Showing papers on "Chemical binding published in 2014"

Strong Sulfur Binding with Conducting Magnéli-Phase TinO2n–1 Nanomaterials for Improving Lithium–Sulfur Batteries

Abstract: Lithium–sulfur batteries show fascinating potential for advanced energy storage systems due to their high specific capacity, low-cost, and environmental benignity. However, the shuttle effect and the uncontrollable deposition of lithium sulfide species result in poor cycling performance and low Coulombic efficiency. Despite the recent success in trapping soluble polysulfides via porous matrix and chemical binding, the important mechanism of such controllable deposition of sulfur species has not been well understood. Herein, we discovered that conductive Magneli phase Ti4O7 is highly effective matrix to bind with sulfur species. Compared with the TiO2–S, the Ti4O7–S cathodes exhibit higher reversible capacity and improved cycling performance. It delivers high specific capacities at various C-rates (1342, 1044, and 623 mAh g–1 at 0.02, 0.1, and 0.5 C, respectively) and remarkable capacity retention of 99% (100 cycles at 0.1 C). The superior properties of Ti4O7–S are attributed to the strong adsorption of su...

Continuous Ultra-Thin MoS2 Films Grown by Low-Temperature Physical Vapor Deposition

Abstract: Uniform growth of pristine two dimensional (2D) materials over large areas at lower temperatures without sacrifice of their unique physical properties is a critical pre-requisite for seamless integration of next-generation van der Waals heterostructures into functional devices. This Letter describes a vapor phase growth technique for precisely controlled synthesis of continuous, uniform molecular layers of MoS2 on silicon dioxide and highly oriented pyrolitic graphite substrates of over several square centimeters at 350 °C. Synthesis of few-layer MoS2 in this ultra-high vacuum physical vapor deposition process yields materials with key optical and electronic properties identical to exfoliated layers. The films are composed of nano-scale domains with strong chemical binding between domain boundaries, allowing lift-off from the substrate and electronic transport measurements from contacts with separation on the order of centimeters.

Continuous Ultra-Thin MOS2 Films Grown by Low-Temperature Physical Vapor Deposition (Postprint)

Abstract: : Uniform growth of pristine two dimensional (2D) materials over large areas at lower temperatures without sacrifice of their unique physical properties is a critical pre-requisite for seamless integration of next-generation van der Waals heterostructures into functional devices. This Letter describes a vapor phase growth technique for precisely controlled synthesis of continuous, uniform molecular layers of MoS2 on silicon dioxide and highly oriented pyrolitic graphite substrates of over several square centimeters at 350 deg C. Synthesis of few-layer MoS2 in this ultra-high vacuum physical vapor deposition process yields materials with key optical and electronic properties identical to exfoliated layers. The films are composed of nano-scale domains with strong chemical binding between domain boundaries, allowing lift-off from the substrate and electronic transport measurements from contacts with separation on the order of centimeters.

Toxic Elements in Food: Occurrence, Binding, and Reduction Approaches

Abstract: Toxic elements such as mercury, arsenic, cadmium, and lead, sometimes called heavy metals, can diminish mental and central nervous system function; elicit damage to blood composition as well as the kidneys, lungs, and liver; and reduce energy levels. Food is considered one of the main routes of their entry into the human body. Numerous studies have been performed to examine the effects of common food processing procedures on the levels of toxic elements in food. While some studies have reported negative effects of processing, several have shown that processing practices may have a positive effect on the reduction of toxic elements in foodstuffs. A number of studies have also introduced protocols and suggested chemical agents that reduce the amount of toxic elements in the final food products. In this review, the reported methods employed for the reduction of toxic elements are discussed with particular emphasis on the chemical binding of both the organic and inorganic forms of each element in various foods. The molecular groups and the ligands by which the food products bind with the metals and the types of these reactions are also presented.

Functional Polymer Nanocomposites with Graphene: A Review

Abstract: Polymer/graphene based nanomaterials have attracted significant scientific interest in the recent years due to marked enhancement in the polymer properties at low filler fractions. The property enhancements are attributed commonly to high aspect ratio of graphene platelets, filler–polymer interactions at the interface, as well as uniform dispersion of the platelets in the polymer matrices. Graphene also provides opportunities to tune its surface in order to achieve compatibility with the polymer matrices. Occasionally, chemical binding of the polymer matrix to the graphene surface has also been achieved.

