Showing papers on "Chemical binding published in 2002"

Structural and Chemical Characterization of Aligned Crystalline Nanoporous MgO Films Grown via Reactive Ballistic Deposition

Abstract: Highly porous (∼ 90%), high-surface area (∼1000 m2/g), thermally stable (1200 K) crystalline films of MgO are synthesized using a novel reactive ballistic deposition technique. The film consists of a tilted array of porous nanoscale crystalline filaments. Surprisingly, the individual filaments exhibit a high degree of crystallographic order with respect to each other. These films have chemical binding sites analogous to those on MgO(100). However, the fraction of chemically active, high energy binding sites is greatly enhanced on the nanoporous film. This unique collection of properties makes these materials attractive candidates for chemical applications such as sensors and heterogeneous catalysts.

Biophysics : An Introduction

Abstract: Preface. 1. Introduction. 2. Chemical Binding. 3. Energies, Forces and Bonds. 4. Rates of Reaction. 5. Transport Processes. 6. Some Techniques and Methods. 7. Biological Polymers. 8. Biological Membranes. 9. Biological Energy. 10. Movement of Organisms. 11. Excitable Membranes. 12. Nerve Signals. 13. Memory. 14. Control of Movement. Appendix A: Elements of Quantum Mechanics. Appendix B: The Hydrogen Atom. Appendix C: Thermal Motion. Appendix D: Probability Distributions. Appendix E: Differential Equations. Name Index. Subject Index.

Detection of Escherichia coli O157:H7 using immunosensor based on surface plasmon resonance

Abstract: An immunosensor based on surface plasmon resonance (SPR) with a self-assembled protein G layer was developed for the detection of Escherichia coli O157:H7. A self-assembled protein G layer on a gold (Au) surface was fabricated by adsorbing the mixture of 11-mercaptoundecanoic acid (MUA) and hexanethiol at various molar ratios and by activating chemical binding between free amine (-NH 2 ) of protein G and 11-(MUA) using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC) in series. The formation of a self-assembled protein G layer on an Au substrate and the binding of the antibody and antigen in series were confirmed by SPR spectroscopy. The surface morphology analyses of the self-assembled protein G layer on the Au substrate, monoclonal antibody (Mab) against E. coli O157:H7 which was immobilized on protein G, and bound E. coli O157:H7 extracts on immobilized Mab against E. coli O157:H7 were performed by atomic force microscopy (AFM). The detection limit of the SPR-based immunosensor for E. coli O157:H7 was found to be about 10 4 cells/ml.

Direct detection by atomic force microscopy of single bond forces associated with the rupture of discrete charge-transfer complexes.

Abstract: Atomic force microscopy (AFM) was used to measure the chemical binding force of discrete electron donor−acceptor complexes formed at the interface between proximal self-assembled monolayers (SAMs). Derivatives of the well-known electron donor N,N,N‘,N‘-tetramethylphenylenediamine (TMPD) and the electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) were immobilized on Au-coated AFM tips and substrates by formation of SAMs of N,N,N‘-trimethyl-N‘-(10-thiodecyl)-1,4-phenylenediamine (I) and bis(10-(2-((2,5-cyclohexadiene-1,4-diylidene)dimalonitrile))decyl) disulfide (II), respectively. Pull-off forces between modified tips and substrates were measured under CHCl3 solvent. The mean pull-off forces associated with TMPD/TCNQ microcontacts were more than an order of magnitude larger than the pull-off forces for TMPD/TMPD and TCNQ/TCNQ microcontacts, consistent with the presence of specific charge-transfer interactions between proximal TMPD donors and TCNQ acceptors. Furthermore, histograms of pull-off forces ...

Comparison of the characteristics of TiO2 films prepared by low-pressure and plasma-enhanced chemical vapor deposition

Abstract: Thin films of titanium dioxide (TiO2) were deposited on silicon wafers at 450 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD), in the same reactor, using Ti(O-i-C3H7)4 and oxygen as the reactants. The crystal structure, surface morphology, composition, chemical binding state and refractive index of the TiO2 films, deposited with various r.f. powers, were characterized. Without plasma, LPCVD TiO2 films show polycrystalline anatase structure, with a rough, granular surface and a typical refractive index of 2.43. On the contrary, the PECVD TiO2 films are amorphous, with a smooth surface. By varying the r.f. power from 50 to 150 W, the refractive index of PECVD TiO2 film increases with increasing power and becomes higher than 2.8 at 125 and 150 W. Despite the very different crystal structure, surface morphology and optical properties, the composition and chemical binding states of LPCVD and PECVD TiO2 films are similar. The effect of plasma on the characteristics of CVD TiO2 films is discussed.

