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  • 1
    ISSN: 1432-1017
    Keywords: Cytochrome P-450 ; photoreversibility ; relaxational enzyme kinetics ; 7-ethoxycoumarin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract We estimate the “active” part of cytochrome P-450, which is involved in a special substrate transformation, by measuring the initial change of the production rate as a function of the relaxation transitions between two different steady states of the reaction cycle of cytochrome P-450 using the light-reversibility of the carbon monoxide inhibition. The kinetic data of such relaxations are interpreted within a model cycle, which reduces the reaction cycle to three steps. The estimation of the rate constant of the first reduction step, derived from model simulation of the production rate, is confirmed by independent experimental study of the reduction kinetics. An application of our model to the O-deethylation of 7-ethoxycoumarin reveals that — in a time average — 10%–15% of the spectroscopically detectable cytochrome P-450 is involved in that transformation.
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  • 2
    ISSN: 1433-0768
    Keywords: Key wordsSpectroelectrochemistry ; Diffuse reflectance spectrometry ; Solid state electrochemistry ; Voltammetry ; Microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An instrumental setup is described which allows electrochemical measurements to be performed with solid particles immobilized on the surface of a graphite electrode with in situ recording of diffuse reflectance spectra under an incident light microscope. The instrument used includes a special electrochemical cell and a microscope which is interfaced by a light␣guide to a transputer-integrated photodiode-array spectrometer allowing measurements ranging from 320 to 950 nm with a resolution of 3.2 nm/pixel and a PC-interfaced potentiostat. The 0R0 geometry of the optical arrangement and the use of crossed polarization filters for blocking specular reflectance makes it possible to use the Kubelka-Munk function for quantifying the optical measurements. The above instrument has been used for the study of the electrochromic system of solid silver octacyanomolybdate(IV/V) adjacent to a silver nitrate solution. The in situ diffuse reflec tance spectroelectrochemical measurements prove that the electrochemical reaction starts at the graphite/sample interface and then advances into the bulk of the sample towards the sample/electrolyte interface. The ratios Red:Ox determined by spectrometry and chronocoulometry as a function of electrode potentials are identical.
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  • 3
    ISSN: 1433-0768
    Keywords: Key words Solid state electrochemistry ; Mössbauer ; Magnetic susceptibility ; X-ray powder diffraction ; Iron(III)-cadmium(II) hexacyanoferrates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Coprecipitates of CdII, KI and FeIII with hexacyanoferrate ions [Fe(CN)6]4− have been studied by solid-state electrochemistry (voltammetry of immobilized microparticles), magnetic susceptibility measurements, X-ray powder diffraction, electron spin resonance, Mössbauer and diffuse reflectance spectroscopy. Most suprisingly, all experimental results point to the formation of a continuous series of complex mixed phases without the formation of phase mixtures. Although CdII and FeIII ions differ too much in their ionic radii to allow the formation of simple substitution mixed hexacyanoferrates, they are capable of forming different kinds of complex insertion and substitution mixed crystals because of the zeolitic structure of both the iron and the cadmium hexacyanoferrate. