Comparative study of materials-binding peptide interactions with gold and silver surfaces and nanostructures : A thermodynamic basis for biological selectivity of inorganic materials

Controllable 3D assembly of multicomponent inorganic nanomaterials by precisely positioning two or more types of nanoparticles to modulate their interactions and achieve multifunctionality remains a major challenge. The diverse chemical and structural features of biomolecules can generate the compositionally specific organic/inorganic interactions needed to create such assemblies. Toward this aim, we studied the materials-specific binding of peptides selected based upon affinity for Ag (AgBP1 and AgBP2) and Au (AuBP1 and AuBP2) surfaces, combining experimental binding measurements, advanced molecular simulation, and nanomaterial synthesis. This reveals, for the first time, different modes of binding on the chemically similar Au and Ag surfaces. Molecular simulations showed flatter configurations on Au and a greater variety of 3D adsorbed conformations on Ag, reflecting primarily enthalpically driven binding on Au and entropically driven binding on Ag. This may arise from differences in the interfacial solvent structure. On Au, direct interaction of peptide residues with the metal surface is dominant, while on Ag, solvent-mediated interactions are more important. Experimentally, AgBP1 is found to be selective for Ag over Au, while the other sequences have strong and comparable affinities for both surfaces, despite differences in binding modes. Finally, we show for the first time the impact of these differences on peptide mediated synthesis of nanoparticles, leading to significant variation in particle morphology, size, and aggregation state. Because the degree of contact with the metal surface affects the peptide's ability to cap the nanoparticles and thereby control growth and aggregation, the peptides with the least direct contact (AgBP1 and AgBP2 on Ag) produced relatively polydispersed and aggregated nanoparticles. Overall, we show that thermodynamically different binding modes at metallic interfaces can enable selective binding on very similar inorganic surfaces and can provide control over nanoparticle nucleation and growth. This supports the promise of bionanocombinatoric approaches that rely upon materials recognition.

Sulfur-doped porous reduced graphene oxide hollow nanosphere frameworks as metal-free electrocatalysts for oxygen reduction reaction and as supercapacitor electrode materials.

Chemical doping with foreign atoms is an effective approach to significantly enhance the electrochemical performance of the carbon materials. Herein, sulfur-doped three-dimensional (3D) porous reduced graphene oxide (RGO) hollow nanosphere frameworks (S-PGHS) are fabricated by directly annealing graphene oxide (GO)-encapsulated amino-modified SiO2 nanoparticles with dibenzyl disulfide (DBDS), followed by hydrofluoric acid etching. The XPS and Raman spectra confirmed that sulfur atoms were successfully introduced into the PGHS framework via covalent bonds. The as-prepared S-PGHS has been demonstrated to be an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR) with the activity comparable to that of commercial Pt/C (40%) and much better methanol tolerance and durability, and to be a supercapacitor electrode material with a high specific capacitance of 343 F g(-1), good rate capability and excellent cycling stability in aqueous electrolytes. The impressive performance for ORR and supercapacitors is believed to be due to the synergistic effect caused by sulfur-doping enhancing the electrochemical activity and 3D porous hollow nanosphere framework structures facilitating ion diffusion and electronic transfer.

Carbon nanotube based elastomer composites-an approach towards multifunctional materials

The current study focuses on giving a basic understanding of tubular graphene sheets or carbon nanotubes (CNTs) and points towards their role in fabricating elastomer composites. Since the properties and the performance of CNT reinforced elastomer composites predominantly depend on the rate of dispersion of fillers in the matrix, the physical and chemical interaction of polymer chains with the nanotubes, crosslinking chemistry of rubbers and the orientation of the tubes within the matrix, here, a thorough study of these topics is carried out. For this, various techniques of composite manufacturing such as pulverization, heterocoagulation, freeze drying, etc. are discussed by emphasizing the dispersion and alignment of CNTs in elastomers. The importance of the functionalization technique as well as the confinement effect of nanotubes in elastomer media is derived. In a word, this article is aimed exclusively at addressing the prevailing problems related to the CNT dispersion in various rubber matrices, the solutions to produce advanced high-performance elastomeric composites and various fields of applications of such composites, especially electronics. Special attention has also been given to the non-linear viscoelasticity effects of elastomers such as the Payne effect, Mullin's effect and hysteresis in regulating the composite properties. Moreover, the current challenges and opportunities for efficiently translating the extraordinary electrical properties of CNTs to rubbery matrices are also dealt with.

