Showing papers on "Chemical binding published in 2003"

Study of 202 natural, synthetic, and environmental chemicals for binding to the androgen receptor.

Abstract: A number of environmental and industrial chemicals are reported to possess androgenic or antiandrogenic activities. These androgenic endocrine disrupting chemicals may disrupt the endocrine system of humans and wildlife by mimicking or antagonizing the functions of natural hormones. The present study developed a low cost recombinant androgen receptor (AR) competitive binding assay that uses no animals. We validated the assay by comparing the protocols and results from other similar assays, such as the binding assay using prostate cytosol. We tested 202 natural, synthetic, and environmental chemicals that encompass a broad range of structural classes, including steroids, diethylstilbestrol and related chemicals, antiestrogens, flutamide derivatives, bisphenol A derivatives, alkylphenols, parabens, alkyloxyphenols, phthalates, siloxanes, phytoestrogens, DDTs, PCBs, pesticides, organophosphate insecticides, and other chemicals. Some of these chemicals are environmentally persistent and/or commercially important, but their AR binding affinities have not been previously reported. To the best of our knowledge, these results represent the largest and most diverse data set publicly available for chemical binding to the AR. Through a careful structure-activity relationship (SAR) examination of the data set in conjunction with knowledge of the recently reported ligand-AR crystal structures, we are able to define the general structural requirements for chemical binding to AR. Hydrophobic interactions are important for AR binding. The interaction between ligand and AR at the 3- and 17-positions of testosterone and R1881 found in other chemical classes are discussed in depth. The SAR studies of ligand binding characteristics for AR are compared to our previously reported results for estrogen receptor binding.

Depth profiling characterisation of the surface layer obtained by pulsed Nd :YAG laser irradiation of titanium in nitrogen

Abstract: We investigated the composition of the surface layer obtained by pulsed Nd:YAG laser (λ=1.064 μm, τ∼120 ns, ν=1 kHz) irradiation of Ti targets in high pressure nitrogen. The surface morphology, the crystalline state, and the depth distribution of the elements were analysed by scanning electron microscopy, X-ray diffractometry, secondary ion mass spectrometry, X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy. The chemical binding states were studied by deconvolution of the XPS spectra. The layer has a uniform surface, and mainly consists of the tetragonal δ′-TiNx crystalline phase. The nitrogen concentration increases firstly in the depth until approximately 0.15 μm, and then decreases until the greatest measured depth of 2 μm. The TiNx stoichiometry changes from x≈0.8 close to the surface to x≈0.5 at a depth of approximately 0.2 μm, it remains around this value until approximately 0.5 μm, and for greater depths decreases until 0.1 at 1.6 μm. Furthermore, the oxygen concentration decreases quickly and reaches the concentration of bulk Ti at approximately 0.2 μm.

Functionalization of carbon nanotubes through the chemical binding of atoms and molecules

Abstract: We present a proposal for altering the electronic properties of single wall carbon nanotubes (SWNT's) through the chemical binding of atoms and molecules. This binding would be performed at Si substitutional defect sites, which would guarantee a high stability to the system. We argue that, by appropriately choosing the atom or radical bound to the Si atom, one can have a greater doping flexibility than has been achieved so far, and can, in principle, engineer transport, optical, or other properties of SWNT's. These conclusions are based on detailed first-principles calculations for a $\mathrm{Si}\ensuremath{-}X$ doped semiconducting (10,0) SWNT, for $X={\mathrm{F},$ Cl, H, ${\mathrm{CH}}_{3},$ and ${\mathrm{SiH}}_{3}}.$

Characterization of parylene‐N and parylene‐C photooxidation

Abstract: Parylene-N and parylene-C are polymers of interest for microelectronic and medical coating applications. Modifications for improved surface properties could make them even more useful in such applications. Parylene-N and parylene-C films were exposed to ultraviolet light in the presence of oxygen and analyzed with Rutherford backscattering spectrometry, secondary-ion mass spectroscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. This study shows that such exposure results in the formation of aldehyde and carboxylic acid groups near the surface of the films. At the maximum exposure dose, the concentration of oxygen in both parylene-N and parylene-C is about 13% at the film surface, and it decreases exponentially with increasing depth. Further modeling and optimization of this process would allow it to be used to tailor the surface concentration of oxygenated species in parylene for the optimization of adhesion and wettability or for the chemical binding of other moieties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1486–1496, 2003