Characterization of rheotaxis of bull sperm using microfluidics

Abstract: We study rheotaxis of bull sperm inside microchannels to characterize the effects of flow and wall shape on sperm swimming behavior. We found that a large percentage of sperm cells, 80 to 84%, exhibited positive rheotaxis (sperm cells swimming against the flow) within flow velocities of 33 to 134 μm s−1. Sperm cells were also found to reverse their swimming direction when the liquid flow direction was reversed. Time taken by sperm cells to reverse their swimming direction was inversely proportional to the flow velocity. Sperm behavior was significantly affected by the sperm position with respect to the channel wall. Sperm cells close to the channel wall moved upstream faster than sperm cells moving along the channel centerline. Shear stress, which is an indicator of velocity distribution, was found to play an important role in regulating rheotactic behavior of sperm cells. Side pockets were added to some microchannels to mimic storage sites in mucosal folds and pockets in the fallopian tube of the female reproductive system and sperm interaction with these pockets was monitored. We found that sperm cells tend to follow channel walls and enter these pockets without any chemical binding, which further confirms the wall tracking behavior of mammalian sperm cells. Our results confirm that sperm rheotaxis is a strong mechanism for guiding sperm cells towards the oocyte along the female genital tract.

Sorption of Cr(VI) on Mg–Al–Fe layered double hydroxides synthesized by a mechanochemical method

Abstract: Mg–Al–Fe layered double hydroxides (LDHs) with a constant Mg2+/(Fe3+ + Al3+) molar ratio but varying Fe3+/(Al3+ + Fe3+) molar ratios (RFe) from 0–1 were synthesized by a mechanochemical method. Sorption of Cr(VI) on the LDHs in aqueous solutions was investigated by a batch technique. The sorption process obeyed pseudo-second-order kinetics, and the sorption equilibrium could be well described with the Freundlich isotherm. The saturated sorption amount increased with increasing RFe, indicating that the replacement of Al by Fe in LDHs is favorable for Cr(VI) sorption. The mechanisms of Cr(VI) sorption included the intercalation of Cr(VI) oxyanions into the LDH gallery, and the surface complexation between dichromate anions and hydroxyl groups of the LDHs. The driving forces of Cr(VI) sorption on LDHs included physical binding (or electrostatic attraction) and chemical binding. The physically sorbed amount of Cr(VI) on the LDHs was almost independent of RFe, while the chemically sorbed amount obviously increased with increasing RFe. That is, the increase of RFe causes the chemical activity of surface sorption sites of the LDHs to increase, resulting in their sorption capacity for Cr(VI) increasing. In addition, the sorption capacity of the LDHs synthesized by the mechanochemical method is comparable with those of LDHs synthesized by coprecipitation and hydrothermal methods. Thus, Mg–Fe LDHs are promising sorbents for treating Cr(VI)-containing wastewater, and the mechanochemical method can be used to synthesize LDH sorbents.

Antimicrobial Cellulose Modified with Nanotitania and Cyclic N-Halamine

Abstract: Organic–inorganic composites have the drawn attention of researchers due to their combined properties. In this work, poly[5,5-dimethyl-3-(3′-triethoxysilylpropyl)hydantoin] (PSPH) was synthesized and coated onto cotton fibers together with titania nanoparticles (TiO2) by chemical binding in a one-bath process. The treated cotton with improved UV stability can produce biocidal properties against S. aureus (ATCC 6538) and E. coli O157:H7 (ATCC 43895) upon chlorination with diluted sodium hypochlorite solutions. The characteristics of the coated cotton were determined by SEM, FTIR, XRD, and XPS, and the washing stability and antibacterial efficacies were tested. Moreover, the N–Cl bond and compound stability under UV irradiation were measured. It was found that the treated cotton showed excellent antimicrobial properties within a brief contact time and great washing stability. The N–Cl bond and compound itself showed excellent stability under UV light irradiation.

Enhancement of the mechanical properties of hydroxyapatite by SiC addition.

Abstract: Improvements of mechanical and anticorrosive properties, as well as superior osseointegration of the hydroxyapatite coated titanium alloy were reported in the last years by the addition of different elements (Si or Ti) into hydroxyapatite structure. The aim of this work was to prepare and to investigate the hydroxyapatite (HAP) coatings enriched with SiC in order to enhance the mechanical properties of HAP films. The coatings were deposited on Ti6Al4V alloy substrates by co-sputtering of HAP and SiC targets, using a magnetron sputtering system. The films were characterized in terms of elemental and phase composition, chemical binding, morphology and mechanical properties by EDS, XRD, FTIR, SEM, AFM, and nanoindentation. Overall, improved mechanical properties were found by adding SiC to the basic HAP structure.

