Showing papers on "Chemical binding published in 2016"

Origin of low sodium capacity in graphite and generally weak substrate binding of Na and Mg among alkali and alkaline earth metals

Abstract: It is well known that graphite has a low capacity for Na but a high capacity for other alkali metals. The growing interest in alternative cation batteries beyond Li makes it particularly important to elucidate the origin of this behavior, which is not well understood. In examining this question, we find a quite general phenomenon: among the alkali and alkaline earth metals, Na and Mg generally have the weakest chemical binding to a given substrate, compared with the other elements in the same column of the periodic table. We demonstrate this with quantum mechanics calculations for a wide range of substrate materials (not limited to C) covering a variety of structures and chemical compositions. The phenomenon arises from the competition between trends in the ionization energy and the ion–substrate coupling, down the columns of the periodic table. Consequently, the cathodic voltage for Na and Mg is expected to be lower than those for other metals in the same column. This generality provides a basis for analyzing the binding of alkali and alkaline earth metal atoms over a broad range of systems.

In Situ Reactive Assembly of Scalable Core-Shell Sulfur-MnO2 Composite Cathodes.

Abstract: The lithium-sulfur battery is the subject of much recent attention, but the polysulfide shuttle remains problematic owing to dissolution of intermediate polysulfide species in the electrolyte. Despite much effort in limiting such dissolution via physical confinement or chemical binding to the sulfur host materials, the high cost and complicated preparation of the related materials present an impediment to their practical application. Here we demonstrate a simple methodology to fabricate an effective nanometric MnO2 shell on sulfur particles, which is realized by an in situ redox reaction between sulfur and KMnO4 under ambient conditions. The bifunctional MnO2 shell provides physical confinement and chemical interaction and shows excellent efficiency for trapping the polysulfides. MnO2 sheets crystallized onto nanosized sulfur particles result in cathodes with a very low fading rate of 0.039% per cycle over 1700 cycles in Li-S cells. Moreover, directly crystallizing nanometric shells of MnO2 on micrometer-sized sublimed sulfur delivers stable Li-S cycling performance over 800 cycles. Since both sulfur and KMnO4 are inexpensive and widely used, the production of MnO2-coated sulfur composites can be easily scaled-up for practical applications of Li-S batteries in light of the very simple reaction processes involved.

Diamond family of nanoparticle superlattices

Abstract: Diamond lattices formed by atomic or colloidal elements exhibit remarkable functional properties. However, building such structures via self-assembly has proven to be challenging because of the low packing fraction, sensitivity to bond orientation, and local heterogeneity. We report a strategy for creating a diamond superlattice of nano-objects via self-assembly and demonstrate its experimental realization by assembling two variant diamond lattices, one with and one without atomic analogs. Our approach relies on the association between anisotropic particles with well-defined tetravalent binding topology and isotropic particles. The constrained packing of triangular binding footprints of truncated tetrahedra on a sphere defines a unique three-dimensional lattice. Hence, the diamond self-assembly problem is solved via its mapping onto two-dimensional triangular packing on the surface of isotropic spherical particles.

Transmutable nanoparticles with reconfigurable surface ligands

Abstract: Unlike conventional inorganic materials, biological systems are exquisitely adapted to respond to their surroundings. Proteins and other biological molecules can process a complex set of chemical binding events as informational inputs and respond accordingly via a change in structure and function. We applied this principle to the design and synthesis of inorganic materials by preparing nanoparticles with reconfigurable surface ligands, where interparticle bonding can be programmed in response to specific chemical cues in a dynamic manner. As a result, a nascent set of “transmutable nanoparticles” can be driven to crystallize along multiple thermodynamic trajectories, resulting in rational control over the phase and time evolution of nanoparticle-based matter.

Lung Structure and the Intrinsic Challenges of Gas Exchange.