Biosorption of organochlorine pesticides using fungal biomass.

Abstract: Cladosporium strain AJR(3)18501 was tested for its ability to sorb the organochlorine pesticide (OCP) p,p'-DDT from aqueous media. When p,p'-DDT was added to distilled water, ethanol or 1-propanol solutions in excess of its solubility, p,p'-DDT was sorbed onto the fungal biomass. Increasing the amount of p,p'-DDT in solution by changing the medium composition increased sorbent uptake: p,p'-DDT uptake by the fungal biomass was 2.5 times greater in 25% 1-propanol (17 mg of p,p'-DDT g(-1) dry weight fungal biomass) than in distilled water. When p,p'-DDT was dissolved in 25% 1-propanol (12 mg x l(-1)), rapid p,p'-DDT sorption occurred during the first 60 min of incubation. p,p'-DDT in solution was reduced to 2.5 mg x l(-1) with the remaining p,p'-DDT recovered from the fungal biomass. A number of environmental parameters were tested to determine their effect on p,p'-DDT biosorption. As arsenic (As) is prevalent at DDT-contaminated cattle dip sites, its effect on p,p'-DDT uptake was determined. The presence of As [As(III) or As(V) up to 50 mg x l(-1)] did not inhibit p,p'-DDT uptake and neither As species could be sorbed by the fungal biomass. Changing the pH of the medium from pH 3 to 10 had a small effect on p,p'-DDT sorption at low pH indicating that an ion exchange process is not the major mechanism for p,p'-DDT sorption. Other mechanisms such as Van der Waals forces, chemical binding, hydrogen bonding or ligand exchange may be involved in p,p'-DDT uptake by Cladosporium strain AJR(3)18501.

Feasibility of using carboxylic-rich polymeric surfaces for the covalent binding of oligonucleotides for microPCR applications

Abstract: The chemical binding of oligonucleotide/DNA on polystyrene-related polymeric surfaces has been investigated using contact angle measurements, x-ray photoelectron spectroscopy and gravimetric analysis. The results of the covalent attachment of the phosphorylated oligonucleotides using the hetero-bifunctional cross linker 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to polystyrene-co-maleic anhydride (PSMAA) and polystyrene-co-maleic acid (PSMA) are described. The immobilization efficiency of covalently coupled 26-mer oligonucleotides to polymeric surfaces was estimated as 0.3 × 1010 and 0.1 × 109 molecules mm−2 for PSMA and PSMAA, respectively. The results suggest that, although the covalent binding on PSMAA per se is not capable of the high density of DNA required by micro-PCR applications, the method has the potential to be used as a cheap alternative for other low-cost, less DNA-sensitive applications such as disposable biosensors.

Analysis of trace metal humic acid interactions using counterion condensation theory.

Abstract: Recent extensions of counterion condensation theory, originally developed for well-defined linear polyelectrolytes, enable us to analyze the interaction of trace metals with humic acid. In the present model, the heterogeneity of the macromolecule is taken into account as well as the chemical binding of the considered metal ions to the humic material. Experimentally, potentiometric titrations have been performed for humic acid in solution in the presence of different environmentally important (heavy) metals (Ca, Cd, Cu, Ni, and Pb) at various metal concentrations by titrating with potassium hydroxide without additional salt. From proton release data obtained for the initial point in the titration, it was estimated that the interaction of the different metals with the humic acid in terms of binding strength increased in the order Ca < Cd ≈ Ni < Pb ≈ Cu. These results were confirmed by model analysis. Experimentally obtained apparent dissociation constants were in good agreement for the humic acid systems co...

Microarray channel devices produced by a block mold process

Abstract: Microarrays are made from sections of a molded block having many channels. These channels, which are formed by casting and/or embedding a rod in a moldable solid, are used to immobilize biological and chemical binding components after rod removal. The microarrays can be used in general biological assays, clinical evaluations and chemical library analyses.

Contact mechanics modeling of pull-off measurements: effect of solvent, probe radius, and chemical binding probability on the detection of single-bond rupture forces by atomic force microscopy.