First-principles study of the interaction between NO and large carbonaceous clusters modeling the soot surface.

Abstract: First-principles calculations are performed to characterize the NO adsorption on large carbonaceous clusters modeling the surface of soot. Adsorption on the face and on the edges of perfect and defective clusters is considered in the calculations. It is shown that the first situation corresponds to physisorption and requires taking into account long-range dispersion interactions in the calculations. In contrast, interaction of NO with the unsaturated edge of a defective cluster leads preferentially to a C–N rather than to a C–O chemical binding. This indicates that soot may be an efficient sink for NO in the troposphere only if it contains a high number of unsaturated carbon atoms. From a more fundamental point of view, this study also clearly evidences that quantum calculations have to be carefully conducted when considering the interaction between radical species and carbonaceous surfaces. Problems encountered with the choice of the functional used in density functional theory approaches as well as with...

Combined Experimental and DFT Study of the Chemical Binding of Copper Ions on the Surface of Nanodiamonds

Abstract: DFT (density functional theory) computations of the chemical fixation of copper ions on the naturally functionalized surface of nanodiamond crystallites bound by (111) planes revealed exothermic fo...

Preparation of novel fibre–silica–Ag composites: the influence of fibre structure on sorption capacity and antimicrobial activity

Abstract: Novel fibre–silica–Ag composites with biocidal activity were successfully produced by chemical modifying cotton (CO), wool (WO), silk (SE), polyamide (PA) and polyester (PES) fabrics and CO/PES and WO/PES fabric blends A silica–Ag coating was prepared using a two-step procedure that included the creation of a silica matrix on the fibre surface via the application of an inorganic–organic hybrid sol–gel precursor [reactive binder (RB)] using a pad-dry-cure method, followed by the in situ synthesis of AgCl particles within the RB-treated fibres from solutions of 010 mM and 050 mM AgNO3 and NaCl The presence of the coating on the fibres was verified by scanning electron microscopy and energy-dispersive X-ray spectroscopy The bulk concentration of Ag in the coated fibres was determined using inductively coupled plasma mass spectroscopy The antimicrobial activity was determined for the bacteria Escherichia coli and Staphylococcus aureus and the fungus Aspergillus niger The results show that the chemical and morphological structures of the fibres directly influenced their absorptivity and affinity for the Ag compound particles As the amorphous molecular structure of the fibres and the amount of functional groups available as binding sites for Ag+ were increased, both the silver solution uptake and the concentration of the absorbed Ag compound particles increased The chemical binding of Ag to the fibres significantly reduced the effectiveness of the antimicrobial activity of the Ag compound particles Accordingly, an increase in the concentration of absorbed Ag was required to achieve a biocidal effect

Development of a solid-phase microextraction fiber by the chemical binding of graphene oxide on a silver-coated stainless-steel wire with an ionic liquid as the crosslinking agent

Abstract: Graphene oxide was bonded onto a silver-coated stainless-steel wire using an ionic liquid as the crosslinking agent by a layer-by-layer strategy. The novel solid-phase microextraction fiber was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and Raman microscopy. A multilayer graphene oxide layer was closely coated onto the supporting substrate. The thickness of the coating was about 4 μm. Coupled with gas chromatography, the fiber was evaluated using five polycyclic aromatic hydrocarbons (fluorene, anthracene, fluoranthene, 1,2-benzophenanthrene, and benzo(a)pyrene) as model analytes in direct-immersion mode. The main conditions (extraction time, extraction temperature, ionic strength, and desorption time) were optimized by a factor-by-factor optimization. The as-established method exhibited a wide linearity range (0.5-200 μg/L) and low limits of determination (0.05-0.10 μg/L). It was applied to analyze environmental water samples of rain and river water. Three kinds of the model analytes were quantified and the recoveries of samples spiked at 10 μg/L were in the range of 92.3-120 and 93.8-115%, respectively. The obtained results indicated the fiber was efficient for solid-phase microextraction analysis.

A rule-based expert system for chemical prioritization using effects-based chemical categories.

Abstract: A rule-based expert system (ES) was developed to predict chemical binding to the estrogen receptor (ER) patterned on the research approaches championed by Gilman Veith to whom this article and journal issue are dedicated. The ERES was built to be mechanistically transparent and meet the needs of a specific application, i.e. predict for all chemicals within two well-defined inventories (industrial chemicals used as pesticide inerts and antimicrobial pesticides). These chemicals all lack structural features associated with high affinity binders and thus any binding should be low affinity. Similar to the high-quality fathead minnow database upon which Veith QSARs were built, the ERES was derived from what has been termed gold standard data, systematically collected in assays optimized to detect even low affinity binding and maximizing confidence in the negatives determinations. The resultant logic-based decision tree ERES, determined to be a robust model, contains seven major nodes with multiple effects-base...