Electrochemical performance of LiFe1-xMnxPO4/C materials prepared by ball milling

LiFe1-xMnxPO4/C composite materials as cathode materials in Li-ion batteries have been synthesised and their electrochemical properties have been investigated. The samples were synthesised by using high energy ball milling of commercially available precursors (Li2C2O4, FeC2O4.2H2O, MnC2O4.2H2O, NH4H2PO4) and then heated at 600°C. The morphology and structure of the heated samples were analysed by means of SEM and X-ray diffraction. The olivine structure of the LiFe1-xMnxPO4/C composite was obtained. A slight shift of the peaks to smaller 2θ angles with the increasing Mn/Fe ratios is observed due to the increase in lattice parameters. The influence of different Mn/Fe ratios on electrical and electrochemical performances were studied by charge-discharge and cyclic voltammetry (CV) testing. The CV curves of the pure LiFePO4 and LiMnPO4 show the expected Fe2+/Fe3+ peak around 3·5 V and Mn2+/Mn3+ peak around 4·1 V, respectively. The addition of manganese increases the discharge voltage from 3·5 to 4·1 V.

Developments in machining of stacked materials made of CFRP and titanium/aluminum alloys

The aim of this article is to investigate the drilling of carbon fiber-reinforced plastic (CFRP) composite/metal stack-ups to have a details picture of the developments in this complex area. The forces and torque, chip shape, surface finish and geometry, and tool material and tool wear for drilling composite/metal stack-ups have been analyzed in details in addition to drilling mechanism of CFRP. The relation between input and output parameters was discussed and the trend of input parameters for damage free and tight tolerance holes has been investigated based on the literature. The main findings are (i) heat, built-up edge and chips generated from drilling of metallic layers damages CFRP surface, (ii) order of material layers affects the drilling outcomes significantly, (iii) coatings and step-shape on the cutting tool improves the tool performance, (iv) tool materials should be selected based on the material of metallic layer, (v) chipping, adhesion, abrasion and attrition are main tool wear mechanisms during machining of CFRP/metal stacks and (vi) application of coolant improves the machinability.

Effect of sintering temperature on electrochemical performance of LiFe0·4Mn0·6PO4/C cathode materials

Carbon coated LiFe0·4Mn0·6PO4 (LiFe0·4Mn0·6PO4/C) was synthesised using high energy ball milling and annealing processes. The starting materials of Li2C2O4, FeC2O4.2H2O, MnC2O4.2H2O, NH4H2PO4 were firstly milled for 40 h, and followed by further milling for 5 h after adding glucose solution. The milled sample was heated at different temperatures (550, 600, 650 and 700°C) for 10 h to produce LiFe0·4Mn0·6PO4/C composites. The structure and morphology of the samples were investigated using X-ray diffraction, field emission scanning electron microscopy, and high resolution electron microscopy. The phase of samples annealed at 550 and 600°C mainly consists of olivine type LiFePO4, but a small amount of Fe2P impurity phase is formed in the samples annealed at 650 and 700°C. Electrochemical analysis results show that LiFe0·4Mn0·6PO4/C synthesised at 600°C exhibits the best performance with the initial discharge capacity of 128 mAh g-1 at 0·1 C, and 109 mAh g-1 at 1 C after 500 cycles. The LiFe0·4Mn0·6PO4/C exhibits excellent electrochemical properties for high energy density lithium ion batteries.

