evolutionary driving forces.

Enhanced mechanical property and freeze-thaw stability of alkali-induced heat-set konjac glucomannan hydrogel through anchoring interface effects of carboxylated cellulose nanocrystals

The alkali-induced heat-set konjac glucomannan (KGM) hydrogels have drawn increasing attention due to their high absorbency and thermal irreversibility ability, but pure KGM hydrogels generally have defects of low strength and high syneresis rate. Cellulose nanocrystals and their derivatives, which have a very high specific surface area, good biocompatibility, biodegradability, and low toxicity, are promising candidates to solve this challenge. In this work, we propose the use of carboxylated cellulose nanocrystals (C–CNCs) as nanofillers for the strengthening of KGM hydrogels. The effects of the C–CNCs content on the microstructure and physical properties of the KGM hydrogels and their possible mechanism were investigated. The compressive test results indicate great improvement in the mechanical properties upon the addition of the C–CNCs for the KGM hydrogel and reached a maximum value at 20% loading. The microstructure analyses of the KGM hydrogel revealed that the well-distributed C–CNCs can act as a physical cross-linker to connect the neighboring KGM chains to strengthen the resultant hydrogel, based on their strong interactions, including hydrogen bonding and chain entanglements. Moreover, adding 20% C–CNCs can significantly decrease the syneresis after five repeated freeze-thaw cycles of the KGM hydrogels. Compared to pure KGM hydrogels, KGM/C–CNCs nanocomposite hydrogels demonstrated higher water-binding capability based on Low-field nuclear magnetic resonance. These findings indicate that C–CNCs are considered anchors for KGM chains as well as reinforcement fillers in the polymer matrix, which contributes significantly to the mechanical property of the nanocomposite. Therefore, C–CNCs were a promising material to be applied for modulating the mechanical and freeze-thaw stability properties of the polysaccharide-based hydrogel in food and biomedical applications.

Dynamics of the extended and intermediate range order in model polymer electrolyte poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide

The dynamics of lithium ions and polymer chains were investigated at the molecular scale in the model polymer electrolyte Poly (ethylene oxide) (PEO)/Lithium bis(trifluoromethanesulfonyl)imide as a function of temperature. This system is known to present an intermediate range order from the arrangement of neighboring chain segments as well as an extended range order of cylindrically arranged chains. The collective dynamics of the systems at lengthscales matching these structural features was measured using Neutron Spin Echo spectroscopy, gaining insights into their lifetime. Moreover, using isotope substitution techniques the dynamics of the lithium ions with respect to the other atoms was probed. The obtained results are compared with the conductivity and the lithium self-diffusion coefficient measured by NMR to gain experimental insight on the molecular processes triggering lithium transport.

Statistical mechanics of coil–rod structure in biopolymer gels

Due to the unique properties of biopolymer gels, they are extensively used in the food industry and biomedical applications such as drug delivery. Different from rubber-like materials, the constituting chains in many biopolymer gels randomly interlock with neighbouring chains by means of physical rather than covalent cross-linking. Such polymer networks are characterized by two principal regions: the disordered zone containing coiled chains and the ordered zone in the form of ion-mediated aggregation of macromolecules and/or helical structures. The ordered regions serve as junction zones between the disordered chains, and the size of these zones may alter as a result of zipping/unzipping phenomena. The entire polymer network can be envisaged as a collection of coil–rod structures serving as the building blocks, where the coil and rod are representative of the disordered and ordered zones, respectively. The present work aims to provide a rigorous formulation of coil–rod structure that can predict its mechanical behaviour including zipping/unzipping characteristics. The coil–rod structure is modelled by a rod attached to a freely jointed chain, where the length of the rod and the number of segments in the freely jointed chain are adjustable input parameters. The relationship between the force and end-to-end distance of the coil–rod structure is derived based on statistical mechanics. The formulation is extended to incorporate the zipping/unzipping mechanism with the aid of Boltzmann averaging. As an example of its applications, the model is implemented into the eight-chain model to describe the macroscopic mechanical response of the network. Another example is demonstrated where the zipping/unzipping mechanism is shown to be able to capture the unwinding of a double-stranded DNA under a tensile force. The formulation presented in this work paves the way for future studies that model biopolymer gel networks with potentially complex chain interactions.

Mapping inhomogeneous network structures within biomolecular condensate using single-molecule imaging and tracking of fluorogenic probes.

