Features Unique Properties Research Articles

Defect engineering enables synergistic action of hierarchical porosity and multifunctionality for efficient catalysis of diverse reactions

The limitations of embedding suitable functional groups as Brønsted and Lewis pairs in metal–organic materials hinder their application especially to promote catalysis reactions. Due to the generation abundance of unsaturated inorganic nodes upon partial ligand decarboxylation, Quasi-MOFs (Q-MOFs) are considered as a potential candidate for the installation of amino acids. Here for the first time, we demonstrated that Q-HKUST-1 possessing a Lewis acid site could be transformed into an excellent multifunctional chiral MOF (Q-HKUST-Cys), via post-synthetic modification by L-Cysteine. Applying this approach, we can fabricate a pore environment spatially decorated with multiple functional groups. The post-modified MOF has been characterized by a variety of techniques including PXRD, N2 sorption, 1HNMR, FT-IR, CD, and SEM/EDS mapping. Q-HKUST-Cys features unique properties, such as mesoporosity, high Lewis acid sites including Cu2+, Lewis base sites (NH2 group), Bronsted acid sites (COOH group), open channels, and optical activity. So, this chiral MOF exhibits excellent catalytic performance in various asymmetric reactions under mild conditions. The Q-HKUST-Cys is highly enantioselective heterogeneous and recyclable catalyst, in ring-opening of epoxide and nitroaldol reaction with up to 99 % ee, as well as 100 % and 90 % conversion, respectively. Besides, in the cycloaddition of CO2 to styrene-epoxide (STO), and production of the corresponding cyclic carbonate, this catalyst showed high performance (90 % conversion, 89 % ee) under mild conditions, at the atmospheric pressure of CO2 and in the solvent-free situation. The simultaneous presence of these properties makes Q-HKUST-Cys an attractive catalyst for the eco-friendly synthesis of fine chemicals through CC and CO bond formation. As a result, in this study, we showed that anchoring defective MOFs with multifunctional amino acids can be an effective approach for the utilization of synergistic effects in the promotion of many catalysis reactions.

A Dual-Purpose Ce(III)-Organic Framework with Amine Groups and Open Metal Sites: Third-Order Nonlinear Optical Activity and Catalytic CO2 Fixation.

The present work focuses on the synthesis and properties of a novel multifunctional cerium(III) MOF, [Ce2(data)3(DMF)4]·DMF (data2-: 2,5-diaminoterephthalate), abbreviated as NH2-Ce-MUM-2. Its crystal structure reveals an intricate 3D 4,5-connected framework with a xah topology. This MOF features unique properties, such as open metal sites, presence of free amino groups, and high stability. Two main applications of NH2-Ce-MUM-2 were investigated: (i) as a heterogeneous catalyst in the CO2 fixation into cyclic carbonates and (ii) as a material with third-order nonlinear optical activity. As a model reaction, the cycloaddition of CO2 to propylene oxide to give the corresponding cyclic carbonate was explored under mild conditions, at the atmospheric pressure of carbon dioxide and in the absence of cocatalyst and added solvent. Various reaction parameters were investigated toward optimization and exploration of substrate scope, revealing up to 99% product yields of cyclic carbonate products. Besides, the structure of NH2-Ce-MUM-2 is highly stable, permitting its recyclability and reusability in further catalytic experiments. The significant contributions of free amino groups and open metal sites within this catalyst were particularly considered when proposing a potential mechanism for the reaction. Z-Scan measurements were used to evaluate the nonlinear optical (NLO) properties of NH2-Ce-MUM-2 at various laser intensities. A high two-photon absorption (TPA) under greater incident intensities shows that NH2-Ce-MUM-2 might be applicable in optical switching devices. Besides, the self-focusing effects of NH2-Ce-MUM-2 under various incident intensities were highlighted by the nonlinear index of refraction (n2). By reporting the synthesis and characterization of a novel MOF, along with its highly promising catalytic and NLO behavior, the current study introduces an additional example of multifunctional material into a growing family of metal-organic frameworks.

