Tunable Surface Wrinkling by a Bio-Inspired Polyamine Anion Coacervation Process that Mediates the Assembly of Polyoxometalate Nanoclusters

A bio-inspired method is used to render controlled wrinkling surface patterns on supramolecular architectures assembled from polyoxometalate (POM) clusters. It involves a polyamine-multivalent anion interaction generating positively charged coacervates, which while dictating the assembly of POM into spherical structures further facilitate an interesting surface morphogenesis with wrinkling patterns. This spontaneous surface wrinkling depends on the type of multivalent anion and the pH. As the polyamine-anion interaction becomes stronger, the wrinkles turn denser with lesser depth, which eventually undergoes post-buckling to engender a complex surface pattern. Interestingly, the order of influence exerted by different anions on the morphology follows the Hofmeister series. Moreover, the mild synthesis conditions keep the functional POM units dispersed in the sphere with a structural transformability to their lacunary form.     

Probing Polyoxometalate–Protein Interactions Using Molecular Dynamics Simulations

The molecular interactions between the Ce^IV‐substituted Keggin anion [PW₁₁O₃₉Ce(OH₂)₄]^3? ( CeK ) and hen egg‐white lysozyme (HEWL) were investigated by molecular dynamics simulations. The analysis of CeK was compared with the Ce^IV‐substituted Keggin dimer [(PW₁₁O₃₉)₂Ce]^10? ( CeK₂ ) and the Zr^IV‐substituted Lindqvist anion [W₅O₁₈Zr(OH₂)(OH)]^3? ( ZrL ) to understand how POM features such as shape, size, charge, or type of incorporated metal ion influence the POM???protein interactions. Simulations revealed two regions of the protein in which the CeK anion interacts strongly: cationic sites formed by Arg21 and by Arg45 and Arg68. The POMs chiefly interact with the side chains of the positively charged (arginines, lysines) and the polar uncharged residues (tyrosines, serines, aspargines) via electrostatic attraction and hydrogen bonding with the oxygen atoms of the POM framework. The CeK anion shows higher protein affinity than the CeK₂ and ZrL anions, because it is less hydrophilic and it has the right size and shape for establishing interactions with several residues simultaneously. The larger, more negatively charged CeK₂ anion has a high solvent‐accessible surface, which is sub‐optimal for the interaction, while the smaller ZrL anion is highly hydrophilic and cannot efficiently interact with several residues simultaneously.     

Patterning Surfaces on Azo‐Based Multilayer Films via Surface Wrinkling Combined with Visible Light Irradiation

Here, a simple combined strategy of surface wrinkling with visible light irradiation to fabricate well tunable hierarchical surface patterns on azo‐containing multilayer films is reported. The key to tailor surface patterns is to introduce a photosensitive poly(disperse orange 3) intermediate layer into the film/substrate wrinkling system, in which the modulus decrease is induced by the reversible photoisomerization. The existence of a photoinert top layer prevents the photoisomerization‐induced stress release in the intermediate layer to some extent. Consequently, the as‐formed wrinkling patterns can be modulated over a large area by light irradiation. Interestingly, in the case of selective exposure, the wrinkle wavelength in the exposed region decreases, while the wrinkles in the unexposed region are evolved into highly oriented wrinkles with the orientation perpendicular to the exposed/unexposed boundary. Compared with traditional single layer‐based film/substrate systems, the multilayer system consisting of the photosensitive intermediate layer offers unprecedented advantages in the patterning controllability/universality. As demonstrated here, this simple and versatile strategy can be conveniently extended to functional multilayer systems for the creation of prescribed hierarchical surface patterns with optically tailored microstructures.

     

Applications of inorganic‐organic hybrid architectures based on polyoxometalates in catalyzed and photocatalyzed chemical transformations

The scope of this article is to reveal the fruitful combination of POM species with metal coordination complexes, leading to the construction of several efficient multifunctional catalysts. In this review, we try to underscore various catalytic and photocatalytic reactions catalyzed by POM‐based inorganic‐organic hybrid. Notably, it has been well established that depending on the type of the reaction, the activity and selectivity of these hybrid catalyst can be drastically improved by the rational and correct choice of the organic metal complex and POM anion providing a marriage of convenience.     

