Chirality‐Assisted Ring‐Like Aggregation of Aβ(1–40) at Liquid–Solid Interfaces: A Stereoselective Two‐Step Assembly Process

Molecular chirality is introduced at liquid–solid interfaces. A ring‐like aggregation of amyloid Aβ(1–40) on N‐isobutyryl‐L ‐cysteine (L ‐NIBC)‐modified gold substrate occurs at low Aβ(1–40) concentration, while D ‐NIBC modification only results in rod‐like aggregation. Utilizing atomic force microscope controlled tip‐enhanced Raman scattering, we directly observe the secondary structure information for Aβ(1–40) assembly in situ at the nanoscale. D ‐ or L ‐NIBC on the surface can guide parallel or nonparallel alignment of β‐hairpins through a two‐step process based on electrostatic‐interaction‐enhanced adsorption and subsequent stereoselective recognition. Possible electrostatic interaction sites (R5 and K16) and a chiral recognition site (H14) of Aβ(1–40) are proposed, which may provide insight into the understanding of this effect.     

Sandwich‐like Catalyst–Carbon–Catalyst Trilayer Structure as a Compact 2D Host for Highly Stable Lithium–Sulfur Batteries

Herein, we propose the construction of a sandwich‐structured host filled with continuous 2D catalysis–conduction interfaces. This MoN‐C‐MoN trilayer architecture causes the strong conformal adsorption of S/Li₂S_x and its high‐efficiency conversion on the two‐sided nitride polar surfaces, which are supplied with high‐flux electron transfer from the buried carbon interlayer. The 3D self‐assembly of these 2D sandwich structures further reinforces the interconnection of conductive and catalytic networks. The maximized exposure of adsorptive/catalytic planes endows the MoN‐C@S electrode with excellent cycling stability and high rate performance even under high S loading and low host surface area. The high conductivity of this trilayer texture does not compromise the capacity retention after the S content is increased. Such a job‐synergistic mode between catalytic and conductive functions guarantees the homogeneous deposition of S/Li₂S_x, and avoids thick and devitalized accumulation (electrode passivation) even after high‐rate and long‐term cycling.     

Two dimensional nanomaterial‐based separation membranes

Two dimensional nanomaterials including graphene, hexagonal boron‐nitride, molybdenum disulfide, etc., provide immense potentials for separation applications. However, the tradeoff between selectivity and permeability in choosing 2D nanomaterial‐based membrane is inevitable, limiting the progress on separation efficiency for mass industrial applications. To target these issues, versatile strategies such as the rational design of predefined interlayer channels, membrane nanopores, and reasonable functionalization, as well as new mechanisms have been emerged. In this review, we introduce the recent progress on separation mechanisms of 2D nanomaterial‐based membranes with different structures (including the interlayer channels type and the membrane nanopores type) and their inner surface functionalization. Moreover, the interface designs are discussed, in terms of employing dynamic liquid–liquid/liquid–gas interfaces, to advance the selectivity and permeability of the membranes. We further discuss the variety of separation applications based on 2D nanomaterial‐based membranes. The authors hope this review will inspire the active interest of many scientists in the area of the development and application of membrane science.     

Coadsorbate‐Induced Reversal of Solid–Liquid Interface Dynamics

Coadsorbed anions are well‐known to influence surface reactivity and dynamics at solid–liquid interfaces. Here we demonstrate that the chemical nature of these spectator species can entirely determine the microscopic dynamic behavior. Quantitative in situ video‐STM data on the surface diffusion of adsorbed sulfur atoms on Cu(100) electrodes in aqueous solution covered by bromide and chloride spectators, respectively, reveal in both cases a strong exponential potential dependence, but with opposite sign. This reversal is highly surprising in view of the isostructural adsorbate arrangement in the two systems. Detailed DFT studies suggest an anion‐induced difference in the sulfur diffusion mechanism, specifically an exchange diffusion on the Br‐covered surface. Experimental evidence for the latter is provided by the observation of Cu vacancy formation in the Br system, which can be rationalized by a side reaction of the sulfur exchange diffusion.     