Biomechanical and Biological Characterization of XGel, a Human-Derived Hydrogel for Stem Cell Expansion and Tissue Engineering.

Hydrogels are 3D scaffolds used as alternatives to in vivo models for disease modeling and delivery of cells and drugs. Existing hydrogel classifications include synthetic, recombinant, chemically defined, plant- or animal-based, and tissue-derived matrices. There is a need for materials that can support both human tissue modeling and clinically relevant applications requiring stiffness tunability. Human-derived hydrogels are not only clinically relevant, but they also minimize the use of animal models for pre-clinical studies. This study aims to characterize XGel, a new human-derived hydrogel as an alternative to current murine-derived and synthetic recombinant hydrogels that features unique physiochemical, biochemical, and biological properties that support adipocyte and bone differentiation. Rheology studies determine the viscosity, stiffness, and gelation features of XGel. Quantitative studies for quality control support consistency in the protein content between lots. Proteomics studies reveal that XGel is predominantly composed of extracellular matrix proteins, including fibrillin, collagens I-VI, and fibronectin. Electron microscopy of the hydrogel provides phenotypic characteristics in terms of porosity and fiber size. The hydrogel demonstrates biocompatibility as a coating material and as a 3D scaffold for the growth of multiple cell types. The results provide insight into the biological compatibility of this human-derived hydrogel for tissue engineering.

Advances in Graphene Based MEMS and Nems Devices: Materials, Fabrication, and Applications

Microelectromechanical systems (MEMS) are generally known as miniaturized mechanical and electro-mechanical systems, whereas NEMS stands for nanoelectromechanical systems. Graphene is an atomically thin material that features unique properties, such as high carrier mobility, high mechanical strength, and piezoresistive electromechanical transduction, which makes it an extremely promising material for future MEMS and NEMS devices. Design and fabrication of MEMS/NEMS devices using graphene process includes trench etching, wafer backside etching, graphene transfer, and mass release, which are described in a comprehensive manner. This review provides interesting perspectives for lock-in detection of weak fluorescent signals, NEMS position detection, electromechanical control of the on-chip transmitter, and single-photon-level fast electromechanical optical modulation. There are various applications of MEMS/NEMS devices, namely radio frequency devices, optic NEMS, pressure sensors, inertial sensors, which have been discussed in detail. The review mainly focusses on the devices made up of graphene (atom-layer distance of ~0.335 nm) as a main electronic/mechanical material due to its remarkable mechanical and electrical (Young’s modulus of up to ~1 TPa cm2Vs-1) and charge-carrier mobility of up to 200,000, which makes it an extremely promising membrane and transducer material for MEMS/NEMS system applications. Modern MEMS/NEMS experiments utilize mechanical resonators to push the bounds of force and mass sensing, demonstrate novel electromechanical circuit applications, measure the structural properties of materials are also covered in this review.

Development of high entropy alloys for brazing applications

High entropy alloys are novel and innovative metallic materials, which have intensively moved into the focus of research over the last decade. The high entropy effect in those multi-component alloys promotes the formation of a characteristic crystal structure, the random solid solution, which features unique material properties, and reduces the number of possible brittle phases. In this publication, the influence of gallium as a melting point depressant on the melting range and the microstructure of the two-phased equimolar CoCrCoFeNi were determined. In order to integrate the vacuum brazing process into the solutioning heat treatment of the nickel-based super alloy Mar-M 247 between 1180 and 1270 °C, the liquidus temperature of CoCrCoFeNi was aimed to be below 1270 °C. The changes in the melting ranges due to the modified compositions were predicted by CALPHAD simulations and verified by differential thermal analysis measurements. The promising multi-component filler alloy CoCrCuFeNiGa was determined for further investigations. For this purpose, the microstructures of the filler metal itself and the brazement were conducted. A shear strength of 388 ± 73 MPa was achieved for a brazing gap of 200 μm. The crack, which led to joint failure propagated through high-entropic, fcc-structured phases in the brazing seam.

