Showing papers on "Chemical binding published in 2015"

Dual‐Confined Flexible Sulfur Cathodes Encapsulated in Nitrogen‐Doped Double‐Shelled Hollow Carbon Spheres and Wrapped with Graphene for Li–S Batteries

Abstract: Batteries with high energy and power densities along with long cycle life and acceptable safety at an affordable cost are critical for large-scale applications such as electric vehicles and smart grids, but is challenging. Lithium–sulfur (Li-S) batteries are attractive in this regard due to their high energy density and the abundance of sulfur, but several hurdles such as poor cycle life and inferior sulfur utilization need to be overcome for them to be commercially viable. Li–S cells with high capacity and long cycle life with a dual-confined flexible cathode configuration by encapsulating sulfur in nitrogen-doped double-shelled hollow carbon spheres followed by graphene wrapping are presented here. Sulfur/polysulfides are effectively immobilized in the cathode through physical confinement by the hollow spheres with porous shells and graphene wrapping as well as chemical binding between heteronitrogen atoms and polysulfides. This rationally designed free-standing nanostructured sulfur cathode provides a well-built 3D carbon conductive network without requiring binders, enabling a high initial discharge capacity of 1360 mA h g−1 at a current rate of C/5, excellent rate capability of 600 mA h g−1 at 2 C rate, and sustainable cycling stability for 200 cycles with nearly 100% Coulombic efficiency, suggesting its great promise for advanced Li–S batteries.

Reversible Hydrophobic to Hydrophilic Transition in Graphene via Water Splitting Induced by UV Irradiation

Abstract: Although the reversible wettability transition between hydrophobic and hydrophilic graphene under ultraviolet (UV) irradiation has been observed, the mechanism for this phenomenon remains unclear. In this work, experimental and theoretical investigations demonstrate that the H2O molecules are split into hydrogen and hydroxyl radicals, which are then captured by the graphene surface through chemical binding in an ambient environment under UV irradiation. The dissociative adsorption of H2O molecules induces the wettability transition in graphene from hydrophobic to hydrophilic. Our discovery may hold promise for the potential application of graphene in water splitting.

Observed and modeled effects of pH on bioconcentration of diphenhydramine, a weakly basic pharmaceutical, in fathead minnows

Abstract: A need exists to better understand the influence of pH on the uptake and accumulation of ionizable pharmaceuticals in fish. In the present study, fathead minnows were exposed to diphenhydramine (DPH; disassociation constant = 9.1) in water for up to 96 h at 3 nominal pH levels: 6.7, 7.7, and 8.7. In each case, an apparent steady state was reached by 24 h, allowing for direct determination of the bioconcentration factor (BCF), blood–water partitioning (PBW,TOT), and apparent volume of distribution (approximated from the whole-body–plasma concentration ratio). The BCFs and measured PBW,TOT values increased in a nonlinear manner with pH, whereas the volume of distribution remained constant, averaging 3.0 L/kg. The data were then simulated using a model that accounts for acidification of the gill surface caused by elimination of metabolically produced acid. Good agreement between model simulations and measured data was obtained for all tests by assuming that plasma binding of ionized DPH is 16% that of the neutral form. A simpler model, which ignores elimination of metabolically produced acid, performed less well. These findings suggest that pH effects on accumulation of ionizable compounds in fish are best described using a model that accounts for acidification of the gill surface. Moreover, measured plasma binding and volume of distribution data for humans, determined during drug development, may have considerable value for predicting chemical binding behavior in fish. Environ Toxicol Chem 2015;34:1425–1435. © 2015 SETAC

Environmental Toxicology OBSERVED AND MODELED EFFECTS OF pH ON BIOCONCENTRATION OF DIPHENHYDRAMINE, A WEAKLY BASIC PHARMACEUTICAL, IN FATHEAD MINNOWS