Rapid Formation of a Supramolecular Polypeptide–DNA Hydrogel for In Situ Three‐Dimensional Multilayer Bioprinting

A rapidly formed supramolecular polypeptide–DNA hydrogel was prepared and used for in situ multilayer three‐dimensional bioprinting for the first time. By alternative deposition of two complementary bio‐inks, designed structures can be printed. Based on their healing properties and high mechanical strengths, the printed structures are geometrically uniform without boundaries and can keep their shapes up to the millimeter scale without collapse. 3D cell printing was demonstrated to fabricate live‐cell‐containing structures with normal cellular functions. Together with the unique properties of biocompatibility, permeability, and biodegradability, the hydrogel becomes an ideal biomaterial for 3D bioprinting to produce designable 3D constructs for applications in tissue engineering.     

A large decoy set of protein–protein complexes produced by flexible docking

Computational methods are needed to help characterize the structure and function of protein–protein complexes. To develop and improve such methods, standard test problems are essential. One important test is to identify experimental structures from among large sets of decoys. Here, a flexible docking procedure was used to produce such a large ensemble of decoy complexes. In addition to their use for structure prediction, they can serve as a proxy for the nonspecific, protein–protein complexes that occur transiently in the cell, which are hard to characterize experimentally, yet biochemically important. For 202 homodimers and 41 heterodimers with known X‐ray structures, we produced an average of 1217 decoys each. The structures were characterized in detail. The decoys have rather large protein–protein interfaces, with at least 45 residue–residue contacts for every 100 contacts found in the experimental complex. They have limited intramonomer deformation and limited intermonomer steric conflicts. The decoys thoroughly sample each monomer's surface, with all the surface amino acids being part of at least one decoy interface. The decoys with the lowest intramonomer deformation were analyzed separately, as proxies for nonspecific protein–protein complexes. Their interfaces are less hydrophobic than the experimental ones, with an amino acid composition similar to the overall surface composition. They have a poorer shape complementarity and a weaker association energy, but are no more fragmented than the experimental interfaces, with 2.1 distinct patches of interacting residues on average, compared to 2.6 for the experimental interfaces. The decoys should be useful for testing and parameterizing docking methods and scoring functions; they are freely available as PDB files at http://biology.polytechnique.fr/decoys . © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Multitechnique characterization of thin films of immiscible polymer systems: PS–b‐PMMA diblock copolymers and PS–PMMA symmetric blends

Immiscible polymer systems are known to form various kinds of phase‐separated structures capable of producing self‐assembled patterns at the surface. In this study, different surface characterization methods were utilized to study the surface morphology and composition produced after annealing thin polymer films. Two different SIMS techniques—static time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and dynamic nano‐SIMS—were used, complemented by x‐ray photoelectron spectrometry (XPS) and atomic force microscopy (AFM). Thin films (spin‐coated onto silicon wafers) of polystyrene (PS)–poly(methyl methacrylate) (PMMA) symmetric blends and diblock copolymers of similar molecular weight were investigated. Surface enrichment by PS was found on all as‐cast samples. The samples were annealed at 160 °C for different time periods, after which the blend and the copolymer films exhibited opposite behaviour as seen by ToF‐SIMS and XPS. The annealed blend surface presented an increase in the PMMA concentration whereas that of copolymers showed a decrease in PMMA concentration compared with the as‐cast sample. For blends, the nano‐SIMS as well as AFM images revealed the formation of phase‐separated domains at the surface. The composition information obtained from ToF‐SIMS and XPS, as well as the surface mapping by nano‐SIMS and AFM, allowed us to conclude that PS formed phase separated droplet‐like domains on a thin PMMA matrix on annealing. The three‐dimensional nano‐SIMS images showed that the PS droplets were supported inside a rim of PMMA and that these droplets continued from the surface like columnar rods into the film until the substrate interface. In the case of annealed copolymer samples, the AFM images revealed topographical features resembling droplet‐like domains on the surface but there was no phase difference between the domains and the matrix. In the case of copolymers, owing to the covalent bonding between the blocks, complete phase separation was not possible. The three‐dimensional nano‐SIMS images showed domain structures in the form of striations inside the film, which were not continuous until the substrate interface. Information from the different techniques was required to gain an accurate view of the surface composition and topographical changes that have occurred under the annealing conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparative study on formamide–water complex