Multivalency by Self‐Assembly: Binding of Concanavalin A to Metallosupramolecular Architectures Decorated with Multiple Carbohydrate Groups

Multiplication of functional units through self‐assembly is a powerful way to new properties and functions. In particular, self‐organization of components decorated with recognition groups leads to multivalent entities, amenable to strong and selective binding with multivalent targets, such as protein receptors. Here we describe an efficient, supramolecular, one‐pot valency multiplication process proceeding through self‐organization of monovalent components into well‐defined, grid‐shaped [2×2] tetranuclear complexes bearing eight sugar residues for multivalent interaction with the tetrameric lectin, concanavalin A (Con A). The grids are stable in water under physiological pH at a relatively high concentration, but dissociate readily at slightly more acidic pH or upon dilution below a certain threshold, in a type of on–off behavior. The carbohydrate‐decorated grids interact strongly and selectively with Con A forming triply supramolecular bio‐hybrid polymeric networks, which lead to a highly specific phase‐separation and quasi‐quantitative precipitation of Con A out of solution. Dramatic effects of valency number on agglutination properties were demonstrated by comparison of grids with divalent carbohydrates of covalent and non‐covalent (L ‐shaped, mononuclear zinc complex) scaffolds. The results presented here provide prototypical illustration of the power of multivalency generation by self‐assembly leading to defined arrays of functional groups and binding patterns.     

Controlled fabrication of hierarchically microstructured surfaces via surface wrinkling combined with template replication

In this paper,we present a simple method by combining surface wrinkling and template replication to create a series of hierarchical structures on polydimethylsiloxane(PDMS) elastomer.The primary stable lined patterns are formed by duplicating commercialized compact disk and digital versatile disk with PDMS.The secondary microscale patterns are from surface wrinkling,which is elicited by oxygen plasma(OP) treatment of the prestrained PDMS stamp followed with the prestrain release.By systematically varying the OP exposure duration,the prestrain,and the angle(θ) between the primary pattern orientation and the prestrain direction,we obtain highly ordered well-organized composite patterns from different patterning techniques and with different length scales and mechanical stabilities.     

Tuning and Erasing Surface Wrinkles by Reversible Visible‐Light‐Induced Photoisomerization

Periodic wrinkling across different scales has received considerable attention because it not only represents structure failure but also finds wide applications. How to prevent wrinkling or create desired wrinkling patterns is non‐trivial because the dynamic evolution of wrinkles is a highly nonlinear problem. Herein, we report a simple yet powerful method to dynamically tune and/or erase wrinkling patterns with visible light. The light‐induced photoisomerization of azobenzene units in azopolymer films leads to stress release and consequently to the erasure of the wrinkles. The wrinkles in unexposed regions are also affected and oriented perpendicular to the exposed boundary during the stress reorganization. Theoretical models were developed to understand the dynamics of the reversible photoisomerization‐induced wrinkle evolution. This method can be applied for designing functional materials/devices, for example, for the reversible optical writing/erasure of information as demonstrated here.     

Supramolecular networks supported by the anion…π linkage of Keggin‐type heteropolyoxotungstates

Anion…π interactions are newly recognized weak supramolecular forces which are relevant to many types of electron‐deficient aromatic substrates. Being less competitive with respect to conventional hydrogen bonding, anion…π interactions are only rarely considered as a crystal‐structure‐defining factor. Their significance dramatically increases for polyoxometalate (POM) species, which offer extended oxide surfaces for maintaining dense aromatic/inorganic stacks. The structures of tetrakis(caffeinium) μ₁₂‐silicato‐tetracosa‐μ₂‐oxido‐dodecaoxidododecatungsten trihydrate, (C₈H₁₁N₄O₂)₄[SiW₁₂O₄₀]·3H₂O, (1), and tris(theobrominium) μ₁₂‐phosphato‐tetracosa‐μ₂‐oxido‐dodecaoxidododecatungsten ethanol sesquisolvate, (C₇H₉N₄O₂)₃[PW₁₂O₄₀]·1.5C₂H₅OH, (2), support the utility of anion…π interactions as a special kind of supramolecular synthon controlling the structures of ionic lattices. Both caffeinium [(HCaf)⁺ in (1)] and theobrominium cations [(HTbr)⁺ in (2)] reveal double stacking patterns at both axial sides of the aromatic frameworks, leading to the generation of anion…π…anion bridges. The latter provide the rare face‐to‐face linkage of the anions. In (1), every square face of the metal–oxide cuboctahedra accepts the interaction and the above bridges yield flat square nets, i.e. {(HCaf⁺)₂[SiW₁₂O₄₀]^4?}_n. Two additional cations afford single stacks only and they terminate the connectivity. Salt (2) retains a two‐dimensional (2D) motif of square nets, with anion…π…anion bridges involving two of the three (HTbr)⁺ cations. The remaining cations complete a fivefold anion…π environment of [PW₁₂O₄₀]^3?, acting as terminal groups. This single anion…π interaction is influenced by the specific pairing of (HTbr)⁺ cations by double amide‐to‐amide hydrogen bonding. Nevertheless, invariable 2D patterns in (1) and (2) suggest the dominant role of anion…π interactions as the structure‐governing factor, which is applicable to the construction of noncovalent linkages involving Keggin‐type oxometalates.     