Abstract: Structural and functional complexities of the mammalian lung evolved to meet a unique set of challenges, namely, the provision of efficient delivery of inspired air to all lung units within a confined thoracic space, to build a large gas exchange surface associated with minimal barrier thickness and a microvascular network to accommodate the entire right ventricular cardiac output while withstanding cyclic mechanical stresses that increase several folds from rest to exercise. Intricate regulatory mechanisms at every level ensure that the dynamic capacities of ventilation, perfusion, diffusion, and chemical binding to hemoglobin are commensurate with usual metabolic demands and periodic extreme needs for activity and survival. This article reviews the structural design of mammalian and human lung, its functional challenges, limitations, and potential for adaptation. We discuss (i) the evolutionary origin of alveolar lungs and its advantages and compromises, (ii) structural determinants of alveolar gas exchange, including architecture of conducting bronchovascular trees that converge in gas exchange units, (iii) the challenges of matching ventilation, perfusion, and diffusion and tissue-erythrocyte and thoracopulmonary interactions. The notion of erythrocytes as an integral component of the gas exchanger is emphasized. We further discuss the signals, sources, and limits of structural plasticity of the lung in alveolar hypoxia and following a loss of lung units, and the promise and caveats of interventions aimed at augmenting endogenous adaptive responses. Our objective is to understand how individual components are matched at multiple levels to optimize organ function in the face of physiological demands or pathological constraints. © 2016 American Physiological Society. Compr Physiol 6:827-895, 2016.

Polydopamine wrapping silicon cross-linked with polyacrylic acid as high-performance anode for lithium-ion batteries

Abstract: A robust silicon electrode for lithium-ion battery has been developed via prepolymerizing dopamine on silicon particle surface and then chemical binding with poly(acrylic acid) (PAA). In this favorable electrode, silicon nanoparticles are covered by a thin layer of polydopamine (PD) through firm hydrogen bonds between phenolic hydroxyl and hydroxyl, while the elastic polymer layer reacts with PAA binder to form three-dimensional cross-linked binding system. The Si@PD/PAA electrode exhibits more stable cycle performance than conventional electrodes. In the case of thick electrode, a capacity of 3.69 mA h cm–2 and fairly good rechargeability for 80 cycles can be achieved.

A ruthenium(ii) based photosensitizer and transferrin complexes enhance photo-physical properties, cell uptake, and photodynamic therapy safety and efficacy

Abstract: Metal-based photosensitizers are of interest as their absorption and chemical binding properties can be modified via the use of different ligands. Ru2+ based photosensitizers are known to be effective photodynamic therapy (PDT) agents against bacteria, whereas use for oncological indications in vivo has not been demonstrated with the same level of evidence. We present data showing that premixing the Ru2+-complex TLD1433 with transferrin increases the molar extinction coefficient, including longer activation wavelengths, reduces photobleaching rates, and reduces the toxicity of the complex improving overall PDT efficacy. As the transferrin receptor is upregulated in most malignancies, premixing the Ru2+ complex with transferrin converts the active pharmaceutical ingredient TLD1433 into a drug of potentially considerable clinical utility.

How Graphene Islands Are Unidirectionally Aligned on the Ge(110) Surface

Abstract: The unidirectional alignment of graphene islands is essential to the synthesis of wafer-scale single-crystal graphene on Ge(110) surface, but the underlying mechanism is not well-understood. Here we report that the necessary coalignment of the nucleating graphene islands on Ge(110) surface is caused by the presence of step-pattern; we show that on the preannealed Ge(110) textureless surface the graphene islands appear nonpreferentially orientated, while on the Ge(110) surfaces with natural step pattern, all graphene islands emerge coaligned. First-principles calculations and theoretical analysis reveal this different alignment behaviors originate from the strong chemical binding formed between the graphene island edges and the atomic steps on the Ge(110) surface, and the lattice matching at edge-step interface dictates the alignment of graphene islands with the armchair direction of graphene along the [-110] direction of the Ge(110) substrate.

Growth factor-eluting technologies for bone tissue engineering

Abstract: Growth factors are essential orchestrators of the normal bone fracture healing response. For non-union defects, delivery of exogenous growth factors to the injured site significantly improves healing outcomes. However, current clinical methods for scaffold-based growth factor delivery are fairly rudimentary, and there is a need for greater spatial and temporal regulation to increase their in vivo efficacy. Various approaches used to provide spatiotemporal control of growth factor delivery from bone tissue engineering scaffolds include physical entrapment, chemical binding, surface modifications, biomineralization, micro- and nanoparticle encapsulation, and genetically engineered cells. Here, we provide a brief review of these technologies, describing the fundamental mechanisms used to regulate release kinetics. Examples of their use in pre-clinical studies are discussed, and their capacities to provide tunable, growth factor delivery are compared. These advanced scaffold systems have the potential to provide safer, more effective therapies for bone regeneration than the systems currently employed in the clinic.