Suspended Graphene Membranes with Attached Silicon Proof Masses as Piezoresistive Nanoelectromechanical Systems Accelerometers.

Graphene is an atomically thin material that features unique electrical and mechanical properties, which makes it an extremely promising material for future nanoelectromechanical systems (NEMS). Recently, basic NEMS accelerometer functionality has been demonstrated by utilizing piezoresistive graphene ribbons with suspended silicon proof masses. However, the proposed graphene ribbons have limitations regarding mechanical robustness, manufacturing yield, and the maximum measurement current that can be applied across the ribbons. Here, we report on suspended graphene membranes that are fully clamped at their circumference and have attached silicon proof masses. We demonstrate their utility as piezoresistive NEMS accelerometers, and they are found to be more robust, have longer life span and higher manufacturing yield, can withstand higher measurement currents, and are able to suspend larger silicon proof masses, as compared to the previous graphene ribbon devices. These findings are an important step toward bringing ultraminiaturized piezoresistive graphene NEMS closer toward deployment in emerging applications such as in wearable electronics, biomedical implants, and internet of things (IoT) devices.

Spin transport in the bulk of two-dimensional Hall insulator

Magneto-fermionic condensate under study is a Bose-Einstein condensate of cyclotron spin-flip magnetoexcitons in a quantum Hall insulator. This condensate features unique properties such as millisecond range lifetime and hundreds of micrometers of propagation length. In this study, utilizing the photo-induced resonant reflection technique, we measured the exciton escape time. Finally, we estimated the exciton condensate propagation velocity as 25 m/s, which is much higher than a single particle propagation velocity. We also proposed a mechanism of exciton condensation.

Trace Amount of Platinum Supported on Carbonized Biomorphic Wood for Efficient Electrochemical Hydrogen Evolution in Alkaline Condition

AbstractCarbonized biomorphic wood (Bio‐C), which features unique properties such as highly ordered microtexture, well‐developed porous structure, and low charge transfer resistance, was prepared as a promising scaffold with trace amount of platinum (Pt) supported to efficiently electrocatalyze hydrogen evolution reaction (HER). Pt/Bio‐C nanocomposites demonstrated superior HER activity with a current density reaching as high as ∼58 mA cm−2 at −0.2 V vs. reversible hydrogen electrode (RHE) in strongly alkaline condition.

Influence of a Novel Dimeric Ceramide Molecule on the Nanostructure and Thermotropic Phase Behavior of a Stratum Corneum Model Mixture.

The stratum corneum (SC) is the outermost layer of the skin and is composed of a multilayered assembly of mostly ceramids (Cer), free fatty acids, cholesterol (Chol), and cholesterol sulfate (Chol-S). Because of the tight packing of these lipids, the SC features unique barrier properties defending the skin from environmental influences. Under pathological conditions, where the skin barrier function is compromised, topical application of molecules that rigidify the SC may lead to a restored barrier function. To this end, molecules are required that incorporate into the SC and bring back the original rigidity of the skin barrier. Here, we investigated the influence of a novel dimeric ceramide (dim-Cer) molecule designed to feature a long, rigid hydrocarbon chain ideally suited to forming an orthorhombic lipid phase. The influence of this molecules on the thermotropic phase behavior of a SC mixture consisting of Cer[AP18] (55 wt %), cholesterol (Chol, 25 wt %), steric acid (SA, 15 wt %), and cholesterol sulfate (Chol-S, 5 wt %) was studied using a combination of neutron diffraction and 2H NMR spectroscopy. These methods provide detailed insights into the packing properties of the lipids in the SC model mixture. Dim-Cer remains in an all-trans state of the membrane-spanning lipid chain at all investigated temperatures, but the influence on the phase behavior of the other lipids in the mixture is marginal. Biophysical experiments are complemented by permeability measurements in model membranes and human skin. The latter, however, indicates that dim-Cer only partially provides the desired effect on membrane permeability, necessitating further optimization of its structure for medical applications.