Dative and Di−σ Binding States of Pyridine on Si(100) and Their Thermal Stability

Abstract: The chemical binding of pyridine on Si(100) has been studied using thermal desorption spectroscopy (TDS), X-ray phototelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and DFT theoretical calculations. XPS results show two chemisorption states of pyridine with N 1s binding energies at 398.8 and 401.8 eV, attributable to the [4+2]-like cycloadduct with two σ-linkages of Si−N1 and Si−C4, and the dative-bonded pyridine through the lone pair electrons of its N atom, respectively. These observations were further confirmed in our vibrational studies. The formation of a dative bond between pyridine and Si(100) demonstrates a new approach for the chemical attachment of unsaturated organic molecules on the Si surface. The 1,4-dihydropyridine-like cycloadduct formed at 350 K can be considered as a template for further modification and functionalization of Si surfaces or as an intermediate for syntheses in a vacuum.

Quantitative structure-activity relationship models for prediction of estrogen receptor binding affinity of structurally diverse chemicals.

Abstract: The demonstrated ability of a variety of structurally diverse chemicals to bind to the estrogen receptor has raised the concern that chemicals in the environment may be causing adverse effects through interference with nuclear receptor pathways. Many structure-activity relationship models have been developed to predict chemical binding to the estrogen receptor as an indication of potential estrogenicity. Models based on either two-dimensional or three-dimensional molecular descriptions that have been used to predict potential for binding to the estrogen receptor are the subject of the current review. The utility of such approaches to predict binding potential of diverse chemical structures in large chemical inventories, with potential application in a tiered risk assessment scheme, is discussed.

Attachment of styrene and phenylacetylene on Si(111)-7 x 7: the influence of substitution groups on the reaction mechanism and formation of pi-conjugated skeletons.

Abstract: The interactions of styrene and phenylacetylene and their isotope substitutions with a Si(111)-7 x 7 surface have been studied as model systems to mechanistically understand the chemical binding of conjugated pi-electron systems to di-radical-like silicon dangling bonds of the adjacent adatom-rest atom pair. Vibrational studies show that styrene mainly binds to the surface through a diradical reaction involving both the external C=C and its conjugated internal C=C of the phenyl ring with an adjacent adatom-rest atom pair, forming a 5-ethylidene-1,3-cyclohexadiene-like skeleton. On the other hand, phenylacetylene was shown to be covalently attached to Si(111)-7 x 7 through the external C[triple bond]C, forming a styrene-like conjugation system. These experimental results are consistent with density functional theory calculations. The different binding mechanisms for styrene and phenylacetylene clearly demonstrate that reaction channels for multifunctional organic molecules are strongly dependent on the chemical and physical properties of the functional groups. The resulting pi-electron conjugation structures may possibly be employed as intermediates for further organic syntheses and fabrication of multilayer organic films on semiconductor surfaces.