Observation of active sites for oxygen reduction reaction on nitrogen-doped multilayer graphene

Active sites and the catalytic mechanism of nitrogen-doped graphene in an oxygen reduction reaction (ORR) have been extensively studied but are still inconclusive, partly due to the lack of an experimental method that can detect the active sites. It is proposed in this report that the active sites on nitrogen-doped graphene can be determined via the examination of its chemical composition change before and after ORR. Synchrotron-based X-ray photoelectron spectroscopy analyses of three nitrogen-doped multilayer graphene samples reveal that oxygen reduction intermediate OH(ads), which should chemically attach to the active sites, remains on the carbon atoms neighboring pyridinic nitrogen after ORR. In addition, a high amount of the OH(ads) attachment after ORR corresponds to a high catalytic efficiency and vice versa. These pinpoint that the carbon atoms close to pyridinic nitrogen are the main active sites among the different nitrogen doping configurations.

Toward design of synergistically active carbon-based catalysts for electrocatalytic hydrogen evolution

Replacement of precious Pt catalyst with cost-effective alternatives would be significantly beneficial for hydrogen production via electrocatalytic hydrogen evolution reaction (HER). All candidates thus far are exclusively metallic catalysts, which suffer inherent corrosion and oxidation susceptibility during acidic proton-exchange membrane electrolysis. Herein, based on theoretical predictions, we designed and synthesized nitrogen (N) and phosphorus (P) dual-doped graphene as a nonmetallic electrocatalyst for sustainable and efficient hydrogen production. The N and P heteroatoms could coactivate the adjacent C atom in the graphene matrix by affecting its valence orbital energy levels to induce a synergistically enhanced reactivity toward HER. As a result, the dual-doped graphene showed higher electrocatalytic HER activity than single-doped ones and comparable performance to some of the traditional metallic catalysts.

Strong oxidation resistance of atomically thin boron nitride nanosheets

Investigation of oxidation resistance of two-dimensional (2D) materials is critical for many of their applications because 2D materials could have higher oxidation kinetics than their bulk counterparts due to predominant surface atoms and structural distortions. In this study, the oxidation behavior of high-quality boron nitride (BN) nanosheets of 1-4 layers thick has been examined by heating in air. Atomic force microscopy and Raman spectroscopy analyses reveal that monolayer BN nanosheets can sustain up to 850 °C, and the starting temperature of oxygen doping/oxidation of BN nanosheets only slightly increases with the increase of nanosheet layer and depends on heating conditions. Elongated etch lines are found on the oxidized monolayer BN nanosheets, suggesting that the BN nanosheets are first cut along the chemisorbed oxygen chains and then the oxidative etching grows perpendicularly to these cut lines. The stronger oxidation resistance of BN nanosheets makes them more preferable for high-temperature applications than graphene.

The addition of a surfactant at regular time intervals in the mechanical alloying process

The impact of regular additions of a surfactant (ethylene bis-stearamide; EBS) at different time intervals was investigated on the powder characteristics of a biomedical Ti-10Nb-3Mo alloy (wt.%). Ball milling was performed for 10 h on the elemental powders in four series of experiments at two rotation speeds (200 and 300 rpm). The addition of 2 wt.% total EBS at different time intervals during ball milling resulted in noticeable changes in particle size and morphology of the powders. The surfactant addition at shorter time intervals led to the formation of finer particles, a more homogenous powder distribution, a higher powder yield, and a lower contamination content in the final materials. Thermal analysis of the powders after ball milling suggested that differing decomposition rates of the surfactant were responsible for the measured powder particle changes and contamination contents. The results also indicated that the addition of surfactant during ball milling at 200 rpm caused a delay in the alloy formation, whereas ball milling at 300 rpm favored the formation of the titanium alloy.Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.

