Showing papers on "Chemical binding published in 1989"

Biodegradation of synthetic organo-metallic complexes of iron and aluminium with selected metal to carbon ratios

Abstract: Synthetic organo-ferric and organo-aluminous complexes with various metal :C ratios were prepared and incubated for 44 days in an Eutrochrept A1 horizon. Citric acid was used as a model of a natural soil acid. Fungal melanins synthesized by Epicoccum purpurescens were separated in fulvic acid-like and humic acid-like polymers and used as models for natural transformed soil organic matter. Under certain conditions, the biodegradation of such metal-organic complexes was slower than that of the free forms of the corresponding organic compounds. The intensity of this protective effect depended mainly on the metal to complexing functional groups molar ratio (M/CG) of the complexes and was also related to their aqueous solubility. For some organics, the protective effect was observed at ratios exceeding the saturation of their complexing sites, and sometimes needed a metal content exceeding more than twice their complexing capacity. In such cases, the formation of a flocculated metallic hydroxide trapping and wrapping the organic molecules is suggested to account better for the observed protective effect than chemical binding per se. As the solubility of the “humic” acids decreased faster than that of the “fulvic” ones when their metallic charge increased, the biodegradability of the former decreased more rapidly than that of the latter by metal complexing. For the same reasons, citric acid was more protected by complexing Al than Fe. The protective effect of both aluminium and iron against the biodegradation of all types of organic matter was high and of a comparable intensity at high M/CG molar ratios. These data are interpreted in terms of pedological processes.

X-Ray Spectra and Chemical Binding

Abstract: In the 12 years that have passed since the publication of Riintgenspektren und chemische Bindung, the original German work on which. this text is based, several aspects of high-resolution X-ray spectroscopy have devel oped rapidly. After accepting the suggestion of Dr. R.D. Deslattes that a translation should be prepared, we thoroughly revised the book in order to include these recent developments in theory, equipment and applications. The latest reSearch results and publications that had appeared by 1987/1988 have been taken into account in the analysis. However, as the general treatment of the German edition is still valid today, the organization of the contents did -not have to be modified. The present status of the field is adequately described just by the addition of supplementary material in the English edition. We have merely rearranged what was previously Chapter 4 into tabular form and placed it as an appendix. This presentation produces greater clarity and increases the ease with which the information can be referred to. We thank Dr. E. Kallne for undertaking the translation. We are grate ful to Dr. R.D. Deslattes and Dr. H. Lotsch for their conscientious and critical checking of the translation. Chapters 3 and 6 were updated by our colleague Dr. H. Sommer, to whom special thanks are due. It is our hope that this transiation and revision will make our text available to a larger section of the scientific community."

Surface and Grain Boundary Segregation on and in Iron and Steels

Abstract: The equilibrium segregation of the elements A=C, Si, Sn, N, P, O, and S was studied for binary systems Fe-A in the stability range of the α-solid solution using surface analytical methods. On the surfaces ordered structures were observed by LEED and surface concentrations were determined by AES in dependence on bulk concentration and temperature. The chemical binding state was characterized by XPS. In grain boundaries the segregation of P and Sn was determined by AES on intergranular fracture faces after equilibration at elevated temperatures and fracture in UHV. Effects of alloying elements, especially C, on grain boundary segregation are described. Correlations of surface and grain boundary segregation with the chemical and mechanical behavior of steels are shortly discussed.

Bombardment-induced compositional change with alloys, oxides, oxysalts, and halides

Abstract: Compositional changes in bombarded alloys are now recognized to arise mainly from bombardment-induced segregation, “BIS” and to only a limited extent from preferential sputtering, i.e. from differences in mass, chemical binding, or volatility. The significant relation is α A (2) α B (2) = (α A (2′) α B (2′) ) K b , where α is the atom fraction, A and B are the components of the alloy, 2 designates atom layer one , 2′ designates atom layer two and K b is the BIS ratio. A very similar relation holds for equilibrium segregation except that K b is replaced with K eq , equivalent to exp ( ΔG seg / kT ). It is shown that K b and K eq are always in the same sense except for NiPt, that K b lies in the interval 1.25 ⩽ K b ⩽ 5.4 for 14 out of 16 different systems and that for ambient temperature the inequality K b ⪡ K eq holds. Most aspects of the relation between K b and K eq can be understood if BIS is caused by chemically guided final steps in some ballistic trajectories. Such a mechanism also accounts for what is otherwise a paradox, namely that the driving force for segregation is so small, ranging from 0.06 eV for CuPd to 0.52 eV for AuNi. The latter values are similar to heats of mixing, proposed by Cheng et al. to govern ion-beam mixing and to differences of heats of formation, proposed by the present author to govern chemical changes in oxides and oxysalts.