Ternary Hybrid γ‐Fe2O3/CrVI/Amine Oxidase Nanostructure for Electrochemical Sensing: Application for Polyamine Detection in Tumor Tissue

Dichromate binds to surface‐active maghemite nanoparticles (SAMNs) to form a stable core–shell nanostructures (SAMN@Cr^VI). The hybrid was characterized by Mössbauer spectroscopy, high‐angle annular dark‐field imaging, electron energy‐loss spectroscopy, and electrochemical techniques, which revealed a strong interaction of dichromate with the nanoparticle surface. Electrochemical characterization showed lower charge‐transfer resistance, better electrochemical performance, and more reversible electrochemical behavior with respect to naked SAMNs. Moreover, SAMN@Cr^VI is an excellent electrocatalyst for hydrogen peroxide reduction. Furthermore, an enzyme, namely, bovine serum amine oxidase (BSAO: EC 1.4.3.6), was immobilized on SAMN@Cr^VI by self‐assembly to give a ternary hybrid nanostructured catalyst for polyamine oxidation (SAMN@Cr^VI‐BSAO). SAMN@Cr^VI‐BSAO was applied for the development of a reagentless, fast, inexpensive, and interference‐free polyamine biosensor, which was successfully exploited for the discrimination of tumorous tissue from healthy tissue in human crude liver extracts.     

多金属氧酸盐及其溶液自聚集行为研究进展

多金属氧酸盐(POM)是一类由过渡金属与氧原子桥连而成的阴离子簇合物,由于其特殊的分子结构及优异的物理化学性质,使其在催化、医药、材料科学、表面化学、超分子化学等领域有广泛的应用价值。 POM在稀的水溶液中能够发生自聚集,形成类似两亲分子溶液中的“有序聚集体结构”,赋予其新的结构和性质,以期开发出新型纳米器件及在催化、药物等领域得到应用。 本文介绍了POM的主要结构、性质和近年来的应用,阐述了其在溶液中自聚集行为的研究状况和新进展。     

Concise,Single‐Step Synthesis of Sulfur‐Enriched Graphene: Immobilization of Molecular Clusters and Battery Applications

The concise synthesis of sulfur‐enriched graphene for battery applications is reported. The direct treatment of graphene oxide (GO) with the commercially available Lawesson's reagent produced sulfur‐enriched‐reduced GO (S‐rGO). Various techniques, such as X‐ray photoelectron spectroscopy (XPS), confirmed the occurrence of both sulfur functionalization and GO reduction. Also fabricated was a nanohybrid material by using S‐rGO with polyoxometalate (POM) as a cathode‐active material for a rechargeable battery. Transmission electron microscopy (TEM) revealed that POM clusters were individually immobilized on the S‐rGO surface. This battery, based on a POM/S‐rGO complex, exhibited greater cycling stability for the charge‐discharge process than a battery with nanohybrid materials positioned between the POM and nonenriched rGO. These results demonstrate that the use of sulfur‐containing groups on a graphene surface can be extended to applications such as the catalysis of electrochemical reactions and electrodes in other battery systems.     