Plasmonic Organic Hybrid Modulators—Scaling Highest Speed Photonics to the Microscale

Complementing plasmonic slot waveguides with highly nonlinear organic materials has rendered a new generation of ultracompact active nanophotonic components that are redefining the state of the art. In this paper, we review the fundamentals of this so-called plasmonic- organic-hybrid (POH) platform. Starting from simple phase shifters to the most compact IQ modulators, we introduce key devices of high-speed data communications. For instance, all-plasmonic Mach-Zehnder modulators (MZMs) are reviewed and long-term prospects are discussed. This kind of modulator already features unique properties such as a small footprint (<; 20 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), a large electro-optic bandwidth (> 110 GHz), a small energy consumption (~25 fJ/b), a large extinction ratio (> 25 dB) in combination with a record small voltage-length product of 40 Vμm. Finally, as an example for seamless integration we introduce novel plasmonic IQ modulators. With such modulators we show the generation of advanced modulation formats (QPSK, 16-QAM) on footprints as small as 10 μm × 75 μm. This demonstration ultimately shows how plasmonics can be used to control both phase and amplitude of an optical carrier on the microscale with reasonably low losses.

Design of heterogeneous multicore fibers as sampled true-time delay lines.

We present a novel procedure for designing a sampled discrete true-time delay line (TTDL) for Microwave Photonics applications based on a heterogeneous MCF. Both simple step-index (SI) and trench-assisted SI profiles are numerically evaluated in terms of physical dimensions and material dopant concentrations in order to individually tailor the group delay and chromatic dispersion of each core. The proposed TTDL features unique properties beyond the current state of the art in terms of record bandwidth, compactness, flexibility, and versatility.

Absorbable Polymer Technology - Viable Solutions for Unmet Needs in PCI: Proceedings of two satellite symposia held at EuroPCR, Paris in May 2015.

The use of drug-eluting stents (DES) has improved clinical outcomes in percutaneous coronary intervention procedures, but many challenges remain. In two symposia at EuroPCR 2015, the factors necessary to ensure successful chronic total occlusion (CTO) intervention were presented. Good preparation, sufficient operator experience and the correct approach are key to the success of CTO interventions. A live case demonstrated the challenges of these complex cases. Stent choice in CTO interventions is crucial; second-generation DES are associated with lower rates of restenosis and re-occlusion compared with first-generation DES. The Coracto™ DES features unique structural properties and rapidly absorbable polymer, resulting in excellent conformability, efficacy and safety.

Demonstration of slow sound propagation and acoustic transparency with a series of detuned resonators

We present experimental results demonstrating the phenomenon of acoustic transparency with a significant slowdown of sound propagation realized with a series of paired detuned acoustic resonators (DAR) side-attached to a waveguide. The phenomenon mimics the electromagnetically induced transparency in atomic physics. By arranging four identical DAR pairs along the waveguide with an equal subwavelength separation between adjacent pairs, we show that this arrangement features unique properties of narrow-band transmission and strong dispersion. In particular, we demonstrate side-lobe suppression of more than 20 dB on both sides of the transparency window, and we quantify directly (using a pulse propagation) the acoustic slowdown effect, resulting in the sound group velocity of \ensuremath{\sim}9.8 m/s (i.e. in the group refractive index of 35). We find very similar values of the group refractive index by using measurements of the phase of the transmitted wave. It is also shown that a direct coupling exists between the DAR in each pair, which cannot be explained by the interference of waves radiated from those resonators. This detrimental coupling becomes noticeable for small values of detuning and also if the cross-sectional area of the neck of the resonators is increased.