Abstract: A need exists to better understand the influence of pH on the uptake and accumulation of ionizable pharmaceuticals in fish. In the present study, fathead minnows were exposed to diphenhydramine (DPH; disassociation constant ¼9.1) in water for up to 96h at 3 nominal pH levels: 6.7, 7.7, and 8.7. In each case, an apparent steady state was reached by 24h, allowing for direct determination of the bioconcentration factor (BCF), blood-water partitioning (PBW,TOT), and apparent volume of distribution (approximated from the whole-body-plasmaconcentrationratio).TheBCFsand measuredPBW,TOTvaluesincreasedinanonlinearmannerwithpH,whereasthe volume of distribution remained constant, averaging 3.0 L/kg. The data were then simulated using amodel that accounts for acidification of the gill surface caused by elimination of metabolically produced acid. Good agreement between model simulations and measured data was obtained for all tests by assuming that plasma binding of ionized DPH is 16% that of the neutral form. A simpler model, which ignores elimination of metabolically produced acid, performed less well. These findings suggest that pH effects on accumulation of ionizable compounds in fish are best described using a model that accounts for acidification of the gill surface. Moreover, measured plasma binding and volume of distribution data for humans, determined during drug development, may have considerable value for predicting chemical binding behavior in fish. Environ Toxicol Chem 2015;9999:1-11. # 2015 SETAC

Classic reaction kinetics can explain complex patterns of antibiotic action

Abstract: Finding optimal dosing strategies for treating bacterial infections is extremely difficult, and improving therapy requires costly and time-intensive experiments. To date, an incomplete mechanistic understanding of drug effects has limited our ability to make accurate quantitative predictions of drug-mediated bacterial killing and impeded the rational design of antibiotic treatment strategies. Three poorly understood phenomena complicate predictions of antibiotic activity: post-antibiotic growth suppression, density-dependent antibiotic effects, and persister cell formation. We show that chemical binding kinetics alone are sufficient to explain these three phenomena, using single-cell data and time-kill curves of Escherichia coli and Vibrio cholerae exposed to a variety of antibiotics in combination with a theoretical model that links chemical reaction kinetics to bacterial population biology. Our model reproduces existing observations, has a high predictive power across different experimental setups ( R 2 = 0.86), and makes several testable predictions, which we verified in new experiments and by analyzing published data from a clinical trial on tuberculosis therapy. Although a variety of biological mechanisms have previously been invoked to explain post-antibiotic growth suppression, density-dependent antibiotic effects, and especially persister cell formation, our findings reveal that a simple model that considers only binding kinetics provides a parsimonious and unifying explanation for these three complex, phenotypically distinct behaviours. Current antibiotic and other chemotherapeutic regimens are often based on trial and error or expert opinion. Our “chemical reaction kinetics”–based approach may inform new strategies, which are based on rational design.

First-Principles Design of a Deep-Ultraviolet Nonlinear-Optical Crystal from KBe2BO3F2 to NH4Be2BO3F2

Abstract: KBe2BO3F2 (KBBF) is so far the sole nonlinear-optical (NLO) material that can be practically applied in the deep-ultraviolet (DUV) region. For the purpose of overcoming its layering tendency in crystal growth, herein a computer-assisted material design system is employed to design a new KBBF analogue, ammonia beryllium fluoroborate (NH4Be2BO3F2, ABBF). The first-principles calculations demonstrate that ABBF possesses NLO properties very close to those of KBBF, thus exhibiting good DUV NLO capability. Moreover, owing to the relatively strong chemical binding between layers, ABBF would have a better growth habit compared with KBBF. Upon synthesis, ABBF would be a very promising DUV NLO material.

A group of novel HIF-1α inhibitors, glyceollins, blocks HIF-1α synthesis and decreases its stability via inhibition of the PI3K/AKT/mTOR pathway and Hsp90 binding.

