Showing papers on "Chemical binding published in 1996"

Low-temperature thermochromism marks a change in coordination for the metal ion in manganese superoxide dismutase.

Abstract: We have observed thermochromism (temperature-dependent absorption) for anion complexes of manganese superoxide dismutase indicating a change in coordination number for the metal complex at low temperatures. The ligand field spectra for the Mn(III) ion, characteristic of five-coordination for the azide complex at 295 K, cleanly convert to spectra reflecting six-coordination at low temperature, with a midpoint for the transition near 200 K. The active site structure is temperature-dependent, a relatively rigid, distorted octahedral low-temperature Mn complex melting with dehydration (or displacement of one of the protein ligands) to form a five-coordinated complex under physiological conditions. Thermodynamic parameters for the transition estimated from van't Hoff analysis (ΔHvH = 5 kcal/mol; ΔSvH = 22 cal/mol K) are consistent with reduced chemical binding and increased fluxionality at room temperature. This thermochromism of MnSD demonstrates the existence of distinct isomeric forms of the active site met...

Polymerization kinetics of polyurethane and vinyl ester resin interpenetrating polymer networks by using fourier transform infrared spectroscopy

Abstract: Fourier transform infrared spectroscopy (FTIR) was applied to the study of polymerization kinetics of simultaneous interpenetrating polymer networks (SINs) composed of polyurethane (PU) and vinyl ester resin (VER), in which the pendent hydroxyl groups were capped with acetyl groups to minimize the possibility of chemical binding between the two networks. It was found that during the course of synthesis the two pairs of reactants interfere with each other in the SIN systems, giving rise to depressed reaction rates, although they follow different polymerization mechanisms. Increasing the reaction temperature could be more effective than increasing the free-radical initiator level with regard to the final conversions of both components. The reaction sequence could be varied through the amount of the step-growth polymerization catalyst and free-radical initiator as well as the reaction temperature adjustment. Using VER containing pendent hydroxyl groups could strongly affect the reaction kinetics of such SINs and lead to hybrid structures. The quick formation of one network would always depress the conversion of the other network in all SINs studied. © 1996 John Wiley & Sons, Inc.

Spectral Theory of Physical and Chemical Binding

Abstract: A spectral method which provides unified quantum mechanical descriptions of both physical and chemical binding phenomena is reported for constructing the adiabatic electronic potential energy surfaces of aggregates of atoms or other interacting fragments. The formal development, based on use of a direct product of complete sets of atomic spectral eigenstates and the pairwise-additive nature of the total Hamiltonian matrix in this basis, is seen to be exact when properly implemented and to provide a separation theorem for N-body interaction energies in terms of response matrices which can be calculated once and for all for atoms and other fragments of interest. Its perturbation theory expansion provides a generalization of familiar (Casimir−Polder) second-order pairwise-additive and (Axilrod−Teller) third-order nonadditive interaction energies, expressions which are recovered explicitly in the long-range-dipole expansion limit. A program of ab initio computational implementation of the formal development i...

Hardening Process and Surface Structure of Lacquer Films Studied byX‐ray Photoelectron Spectroscopy

Abstract: The changes of the composition ratios and chemical binding states of the component elements in the surfaces of four varieties of lacquer films during the hardening process were studied by x-ray photoelectron spectroscopy (XPS). Additionally, the relationship between the surface structure and hardening process of lacquer films was studied by the pencil hardness testing method. The relative oxygen contents and the existence ratios among the COO, C=O, C-O-C, C-OH, C-N and N=O functional groups in the surfaces of the lacquer films increased significantly with the progress of hardening. In addition, it was revealed that a lacquer film with a faster hardening rate showed a higher relative oxygen content and a larger existence ratio among these functional groups in the surface. The increases support the progress of the following three phenomena in the surface of lacquer film during the hardening process, i.e. the concentration of gummy substances and nitrogen-containing compounds, laccase-catalysed oxidative polymerization and autoxidative polymerization.