Immobilization of β-glucosidase onto mesoporous silica support: Physical adsorption and covalent binding of enzyme

Abstract: In this study, the immobilization of β-glucosidase onto mesoporous silica support by physical adsorption and covalent binding was investigated. The immobilization was performed onto micro-sized silica aggregates with an average pore size of 29 nm. During physical adsorption, the highest yield of immobilized β-glucosidase was obtained with an initial protein concentration of 0.9 mg mL -1 . The addition of NaCl increased 1.7-fold, while the addition of Triton X-100 decreased 6-fold adsorption yield in comparison to the one obtained without any addition. Covalently bonded β-glucosidase, via glutaral- dehyde previously bonded to silanized silica, had a higher yield of immobilized enzyme as well as higher activity and substrate affinity in comparison to the one physically adsorbed. Covalent binding did not considerably change pH and temperature stability of the obtained biocatalyst in range of values that are commonly used in reactions in comparison to the unbound enzyme. Further- more, covalent binding provided a biocatalyst that retained over 70 % of its activity after 10 cycles of reuse.

Organic-inorganic interface-induced multi-fluorescence of MgO nanocrystal clusters and their applications in cellular imaging

Abstract: Surface functionalization of inorganic nanomaterials through chemical binding of organic ligands on the surface unsaturated atoms, forming unique organic-inorganic interfaces, is a powerful approach for creating special functions for inorganic nanomaterials. Herein, we report the synthesis of hierarchical MgO nanocrystal clusters (NCs) with an organic-inorganic interface induced multi-fluorescence and their application as new alternative labels for cellular imaging. The synthetic method was established by a dissolution and regrowth process with the assistance of carboxylic acid, in which the as-prepared MgO NCs were modified with carboxylic groups at the coordinatively unsaturated atoms of the surface. By introducing acetic acid to partially replace oleic acid in the reaction, the optical absorption of the produced MgO NCs was progressively engineered from the UV to the visible region. Importantly, with wider and continuous absorption profile, those MgO NCs presented bright and tunable multicolor emissions from blue-violet to green and yellow, with the highest absolute quantum yield up to (33±1) %. The overlap for the energy levels of the inorganic-organic interface and low-coordinated states stimulated a unique fluorescence resonance energy transfer phenomenon. Considering the potential application in cellular imaging, such multi-fluorescent MgO NCs were further encapsulated with a silica shell to improve the water solubility and stability. As expected, the as-formed MgO@SiO2 NCs possessed great biocompatibility and high performance in cellular imaging.

Methods of microorganism immobilization for dynamic atomic-force studies (review)

Abstract: Atomic-force microscopy (AFM) is an efficient method for studying the surface ultrastructure and nanomechanical properties of biological objects, including microorganisms. A correctly selected method of microorganism immobilization that provides a strong attachment of cells on the surface of a biologically inert substrate and preservation of their native properties is important for AFM scanning in liquid media. Comparative characteristics of methods of microorganism immobilization applied in dynamic AFM studies are discussed in the review. Technologies of mechanical entrapment and chemical binding of cells to a substrate, as well as protein and immunospecific adsorption, are considered.

Plasma Polymerization Inside Tubes in Hexamethyldisiloxanes and Ethyne Glow Discharges: Effects of Deposition Atmosphere on Wetting and Ageing in Solvents

Abstract: The coating deposition inside tubes becomes increasingly important for fluidic applications, in which inner surfaces are chemically and mechanically strained by the flowing liquid and by scratching of particles. The developed process for tube coating, presented in this work, is based on the discharge in the precursor gas atmosphere between two mesh electrodes at the ends of the tube. The gas mixture is introduced on one end and pumped through the electrode on the other end. Igniting plasma inside the tube, the tube walls are the barrier to the atmosphere. Especially pulsed DC discharges for plasma polymerization in this alignment lead to good coating results, which is shown in this work focusing on deposition in pure and mixed hexamethyldisiloxane, ethyne, and oxygen atmospheres. Chemical binding, wetting, and ageing are strongly influenced by the choice of the gas mixtures. Sufficient oxygen partial pressure in the deposition atmosphere leads to hydrophilic behavior of the SiO2-like polymer-like carbon coatings, all other applied atmospheres to generally hydrophobic behavior of pure and Si-doped plasma polymers, respectively.