Self sustaining vitrification for immobilisation of radioactive and toxic waste

Abstract: The immobilisation of hazardous (toxic and radioactive) waste using self sustaining vitrification processes is reviewed. Self sustaining vitrification processes utilise the energy released during exothermic chemical reactions in a mixture of waste and powder metal fuel (PMF) to form a glass-like material without requiring an external power supply. The self sustaining vitrification process is controlled by the composition of the initial mixture of waste and PMF. A number of wastes have been successfully vitrified into durable glass-like waste forms. Since they do not require complex equipment or energy supplies, self sustaining vitrification processes are particularly attractive for immobilising relatively small amounts of problematic wastes. Heavy metals (Pb, Hg, Cd, Zn) are known to have adverse effects on human health and are stable and persistent environmental contaminants that cannot be degraded or destroyed. (1) Important waste streams containing heavy metals as contaminants are ashes, foundry and smelter residues, combustion by-products, furnace slag, electro-galvanic residues, and cullet from cathode ray tubes. Radioactive waste is generated from reprocessing of spent nuclear fuel, various applications of radionuclides in hospitals, research activities at universities and institutes and from industrial use of radionuclides. Both chemically toxic and radioactive wastes need a reliable immobilisation route to limit contamination of the environment. Immobilisation of nonradioactive contaminants may enable them to be reused in some industrial applications, e.g. developments in using Zn containing slags as cement additives. However immobilisation of radioactive waste via vitrification is intended to make it safe for long term storage and disposal. Vitrification is one of the most developed of the immobilisation technologies. Vitrification of waste comprises melting or sintering of waste materials with the necessary glass-forming additives so that the final vitreous product incorporates the waste contaminants in its microstructure. Vitrification is particularly attractive because of the high chemical durability of the vitrified glass product. This characteristic has been used by industry for centuries. The chemical resistance of glass can allow it to remain in a corrosive environment for many thousands and even millions of years. Several glasses are found in nature such as obsidians (volcanic glasses), fulgarites (formed by lightning strikes), tektites found on land in Australasia and associated microtektites from the bottom of the Indian Ocean, moldavites from central Europe, and Libyan Desert glass from western Egypt. Some of these glasses have been in the natural environment for up to 300 million years with a very low alteration of only hundredths of a centimetre per million years. (2,3) In addition to its good durability glass has the ability to incorporate a vast range of elements into its structure. Vitrification is especially well suited to wastes that contain heavy metals or radioactive constituents enabling chemical binding of waste metals into the glass. Hazardous constituents from the waste can be immobilised into a vitreous product by two mechanisms: either by direct incorporation into the glass network or encapsulation. In the first case the waste constituents are dissolved in the glass melt and on cooling some of them are incorporated in the glass network, while others are confined as modifiers. Immobilisation by encapsulation is applied to elements and compounds that have low reduced solubility in the glass and thus are unable to be dissolved in the glass network. These are refractory oxides with very high liquidus temperatures such as spinels, sulphates, chlorides and molybdates. They are immobilised by the glass matrix by encapsulation into its structure in the form of a dispersed phase. Encapsulation can be carried out either by sintering or dispersion of insoluble compounds into the glass melt. Vitreous products in the form of both homogeneous glasses (e.g. having a relative small volume fraction of inhomogeneities) and

Investigation of Copper Agglomeration at Elevated Temperatures

Abstract: In this work, the agglomeration behavior of copper thin films after high temperature annealing was investigated. Cu ~ 200 or 50 nm!/Ta ~10 nm, or no Ta!/TaN ~50 nm!/Ta ~10 nm! layers were deposited onto SiO2 ~270 nm!/Si substrates by magnetron sputtering. All samples were annealed in vacuum at temperatures ranging from 400 to 800°C. The sheet resistance, phases, surface morphology, elemental depth profiles, and chemical binding states were investigated by four-point probe, u-2u X-ray diffraction, scanning electron microscopy ~SEM!, Auger electron spectroscopy, and X-ray photoelectron spectroscopy ~XPS!. Experimental results revealed that 50 nm thick copper films deposited directly onto TaN agglomerated after annealing at 600°C. No copper agglomeration was observed for 200 nm thick copper films even after annealing at 800°C. It is also observed that copper agglomeration was prevented while a Ta layer was interposed between Cu and TaN. SEM and XPS results showed that, with a Ta interposed interlayer, copper grain growth was slowed down and Ta out-diffused to the copper surface to form a TaOx layer. The slow grain growth rate of copper and forming of TaOx cap layer are believed to be the main reasons for preventing copper

Reversibly Altering Electronic Conduction through a Single Molecule by a Chemical Binding Event

Abstract: This letter presents experimental evidence that the electrical conductance of a single molecule can be altered by a chemical binding event. Self-assembled monolayers of electron donor tetramethyl xylyl dithiol (TMXYL) have been synthesized and chemically switched to a conducting state by reaction with an electron acceptor tetracyanoethylene (TCNE). Low bias conductance measurements obtained by scanning tunneling spectroscopy under ultrahigh vacuum conditions show a change from insulating to ohmic behavior as a result of the electron donor/acceptor interaction.