Optical-fibre sensors for blood gases and pH, based on porous glass tips

Abstract: Optical-fibre sensors have been developed for the determination of blood gases and pH. Chemical binding of pyrenebutyric acid and 7-hydroxy-4-methylcoumarine-3-acetic acid to a porous tip of a fused silica fibre produces a sensitive measuring device for molecular oxygen and pH. Insertion of the pH sensor into a solution of bicarbonate, entrapped within a polypropylene membrane, yields a pCO2 sensor. Excitation of the oxygen-sensor tip within the range 340–360 nm yields emission with a maximum intensity at 460 nm. An intensity ratio ≈ 10 between signals measured in pure gas-phase nitrogen and oxygen is obtained. Excitation of the sensitive tip within the range 360–380 nm yields emission with a maximum intensity at 457 ± 3 nm. The excitation spectrum is red shifted about 19–30 nm relative to that obtained in solution. The maximum intensity of the excitation spectrum for the acidic form of the bound coumarine derivative is at 356 ± 3 nm, whereas for the basic form it is at 380 ± 3 nm. The apparent pK of the bound coumarine derivative is 7.45 ± 0.30. The bias and the precision for pO2 determinations in blood samples are about −1 and ± 1.5 torr, respectively. For pH determinations, the respective values are about 0.02 and 0.04 pH units and for pCO2 about 1 and 2.5 torr. The sensors described are suited for production on an industrial scale.

Adhesion Between Rubbers and Grafted Solids

Abstract: The adhesion energy, G (at low separation velocities), between a rubber and a solid surface, is expected to increase when flexible chains, chemically identical to the rubber, are attached to the surface. This can be set up with or without chemical binding of the chains to the rubber (“bound” chains or “free” chains).

Hydrodynamic model for ultrashort-pulse albation of hard dental tissue

Abstract: A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 fsec and intensity greater than 1012 W/cm2 are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Influence of additives on combustion of ultradisperse aluminum powder and chemical binding of air nitrogen

Abstract: Experimental results are presented on combustion in air of ultradisperse aluminum powder with additives of ultradisperse powders of copper, nickel, iron, tin, silicon, graphite, boron, tungsten, and molybdenum.X-Ray diffraction and chemical analyses were used to study the composition of the end products. A tin additive has an inhibiting action on the chemical combining of air nitrogen as aluminum nitride and oxynitride, whereas iron, tungsten, and molybdenum additives favor an increase in nitrogen content. As is established, the influence of additives on the processes determining the duration of two combustion stages is greater than on the content of bound nitrogen in the products.

Phosphorescence lifetime of naphthalene and phenanthrene in aggregated aromatic molecule-β-cyclodextrin-precipitant complexes

Abstract: Aggregated aromatic molecule-β-cyclodextrin-precipitant complexes exhibit long-lived phosphorescence at room temperature in water after the chemical binding of oxygen. The temperature dependences of the phosphorescence lifetimes of naphthalene-h8, naphthalene-de, and phenanthrene in the aggregates were measured. For example, the phosphorescence lifetimes of naphthalene-d8 aggregated with β-cyclodextrin and cyclohexane are equal to 25.1, 17.6, and 6.8 s at 77, 276, and 347 K, respectively, and that of phenanthrene aggregated with isooctane and β-cyclodextrin are 3.24, 3.06, and 1.26 s at 268, 274, and 335 K, respectively. The temperature dependences of the phosphorescence lifetimes at room temperature are determined by the rate constants of the radiative and nonradiative transitions from the triplet state of an aromatic molecule.

Functionalization at the double-bond region of jojoba oil. 7. Chemical binding of jojoba liquid wax to polystyrene resins

Abstract: Jojoba wax was chemically bonded to a polystyrene matrixvia a stable C-C covalent bond. This was achieved by binding allyl-brominated jojoba derivatives to lithiated crosslinked polystyrene-2% divinylbenzene or XAD-4 polymeric beads via a nucleophilic substitution reaction. The double-bond regions in the jojoba wax were preserved. A side reaction that accompanied the nucleophilic substitution was HBr elimination, which produced diene and triene systems in the bound jojoba. Phosphonation and sulfur chlorination at the double bonds of the jojoba wax, bonded to the polystyrene matrix, were also performed.