How To Design a Successful p53-MDM2/X Interaction Inhibitor: A Thorough Overview Based on Crystal Structures.

Abstract: A recent therapeutic strategy in oncology is based on blocking the protein-protein interaction between the murine double minute (MDM) homologues MDM2/X and the tumor-suppressor protein p53. Inhibiting the binding between wild-type (WT) p53 and its negative regulators MDM2 and/or MDMX has become an important target in oncology to restore the antitumor activity of p53, the so-called guardian of our genome. Interestingly, based on the multiple disclosed compound classes and structural analysis of small-molecule-MDM2 adducts, the p53-MDM2 complex is perhaps the best studied and most targeted protein-protein interaction. Several classes of small molecules have been identified as potent, selective, and efficient inhibitors of the p53-MDM2/X interaction, and many co-crystal structures with the protein are available. Herein we review the properties as well as preclinical and clinical studies of these small molecules and peptides, categorized by scaffold type. A particular emphasis is made on crystallographic structures and the observed binding modes of these compounds, including conserved water molecules present.

Nanoparticles cyto and genotoxicity in plants: Mechanisms and abnormalities

Abstract: This report presents an overview related to genotoxicity and the cytotoxicity of nanoparticles in plants in order to better understanding of NPs (nanoparticles) interactions with DNA, chromosomes components, nuclear proteins and,etc Genotoxicity of NPs has been poorly studied in plants, and majority of studies have focused on mammalian and bacteria cytotoxicity Therefore further studies in plants field are required Nanoparticles induce genotoxicity as either direct or indirect mechanisms In direct genotoxicity NPs after passing through the cell and nucleus membrane through diffusion or endocytosis mechanisms could interact directly with the DNA mechanically or by chemical binding to DNA Indirect genotoxicity resulting from interaction of NPs with the nuclear proteins (proteins involve in replication, transcription, translations, microtubule, microfilaments, and centrioles) or stress oxidative induced by reactive oxygen species and also by reduced DNA repair functions Genotoxicity as a biotic response to NP exposure increases with decreasing in NPs size and increasing in concentration and exposer duration, which leads to an inhibitory effect on cell cycle Micronuclei formation, disturbed chromosomes, chromosome fragments, stickiness, bridge, laggards’ chromosomes and decrease in mitotic index are the most obvious anomalies in plants exposer to silver, copper, titanium dioxide, zinc, zinc oxide, selenium oxide, multi wall carbon nano tube, Tetramethylammonium hydroxide and Bismuth (III) oxide nanoparticles The severity of abnormalities depending on the concentration, duration time and particle size are different Finally if the DNA repair mechanisms were not enough to overcome this crisis (genotoxicity), it can lead to loss of genetic material and mutation in DNA

Theoretical Investigation on the Role of the Central Carbon Atom and Close Protein Environment on the Nitrogen Reduction in Mo Nitrogenase

Abstract: A theoretical study elucidating the mechanism of N2 reduction in Mo nitrogenase was carried out using a QM/QM′ approach based on density functional theory/semiempirical methods. Resting on the consolidated Lowe–Thorneley catalytic cycle, the identified reaction mechanism corresponds to an alternating pathway where the two nitrogen atoms are alternately reduced. Furthermore, this new mechanism provides a clear mechanistic basis to most of the experimental observations, including the noninnocent role played by the carbon atom located in the center of the MoFe cofactor and by the surrounding amino acids (such as α-96ARG, α-195HIS, and α-70VAL). It also provides evidence for the presence of H2 evolution in the global reaction cycle. Our calculations indicate a large flexibility of the cofactor upon hydrogenation and subsequent N2 chemical binding, with the average Fe–C distance increasing of 0.26 A in going from the E0 to the E4 state, in agreement with experimental evidence. Taken together, these results giv...