Surface plasmon resonance immunosensor for detection ofLegionella pneumophila

Abstract: An immunosensor based on surface plasmon resonance (SPR) onto a protein G layer by self-assembly technique was developed for detection ofLegionella pneumophila. The protein G layer by self-assembly technique was fabricated on a gold (Au) surface by adsorbing the 11-mercaptoundecanoic acid (MUA) and an activation process for the chemical binding of the free amine (-NH2) of protein G and 11-(MUA) using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDAC) in series. The formation of the protein G layer by self-assembly technique on the Au substrate and the binding of the antibody and antigen in series were confirmed by SPR spectroscopy. The surface topographies of the fabricated thin films on an Au substrate were also analyzed by using an atomic force microscope (AFM). Consequently, an immunosensor for the detection ofL. pneumophila using SPR was developed with a detection limit of up to 102 CFU per mL.

Laser microprocessing of wide bandgap materials

Abstract: Laser direct-write and doping technique (LDWD) is used to introduce variations in electric properties of wide band gap materials such as SiC and diamond. Conductive, p-type doped, n-type doped and insulative tracks are created on different diamond and SiC substrates using this method. The effects of various processing parameters such as laser-matter interaction time, number of repeated exposures, and type of irradiation environment are investigated. SEM, SIMS, XPS and Raman spectroscopy are used to study the effect of laser irradiation on the microstructure, chemical binding and to obtain dopant depth profile in the substrates, respectively. LDWD technique proved to enhance the dopant (nitrogen) diffusivity into SiC resulted in a diffusion coefficient (available in paper)that is four orders of magnitudes faster than the reported value (5 x 10 -12 cm 2 s -1 ). Process modeling is conducted to study the atomistic of laser-doping process and to utilize laser irradiation to increase both dopant penetration and concentration. Laser doping of nitrogen alters the Raman spectrum of the 4H-SiC suggesting that Raman spectroscopy can be used as a non-contact method to characterize the laser-doped SiC.

Signaling to p53: the use of phospho-specific antibodies to probe for in vivo kinase activation.

Abstract: Phospho-specific antibody technology has been recently adopted to study p53 phosphorylation both in vivo and in vitro. We have developed and carefully characterized p53 phosphospecific reagents directed to major amino- and carboxy-terminal regulatory sites. The specificities of both polyclonal and monoclonal reagents targeting the same phospho-epitope are discussed. We have defined the major chemical binding determinants for specific monoclonal reagents by determining the relative contribution of charge and sequence to epitope recognition. Remarkably, we have found that the utility of these reagents in different assay systems is not universal and depends both on epitope conformation and affinity. This is reflected in the striking differences in their ability to detect endogenous p53 and recombinant protein. Therefore, we conclude that this novel class of reagents is not generally applicable, but that the utility of each reagent must be determined empirically.

Density functional theory and multiscale materials modeling

Abstract: One of the vital ingredients in the theoretical tools useful in materials modeling at all the length scales of interest is the concept of density. In the microscopic length scale, it is the electron density that has played a major role in providing a deeper understanding of chemical binding in atoms, molecules and solids. In the intermediate mesoscopic length scale, an appropriate picture of the equilibrium and dynamical processes has been obtained through the single particle number density of the constituent atoms or molecules. A wide class of problems involving nanomaterials, interfacial science and soft condensed matter has been addressed using the density based theoretical formalism as well as atomistic simulation in this regime. In the macroscopic length scale, however, matter is usually treated as a continuous medium and a description using local mass density, energy density and other related density functions has been found to be quite appropriate. A unique single unified theoretical framework that emerges through the density concept at these diverse length scales and is applicable to both quantum and classical systems is the so called density functional theory (DFT) which essentially provides a vehicle to project the many-particle picture to a single particle one. Thus, the central equation for quantum DFT is a one-particle Schrodinger-like Kohn-Sham equation, while the same for classical DFT consists of Boltzmann type distributions, both corresponding to a system of noninter-acting particles in the field of a density-dependent effective potential. Selected illustrative applications of quantum DFT to microscopic modeling of intermolecular interaction and that of classical DFT to a meso-scopic modeling of soft condensed matter systems are presented.