Abstract: Glyceollins, a group of phytoalexins isolated from soybean, are known to exhibit anticancer, antiestrogenic, and antiangiogenic activities. However, whether glyceollins regulate tumor growth through regulation of hypoxia-inducible factor (HIF)-1α has not been investigated. We determined whether and how glyceollins regulate the synthesis and stability of HIF-1α. Quantitative real-time PCR revealed that glyceollins inhibited the expression of HIF-1-induced genes such as vascular endothelial growth factor (VEGF) in cancer cells. Enzyme-linked immunosorbent assay and reporter luciferase assay showed that glyceollins decreased VEGF secretion and its promoter activity, respectively. Treatment of various cancer cells with 0.5–100 µM glyceollins under hypoxic conditions reduced the expression of HIF-1α. Glyceollins blocked translation of HIF-1α by inhibiting the PI3K/AKT/mTOR pathway under hypoxic conditions. Glyceollins decreased the stability of HIF-1α after treatment with cycloheximide, a protein synthesis inhibitor, and increased the ubiquitination of HIF-1α after treatment with MG132, a proteasome inhibitor. Glyceollins blocked the interaction of Hsp90 with HIF-1α, as shown by immunoprecipitation assay. Chemical binding of Hsp90 with glyceollins, as confirmed by computational docking analysis, was stronger than that with geldanamycin at the HSP90 ATP-binding pocket. We found that glyceollins decreased microvessel density, as well as expression of phosphorylated AKT/mTOR and the Hsp90 client protein CDK4, in solid tumor tissues. Glyceollins potently inhibited HIF-1α synthesis and decreased its stability by blocking the PI3K/AKT/mTOR pathway and HSP90 binding activity, respectively. These results may provide new perspectives into potential therapeutic application of glyceollins for the prevention and treatment of hypervascularized diseases and into the mechanism of their anticancer activity. J. Cell. Physiol. 230: 853–862, 2015. © 2014 Wiley Periodicals, Inc.

Fabrication of graphene oxide decorated with Fe 3 O 4 @SiO 2 for immobilization of cellulase

Abstract: Fe3O4@SiO2–graphene oxide (GO) composites were successfully fabricated by chemical binding of functional Fe3O4@SiO2 and GO and applied to immobilization of cellulase via covalent attachment. The prepared composites were further characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. Fe3O4 nanoparticles (NPs) were monodisperse spheres with a mean diameter of 17 ± 0.2 nm. The thickness of SiO2 layer was calculated as being 6.5 ± 0.2 nm. The size of Fe3O4@SiO2 NPs was 24 ± 0.3 nm, similar to that of Fe3O4@SiO2–NH2. Fe3O4@SiO2–GO composites were synthesized by linking of Fe3O4@SiO2–NH2 NPs to GO with the catalysis of EDC and NHS. The prepared composites were used for immobilization of cellulase. A high immobilization yield and efficiency of above 90 % were obtained after the optimization. The half-life of immobilized cellulase (722 min) was 3.34-fold higher than that of free enzyme (216 min) at 50 °C. Compared with the free cellulase, the optimal temperature of the immobilized enzyme was not changed; but the optimal pH was shifted from 5.0 to 4.0, and the thermal stability was enhanced. The immobilized cellulase could be easily separated and reused under magnetic field. These results strongly indicate that the cellulase immobilized onto the Fe3O4@SiO2–GO composite has potential applications in the production of bioethanol.

Passivation of Metal Oxide Surfaces for High-Performance Organic and Hybrid Optoelectronic Devices

Abstract: The exciton quenching properties of solution-processed nickel oxide (NiOx) and vanadium oxide (VOx) are studied by measuring the photoluminescence (PL) of a thin emitting layer (EML) deposited on top of the metal oxides. Strong exciton quenching is evidenced at the metal oxide/EML interface, which is proved to be detrimental to the performance of optoelectronic devices. With a thin polyvinylpyrrolidone (PVP) passivation polymer adsorbed on top of metal oxides, the PL quenching is found to be effectively suppressed. A short UV–O3 treatment on top of the PVP-passivated metal oxides turns out to be a key procedure to trigger the chemical binding between the PVP passivation polymer and the metal oxide surface species, which turns out to be necessary for efficient hole injection and extraction for organic light emitting diodes (OLEDs) and solar cell devices, respectively. With the PVP passivation layer followed by UV–O3 treatment, the OLEDs incorporating NiOx as a hole transport layer (HTL) shows a record curr...