Abstract: Pull-off forces for chemically modified atomic force microscopy tips in contact with flat substrates coated with receptor molecules are calculated using a Johnson, Kendall, and Roberts contact mechanics model. The expression for the work of adhesion is modified to account for the formation of discrete numbers of chemical bonds (nBonds) between the tip and substrate. The model predicts that the pull-off force scales as nBonds(1/2), which differs from a common assumption that the pull-off force scales linearly with nBonds. Periodic peak progressions are observed in histograms generated from hundreds of computed pull-off forces. The histogram periodicity is the signature of discrete chemical interactions between the tip and substrate and allows estimation of single-bond rupture forces. The effects of solvent, probe tip radius, and chemical binding probability on the detection of single-bond forces are examined systematically. A dimensionless parameter, the effective force resolution, is introduced that serves as a quantitative predictor for determining when periodicity in force histograms can occur. The output of model is compared to recent experimental results involving tips and substrates modified with self-assembled monolayers. An advantage of this contact mechanics approach is that it allows straightforward estimation of solvent effects on pull-off forces.

Unusual Benefits of Macromolecular Shielding by Polyethylene Glycol for Reactions at the Diffusional Limit: The Case of Factor VIIai and Tissue Factor†

Abstract: Protein modification with poly(ethylene glycol) (PEG) can prolong circulatory lifetime and lower protein antigenicity in an animal. These benefits may arise from the proposed mechanism of PEG action, molecular shielding of the protein surface, and lowered interaction with other macromolecules. Proteins that depend on macromolecule association for their function would not seem good targets for PEG modification as the benefits may be mitigated by loss of function. Indeed, high loss of function applied to PEG-modified factor VIIa and to active site-blocked blood clotting factors Xa or IXa was studied. A surprising finding was that PEG-modified, active site-blocked factor VIIa (PEG-VIIai, PEG-40 000) retained 40% of its function despite an 18-fold increase in circulatory lifetime. The discrepancy between functional loss and increased circulatory lifetime was consistent with a process that was limited by the diffusion step of assembly rather than the chemical binding step. The impact of PEG-40 000 on diffusion...

Relationship between electronic and geometric structures of the O/Cu(001) system

Abstract: The electronic structure of the (22×2)R45° O/Cu(001) system has been calculated using locally self-consistent, real space multiple scattering technique based on first principles. Oxygen atoms are found to perturb differentially the long-range Madelung potentials, and hence the local electronic subbands at neighboring Cu sites. As a result the hybridization of the oxygen electronic states with those of its neighbors leads to bonding of varying ionic and covalent mix. Comparison of results with those for the c(2×2) overlayer shows that the perturbation is much stronger and the Coulomb lattice energy much higher for it than for the (22×2)R45° phase. The main driving force for the 0.5 ML oxygen surface structure formation on Cu(001) is thus the long-range Coulomb interaction which also controls the charge transfer and chemical binding in the system.

A physical model for atoms and nuclei—part 1

Abstract: A physical geometrical packing model for the structure of the atom is developed based on the physical toroidal ring model of elementary particles proposed by Bergman.(1) From the physical characteristics of real electrons from experiments by Compton (2,3,4) this work derives, using combinatorial geometry, the number of electrons that will pack into the various physical shells about the nucleus in agreement with the observed structure of the Periodic Table of the Elements. The constraints used in the combinatorial geometry derivation are based upon Joseph's simple but fundamental ring dipole magnet experiments and spherical symmetry. From a magnetic basis the model explains the physical origin of the valence electrons for chemical binding and the reason why the periodic table has only seven periods. The same geometrical packing model is extended to describe the physical geometrical packing of protons and neutrons in the physical shells of the nucleus. It accurately predicts the nuclear "magic numbers" indicative of nuclear shell structure as well as suggesting the physical origin of the nuclide spin and the liquid- drop features of nuclides.

Modification of capillary electrophoresis capillaries by poly(hydroxyethyl methacrylate), poly(diethylene glycol monomethacrylate) and poly(triethylene glycol monomethacrylate).

Abstract: Modification of capillary electrophoresis (CE) capillaries by poly(hydroxyethyl methacrylate) (poly(HEMA), poly(diethylene glycol monomethacrylate) (poly(DEGMA) and poly(triethylene glycol monomethacrylate) (poly(TEGMA), was studied Methods based on physical adsorption of the modifier and on its chemical binding were compared on the basis of the electroosmotic flow (EOF) reproducibility, the EOF dependence on the pH, the symmetry of the peak of positively charged tyramine, the stability of the coating and the separation of standard and milk proteins in the modified capillaries Reproducible coatings were obtained by chemical binding of the polymers to the capillary walls and by coating with a solution of a polymer, as also demonstrated by the atomic force microscopy