Spin-label ESR studies on the interaction of bovine spinal cord myelin basic protein with dimyristoylphosphatidylglycerol dispersions

Abstract: Electron spin resonance (ESR) spectroscopy and chemical binding assays were used to study the interaction of bovine spinal cord myelin basic protein (MBP) with dimyristoylphosphatidylglycerol (DMPG) membranes. Increasing binding of MBP to DMPG bilayers resulted in an increasing motional restriction of PG spin-labeled at the C-5 atom position in the acyl chain, up to a maximum degree of association of 1 MBP molecule per 36 lipid molecules. ESR spectra of PG spin-labels labeled at other positions in the sn-2 chain showed a similar motional restriction, while still preserving the chain flexibility gradient characteristic of fluid lipid bilayers. In addition, labels at the C-12 and C-14 atom positions gave two-component spectra, suggesting a partial hydrophobic penetration of the MBP into the bilayer. Spectral subtractions were used to quantitate the membrane penetration in terms of the stoichiometry of the lipid-protein complexes. Approximately 50% of the spin-labeled lipid chains were directly affected at saturation protein binding. The salt and pH dependence of the ESR spectra and of the protein binding demonstrated that electrostatic interaction of the basic residues of the MBP with the PG headgroups is necessary for an effective association of the MBP with phospholipid bilayers. Binding of the protein, and concomitant perturbation of the lipid chain mobility, was reduced as the ionic strength increased, until at salt concentrations above 1 M NaCl the protein was no longer bound. The binding and ESR spectral perturbation also decreased as the protein charge was reduced by pH titration to above the pI of the protein at approximately pH 10.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of two complementary fragments of the bovine spinal cord myelin basic protein with phospholipid bilayers. An ESR spin-label study.

Abstract: The myelin basic protein (MBP) from bovine spinal cord was cleaved at the single tryptophan residue to produce an N-terminal fragment (F1) of molecular weight 12.6K and a C-terminal fragment (F2) of molecular weight 5.8K. The interactions of the two fragments with bilayers of the acidic lipid dimyristoylphosphatidylglycerol (DMPG) were compared with those of the intact protein, by using both chemical binding assays and spin-label electron spin resonance spectroscopy. The saturation binding stoichiometries of the two fragments were found to sum to that of the MBP, having values of 11, 24, and 36 mol of DMPG/mol of protein for F2, F1, and the MBP, respectively. The strength of binding was found to increase in the order F2 less than F1 less than MBP, which follows that of the net charges on the different fragments. The ionic strength dependence of the protein binding indicated that the interaction is primarily of electrostatic origin. The efficiency of displacement of the proteins by salt was in the order F2 greater than F1 greater than MBP, which correlates with both the strength of binding and the net charge on the different protein fragments. Nitroxide derivatives of phosphatidylglycerol (PG) labeled on the sn-2 chain were used to probe the protein-induced changes in the acyl chain dynamics. Both the fragments and the MBP decreased the lipid chain mobility as recorded by the C-5 atom and C-12 atom position nitroxide-PG spin-labels, in a manner which followed the protein binding curves.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical aspects and the correlated electronic structure of superconductor oxocuprates

Abstract: An analysis of structure and chemical binding of the superconducting oxocuprates is made resulting in approximate groundstate configurations of their anionic complexes. A simple analytic tight-binding model is introduced which allows to consider self-consistently the interplay of charge transfer and strong on-site correlation (self-interaction correction to the mean-field theory). Besides yielding the charge transfer gap, it naturally explains the collectivization of strongly localized electrons at integer occupation numbers. This is due to occupation number frustration by bonding charge transfer and also explains heavy-fermion behaviour near integer valences. An analytic LCAO analysis of the electronic structure of the oxocuprates yields a spin-polarized groundstate with one copper 3d-hole and about one half of an oxygen 2p-hole per unit cell in the undoped [CuO 2 ] 2− -layer Whereas the level of the missing 3d-electron is high above the Fermi level, the conduction gap is from oxygen holes to conduction states with oxygen 2p-admixture. Doping this layer by extracting electrons (e.g. by transferring them into an overlapping chain band in the case of the 1 2 3 structure) leads to metallic oxygen hole conductivity and at the same time to collectivization of the copper d-electrons. All features of this picture are confirmed by the known results of polarized core-level spectroscopy. As a further common peculiarity of all superconducting oxocuprates a strong anharmonicity of one special oxygen atom which lies outside of the CuO 2 -layers but which is responsible for doping them, is discussed.