N-modified TiO2 photocatalytic activity towards diphenhydramine degradation and Escherichia coli inactivation in aqueous solutions

Abstract: Nitrogen modified TiO2 samples were prepared by grinding the benchmark TiO2 photocatalyst (P25, Evonik Degussa Corporation) with different amounts of urea and applying calcination temperatures between 340 and 420 °C. Several characterization techniques, including X-ray photoelectron spectroscopy (XPS), N2 porosimetry, X-ray diffraction (XRD), scanning electronic microscopy (SEM), and diffuse reflectance UV–vis spectroscopy (UV-DRS), were used to obtain information about the morphology, crystalline phases of TiO2 and chemical binding of nitrogen. Nitrogen modification did not affect the crystalline phase of TiO2 as far as XRD analysis concerns; on the other hand the modified materials developed an absorption in the visible part of the electromagnetic spectrum. The material with a urea:TiO2 weight ratio of 1:2, calcined at 380 °C, exhibited the highest photocatalytic activity under visible light illumination (λ > 430 nm), towards degradation of diphenhydramine, an emerging water pollutant of pharmaceutical origin. The measured band gap energy of the material was 2.99 eV, which is in-line with observed optical absorption properties. In addition, this photocatalyst was also the most efficient for complete inactivation of Escherichia coli in aqueous solution when ultraviolet radiation (λ = 365 nm) was used. From the XPS analysis on the chemical states of this photocatalyst it is concluded that nitrogen is interstitial to the TiO2 structure.

Space-confined growth of Ag3PO4 nanoparticles within WS2 sheets: Ag3PO4/WS2 composites as visible-light-driven photocatalysts for decomposing dyes

Abstract: A highly efficient Ag3PO4/WS2 composite photocatalyst was synthesized by controlling the growth of Ag3PO4 nanoparticles within WS2 sheets. The process can tune the microstructure, stability and visible-light photocatalytic performance of Ag3PO4. The WS2 sheets, possessing uncoordinated sulfur atoms on exposed surfaces and edges, play an important role in the formation of Ag3PO4/WS2 composite. With 0.05 mol of AgAc added, the Ag3PO4/WS2 composite shows the highest photocatalytic activity. The matched energy level between Ag3PO4 and WS2 inhibits the recombination of the photogenerated electrons and holes. The enhanced photocatalytic activity is also attributed to the multi-interface heterojunction structure assembled by two-dimensional sheets and nanoparticles, driven by chemical binding. The addition of WS2 sheets can also reduce the rate at which Ag+ dissolves from Ag3PO4 into the water, improving the stability of Ag3PO4. This work could provide new insights into fabricating highly efficient and stable Ag3PO4-transition-metal dichalcogenide composite photocatalysts for dye degradation.

Effect of silicate doping on the structure and mechanical properties of thin nanostructured RF magnetron sputter-deposited hydroxyapatite films