Binding and migration paths of Au adatoms on the GaAs(001) surface

Abstract: The binding and the migration paths of an isolated Au adatom on the GaAs (001)-β2(2 ×4) reconstructed surface have been investigated by first-principle total-energy calculations in the Car-Parrinello scheme. The potentialenergy surface calculated for the Au adatom shows that the most interesting Au binding sites are located at short-bridge sites next the As-As dimers of the surface. Similar binding sites were found for Ga adatoms on the same surface. However, the Au chemical binding is different from that of Ga. A Ga adatom forms strong covalent Ga-As bonds with a marked ionic character when interacting with the As dimers, while the Au-dimer interaction is characterized by the formation of weaker pure covalent Au-As bonds. Accordingly, Au adatoms do not break the As-As dimers at variance with the case of Ga adatoms. The characteristics of the Au binding also account for an anisotropic Au migration that results to be faster along the dimer rows than perpendicular to them.

EPR studies of free radical reactions of C60 embedded in mesoporous MCM-41 materials in aqueous solution

Abstract: The channels of the molecular sieve MCM-41 are employed as nanoreactors to study free radical attacks on C60 in aqueous media. Samples of C60 embedded in the nanochannels of mesoporous materials were prepared by the chemical binding of C60 to the amino-modified surface of MCM-41 solids. The spin trapping/EPR technique was employed to study the reactions of hydroxyl and methyl radicals with the embedded C60 in the nanochannels. The study enables us to examine the chemistry of C60 in aqueous solution, and the efficacy of free radical scavenging by C60 embedded in the nanochannels. The study further reveals the proximity effect of free radical reactions in a nano-restricted environment.

Comparison of metal sorption properties of three silica gel phases-physically adsorbed and chemically immobilized-1-aminoanthraquinone

Abstract: 1-Aminoanthraquinone was used for the modification of a silica surface by chemical reaction procedure as well as physical adsorption approach. Two different silica gel phases were synthesized on the basis of chemical binding of either nitrogen or oxygen atom of the organic modifier and one silica gel phase was formed upon physical adsorption of 1-aminoanthraquinone on the surface of silica gel. The stability test of the three newly synthesized silica gel phases (I–III) was performed in different buffer solutions (pH 1–6) for evaluation of the leaching process as well as identification of the most suitable buffer range for the analytical applications of phases (I–III). The physically adsorbed silica gel phase (I) was found to exhibit maximum hydrolysis percentage values while phases (II) and (III) were found to be fairly resistant to hydrolysis. The experimental buffer range for application of each phase was also stated on such phase hydrolysis. Applications of phases (I–III) for metal sorption pr...

A novel one-dimensional Ni(II)–Fe(II) polymer containing μ3-cyanides: [Ni(cyclen)]2[Fe(CN)6]·8H2O

Abstract: Reaction of K4[Fe(CN)6] with Ni(CH3COO)2 and cyclen produced an unusual one-dimensional paramagnetic complex, [Ni(cyclen)]2[Fe(CN)6]·8H2O (cyclen = 1,4,7,10-tetraazacyclododecane), that consists of [Ni(cyclen)]2 dimers bridged by μ3-cyanides from [Fe(CN)6]4−. The Ni⋯Ni distance is 3.303 A, which is significantly shorter than the corresponding distance of 3.449 A in [Ni2(μ-N3)2(232-tet)2](PF6)2. Moderate antiferromagnetic coupling occurs between the Ni2+ ions.

Guardrail posts and spacer blocks made with recycled rubber from shredded tires

Abstract: Mounting posts and spacer blocks, for installing and supporting guardrails near roads and other conveyances, can be made from rubber particles that have been obtained from shredded discarded tires. The posts and spacer blocks can be manufactured in any desired lengths (which normally will range from about 1 to about 3 meters, or 3 to 10 feet long for the posts, and up to about 40 cm or 16 inches long for the spacer blocks), and any desired thicknesses (such as with square or rectangular cross-sections ranging from about 10 to about 25 cm, or 4 to 10 inches on each side). The molding process can use an adhesive or other chemical binding agent, and/or heat combined with pressure, and can be done in molding cavities or by extrusion. These posts must have levels of strength and durability which have been declared acceptable, in all respects, to at least one governmental agency which is responsible for purchasing guardrails for installation along highways. These posts and spacer blocks are not brittle, and have a consistency similar to wood, and can be sawed, drilled, and otherwise worked, using conventional tools. They are highly durable and weather-resistant, and will provide longer lifespans in outdoor conditions than wooden posts. These devices also eliminate various other problems associated with wooden posts (such as the leaching of toxic chemicals out of treated wood), and provide a highly useful method for recycling discarded tires that otherwise create solid waste and public health problems.