Functionalization at the double-bond region of jojoba oil. 8. Chemical binding of jojoba liquid wax to a polymer matrixvia an amine “spacer”

Abstract: Jojoba wax was chemically bonded to a polymer matrixvia stable C-N covalent bonds. The polymer matrix was prepared by amination of several types of styrene-divinyl benzene or styrene-vinylbenzylchloride-divinylbenzene copolymers with diamines or polyethylene imines (polyamines). The jojoba wax was attached to the aminated polystyrene matrix by reacting an allyl-brominated derivative of jojoba with the matrix to form a C-N bond between the matrix and the jojoba wax. The amount of bound jojoba wax added to the polymer was in the range of 20–70% (w/w), depending on the type of polymer matrix and reaction conditions. The double-bond regions in the jojoba wax bonded to the matrix were preserved, and they were subsequently functionalized by phosphonation and sulfur-chlorination reactions.

Hydrodynamic model for ultra-short pulse ablation of hard dental tissue

Abstract: A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 fsec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.

Method for manufacturing a solidified fiber fleece, the resulting solidified fiber fleece, and use of this fleece

Abstract: Fiber fleeces made entirely of pure artificial (polymeric) fibers or mixed with natural fibers have to be solidified after formation by carding, or laying only in the case of filament fleeces. In the fleece according to the invention, which is particularly bulky and thus needs to be solidified, neither lower-melting binding fibers nor chemical binding agents are used. Also, the mechanical needling process which uses needles is eliminated because this reduces the bulk too severely. The desired bulk is retained by producing solidification by a single water needling process (when performed on one side), with the desired water pressure being no higher than 60 bars, preferably 20-30 bars.

New Tests of Models in Chemical Binding — Extra-Mechanical Effects and Molecular Properties

Abstract: We examine the validity of two models according to which we derive information about structural, dynamic, electric and magnetic properties of small molecules from analysis of frequency data of vibration-rotational spectra in absorption or emission. One model is the atomic approximation, according to which we associate with a particular atomic centre (atomic nucleus) electrons of number approximately equal to the protonic number of the nucleus; by this means we derive structural and dynamic information. Another model of the diatomic molecule is a rotating electric dipole, according to which parameters associated with extra-mechanical (adiabatic and nonadiabatic) effects yield information about electric and magnetic properties, namely the permanent electric dipolar moment and the rotational g factor. Spectral data of LiH and GeS are employed as tests of these models, on the basis of which evaluation of these properties proves practicable for other small molecules, for which illustrations are presented.

Computational modeling of ultrashort-pulse ablation of enamel

Abstract: A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 sec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.

Nonwoven sheet material, method for its production and adhesive tape based on this material

Abstract: FIELD: nonwoven sheet materials and sensitive to pressure adhesive tapes produced from nonwoven sheet materials. SUBSTANCE: nonwoven sheet material includes fibrous cloth of random weaving from tensioned nonbreaking staple fibers and binding fibers. Fiber cloth has pattern stamping and bound with chemical binding agent, physical holding or by their combination. Nonwoven sheet material is easily ruptured by hands in transverse machine direction. Provision is also made of the method for production of such sheet material and adhesive tape. EFFECT: higher efficiency.

High-Tc Ramp-Type Josephson Junctions with PrBa2Cu3-xGaxO7-δ barrier

Abstract: Superconducting three terminal devices [1] of sufficient current and voltage gain and integrability are not yet available, so Josephson junctions are still the basic active elements in superconducting electronics. In recent years a lot of effort has been put into the development of reproducible high-Tc Josephson junctions — with mixed success. Even though Josephson behaviour can easily be demonstrated in very simple configurations, the fabrication of reproducible junctions is still quite a problem and is not yet sufficient for medium or large scale levels of integration. Apart from a lack of the understanding of the basic mechanisms of high-Tc superconductivity, also the charge transport properties in high-Tc Josephson junctions are not yet fully understood. This, together with the extremely short coherence length of the order of the chemical binding length and the difficulties in preparing these materials, resulted in junction realisations that were quite often intrinsically complicated and not well understood in their physical behaviour but showed reasonably good current-voltage characteristics, e.g. the different types of grain boundary junctions [2]. In contrast, junctions with simple artificial barriers like normal conductor barriers made of Ag between YBa2Cu3O7-δ show a quite reproducible behaviour if the interface between YBa2Cu3O7-δ and the barrier is reasonably clean [3]. Due to the SNS characteristics and the low normal resistance of these junctions they are only useful for a very limited number of applications.