Tuning molecular interactions in lipid-oligonucleotides assemblies via locked nucleic acid (LNA)-based lipids

Hybrid nucleotide-lipids containing locked nucleic acid (LNA) show enhanced hybridization properties with complementary single strand RNAs compared to DNA lipid analogues. The LNA adenosine lipid features unique binding properties with a high binding affinity for poly-uridine and the entropically driven formation of a stable complex (K(d) ≈ 43 nM). Enhanced hybridization properties of LNA-based lipids should be applicable for the development of oligonucleotide (ON) delivery systems or as small molecule binders to RNA for novel therapeutic strategies.

Annuitization and Cross-Subsidies in the Swiss System of Retirement Savings

The Swiss second pillar of retirement saving features unique properties and remarkable outcomes. These include both high levels of savings and (unforced) annuitization, as well as a non-trivial level of internal cross-subsidies between the two tiers of the system. We formulate a quantitative model of financial flows within this system. We then analyze the significant cross-subsidies in Switzerland's system and discuss their interaction with the high level of annuitization. We also touch on some of the issues the Swiss system is currently facing. Furthermore, we discuss how this extraordinary system can be seen as a generalization of the World Bank (1994) plain vanilla system of forced savings. This broader model consists of two tiers of second pillar savings together with gazetted annuity rates which allow for internal cross-subsidies that can be used to encourage annuitization in one of the tiers.

Meso-origami: Folding multilayer graphene sheets

Graphene features unique electronic, thermal, and mechanical properties, and the flexibility and strong attraction between graphene layers promotes the formation of self-folded nanostructures. Here we study the self-folding of mono- and multilayer graphene sheets, utilizing a coarse-grained hierarchical multiscale model derived directly from atomistic simulation. Our model, developed by enforcing assertion of energy conservation, enables the simulation of graphene folding across a range of length scales from nanometers to micrometers. Through theoretical and simulation analysis we show that the critical self-folded length is πC/γ, where C and γ are the bending stiffness per unit length and the surface energy per unit length.

On a Generalization of the World Bank Model of Retirement Savings: A Taxonomy of Systems with Two Cross-Subsidized Tiers

We develop a generalization of the World Bank (1994) model of forced saving for retirement. This broader model consists of two tiers of second pillar savings --- mandated and non-mandated (voluntary). Furthermore, the government can set two types of guarantees on the first (mandated) tier --- investment returns and annuity prices --- leading to possible cross-subsidization between the tiers. This has the potential to induce social redistribution, foster a liquid private market for life annuities, as well as obviate some of the investment risk and annuity price risk that retirees face. We formulate a quantitative model of financial flows within such a system, which explains the mechanism by which cross-subsidization occurs. Based on this analysis, a taxonomy of two-tiered retirement systems is presented, that is based on the choices that the government makes. Our modelling is inspired by the Swiss second pillar model, which serves as a motivation and illustration. The Swiss system features unique properties and remarkable outcomes. These include both high levels of savings and (unforced) annuitization, as well as a non-trivial level of internal cross-subsidies between the two tiers of the system. The analysis allows us to shed some light on some of the issues the Swiss system is currently facing.

The CXCL12γ Chemokine Displays Unprecedented Structural and Functional Properties that Make It a Paradigm of Chemoattractant Proteins