Molecular targets, DNA breakage, DNA repair: Their roles in mutation induction in mammalian germ cells

Abstract: Variability in genetic sensitivity among different germ-cell stages in the mammal to various mutagens could be the result of how much chemical reaches the different stages, what molecular targets may be affected in the different stages and whether or not repair of lesions occurs. Several chemicals have been found to bind very strongly to protamine in late-spermatid and early-spermatozoa stages in the mouse. The chemicals also produce their greatest genetic damage in these same germ-cell stages. While chemical binding to DNA has not been correlated with the level of induced genetic damage, DNA breakage in the sensitive stages has been shown to increase. This DNA breakage is believed to indirectly result from chemical binding to sulfhydryl groups in protamine which prevents normal chromatin condensation within the sperm nucleus. 22 refs., 5 figs.

Bio-organic studies of insect olfaction

Abstract: Pheromones interact with binding and catabolic proteins in insect olfactory sensilla, and the activated dendritic receptors are important in the transduction of a chemical binding event into an electrical signal. Selected results will be presented in which high specific activity tritium-labeled pheromones and pheromone analogs are synthesized and used to study proteins from insect antennae which bind and degrade pheromone molecules.

Filter and method of treating tobacco smoke to reduce materials harmful to health

Abstract: A method for treating nicotine containing materials such as tobacco, tobacco smoke and tobacco extracts involves adding to an adsorptional filter material postassium aluminum sulfate, KAl (SO4)2, commonly known as alum, in a quantity of 10 to 200 mg per cigarette, which additive is capable of chemical binding of nicotine and other toxic materials in the tobacco smoke.

Chemical binding, stability and metastability of defects in semiconductors

Abstract: The paper describes recent theoretical studies of the electronic and structural properties of defects in semiconductors. In particular we discuss iron-acceptor pairs and chalcogen pairs in silicon, the AsGa-As pair in GaAs and the AsGa antisite defect. The results explain mechanisms which give rise to pair formation and they show possibilities of structural metastabilities.

The oxidation resistance and constitution of compounds of groups IIIA and IVA with d-transition elements

Abstract: The thermal oxidation resistance of compounds of types RCo, R3Ni and RCu, where R is a rare earth element, has been tested by an isochronal method. It is found that the ratioTp/Tm of the oxidation parameter to the melting point decreases from about 0.75 to 0.6 with increasing atomic number, indicating a relaxation of chemical binding, and displays ‘saw-tooth’ variability as we pass from a compound of one element to another. This variability may be due either to weaknesses from valency-induced changes with elements such as terbium, or to deep-seated changes between odd- and even-Z elements. In a further development of the work, contours forTp/Tm of 0.6 and 0.7 have been charted on synoptic diagrams characterized by a constant row of 4f/5d elements on one ordinate and a variable 3d element (V to aluminium) on the other. We note that the largest area of high ground is found for cobalt compounds, followed by nickel, then copper; and that with copper only elements from barium to gadolinium contribute, in contrast with cobalt and nickel (lanthanum to at least thulium). Evidently a strong transition metal contribution to bonding in cobalt compounds has weakened in the copper counterparts, and s-d resonance/attenuation across the composite divide from the 4f element into the copper d-shell is only possible for the lighter rare earths.

Binding of hydrogen and helium in silicon, the mass difference between 3H and 3He, and the mass of nu e.

Abstract: Precision measurements of the /sup 3/H/minus//sup 3/He atomicmass difference afford a means for assessing the reliability of measurements ofthe electron antineutrino mass from tritium ..beta.. decay. We show that along-standing discrepancy between measurements of the/sup 3/H/minus//sup 3/He mass difference obtained withtritium-implanted silicon detectors and those obtained by other techniques isdue to neglect of chemical binding effects in the former experiments. Thecorrection reconciles the silicon-detector results with modern determinationsmade by mass spectrometry and by ..beta.. spectrometry. With this and othernew data, a revised average value for the /sup 3/H/minus//sup 3/Hemass difference of 18 591(2) eV is found. The scatter in the extant datasuggests the presence of systematic errors in some of the modern measurements,and at present there seems to be no compelling basis for a model-independentlower limit on the mass of ..nu../sub /ital e//. .AE

Bombardment-induced compositional change with alloys, oxides, and oxysalts. i the role of the surface binding energy

Abstract: Bombardment-induced compositional change with alloys, oxides, and oxysalts has been the subject of both experimental and theoretical study for the past two decades. Concerning theoretical work, it is worth pointing out that the emphasis has changed to a remarkable extent as the experimental base has grown. Work written before 1980 tended to emphasize preferential sputtering as triggered by differences of mass, chemical binding, or volatility. Mass and chemical binding were envisaged as governing collisional sputtering, volatility as governing thermal sputtering.