The hydrogen bonding of 1:1 complexes formed between formamide and water molecule have been investigated systematically using Hartree–Fock (HF), hybrid density functional theory (B3LYP), and post‐Hartree–Fock (MP2 and CCSD(T)) methods with range of basis sets 6‐31G(d), cc‐pVXZ (X = D, T, Q) and aug‐cc‐pVYZ (Y = D, T). Three stable structures are considered on the potential energy surface of formamide and water system. The optimized geometric parameters and interaction energies for various isomers at different levels are estimated. The IR frequencies, intensities, and frequency shifts are reported. This study shows that B3LYP/aug‐cc‐pVDZ method gives better performance for formamide‐water complexes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010.     

Single Fusion Events at Polarized Liquid–Liquid Interfaces

A new electrochemical framework for tracking individual soft particles in solution and monitoring their fusion with polarized liquid–liquid interfaces is reported. The physicochemical principle lies in the interfacial transfer of an ionic probe confined in the particles dispersed in solution and that is released upon their collision and fusion with the fluid interface. As a proof‐of‐concept, spike‐like transients of a stochastic nature are reported in the current–time response of 1,2‐dichloroethane(DCE)|water(W) submilli‐interfaces after injection of DCE‐in‐W emulsions. The sign and potential dependence of the spikes reflect the charge and lipophilicity of the ionic load of the droplets. A comparison with dynamic light scattering measurements indicates that each spike is associated with the collision of a single sub‐picoliter droplet. This opens a new framework for the study of single fusion events at the micro‐ and nanoscale and of ion transport across biomimetic soft interfaces.     

A Convergent Strategy for the Synthesis of Type‐1 Elongated Mucin Cores 1–3 and the Corresponding Glycopeptides

Mucins are a class of highly O‐glycosylated proteins found on the surface of cells in epithelial tissues. O‐Glycosylation is crucial for the functionality of mucins and changes therein can have severe consequences for an organism. With that in mind, the elucidation of interactions of carbohydrate binding proteins with mucins, whether in morbidly altered or unaltered conditions, continue to shed light on mechanisms involved in diseases like chronic inflammations and cancer. Despite the known importance of type‐1 and type‐2 elongated mucin cores 1–4 in glycobiology, the corresponding type‐1 structures are much less well studied. Here, the first chemical synthesis of extended mucin type‐1 O‐glycan core 1–3 amino acid structures based on a convergent approach is presented. By utilizing differentiation in acceptor reactivity, shared early stage Tn‐ and T‐acceptor intermediates were elongated with a common type‐1 [β‐D ‐Gal‐1,3‐β‐D ‐GlcNAc] disaccharide, which allows for straightforward preparation of diverse glycosylated amino acids carrying the type‐1 mucin core 1–3 saccharides. The obtained glycosylated 9‐fluorenylmethoxycarbonyl (Fmoc)‐protected amino acid building blocks were employed in synthesis of type‐1 mucin glycopeptides, which are useful in biological applications.     

Molecular‐level structures at poly(4‐vinyl pyridine)/acid interfaces probed by nonlinear vibrational spectroscopy

The molecular structures of the interfaces between a solid poly(4‐vinyl pyridine) (P4VP) surface and poly(acrylic acid) (PAA) as well as hydrochloric acid (HCl) solutions were probed using sum frequency generation (SFG) vibrational spectroscopy in situ in real time. Spectroscopic results clearly reveal that the PAA molecules are adsorbed onto the P4VP surface via hydrogen bonding at the P4VP/PAA solution interface while the P4VP surface is protonated at the P4VP/HCl solution interface. Consequently, the water molecules near the interfaces are strongly perturbed by these two interactions, exhibiting different orderings at the two interfaces. This work clearly demonstrates the power of studying the interfacial molecular‐level structures via nonlinear vibrational spectroscopy when molecular adsorption happens at the solid–liquid interface and paves a way for our future study on tracing the adsorption dynamics of polymer chains onto solid surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 848–852     