Biomolecular condensates form via phase separation coupled to percolation. These phase transitions are driven by multivalent macromolecules. Network structures within condensates and the interfaces of condensates are difficult to interrogate experimentally. Here, we leverage single-molecule (SM) techniques and three fluorogenic probes, Nile blue (NB), Nile red (NR), and merocyanine 540 (MC540), to study the network structures within biomolecule condensates of the low-complexity domain of the hnRNPA1 protein (A1-LCD). Importantly, the fluorescent probes are not covalently bound to A1-LCD but instead diffuse in solution and become fluorescent in response to inhomogeneities of the local chemical environments within condensates. Interestingly, epifluorescence microscopy shows that the three probes respond in unique ways within condensates: NB gives a uniform intensity distribution, MC540 shows a higher intensity at the interface, and NR highlights hot spots inside the condensates. We then use SM localization microscopy to correlate localizations of the three probes. Surprisingly, the high-resolution SM reconstructions all show inhomogeneous network structures but with different emphases: NR shows the largest number of hotspots, NB exhibits the most spatial uniformity, and MC540 shows the greatest spatial variation within each condensate. Further, NB and MC540 localizations are highly correlated within each condensate. SM tracking experiments show that slower-moving NB molecules form high-contrast inhomogeneous network structures with hot spots, in agreement with SMLM. On the other hand, highly diffusive NB molecules are uniformly distributed throughout the condensate. We therefore conclude that network structures within the condensate are heterogeneous; protein chains with strong connections to neighboring chains form a relatively stable inhomogeneous network with hot spots, while chains with weak interactions are diffusive throughout the condensates. The mesoscale and sub-mesoscale structural organizations of molecules within condensates inferred from SM measurements agree with recent computational studies.

Non-affine dissipation in polymer fracture

Viscoelasticity is a universal property in most soft solids. Specifically, for the fracture of polymeric materials, viscoelasticity has often been regarded as a major mechanism of toughening, and the excess fracture energy beyond the intrinsic value correlated to the stress–strain hysteresis, which is commonly used to characterize viscoelasticity in the framework of continuum mechanics. Through systematically planned experiments, the current study shows that a noticeable package of energy dissipation exists besides that associated with the hysteretic deformation. This package of energy is attributed to the highly non-affine deformation near the crack tip — the rearrangement and mutual sliding of the neighboring chains caused by the rupture of a polymer chain, which are insignificant in samples under homogeneous deformation. Various means of inter-chain-friction reduction, e.g., by applying lateral stretches, diluting the chains with solvent, or subject the material to dynamic or static fatigue, can mitigate the effect of non-affine dissipation, and bring the fracture energy down to the intrinsic threshold. In contrast, by making an elastomer more elastic, e.g., by training through cyclic loading, the non-affine dissipation remains effective, and the limiting fracture energy is significantly higher than the threshold even when the hysteresis is negligible. The identification of the non-affine-dissipation mechanism paves the way to the development of new soft materials with both excellent elasticity and significant fracture toughness.

Study of ordering in 2D ferromagnetic nanoparticles arrays: Computer simulation

<abstract> <p>This article describes ordering in a 2D ferromagnetic nanoparticles array by computer simulation. The Heisenberg model simulates the behavior of spins in nanoparticles. Nanoparticles interact using dipole-dipole forces. Computer simulations use the Monte Carlo method and Metropolis algorithm. Two possible types of ordering for the nanoparticles' magnetic moments are detected in the system. The magnetic anisotropy direction for the nanoparticles determines the type of ordering. If the anisotropy direction is oriented perpendicular to the substrate plane, then a superantiferromagnetic phase with staggered magnetization is realized. If the magnetic anisotropy is oriented in the nanoparticle plane, the superantiferromagnetic phase has a different structure. The nanoparticle array is broken into chains parallel to the anisotropy orientations. In one chain of nanoparticles, magnetic moments are oriented in the same way. The magnetic moments of the nanoparticles are oriented oppositely in neighbor chains. The temperature of phase transitions is calculated based on finite dimensional scaling theory. Temperature depends linearly on the intensity of the dipole-dipole interaction for both types of superantiferromagnetic transition.</p> </abstract>

Visualization of single crosslinks and heterogeneity in polymer networks

At the very heart of any polymer networks are the crosslinks that interconnect neighboring chains and lock them in position to resist stress. The crosslinks and their spatial heterogeneity are expected to dictate network architecture, origin of elasticity, and transmission from macroscopic forces to local responses. Yet, direct confirmations of these predictions have been elusive largely because the traditional experimental means are limited to ensemble-averaged or reciprocal-space information. In this perspective, we call attention to the very recent developments that managed to visualize the crosslinks on a single-molecule level, which further localized their static, equilibrium positions in space and tracked their fluctuations around the equilibrium positions in time. Hopefully, these real-space information with unprecedent details can allow us to fully understand networks of complexity and to correlate macroscopic properties to nanoscopic structures.

Analyzing the effect of data preprocessing techniques using machine learning algorithms on the diagnosis of COVID-19.