The CXCL12γ chemokine arises by alternative splicing from Cxcl12, an essential gene during development. This protein binds CXCR4 and displays an exceptional degree of conservation (99%) in mammals. CXCL12γ is formed by a protein core shared by all CXCL12 isoforms, extended by a highly cationic carboxy-terminal (C-ter) domain that encompass four overlapped BBXB heparan sulfate (HS)-binding motifs. We hypothesize that this unusual domain could critically determine the biological properties of CXCL12γ through its interaction to, and regulation by extracellular glycosaminoglycans (GAG) and HS in particular. By both RT-PCR and immunohistochemistry, we mapped the localization of CXCL12γ both in mouse and human tissues, where it showed discrete differential expression. As an unprecedented feature among chemokines, the secreted CXCL12γ strongly interacted with cell membrane GAG, thus remaining mostly adsorbed on the plasmatic membrane upon secretion. Affinity chromatography and surface plasmon resonance allowed us to determine for CXCL12γ one of the higher affinity for HS (Kd = 0.9 nM) ever reported for a protein. This property relies in the presence of four canonical HS-binding sites located at the C-ter domain but requires the collaboration of a HS-binding site located in the core of the protein. Interestingly, and despite reduced agonist potency on CXCR4, the sustained binding of CXCL12γ to HS enabled it to promote in vivo intraperitoneal leukocyte accumulation and angiogenesis in matrigel plugs with much higher efficiency than CXCL12α. In good agreement, mutant CXCL12γ chemokines selectively devoid of HS-binding capacity failed to promote in vivo significant cell recruitment. We conclude that CXCL12γ features unique structural and functional properties among chemokines which rely on the presence of a distinctive C-ter domain. The unsurpassed capacity to bind to HS on the extracellular matrix would make CXCL12γ the paradigm of haptotactic proteins, which regulate essential homeostatic functions by promoting directional migration and selective tissue homing of cells.

The Novel CXCL12γ Isoform Encodes an Unstructured Cationic Domain Which Regulates Bioactivity and Interaction with Both Glycosaminoglycans and CXCR4

BackgroundCXCL12α, a chemokine that importantly promotes the oriented cell migration and tissue homing of many cell types, regulates key homeostatic functions and pathological processes through interactions with its cognate receptor (CXCR4) and heparan sulfate (HS). The alternative splicing of the cxcl12 gene generates a recently identified isoform, CXCL12γ, which structure/function relationships remain unexplored. The high occurrence of basic residues that characterize this isoform suggests however that it could feature specific regulation by HS.Methodology/Principal FindingsUsing surface plasmon resonance and NMR spectroscopy, as well as chemically and recombinantly produced chemokines, we show here that CXCL12γ first 68 amino acids adopt a structure closely related to the well described α isoform, followed by an unfolded C-terminal extension of 30 amino acids. Remarkably, 60 % of these residues are either lysine or arginine, and most of them are clustered in typical HS binding sites. This provides the chemokine with the highest affinity for HP ever observed (Kd = 0.9 nM), and ensures a strong retention of the chemokine at the cell surface. This was due to the unique combination of two cooperative binding sites, one strictly required, found in the structured domain of the protein, the other one being the C-terminus which essentially functions by enhancing the half life of the complexes. Importantly, this peculiar C-terminus also regulates the balance between HS and CXCR4 binding, and consequently the biological activity of the chemokine.Conclusions/SignificanceTogether these data describe an unusual binding process that gives rise to an unprecedented high affinity between a chemokine and HS. This shows that the γ isoform of CXCL12, which features unique structural and functional properties, is optimized to ensure its strong retention at the cell surface. Thus, depending on the chemokine isoform to which it binds, HS could differentially orchestrate the CXCL12 mediated directional cell kinesis.

Unique supramolecular assembly of a redox protein with nucleic acids onto hybrid bilayer: towards a dynamic DNA chip

Highly controlled supramolecular assemblies combining a genetically engineered redox protein, cytochrome b5, and modified oligonucleotides are presented. Modified b5 and DNA are covalently assembled through a hetero bifunctional cross-linker to give a unique hybrid molecular species. Moreover, the assembly includes a histidine tag head able to bind to modified phospholipids which lead to a new generation of self-assembled dynamic DNA chips. The interaction of the construction with a complementary oligonucleotide sequence can be monitored in real time by surface plasmon resonance using Biacore technology. The biochip, presented herein, features unique properties including tunable surface density of probes, very low non-specific interactions and optimization of hybridization efficiency. In addition, we demonstrated that the phase transition of the lipidic layer can modulate the dynamic of the association of the complex to the supported membrane. Potential applications of this new device are multiple including high sensitivity and high selectivity biochips, especially for studies of the DNA-ligands interactions in a biomimetic environment.