Use of Lanthanide‐Containing Polyoxometalates to Sensitise the Emission of Fluorescent Labelled Serum Albumin

Monitoring the interaction of biomolecules is important, and the use of energy transfer is a principal technique in elucidating nanoscale interactions. Lanthanide compounds are promising luminescent probes for biological samples as their emission is longer‐lived than any native autofluorescence. Polyoxometalates (POMs) are interesting structural motifs to incorporate lanthanides, offering low toxicity and a size pertinent for biological applications. Here, we employ iso‐structured POMs containing either terbium or europium and assess their interaction with serum albumin by sensitisation of a fluorescent tag on the protein via LRET (luminescence resonance energy transfer) by exciting the lanthanide. Time‐resolved measurements showed energy transfer with an efficiency of over 90 % for the POM–protein systems. The Tb–POM results were relatively straightforward, while those with the iso‐structured Eu–POM were complicated by the effect of protein shielding from the aqueous environment.     

Surface Wrinkling Induced by Photofluidization of Low Molecular Azo Glasses

Photoinduced surface wrinkling is demonstrated for a low molecular azo compound confined between a substrate and a thin inorganic elastic layer. The wrinkling process is investigated by time‐resolved light scattering as well as by two‐dimensional autocorrelation analysis of microscopic images. It is shown that the temporal evolution of the wrinkling pattern is directly controlled by the amount of photons absorbed by the sample and that there is no significant dependence of the equilibrium wavelength on irradiation intensity. Finally, the comparison of thermal and photoinduced wrinkling revealed that photoinduced wrinkles are characterized by a narrower mode distribution and less coarsening.     

Preparation of a weak anion exchange/hydrophobic interaction dual‐function mixed‐mode chromatography stationary phase for protein separation using click chemistry

In this study, 3‐diethylamino‐1‐propyne was covalently bonded to the azide‐silica by a click reaction to obtain a novel dual‐function mixed‐mode chromatography stationary phase for protein separation with a ligand containing tertiary amine and two ethyl groups capable of electrostatic and hydrophobic interaction functionalities, which can display hydrophobic interaction chromatography character in a high‐salt‐concentration mobile phase and weak anion exchange character in a low‐salt‐concentration mobile phase employed for protein separation. As a result, it can be employed to separate proteins with weak anion exchange and hydrophobic interaction modes, respectively. The resolution and selectivity of the stationary phase were evaluated in both hydrophobic interaction and ion exchange modes with standard proteins, respectively, which can be comparable to that of conventional weak anion exchange and hydrophobic interaction chromatography columns. Therefore, the synthesized weak anion exchange/hydrophobic interaction dual‐function mixed‐mode chromatography column can be used to replace two corresponding conventional weak anion exchange and hydrophobic interaction chromatography columns to separate proteins. Based on this mixed‐mode chromatography stationary phase, a new off‐line two‐dimensional liquid chromatography technology using only a single dual‐function mixed‐mode chromatography column was developed. Nine kinds of tested proteins can be separated completely using the developed method within 2.0 h.     

Effect of surface treatment of UHMWPE fiber on mechanical and impact fracture behavior of PTFE/POM composites

Ultra‐high‐molecular‐weight polyethylene (UHMWPE) fiber was treated to reinforce the polytetrafluoroethylene/polyoxymethylene (PTFE/POM), and the mechanical properties of surface‐treated UHMWPE were investigated. Scanning electron microscopy was utilized to study the fracture surfaces of UHMWPE/POM/PTFE composites. Experimental results showed that the surface treatment of UHMWPE fiber effectively improves the mechanical property of POM/PTFE composites. Scanning electron microscopy studies indicated that surface modification could improve the interfacial adhesion of POM/PTFE composites. And the dispersion of UHMWPE in POM/PTFE composites was also improved after the surface modification. Copyright © 2017 John Wiley & Sons, Ltd.     

