Showing papers on "Chemical binding published in 1997"

Dependence of atomic layer-deposited Al2O3 films characteristics on growth temperature and Al precursors of Al(CH3)3 and AlCl3

Abstract: The materials characteristics of Al2O3 films grown on a Si (100) substrate by traveling wave reactor atomic layer deposition were investigated in the growth temperature ranging from 250 to 500 °C. The Al2O3 films grown using Al(CH3)3 trimethylaluminum (TMA) and H2O as precursors were characterized and also compared with the films grown using AlCl3 and H2O. Both samples grown with different precursors revealed identical chemical binding state of oxidized Al and very flat surface morphology. In the study of impurity incorporation, the films grown using TMA showed the C and H count rates of secondary ion mass spectrometry (SIMS) approximately six and 10 times higher than those of the film grown using AlCl3, respectively. For the Al2O3 films grown using TMA, the results showed that the impurity contents and the growth rate of the films decreased and the refractive index increased with the growth temperature. The content of impurities could be also lowered by increasing the N2 purge time after TMA pulse. Howev...

Role of Carbonation in Transient Leaching of Cementitious Wasteforms

Abstract: A combined experimental and modeling program approach was applied to evaluate the role of the carbon dioxide reactive component of soil gas on the long-term performance of cementitious wasteforms. Small wasteforms were cast with Portland cement and synthetic wastewater containing metals and nitrate as a tracer. A series of wasteforms was exposed to an accelerated environment for carbonation and then subjected to transient leaching tests in deionized water. A second set of control wasteforms was not carbonated but was otherwise treated identically. Results are analyzed by comparison of experimental data with theoretical models of the leaching process. The results indicate that carbonation increases the apparent diffusion coefficient for unreactive species while resulting in chemical binding of metals through solid solution in calcite. For strontium, carbonation resulted in lower net leaching while leaching of calcium and nitrate was increased by carbonation.

Formation of non-bioavailable organic residues in soil: Perspectives for site remediation

Abstract: Whenever possible, total clean-up of soils and sediments should have priority over methods to contain the pollutants in the soil environment in a way which reduces their potential eco-toxicological effects. Nevertheless, often a very important fraction of the pollutant remains non-available to the cleaning process, either physico-chemical or biological. This constitutes a major obstacle for both environmental technologists and legislators. Yet, the concept of non-extractable organic residues is well accepted in the EU-legislation for pesticides. In this context, an assessment is made to bind organic pollutants to soil. Physical sorption (comprising surface adsorption, absorption and migration in micro- and nanopores) and chemical binding are examined in terms of quantities and kinetics. Chemical binding offers at present no direct possibilities for practice. Making toxic pollutants less bioavailable by increasing physical sorption represents a pragmatic approach to contractors and regulators. For organic pollutants with acceptable concentration in the soil solution of the order of 1 mg/l, a sorptive loading of the order of 10 000 mg pollutant per kg activated carbon respectively organic matter appears a workable assumption. In case of toxic substances such as pesticides which have a 1000 times lower acceptable level, a sorptive loading of up to 10 mg organic pollutant per kg sorbent can be used. Non-bioavailable pollutants can be considered as representing no direct harm to the environment. In practice, the application of up to 100–200 kg dry weight quality compost per ton dry weight soil or alternatively the supplementation of other sorbents such as powdered activated carbon (up to 100 kg per ton soil) offer possibilities to cost-effective remediation of organic pollutants. Yet, aspects of worst-case ecotoxicology as e.g. excessive leaching with dissolved humic substances or ingestion of soil containing substantial amounts of poorly extractable contaminants by human and soil organisms, need to be examined.

Viscoelasticity of frozen/thawed egg yolk

Abstract: Dynamic rheological measurements indicate that the gel formed during freezing is based on physical aggregation rather than chemical binding, with a nonhomogeneous structure. The gelation was highly dependent on frozen storage temperature in the range -10 to -14°C, but there was no appreciable difference in the range -14 to -24°C. When yolk was maintained motionless and supercooled at -10°C and -12°C for 23 hr, no change in the complex modulus, G * , was observed, but there was a considerable increase when yolk was disturbed and became frozen at the same temperatures for the same time.

Ionoluminescence and pixe study of inorganic materials

Abstract: The combined use of IL and PIXE is promising in characterizing the inorganic materials. IL is sensitive to the condition of chemical binding and ion valence state, crystallinity and defects. IL can also provide a unique way to monitor and study the ion-beam induced effects in samples. PIXE can provide quantitative information on the elemental distribution of major and trace elements in samples, which in turn helps to understand IL results. The combination of the two techniques provides a new tool for studying the intrinsic and extrinsic luminescence phenomena and is capable of micro-characterizing various inorganic materials, including the ones of geological and synthetic origins.

Modulation of Intracellular Second Messengers by Dietary Fat during Colonic Tumor Development

Abstract: Marked differences in the incidence of colon cancer in populations migrating from low to high risk areas suggest that environmental factors, specifically dietary factors, play an important role in the etiology of colon cancer.1,2 Dietary fat has received considerable attention as a possible risk factor in the etiology of colon cancer. A proposed hypothesis regarding the induction of colon cancer suggests that fats increase the amount of bile acids in the colon, which in turn are metabolized to secondary carcinogens to promote the growth of adenomas and subsequently invasive cancer.3 Moreover, the amount and type of fat in the diet directly affects the concentration of free fatty acids, eicosanoids and diacylglycerols in the colonic lumen which can influence colonic intracellular second messengers and modify the risk of colon cancer development.4,5,26,93 In comparison, dietary fiber is postulated to reduce the adverse effects of certain fats through several mechanisms, including dilution of carcinogens, decrease in transit time, reduction in fecal pH, chemical binding, and alteration in microflora metabolism6,7. However, experiments in animal models using a variety of fats and fibers have produced conflicting results. In some studies, fiber failed to protect,8,9 and in others, fat failed to promote colon carcinogenesis.10 The interpretation of this data is made even more complicated by the fact that different types of dietary fiber and fat may affect colon carcinogenesis in an interactive site-specific manner.11