What happens during natural protein fibre dissolution in ionic liquids

Here, we monitor the dissolution of several natural protein fibres such as wool, human hair and silk, in various ionic liquids (ILs). The dissolution of protein-based materials using ILs is an emerging area exploring the production of new materials from waste products. Wool is a keratin fibre, which is extensively used in the textiles industry and as a result has considerable amounts of waste produced each year. Wool, along with human hair, has a unique morphology whereby the outer layer, the cuticle, is heavily cross linked with disulphide bonds, whereas silk does not have this outer layer. Here we show how ILs dissolve natural protein fibres and how the mechanism of dissolution is directly related to the structure and morphology of the wool fibre. © 2014 by the authors; licensee MDPI, Basel, Switzerland.

Temperature conditions during 'cold' sheet metal stamping

This paper investigates the friction and deformation-induced heating that occurs during the stamping of high strength sheet steels, under room temperature conditions. A thermo-mechanical finite element model of a typical plane strain stamping process was developed to understand the temperature conditions experienced within the die and blank material; and this was validated against experimental measurements. A high level of correlation was achieved between the finite element model and experimental data for a range of operating conditions and parameters. The model showed that the heat generated during realistic production conditions can result in high temperatures of up to 108 °C and 181 °C in the blank and die materials, respectively, for what was traditionally expected to be 'cold' forming conditions. It was identified that frictional heating was primarily responsible for the peak temperatures at the die surface, whilst the peak blank temperatures were caused by a combination of frictional and deformation induced heating. The results provide new insights into the local conditions within the blank and die, and are of direct relevance to sheet formability and tool wear performance during industrial stamping processes. © 2014 Elsevier B.V. All rights reserved.

Fabrication of boron nitride nanotube-gold nanoparticle hybrids using pulsed plasma in liquid

Plasma, generated in liquid at atmospheric pressure by a nanosecond pulsed voltage, was used to fabricate hybrid structures from boron nitride nanotubes and gold nanoparticles in deionized water. The pH was greatly reduced, conductivity was significantly increased, and concentrations of reactive oxygen and nitrogen species in the water were increased by the plasma treatment. The treatment reduced the length of the nanotubes, giving more individual cuplike structures, and introduced functional groups onto the surface. Gold nanoparticles were successively assembled onto the functionalized surfaces. The reactive species from the liquid plasma along with the nanosecond pulsed electric field seem to play a role in the shortening and functionalization of the nanotubes and the assembly of gold nanoparticles. The potential for targeted drug delivery was tested in a preliminary investigation using doxorubicin-loaded plasma-treated nanotubes which were effective at killing ∼99% of prostate cancer cells.

Decoupled ion conduction in poly(2-acrylamido-2-methyl-1-propane-sulfonic acid) homopolymers

As the focus on developing new polymer electrolytes continues to intensify in the area of alternative energy conversion and storage devices, the rational design of polyelectrolytes with high single ion transport rates has emerged as a primary strategy for enhancing device performance. Previously, we reported a series of sulfonate based copolymer ionomers based on using mixed bulky quaternary ammonium cations and sodium cations as the ionomer counterions. This led to improvements in the ionic conductivity and an apparent decoupling from the Tg of the ionomer. In this article, we have prepared a new series of ionomers based on the homopolymer of poly(2-acrylamido-2-methyl-1-propane-sulfonic acid) using differing sizes of the ammonium counter-cations. We observe a decreasing Tg with increasing the bulkiness of the quaternary ammonium cation, and an increasing degree of decoupling from Tg within these systems. Somewhat surprisingly, phase separation is observed in this homopolymer system, as evidenced from multiple impedance arcs, Raman mapping and SEM. The thermal properties, morphology and the effect of plasticizer on the transport properties in these ionomers are also presented. The addition of 10 wt% plasticizer increased the ionic conductivity between two and three orders of magnitudes leading to materials that may have applications in sodium based devices. This journal is