C-doped and N-doped reduced graphene oxide/TiO2 composites with exposed (0 0 1) and (1 0 1) facets controllably synthesized by a hydrothermal route and their gas sensing characteristics

Abstract: Element doping and controllably facet exposing are efficient solutions for enhancing gas sensing performances of TiO2 nanomaterials. In this study, C-doped and N-doped reduced graphene oxide/TiO2 composites with special exposed facets C-RGO/TiO2 (with HF) and N-RGO/TiO2 (with HF) were controllably synthesized via a hydrothermal method using HF as the morphology-controlling agent at 180 °C for 12 h. The as-prepared composites were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and other measurements. Their gas sensing results demonstrate that the gas sensing performance of N-RGO/TiO2 (with HF) is much better than that of C-RGO/TiO2 (with HF), such as higher sensitivity, and shorter response and recovery time. The sensor based on N-RGO/TiO2 (with HF) exhibits the highest gas response toward isopropanol, ethanol, and acetone at a working temperature of 210, 240, and 270 °C, respectively. The lowest detection of these gases was 1 ppm. The gas sensing mechanism was also carefully analyzed. The TiO2 particles of composite with exposed facets generate electron–hole pairs efficiently. The N element dopant plays the roles of narrowing the band gap of TiO2 based composite, and strengthening the chemical binding between N-RGO and TiO2, which is of benefit to charge separation and electron mobility.

Operating and Sensing Mechanism of Electrolyte-Gated Transistors with Floating Gates: Building a Platform for Amplified Biodetection

Abstract: Electrolyte-gated transistors (EGTs) with floating gates (FGs) are an emerging platform for label-free electronic biodetection. Advantages of floating gate EGTs (FG-EGTs) include signal amplification and inherent sensitivity to small voltages, on the order of 10 mV, associated with chemical binding events on the floating gate electrode surface. Here we examine how the performance of these devices depends on their architecture, specifically the relative sizes (areas) of the control gate, the floating gate, and the source–semiconductor–drain channel. The results allow optimization of the geometry for future biodetection studies. Further, using self-assembled monolayer (SAM) chemistry, we also examine the effect of chemisorption on the floating gate on the current voltage (I–V) characteristics. We find the FG-EGTs respond to both interfacial dipoles and capacitance changes and that the I–V behavior can be reasonably predicted with a lumped capacitor model. Overall, this work provides the most detailed pictur...

Investigation of Charge Transfer in Ag/N719/TiO2 Interface by Surface-Enhanced Raman Spectroscopy

Abstract: The interfaces of metal–dye molecule–semiconductor sandwich structure are very important in the investigation of dye-sensitized solar cells (DSSCs) where metals are used to enhance absorption. In this work, we first designed and synthesized Ag/N719 and Ag/N719/TiO2 sandwich systems to investigate the chemical binding type at the interfaces of Ag/N719/TiO2. The results of the Raman spectra under the laser excitations of 532, 633, and 785 nm clarified that the SCN groups adsorbed on the Ag surface via the S terminal and the TiO2 layer possibly bound to Ag/N719 via the ester linkage (—O—C═O) of the COOH group in N719. Then, we optimized the Ag substrate as an SERS detection platform and selected the Ag sol film as the substrate. Last, the relationship between the “degree of CT (ρCT)” in the SERS spectra and the charge transfer (CT) process was investigated by tuning the contribution from the chemical effect. We found that, owing to the introduction of TiO2, the intensity and ρCT first increased (n = 0–2) and...

Ultracold molecular Rydberg physics in a high density environment

Abstract: Sufficiently high densities in Bose–Einstein condensates provide favorable conditions for the production of ultralong-range polyatomic molecules consisting of one Rydberg atom and a number of neutral ground state atoms. The chemical binding properties and electronic wave functions of these exotic molecules are investigated analytically via hybridized diatomic states. The effects of the molecular geometry on the system's properties are studied through comparisons of the adiabatic potential curves and electronic structures for both symmetric and randomly configured molecular geometries. General properties of these molecules with increasing numbers of constituent atoms and in different geometries are presented. These polyatomic states have spectral signatures that lead to non-Lorentzian line-profiles.