Carbon bake refractories

Abstract: The present invention relates to an unfired refractory brick for use in reducing conditions at temperatures above 1800° F. The brick comprises a matrix of alumino-silicate clays, alumino-silicate-aggregates and high alumina aggregates. It also has 2 to 20% by weight of finally ground silicon carbide and 2 to 20% by weight of fine carbon particles distributed throughout the matrix. The matrix also includes a water soluble ammonium lignin sulphonate as a chemical binding agent. The brick of the present invention finds particular use in a furnace for kiln baking anodes used in the electrolytic production of aluminum metal.

Ion-capture reagents for performing binding assays

Abstract: This invention presents novel polymeric anionic molecules and novel negatively charged capture reagents comprising the reaction products of said anionic molecules and a specific binding member for use in separation techniques and assay procedures wherein said activated polymeric anionic molecule comprises a compound having the formula: wherein n is about 10 to about 500; z is about 1 to about 6; W is selected from the group consisting of H⁺, Na⁺, K⁺, Li⁺, amine salts, and derivatives thereof; and X is a reactive group or a structure having a reactive group that enables the chemical binding of said activated polymer to a specific binding member.

The Role of Chemical Driving Forces in Bombardment-Induced Compositional Change

Abstract: This constitutes part of a discussion on bombardment-induced compositional change with alloys, oxides, oxysalts, and halides. Already treated are the role of the surface binding energy (1), the role of bombardment-induced Gibbsian segregation (“BIS”) (2), as well as an extended version of the present material (3). We here consider three aspects of what will be termedchemical driving forcesWe first consider how it is possible for BIS to occur at all given the small numerical value of the driving force, 0.06 to 0.52 eV. The same is then done for bombardment-induced mixing, now recognized to be chemically driven by the heat of mixing, now recognized to be chemically driven by the heat of mixing, typically <1.3 eV (4,5). We finally consider bombardment-induced decomposition, i.e. the characteristic compositional changes found with many oxides and oxysalts. In early work these changes were normally inferred from electron diffraction (e.g. 6) or AES (e.g. 7), but more recently there has been an increasing use of XPS (“x-ray photoelectron spectroscopy”), thence the possibility of confirming valence states which do not give stable bulk compounds (e.g. 8–11). A typical example of BIS is shown in Fig. 1 (12–14) and of decomposition in Fig. 2 (10).

Argon ion beam effects upon photoemissive thin films

Abstract: This work is concerned with photoemissive materials such as Na 3 Sb and Na 2 KSb deposited on glass substrates under ultrahigh vacuum conditions. Auger electron spectroscopy associated with optical transmittance and reflectance measurements, has been performed during thin film growth and ion bombardment. The argon ion beam deeply disturbs the alkali-antimonide films. This alteration takes place up to more than 100 nm in depth and produces a linear composition which is thickness dependent. The chemical binding energy between atoms appears to control the ion-bombardment-induced composition changes at the surface and in depth.

Method for forming by low pressure deposition a layer of insulating material on a substrate, and product obtained thereby

Abstract: Treatment of material surfaces. The formation method according to the invention comprises: maintaining in a container an oxidizing medium for the material to be transferred; causing, according to stable parameters, the transfer of material to form on the substrate at least one prelayer having a thickness smaller than that of the insulating layer to be obtained; interrupting the formation of said prelayer; subjecting during a predetermined time duration the deposited atoms or molecules forming the prelayer to an oxidation in order to perfect their chemical binding and their mutual organization ; growing again on the prelayer a layer of insulating material according to the same stable parameters up to the obtention of the desired thickness. Application to the fabrication of electronic components.

Electronic structure and optical absorption spectra of the dimers Y2 and Zr2

Abstract: 1. According to calculations by the discrete variation Xα method the ground states of the dimers Y2 and Zr2 have the symmetry\({}^1\sum _g ^ +\), and the atoms in the dimers are in the high-spin configuration 4dn+15s1. 2. The chemical binding in Y2 is predominantly 5s-5s in character, as shown by the fairly considerable interatomic distance; in the dimer Zr2 the participation of 4d electrons in the binding leads to an appreciably shorter bond. 3. The theoretical optical absorption spectrum of Zr2 agrees well with that observed experimentally for this molecule isolated in an argon matrix.