Abstract: Silicon-doped hydroxyapatite-based (Si-HA) coatings were deposited via radio frequency (RF) magnetron sputtering on the surface of titanium that was treated with a pulsed electron beam. This study aimed to evaluate the effect of Si doping on the structure and mechanical properties of thin HA films. The content of the silicon was 1.2 and 4.6 at.% for the coatings prepared using the Si-HA precursor powders with a chemical formula Ca 10 (PO 4 ) 6 − x (SiO 4 ) x (OH) 2 − x where, x = 0.5 and 1.72. Pure HA (Ca 10 (PO 4 ) 6 (OH) 2 ) coatings were deposited for comparison. The as-deposited films were analysed with respect to their composition, state of chemical binding and microstructure using XPS, FTIR, XRD, and SEM. We hypothesized that the addition of Si would affect the mechanical features of the coatings due to microstructure changes. The effect of the introduction of Si on the nanohardness and the Young's modulus as well as the adhesion strength and scratch resistance of the HA coating was investigated using nanohardness testing and a scratch test, respectively. Examination of the coating microstructure using SEM and AFM revealed that Si doping influenced the surface morphology and led to a smaller grain size. The tendency to form an amorphous structure also increased with an increase in the Si content. A monotonous decrease in both the nanohardness and the elastic modulus was observed with an increase in the Si content. A maximum nanohardness of ~ 7 GPa was obtained for the Si-free HA coating, whereas the hardness decreased to ~ 4.3 GPa for the films with a Si content of 1.2 at.%. The addition of 4.6 at.% Si to the HA coating resulted in a reduction in the elastic modulus, whereas the nanohardness was very similar to that of the uncoated substrate. The adhesion behaviour of the coatings demonstrated different responses. In the case of pure HA coatings, failure occurred due to the low cohesion of the coating, whereas the crystalline Si-HA coatings with a Si content of 1.2 at.% deformed plastically without crack formation and without detaching from the titanium substrate, which resulted in a greater coating stability.

Electrochemical Performance of Carbon/MnO2 Nanocomposites Prepared via Molecular Bridging as Supercapacitor Electrode Materials

Abstract: The chemical binding of amorphous manganese oxide and carbon particles was achieved with the diazonium chemistry. The synthesis was performed in two steps, with a first step consisting in the surface functionnalization of carbon particles with aminophenyl groups and the subsequent attachment of amorphous manganese oxide particles through generated phenyl groups. The bond between carbon and MnO2 particles is believed to occur between the carbon from the phenyl groups attached to carbon particles, and the oxygen atoms from the manganese oxide lattice. The capacitance of the carbon/MnO2 grafted nanocomposite electrode is doubled compared to a simple mixture of its two components. The capacitance of the nanocomposite electrode is also retained for faster cycling rates, thus highlighting the role of intimate coupling of carbon and MnO2. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0221505jes] All rights reserved.

Development and Validation of Decision Forest Model for Estrogen Receptor Binding Prediction of Chemicals Using Large Data Sets

Abstract: Some chemicals in the environment possess the potential to interact with the endocrine system in the human body. Multiple receptors are involved in the endocrine system; estrogen receptor α (ERα) plays very important roles in endocrine activity and is the most studied receptor. Understanding and predicting estrogenic activity of chemicals facilitates the evaluation of their endocrine activity. Hence, we have developed a decision forest classification model to predict chemical binding to ERα using a large training data set of 3308 chemicals obtained from the U.S. Food and Drug Administration’s Estrogenic Activity Database. We tested the model using cross validations and external data sets of 1641 chemicals obtained from the U.S. Environmental Protection Agency’s ToxCast project. The model showed good performance in both internal (92% accuracy) and external validations (∼70–89% relative balanced accuracies), where the latter involved the validations of the model across different ER pathway-related assays in...

ALD of Ultrathin Ternary Oxide Electrocatalysts for Water Splitting

Abstract: Semiconducting oxides, particularly mixtures of different transition-metal oxides, are promising materials for oxygen evolution reaction (OER) catalysts. Assessment of these materials is often complicated by inadequate dispersion of the materials, charge transport limitations, and lack of surface area characterization. Thin films deposited by atomic layer deposition (ALD) present an excellent way to overcome these issues. Here, we present the first work using ALD to investigate ternary oxide electrocatalysts, specifically with the Ti–Mn ternary oxide system. Thin-film mixtures of between 1.4 and 2.8 nm in thickness are successfully synthesized by ALD and show a high degree of mixing. At compositions between ∼10 and 70% Mn:(Mn+Ti), there is a reduction in ALD growth rate relative to the growth rates of the binary constituents. Moreover, we observe a shift in the chemical binding energies of both Mn and Ti over this composition range. An elevation in the activity of Mn active sites for OER is observed with ...