Influence of Ocean Acidification on the Organic Complexation of Iron and Copper in Northwest European Shelf Seas; a Combined Observational and Model Study

Abstract: The pH of aqueous solutions is known to impact the chemical speciation of trace metals. In this study we conducted titrations of coastal seawaters with iron and copper at pH 7.91, 7.37 and 6.99 (expressed on the total pH scale). Changes in the concentration of iron and copper that complexed with the added ligands 1-nitroso-2-napthol and salicylaldoxime respectively were determined by adsorptive cathodic stripping voltammetry - competitive ligand equilibrium (AdCSV-CLE). Interpretation of the results, assuming complexation by a low concentration of discrete ligands, showed that conditional stability constants for iron complexes increased relative to inorganic iron complexation as pH decreased by approximately 1 log unit per pH unit, whilst those for copper did not change. No trend was observed for concentrations of iron and copper complexing ligands over the pH range examined. We also interpreted our titration data by describing chemical binding and polyelectrolytic effects using non-ideal competitive adsorption in Donnan-like gels (NICA-Donnan model) in a proof of concept study. The NICA-Donnan approach allows for the development of a set of model parameters that are independent of ionic strength and pH, and thus calculation of metal speciation can be undertaken at ambient sample pH or the pH of a future, more acidic ocean. There is currently a lack of basic NICA-Donnan parameters applicable to marine dissolved organic matter (DOM) so we assumed that the measured marine dissolved organic carbon could be characterized as terrestrial fulvic acids. Generic NICA-Donnan parameters were applied within the framework of the software program visual MINTEQ and the metal –added ligand concentrations [MeAL] calculated for the AdCSV-CLE conditions. For copper, calculated [MeAL] using the NICA-Donnan model for DOM were consistent with measured [MeAL], but for iron an inert fraction with kinetically inhibited dissolution was required in addition to the NICA-Donnan model in order to approximate the trends observed in measured [MeAL]. We calculated iron and copper speciation in Northwest European shelf water samples at ambient alkalinity and projected increased pCO2 concentrations as a demonstration of the potential of the approach.

Improving the antifouling properties of ceramic membranes via chemical grafting of organosilanes

Abstract: For enhanced antifouling surface properties, the alumina membranes were modified through a simple silanization process. Three organosilanes presenting neutral, positive, and negative charges were allowed to graft onto alumina membranes. A small decrease in the pore size and the successful chemical binding of organosilanes were confirmed, respectively. The membrane filtration test using humic acid (HA) was conducted to evaluate the effect of surface charges on fouling resistance. The neutral and negatively charged membranes achieved remarkable flux behaviour due to no charge interaction and electrostatic repulsion force, respectively. Especially, the negatively charged membranes presented the lowest flux decline, the highest flux recovery, and the lowest membrane fouling.

Microscale Rockets and Picoliter Containers Engineered from Electrospun Polymeric Microtubes.

Abstract: Chemically functional core/shell microtubes made of biodegradable polymers are fabricated using coaxial electrospinning. The luminal walls are chemically functionalized, allowing for regioselective chemical binding or adsorption inside the microtube. Attaching catalytic nanoparticles or enzymes to the luminal walls converts the microtubes into bubble-propelled microrockets. Upon exposure to ultrasound, the microtubes undergo shape shifting, transforming them into picoliter-scale containers.

Uptake of macro nutrients, barium, and strontium by vegetation from mineral soils on carbonatite and pyroxenite bedrock at the Lillebukt Alkaline Complex on Stjernøy, Northern Norway