Real-time polymerase chain reaction (RT-PCR) known as the swab test is a diagnostic test that can diagnose COVID-19 disease through respiratory samples in the laboratory. Due to the rapid spread of the coronavirus around the world, the RT-PCR test has become insufficient to get fast results. For this reason, the need for diagnostic methods to fill this gap has arisen and machine learning studies have started in this area. On the other hand, studying medical data is a challenging area because the data it contains is inconsistent, incomplete, difficult to scale, and very large. Additionally, some poor clinical decisions, irrelevant parameters, and limited medical data adversely affect the accuracy of studies performed. Therefore, considering the availability of datasets containing COVID-19 blood parameters, which are less in number than other medical datasets today, it is aimed to improve these existing datasets. In this direction, to obtain more consistent results in COVID-19 machine learning studies, the effect of data preprocessing techniques on the classification of COVID-19 data was investigated in this study. In this study primarily, encoding categorical feature and feature scaling processes were applied to the dataset with 15 features that contain blood data of 279 patients, including gender and age information. Then, the missingness of the dataset was eliminated by using both K-nearest neighbor algorithm (KNN) and chain equations multiple value assignment (MICE) methods. Data balancing has been done with synthetic minority oversampling technique (SMOTE), which is a data balancing method. The effect of data preprocessing techniques on ensemble learning algorithms bagging, AdaBoost, random forest and on popular classifier algorithms KNN classifier, support vector machine, logistic regression, artificial neural network, and decision tree classifiers have been analyzed. The highest accuracies obtained with the bagging classifier were 83.42% and 83.74% with KNN and MICE imputations by applying SMOTE, respectively. On the other hand, the highest accuracy ratio reached with the same classifier without SMOTE was 83.91% for the KNN imputation. In conclusion, certain data preprocessing techniques are examined comparatively and the effect of these data preprocessing techniques on success is presented and the importance of the right combination of data preprocessing to achieve success has been demonstrated by experimental studies.

Leveraging the Inductive Effect to Promote Oxygen Evolution on Oxides and Metal Hydroxide-Organic Frameworks

Late transition metal oxides are reported to be the most active non-precious catalysts for the oxygen evolution reaction (OER), but the most active oxides based on Ni or Co still have turnover frequencies per metal site at least one order of magnitude lower than that of oxygen-evolving complex (OEC) in biological systems.[1] The OEC contains an intricate manganese-calcium-oxo cluster, and its unparalleled OER activity can be attributed to the unique characteristics of Mn centers regulated by Ca2+ cations. Such electronic structure tuning can be generalized as the inductive effect.[2] Specifically, substituting metal oxides and complexes using foreign metals with higher electronegativity can increase their redox potentials and promote their activity. We have employed this concept to design bismuth-substituted strontium cobaltite, where the strongly electronegative Bi3+ ions give rise to Co centers with record intrinsic OER activity in alkaline solutions.[3] Unfortunately, metal substitution in oxides exhibits a much smaller tunability of electronic structures than that found in metal-oxo clusters. For instance, Ca2+ substitution of Mn4+ in synthetic [CaMn3O4] clusters can modulate the Mn3+/4+ redox potential by ~1 V,[4] whereas negligible changes of ~0.02 V are typically observed for oxides.[5] To tackle this limitation, we have designed metal hydroxide-organic frameworks (MHOFs) that combine the great tunability of enzymatic systems with known oxide-based chemistries.[6] A series of MHOFs were constructed by transforming layered hydroxides into 2D sheets composed of metal-octahedra chains cross-linked with neighboring chains using organic linkers. MHOFs can act as a tunable platform for the OER, where the nature of π-π-interactions between adjacent stacked linkers and the transition metals in the layered metal hydroxides dictate stability and activity, respectively. Substituting MHOF nanosheets with more electron-withdrawing cations increased their OER activity, where Fe-substituted Ni-based MHOFs exhibited three orders of magnitude enhancement in activity per metal site, rivaling those of state-of-the-art OER catalysts. This enhancement was correlated with the MHOF-based modulation of Ni redox potentials and the optimized binding of reaction intermediates. These results represent a step forward toward designing metal centers with ligand fields akin to those in homogenous/enzymatic systems, where MHOFs can act as a versatile platform to develop catalysts with unparalleled tunability.

High-heat and UV-barrier poly(lactic acid) by microwave-assisted functionalization of waste natural fibers

The application of poly(lactic acid) (PLA) in the packaging area is frequently dwarfed by the inadequate gas/water barrier properties, low heat resistance and high UV transmittance. Herein, an environmentally friendly and high-efficiency microwave-assisted functionalization (MAF) approach was proposed to aqueous grafting waste bamboo fibers with the bridging agent. It permitted significant promotion of interfacial interactions between the MAF bamboo fibers (MAFBs) and neighboring PLA chains, contributing to uniform dispersion and intimate interphase. Featuring the morphological features, the MAFB-reinforced (5, 10 and 20 wt%) PLA biocomposites achieved an unexpected combination of high mechanical properties, exceptional resistance to heat deflection and UV irradiation, and excellent water barrier performance. Upon addition of only 5 wt% MAFBs, the tensile strength and toughness of PLA composite films were increased to 46.5 MPa and 0.6 MJ/m3, increasing over 52 % and nearly 107 % compared to those of the counterpart loaded pristine bamboo fibers (PBFs), respectively. This was favorably accompanied by the remarkably reduced water vapor permeability, falling down to the lowest value of 3.5 × 10−11 g∙m/Pa∙s∙m2 for PLA/MAFB (80/20) with a decrease of nearly 79 % compared to the counterpart. It is of interest to note the MAFB-enabled nearly 100 % UV-blocking ratio for PLA loaded 10 and 20 wt% fibers, as well as excellent resistance to heat deflection even at high temperatures like 120 °C. This effort paves the way to multifunctional natural fibers with high affinity to PLA for elegant implementation of high-heat and UV-resistant packaging materials in an ecofriendly manner.