The structure of self-assembled multilayers with polyoxometalate nanoclusters

Using electrostatic layer-by-layer self-assembly (ELSA), the formation of multilayers with polyelectrolytes and nanoscopic polyoxometalate (POM) clusters of different sizes and charges is investigated. The multilayers are characterized by UV-vis absorption spectroscopy, optical ellipsometry, cyclic voltammetry, and atomic force microscopy. In all cases, it is possible to find experimental conditions to achieve irreversible adsorption and regular multilayer deposition. Most importantly, the surface coverage is directly related to the total charge of the POM anion and can be controlled from submonolayer to multilayer coverage by adjusting the ionic strength of the dipping solutions. Imaging the interfaces after POM deposition by atomic force microscopy reveals a granular surface texture with nanometer-sized features. The average interfacial roughness amounts to approximately 1 nm. Cyclic voltammetry indicates that the electrochemical properties of the POM clusters are fully maintained in the polyelectrolyte matrix, which opens a route toward practical applications such as sensors or heterogeneous catalysts. Moreover, the permeability toward electrochemically active probe molecules can be tailored through the multilayer architecture and deposition conditions. Finally, we note that despite the low total charge and comparably small size of the discrete POM anions, the multilayers are remarkably stable. This work provides basic guidelines for the assembly of POM-containing ELSA multilayers and provides detailed insight into characteristic surface coverage, permeability, and electrochemical properties.     

Light‐Triggered Capture and Release of DNA and Proteins by Host–Guest Binding and Electrostatic Interaction

The development of an effective and general delivery method that can be applied to a large variety of structurally diverse biomolecules remains a bottleneck in modern drug therapy. Herein, we present a supramolecular system for the dynamic trapping and light‐stimulated release of both DNA and proteins. Self‐assembled ternary complexes act as nanoscale carriers, comprising vesicles of amphiphilic cyclodextrin, the target biomolecules and linker molecules with an azobenzene unit and a charged functionality. The non‐covalent linker binds to the cyclodextrin by host–guest complexation with the azobenzene. Proteins or DNA are then bound to the functionalized vesicles through multivalent electrostatic attraction. The photoresponse of the host–guest complex allows a light‐induced switch from the multivalent state that can bind the biomolecules to the low‐affinity state of the free linker, thereby providing external control over the cargo release. The major advantage of this delivery approach is the wide variety of targets that can be addressed by multivalent electrostatic interaction, which we demonstrate on four types of DNA and six different proteins.     

Molecular printboards: versatile platforms for the creation and positioning of supramolecular assemblies and materials

This tutorial review describes the development of molecular printboards, which are tailor-made surfaces functionalized with receptor (host) molecules. Such substrates can be used for the binding of complementary ligand (guest) molecules through multivalent interactions. Supramolecular multivalent interactions are ideal to attain a quantitative and fundamental understanding of multivalency at interfaces. Because of their quantitative interpretation, the focus is on (i) the interaction of cyclodextrin host surfaces with multivalent hydrophobic guest molecules, (ii) the vancomycin-oligopeptide system, and (iii) the multivalent binding of histidine-tagged proteins to NiNTA receptor surfaces. The review will be of interest to researchers in the fields of supramolecular chemistry, chemical biology, surface chemistry, and molecular recognition.     

基于表面起皱法的梯度图案的可控制备

报道了基于非刻蚀法的表面起皱机制来实现高分子薄膜表面的周期性梯度图案的简单可控制备.即对于处于机械拉伸状态的聚二甲基硅氧烷(PDMS)弹性基底,在其底部垫入"积木",而后对其进行紫外-臭氧(UVO)和氧等离子体(OP)的联合表面处理."积木"的加入引起了表面处理后表面硅氧层(SiOx)梯度厚度的形成,进而当释放拉伸应变后,诱导产生了梯度皱纹图案.结果表明:当UVO与OP联用处理时,不仅实现了较小拉伸应变下梯度皱纹形貌的制备,而且扩大了UVO单独使用时梯度皱纹周期的变化范围.通过OP与UVO的处理顺序和处理时间等因素的简单调节,进一步实现了不同梯度皱纹微结构的精细构筑.     

Quantifying the elasticity and viscosity of geometrically confined polymer films via thermal wrinkling

We apply thermal wrinkling, which is a surface instability that occurs during thermal annealing of polymer films geometrically confined by a rigid substrate and a flexible superstrate, to study the elasticity and viscosity of chemically crosslinked polymer systems. Specifically, we study the thermal wrinkling of aluminum‐capped polyhydroxystyrene films with different extent of chemical crosslinking and find that that the rate of change of the wrinkling wavelength with annealing time and temperature has unique relationships with the elasticity and viscosity of the polymer network. With the aid of analytical expressions that relate the time‐ and temperature‐dependent evolution of the wrinkle wavelength to the elasticity and viscosity, we are able to quantify the elastic modulus and shear viscosity of geometrically confined polymer thin films as a function of the degree of crosslinking. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012