Xe irradiation of graphene on Ir(111): From trapping to blistering

Abstract: Using x-ray photoelectron spectroscopy, thermal desorption spectroscopy, and scanning tunneling microscopy, we show that upon keV Xe+ irradiation of graphene on Ir(111), Xe atoms are trapped under the graphene. Upon annealing, aggregation of Xe leads to graphene bulges and blisters. The efficient trapping is an unexpected and remarkable phenomenon given the absence of chemical binding of Xe to Ir and to graphene, the weak interaction of a perfect graphene layer with Ir(111), as well as the substantial damage to graphene due to irradiation. By combining molecular dynamics simulations and density functional theory calculations with our experiments, we uncover the mechanism of trapping. We describe ways to avoid blister formation during graphene growth, and also demonstrate how ion implantation can be used to intentionally create blisters without introducing damage to the graphene layer. Our approach may provide a pathway to synthesize new materials at a substrate-2D material interface or to enable confined reactions at high pressures and temperatures. (Less)

Experimental charge density evidence for pnicogen bonding in a crystal of ammonium chloride.

Abstract: Chemical binding in crystalline ammonium chloride, a simple inorganic salt with an unexpectedly complex bonding pattern, was studied by using a topological analysis of electron density function derived from high-resolution X-ray diffraction. Supported by periodic quantum chemical calculations, it provided experimental evidence for weak σ-hole bonds (1.5 kcal mol(-1) ) that involve ammonium cations in a crystal. Our results show this type of supramolecular interaction to be more numerous than has been found to date by using gas-phase calculations or statistical analysis of CSD.

Surface coatings with covalently attached caspofungin are effective in eliminating fungal pathogens.

Abstract: In this work we have prepared surface coatings formulated with the antifungal drug caspofungin, an approved pharmaceutical lipopeptide compound of the echinocandin drug class. Our hypothesis was to test whether an antifungal drug with a known cell-wall disrupting effect could be irreversibly tethered to surface coatings and kill (on contact) biofilm-forming fungal human pathogens from Candida spp. The first aim of the study was to use surface analysis to prove that the chemical binding to the surface polymer interlayer was through specific and irreversible bonds (covalent) and not due to non-specific adsorption through weak forces that could be later reversed (physisorption). Secondly, we quantified the antifungal nature of these coatings in a biological assay showing excellent killing against C. albicans and C. tropicalis and moderate killing against C. glabrata and C. parapsilosis. We concluded that caspofungin retains antifungal activity even when it is irreversibly immobilized on a surface, providing a new insight into its mechanism of action. Thus, surface coatings that have echinocandins permanently bound will be useful in preventing the establishment of fungal biofilms on materials.