Alternating Donor–Acceptor Arrays from Hexa‐peri‐hexabenzocoronene and Benzothiadiazole: Synthesis,Optical Properties,and Self‐Assembly

Donor–acceptor (D–A) structures were obtained by alternating arrays of hexa‐peri‐hexabenzocoronene (HBC) and benzo[c][1,2,5]thiadiazole (BTZ). Optoelectronic investigations revealed a charge transfer due to strong push–pull interactions. 2 D wide‐angle X‐ray scattering (WAXS) data indicated an arrangement in liquid‐crystalline columnar assemblies, in which the π‐stacking distances and molecular orientation depend on the number of HBC units in the molecules.     

Self‐Assembly of MXene‐Surfactants at Liquid–Liquid Interfaces: From Structured Liquids to 3D Aerogels

2D transition metal carbides and nitrides (MXenes), a class of emerging nanomaterials with intriguing properties, have attracted significant attention in recent years. However, owing to the highly hydrophilic nature of MXene nanosheets, assembly strategies of MXene at liquid–liquid interfaces have been very limited and challenging. Herein, through the cooperative assembly of MXene and amine‐functionalized polyhedral oligomeric silsesquioxane at the oil–water interface, we report the formation, assembly, and jamming of a new type MXene‐based Janus‐like nanoparticle surfactants, termed MXene‐surfactants (MXSs), which can significantly enhance the interfacial activity of MXene nanosheets. More importantly, this simple assembly strategy opens a new platform for the fabrication of functional MXene assemblies from mesoscale (e.g., structured liquids) to macroscale (e.g., aerogels), that can be used for a range of applications, including nanocomposites, electronic devices, and all‐liquid microfluidic devices.     

Structural identification of degradants of moexipril by LC–MS/MS

A gradient LC–MS method was developed for the identification and characterization of degradants of moexipril using liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS). Moexipril was subjected to hydrolysis (acid, base and neutral), oxidation, photolytic and thermal degradation conditions as mentioned in ICH guidelines Q1A (R2). The drug degraded under hydrolysis, oxidation and photolytic conditions, but it was stable under thermal conditions. In total, five degradants were formed and separated on an Agilent XDB C‐18 column (4.6 × 150 mm, 5 μm) in a gradient elution method. Four degradants ( D1 , D2 , D4 and D5 ) under acidic conditions, three degradants ( D2 , D3 and D4 ) under basic conditions and three degradants ( D1 , D4 and D5 ) under neutral and oxidative stress conditions were formed. In addition, two degradants ( D4 and D5 ) were formed under photolytic stress conditions. To elucidate the structures of degradants, fragmentation of moexipril and its degradants was studied using LC–MS/MS experiments and accurate mass measurements (HRMS) data. The fragment ions in the product ion tandem mass spectra of all the degradants were compared with those of moexipril and assigned the probable structures for the degradants.     

The structure of the water–propane interface investigated by x‐ray reflectivity measurements

We present an x‐ray reflectivity study of the water–propane interface. The vertical structure of the interface is analyzed and the adsorption of thin layers of propane on the water surface is observed. An increase of layer thickness with rising pressure is found. The electron density of the thin films is identical with the corresponding value of bulk liquid propane. From the adsorption isotherm we determine the Hamaker constant of the system, which shows a considerably higher value compared to calculations based on the Lifshitz theory. The surface tension of the molecularly thin layer is reduced in comparison to the bulk value. The measured surface roughness is in good agreement with a modified model based on capillary wave fluctuations of the water‐propane–gas interfaces. Copyright © 2008 John Wiley & Sons, Ltd.     

3D Photofixation Lithography in Diels–Alder Networks

3D structures are written and developed in a crosslinked polymer initially formed by a Diels–Alder reaction. Unlike conventional liquid resists, small features cannot sediment, as the reversible crosslinks function as a support, and the modulus of the material is in the MPa range at room temperature. The support structure, however, can be easily removed by heating the material, and depolymerizing the polymer into a mixture of low‐viscosity monomers. Complex shapes are written into the polymer network using two‐photon techniques to spatially control the photoinitiation and subsequent thiol–ene reaction to selectively convert the Diels–Alder adducts into irreversible crosslinks.     