Robust chemiresistor sensor

Abstract: A chemiresistor sensor probe for detecting target analytes. The probe includes a body having a first control surface and a second control surface recessed within the first. A sensor film comprises numerous conductive particles disposed upon the second surface. The film swells upon absorbing one or more analytes for which it has an affinity, thus causing the conductive particles to become more dispersed and increasing the resistance between the particles. The thickness of the film is equal to the distance between the first surface and the second surface, thus permitting the thickness to be controlled by varying the distance between the control surfaces. The robustness of the sensor probe is enhanced by placing a porous or mesh electrode along with, or in place of, a chemical binding agent between the film and the terminals. The robustness is also improved by placing a diode in series with the sensor circuit.

Ultrastructure and early embryonic shell formation in the terrestrial pulmonate snail, euhadra hickonis

Abstract: The distribution of calcium ion (Ca-ion) was demonstrated in the mantle epithelial cells by means of two-step chemical precipitation of Ca-ion in the pulmonate snail, Euhadra hickonis. K-oxalate/ K-antimonate chemical replacement was done using a simultaneous computerized microwavestimulated fixation method. These precipitates in the mantle epithelial cells were studied by electronprobe X-ray microanalysis (EDX) and electron energy-filtered imaging (EFI). The calculated values of the essential-elemental X-ray pulse ratios, which were obtained by computerized EDX analysis, agreed with those of the standard samples and theoretical values of Ca-antimonate. Typical EFI images and spectra energy of Ca and Sb were obtained from the surface mantle epithelial cells in the same tissue block as that used for EDX analysis where the elemental distribution of Ca and Sb was the same. The Ca-antimonate precipitates were formed in the intercellular space, vesicles and microvilli of mantle cells. In day 13 embryos, the columella and peripheral area were almost calcified, but in the dorsal area, Ca was still in the ionic state; the binding ratio of the former case was Ca:Sb = 1:0, that of the latter was Ca:Sb = 1:2, and that of the small intermediate area was Ca:Sb = 1:1.4. After day 17, the embryonal periostracum was almost calcified. Between days 15 and 20, strong Ca 2+ -ATPase and carbonic anhydrase (CAHase) enzymatic activities were observed at the sites where Ca-ion was observed; intercellular spaces, vacuoles in the mantle cells, periostracum and homogeneous layer between the periostracum and mantle cell, and in the mitochondria. Ca 2+ -ATPase may play important roles in the transportation of Ca-ion from the basal cell layer to the surface layer of the mantle cells and CAHase may play important roles in the chemical binding of Ca-ion and carbonate ion to produce calcium carbonate crystals in the newly developing embryonal shell.

De-gasifier for feed water for technical plant e.g. steam powered electrical energy generation plant, using chemical binding process or adsorption medium for reducing partial pressure of selected gases

Abstract: The de-gasifier (20) has a container (24) for the feed water coupled to a gas space (36) containing a device (30) for reducing the partial pressure of selected gases while the partial pressure of the remaining gases remains constant, using a chemical binding process or an absorption medium.

Structural characterization and effects of annealing on the electrical properties of stacked SiOxNy/Ta2O5 ultrathin films on strained-Si0.82Ge0.18 substrates

Abstract: Stacked SiOxNy/Ta2O5 films have been deposited on strained-Si0.82Ge0.18 layers at a low temperature in a microwave plasma using NO and tantalum pentaethoxide. The chemical binding states and composition of stacked Ta2O5/SiOxNy/SiGe films have been studied by time of flight secondary ion mass spectroscopy and x-ray photoelectron spectroscopy. Effects of annealing on the electrical properties of the dielectric films have been studied using high frequency capacitance–voltage, current–voltage and conductance–voltage techniques.

Van der Waals interactions of parallel and concentric nanotubes

Abstract: For sparse materials like graphitic systems and carbon nanotubes the standard density functional theory (DFT) faces significant problems because it cannot accurately describe the van der Waals interactions that are essential to the carbon-nanostructure materials behavior. While standard implementations of DFT can describe the strong chemical binding within an isolated, single-walled carbon nanotube, a new and extended DFT implementation is needed to describe the binding between nanotubes. We here provide the first steps to such an extension for parallel and concentric nanotubes through an electron-density based description of the materials coupling to the electrodynamical field. We thus find a consistent description of the (fully screened) van der Waals interactions that bind the nanotubes across the low-electron-density voids between the nanotubes, in bundles and as multiwalled tubes.