Hydrogen storage in rippled graphene: perspectives from multi-scale simulations

Abstract: Exploring new perspectives for green technologies is one of the challenges of the third millennium, in which the need for non-polluting and renewable powering has become primary. In this context, the use of hydrogen as a fuel is promising, since the energy released in its oxidation per unit mass (~142 MJ/kg) is three times that released, on average, by hydrocarbons, and the combustion product is water (Ramage, 1983). Being hydrogen a vector of chemical energy, efficient conservation, and non-dispersive transportation are the main goals. Three issues must be considered to this respect: (i) storage capacity, (ii) storage stability, and (iii) kinetics of loading/release. Commercial technologies are currently based on cryo-compression or liquefaction of H2 in tanks. These ensure quite a high gravimetric density [GD, point (i)], namely 8–13% in weight of stored hydrogen, and a relatively low cost (Zuttel, 2003). However, concerning points (ii) and (iii), these technologies pose problems of safety, mainly due to explosive flammability of hydrogen, and consequent unpractical conditions for transportation and use (Mori and Hirose, 2009). Therefore, research efforts are directed toward solidstate based storage systems (energy.gov, Bonaccorso et al., 2015). Interactions of hydrogen with materials are classified as physisorption, occurring with H2 by means of van der Waals (vdW) forces, or chemisorption, i.e., chemical binding of H leading to the formation of hydrides (Mori and Hirose, 2009), requiring dissociative(associative) chemi(de)sorption of H2. Intermediate nature interactions, sometimes called “phenisorption,” can also occur between hydrogen electrons and the electrons of external orbital of metals. Indeed, stable and robust (light) metal hydrides (Sakintuna et al., 2007; Harder et al., 2011) are currently considered an alternative to tanks. Their main drawback is their high chemisorption and chemidesorption barrier, both many times the typical thermal energy, implying slow operational kinetics, which becomes acceptable only at very high temperature. Physisorption, conversely, generally results in barrierless and weak binding. It was considered as a storage mechanism in layered (Zhirko et al., 2007) or porous (Sastre, 2010) materials, and shown to be effective at low temperatures and/or high pressure. Therefore, it generally seems that if storage stability (ii) is improved then the loading/release kinetics (iii) is worsened. Graphene shows good potential to be an efficient hydrogen-storage medium (Tozzini and Pellegrini, 2013): carbon is among the lightest elements forming layered and porous structures, and graphene is probably the material with the largest surface to mass ratio. These two conditions are in principle optimal to produce high GD [point (i)]. In addition, the chemical versatility of carbon allows it to interact with hydrogen both by physisorption (in sp2 hybridization) and chemisorption (Goler et al., 2013a) (in sp3 hybridization). [“Phenisorption is also obtained in graphene by functionalization with metals (Mashoff et al., 2013)]. On the other hand, concerning points (ii) and (iii), pure graphene does not perform dramatically better than other materials. H2 easily physisorbs onto graphene layers or within multilayers, but it was theoretically shown (Patchkovskiim et al., 2005) that large GD (6–8%) are reached within multi-layered graphene at cryogenic temperatures, while the room temperature value is at best ~2–3%. This was confirmed by measurements (Klechikov et al., private communication), which also indicate that graphene does not perform better than other carbon based bulk materials, such as nanoporous carbon or carbon nanotubes. In all cases, a key parameter determining GD is the specific surface to volume ratio. Theoretical works also show that stability can be improved (and GD optimized) at specific interlayer spacing (~7–8 A), due to a cooperative effect of vdW forces (Patchkovskiim et al., 2005). A similar effect is responsible for the accumulation of physisorbed hydrogen within graphene troughs at low temperatures (~100 K) observed in simulations (Tozzini and Pellegrini, 2011). On the other hand, hydrogen chemisorption on graphene produces graphane (Sofo et al., 2007), its completely hydrated alkane counterpart, stable at room temperature [point (ii)] and with 8.2% GD [point (i)]. Graphane, however, shares with other hydrides high chemi(de)sorption barrier (~1.5 eV/atom). As in other materials, physisorption has good kinetics (iii), and

Selective chemical binding enhances cesium tolerance in plants through inhibition of cesium uptake

Abstract: Selective chemical binding enhances cesium tolerance in plants through inhibition of cesium uptake

Hydrogen–deuterium exchange mass spectrometry for determining protein structural changes in drug discovery

Abstract: Protein structures are dynamically changed in response to post-translational modifications, ligand or chemical binding, or protein–protein interactions. Understanding the structural changes that occur in proteins in response to potential candidate drugs is important for predicting the modes of action of drugs and their functions and regulations. Recent advances in hydrogen/deuterium exchange mass spectrometry (HDX-MS) have the potential to offer a tool for obtaining such understanding similarly to other biophysical techniques, such as X-ray crystallography and high resolution NMR. We present here, a review of basic concept and methodology of HDX-MS, how it is being applied for identifying the sites and structural changes in proteins following their interactions with other proteins and small molecules, and the potential of this tool to help in drug discovery.