Abstract: Carbonatite originating from the Lillebukt Alkaline Complex at Stjernoy in Northern Norway possesses favorable lime and potassium (K) fertilizer characteristics. However, enrichments of barium (Ba) and strontium (Sr) in carbonatite may cause an undesired uptake by plants when applied to agroecosystems. A field survey was carried out to compare concentrations of Ba, Sr, and macronutrients in indigenous plants growing in mineral soil developed on a bedrock of apatite–biotite–carbonatite (high in Ba and Sr) and of apatite–hornblende–pyroxenite (low in Ba and Sr) at Stjernoy. Samples of soil and vegetation were collected from three sites, two on carbonatite bedrock and one on pyroxenite bedrock. Ammonium lactate (AL)-extracted soil samples and nitric acid microwave-digested samples of soil, grasses, dwarf shrubs, and herbs were analyzed for element concentration using ICP-MS and ICP-OES. Concentrations of magnesium (Mg) and calcium (Ca) in both soil (AL) and plants were equal to or higher compared to values commonly reported. A high transfer of phosphorus (P) from soil to plants indicates that the apatite-P is available to plants, particularly in pyroxenite soil. The non-exchangeable K reservoir in the soil made a significant contribution to the elevated K transfer from soil to plant. Total concentrations of Ba and Sr in surface soil exhibited a high spatial variation ranging from 490 to 5,300 mg Ba kg−1 and from 320 to 1,300 mg Sr kg−1. The transfer of AL-extractable elements from soil to plants increased in the order Ba < Sr < Ca < Mg < K, hence reflecting the chemical binding strength of these elements. Concentrations of Ba and Sr were low in grasses (≈ 20 mg kg−1), intermediate in dwarf shrubs and highest in herbs. Plant species and their affinity for Ca seemed more important in explaining the uptake of Ba and Sr than the soil concentration of these elements. The leguminous plant species Vicia cracca acted as an accumulator of both Ba (1.800 mg kg−1) and Sr (2.300 mg kg−1).

The adverse outcome pathway (AOP) for chemical binding to tubulin in oocytes leading to aneuploid offspring

Abstract: The Organisation for Economic Co-operation and Development (OECD) has launched the Adverse Outcome Pathway (AOP) Programme to advance knowledge of pathways of toxicity and improve the use of mechanistic information in risk assessment. An AOP links a molecular initiating event (MIE) to an adverse outcome (AO) through intermediate key events (KE). Here, we present the scientific evidence in support of an AOP whereby chemicals that bind to tubulin cause microtubule depolymerization resulting in spindle disorganization followed by altered chromosome alignment and segregation and the generation of aneuploidy in female germ cells, ultimately leading to aneuploidy in the offspring. Aneuploidy, an abnormal number of chromosomes that is not an exact multiple of the haploid number, is a well-known cause of human disease and represents a major cause of infertility, pregnancy failure, and serious genetic disorders in the offspring. Among chemicals that induce aneuploidy in female germ cells, a large majority impairs microtubule dynamics and spindle function. Colchicine, a prototypical chemical that binds to tubulin and causes microtubule depolymerization, is used here to illustrate the AOP. This AOP is specific to female germ cells exposed during the periovulation period. Although the majority of the data come from rodent studies, the available evidence suggests that the MIE and KEs are conserved across species and would occur in human oocytes. The development of AOPs related to mutagenicity in germ cells is expected to aid the identification of potential hazards to germ cell genomic integrity and support regulatory efforts to protect population health.

Dual-Confined Sulfur Nanoparticles Encapsulated in Hollow TiO2 Spheres Wrapped with Graphene for Lithium-Sulfur Batteries.

Abstract: Lithium–sulfur (Li−S) batteries are attractive owing to their higher energy density and lower cost compared with the universally used lithium-ion batteries (LIBs), but there are some problems that stop their practical use, such as low utilization and rapid capacity-fading of the sulfur cathode, which is mainly caused by the shuttle effect, and the uncontrollable deposition of lithium sulfide species. Herein, we report the design and fabrication of dual-confined sulfur nanoparticles that were encapsulated inside hollow TiO2 spheres; the encapsulated nanoparticles were prepared by a facile hydrolysis process combined with acid etching, followed by “wrapping” with graphene (G−TiO2@S). In this unique composite architecture, the hollow TiO2 spheres acted as effective sulfur carriers by confining the polysulfides and buffering volume changes during the charge-discharge processes by means of physical force from the hollow spheres and chemical binding between TiO2 and the polysulfides. Moreover, the graphene-wrapped skin provided an effective 3D conductive network to improve the electronic conductivity of the sulfur cathode and, at the same time, to further suppress the dissolution of the polysulfides. As results, the G−TiO2@S hybrids exhibited a high and stable discharge capacity of up to 853.4 mA h g−1 over 200 cycles at 0.5 C (1 C=1675 mA g−1) and an excellent rate capability of 675 mA h g−1 at a current rate of 2 C; thus, G−TiO2@S holds great promise as a cathode material for Li−S batteries.