Mechanical properties of hand‐cast and reaction injection molded polyurethane and vinyl ester resin interpenetrating polymer networks

Abstract: A series of simultaneous interpenetrating polymer networks (SINs) composed of polyurethane (PU) and vinyl ester resin (VER) was prepared from different rigid phase components, where the pendent hydroxyl groups of VER were retained or capped, and through different molding processes, i.e., hand-casting or reaction injection molding (RIM). It was recognized that the occurrence of chemical binding between PU and VER networks through the reaction of the diisocyanate and the pendent hydroxyl groups of VER played an important role in determining the mechanical properties of these SINs. The hand-cast SINs, with VER containing pendent hydroxyl groups as the rigid phase component and with these pendent hydroxyl groups counted for the metering of diisocyanate besides that due to polyether polyol and chain extender of PU phase, behaved like the hybrid polyester matrix. For the RIM-molded SIN samples, an obvious reinforcing effect of VER network, whose pendent hydroxyl groups were capped with acetyl groups, upon PU network was observed. These results correlated well with the knowledge of polymerization kinetics and morphology development of these PU/VER SINs.

Process for producing radioisotope source

Abstract: A process for implanting radioisotope ions into a substrate to create a radioisotope source, utilizing the chemical binding of selected ions to the surface of the substrate. Extraneous material not chemically bound to the substrate is removed and the chemically bound ions are diffused below the surface of the substrate in a non-oxidizing environment.

Nitric Oxide, Nitrogen Metabolism and Inflammatory Respiratory Disease An hypothesis

Abstract: A novel hypothesis suggesting a link between gastro-intestinal production of nitric oxide, its chemical binding in and slow release from S-nitroso proteins, and the early development of inflammatory respiratory disease is offered.

Aspects of the Chemical Bond 1996

Abstract: In a preceding essay [1] I outlined the historical, mathematical and physical bases of our present qualitative knowledge about the chemical bond, specifically about covalent binding in simple molecules. An expanded version [2] of that material afforded the opportunity to clarify and to extend the arguments somewhat, and to discuss the reaction to the previously printed version. In the present essay I consider important aspects of chemical binding previously ignored, namely ionic substances, the transition state purported to occur between reactants and products during the course of a simple chemical reaction, and a description of the mechanism of an intramolecular rearrangement. As for the covalent bond, these topics evolved largely during three quarters of a century since quantum mechanics was discovered and developed, but involve, more or less implicitly, many ideas based on the classical notion of molecular structure emanating from the nineteenth century. The final section consists of a discussion of the context of quantum chemistry in a contemporary scientific milieu.

High resolution core-level electron spectroscopy on free molecules and atoms

Abstract: Electron spectroscopy on free atoms and molecules using synchrotron radiation from an undulator is outlined. The high brilliance of the synchrotron radiation in combination with high efficiency monochromators and modern high resolution electron spectrometers make it possible to record electron spectra from core levels with a resolution of the order of 10–100 meV, even at high kinetic energies. New aspects of the spectroscopy are discussed, Auger resonant Raman spectra are presented, both in the case of atoms and molecules, and also angular resolved results at sub-natural resolution are reviewed. Particular attention is paid to the dissociation of core excited molecules in connection with resonant Auger decay. Vibrational resolution in core photoelectron spectra is also discussed using propene as an example, and the relevance of high precision chemical binding energy shifts is discussed.

Tin Telluride (SnTe)

Abstract: Publisher Summary The binary compound semiconductor tin telluride (SnTe) is known to be isomorphous with rock salt. The nature of chemical binding is mixed ionic-covalent. SnTe has direct interband optical transitions at the L point in the Brillouin zone. The band structure near the fundamental gap is more complicated than in the lead salts. For large hole concentrations, it is required to observe a positive temperature coefficient of the fundamental gap. Optical experiments by Murase et al exhibits that the temperature coefficient of the gap changes its sign from negative to positive with increasing hole concentration in the temperature region between 50 and 150 K. The first detailed study of the reflectivity of SnTe was performed by Cardona and Greenaway. The measurement of reflectivity and absorption of a semiconductor provides a direct method of studying the band structure. Epitaxial layers of SnTe on KCl were used for the reflection and transmission measurements. The SnTe layers were evaporated onto KCl single-crystal substrates, cleaved in air, and held at a temperature of approximately 573 K. X-ray results showed all the films to be single-crystal and to have the crystal orientation of the substrate.

Binding of Daunorubicin and Doxorubicin to Erythrocytes Treated with Glutaraldehyde

Abstract: Intact human erythrocytes can bind anthracycline antibiotics (daunorubicin and doxorubicin) during incubation in the isotonic medium containing the antibiotic. Bound antibiotics can be immobilized in the erythrocytes using glutaraldehyde treatment. It was found, however, that erythrocytes pretreated with glutaraldehyde can uptake daunorubicin and doxorubicin from the incubation medium and do it faster than untreated cells. The antibiotics are readily released from these erythrocytes in the antibiotic-free medium. Our findings provide evidence that immobilization of anthracycline antibiotics in the erythrocytes using glutaraldehyde treatment is connected with the chemical binding of the antibiotics to different erythrocyte components.

Electrons in molecules

Abstract: The electron density distribution in a molecule determines its stability, geometry and reactivity, in short its chemistry.