XPS study of the An5f electronic states in actinide (Th, U, Np, Pu, Am, Cm, Bk) compounds.

Abstract: In the present work it was found that the relative intensity of the quasiatomic An5f- electron line correlates with the number n5f of such electrons in actinide compounds. The experimental dependence of the relative An5f line intensity for Th, U, Np, Pu, Am, Cm, and Bk in various compounds on the number n5f (I5f = 0.02 n5f) in the range from 0 to 7 was obtained. It gave a unique opportunity to determine the oxidation state of actinides in compounds, to conduct the X-ray photoelectron quantitative ionic analysis on the basis of the An5f line intensity, to study the participation degree of electrons in the chemical binding, and to carry out the comparison with the results of the theoretical calculations of the photoemission cross-sections.

Method for cleaning soil contaminated with heavy metal

Abstract: PROBLEM TO BE SOLVED: To provide a method for cleaning soil contaminated with heavy metals, which can effectively separate and remove particles containing the heavy metals in a high concentration from the soil to obtain a larger amount of clean soil capable of being refilled into the ground. SOLUTION: The soil contaminated with the heavy metals is mixed and agitated with a reducing agent, a chemical binding agent, or an adsorbent to insolubilize the soil. The insolubilized soil is classified according to particle diameters and is separated into a portion having a high heavy metal content and a portion having a low heavy metal content. The low-content portion is refilled into the ground after a simple treatment, and as regards the high-content portion, each soil classified according to particle diameters is subjected to gravitational separation, eluviation, electrolysis, etc., and the high-contaminant content portion is separated. By the insolubilization of the soil before the classification, it is possible to lessen the amount of the heavy metals dissolved in water in washing and classification steps to prevent the readhesion of the heavy metals separated from the soil particles on the particles. It is therefore possible to efficiently separate the high heavy metal content portion and the low heavy metal content portion in subsequent steps. COPYRIGHT: (C)2004,JPO&NCIPI

XPS Depth Profiling Studies of YBCO Layer on Buffered Substrates

Abstract: XPS studies of a typical YBCO coated conductor architecture were conducted to investigate the chemical and microstructural profiles The detailed XPS depth profiling study was performed on one sample (YBCO/CeO2/YSZ/CeO2/Ni) of coated conductor The chemical depth profiling involved bombarding a small area of the specimen surface with 3 keV Ar+ ions and analyzing the freshly exposed surface after each bombardment Results of the process show that the Y(3d) photo-electronic peak shape in these films is very different from bulk (sintered and oxygen annealed) YBCO superconductors and surface analysis of YBCO thin films This may indicate a possible difference in the atomic co-ordination between some laser-ablated films and bulk sintered ones The correlation between chemical binding states of the ions and superconducting properties need to be investigated in details The lower portion of the YBCO film showed distinct signs of contamination including Ce, and traces of Ni An initial report of Zr diffusion into this YBCO layer is also reported

Etch characteristics of Pt by using BCl3/Cl2-gas mixtures

Abstract: The inductively coupled plasma etching of platinum with \(BCl_3 /Cl_2\)-gas chemistries was examined. Plasma characteristics were investigated with increasing \(Cl_2\) ratios using a Langmuir probe and optical emission spectroscopy. The chemical reaction during the Pt etching was also examined via the chemical binding states of the etched surface, by X-ray photoelectron spectroscopy. The relationship between plasma and etch characteristics with various \(Cl_2\) gas mixing ratios is discussed. On the basis of the relationship, the Pt etching mechanism with \(BCl_3 /Cl_2\)-gas chemistries is described.

Preparation and characterization of poly (ethylene glycol)-coated Stoeber silica nanoparticles for biomedical applications

Abstract: Monodisperse, spherical, polyethylene glycol (PEG)-coated silica nanoparticles have been prepared in the size range of 50-350 nm, and their size distribution were characterized by SEM and multi-angle static light scattering experiments. The chemical binding of PEG to the silica nanoparticles was confirmed by IR spectroscopy. The biocompatibility of these PEGylated nanoparticles was also studied by non-specific protein binding tests and in-vivo toxicology studies in live animals. These silica nanoparticles, as a matrix for encapsulation of certain reagents, have been used for the fabrication of intracellular sensors and have potential for applications to in vivo diagnosis, analysis and measurements, due to their small physical size and their biocompatibility, both stemming from the specialized PEG coating.