Geometric similarity between protein–RNA interfaces

A new method is described to measure the geometric similarity between protein–RNA interfaces quantitatively. The method is based on a procedure that dissects the interface geometry in terms of the spatial relationships between individual amino acid nucleotide pairs. Using this technique, we performed an all‐on‐all comparison of 586 protein–RNA interfaces deposited in the current Protein Data Bank, as the result, an interface–interface similarity score matrix was obtained. Based upon this matrix, hierarchical clustering was carried out which yielded a complete clustering tree for the 586 protein–RNA interfaces. By investigating the organizing behavior of the clustering tree and the SCOP classification of protein partners in complexes, a geometrically nonredundant, diverse data set (representative data set) consisting of 45 distinct protein–RNA interfaces was extracted for the purpose of studying protein–RNA interactions, RNA regulations, and drug design. We classified protein–RNA interfaces into three types. In type I, the families and interface structural classes of the protein partners, as well as the interface geometries are all similar. In type II, the interface geometries and the interface structural classes are similar, whereas the protein families are different. In type III, only the interface geometries are similar but the protein families and the interface structural classes are distinct. Furthermore, we also show two new RNA recognition themes derived from the representative data set. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

Ion‐Pair‐Based Assemblies Comprising Pyrrole–Pyrazole Hybrids

Modified 3,5‐dipyrrolylpyrazole (DPP) derivatives in their protonated form produce planar [2+2]‐type complexes with trifluoroacetate (TFA) ions. These complexes serve as constituent components of ion‐pair‐based assemblies. An essential strategy for the construction of dimension‐controlled organized structures based on these [2+2]‐type complexes is the introduction of aryl rings bearing long alkyl chains, which enables the formation of 2D patterns at interfaces, supramolecular gels, and mesophases.     

Cu Nanoparticles Electrodeposited at Liquid–Liquid Interfaces: A Highly Efficient Catalyst for the Hydrogen Evolution Reaction

The electrochemical deposition of Cu nanoparticles with an average diameter of approximately 25–35 nm has been reported at liquid–liquid interfaces by using the organic‐phase electron‐donor decamethylferrocene (DMFc). The electrodeposited Cu nanoparticles display excellent catalytic activity for the hydrogen evolution reaction (HER); this is the first reported catalytic effect of Cu nanoparticles at liquid–liquid interfaces.     

Nanostructures of polyelectrolyte gel–surfactant complexes

Small‐angle X‐ray scattering was used to investigate the nanostructures of complexes formed by slightly crosslinked anionic copolymer gels of poly(sodium methacrylate‐co‐N‐isopropylacrylamide) [P(MAA/NIPAM)] with cetyltrimethylammonium bromide (CTAB), and didodecyldimethylammonium bromide (DDAB), respectively, at room temperature (∼ 23°C). Several highly ordered supramolecular structures were observed in the polyelectrolyte gel–surfactant complexes. In P(MAA/NIPAM)–CTA systems, in sequence with decreasing charge density of the P(MAA/NIPAM) copolymer chains, structures of the Pm3n space group cubic, face‐centered cubic close packing of spheres, and hexagonal close packing of spheres were determined at a charge content of ≥ 75, 67, and 50%, respectively. The spheres and rods in these structures were the spherical and cylindrical micelles formed by the self‐assembly of CTA cations with their paraffin chains inside. Both the aggregation number and the size of the micelles decreased with a decreasing charge density of the copolymer chains. In the P(MAA/NIPAM)–DDA systems, the bilayer lamellar structures formed at charge contents ≥ 75% transferred to bicontinuous cubic structures of the Ia3d space group at charge contents of 50–67%. The rods in the Ia3d cubic structures were formed by the self‐assembly of double‐tailed DDA cations with polar moieties inside. The formation of these highly ordered structures were driven by both electrostatic and hydrophobic interactions of the charged copolymer chains/surfactants and the surfactants/surfactants inside the charged gels. The structures became less ordered by further decreasing the charge content of the P(MAA/NIPAM) chains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2165–2172, 1999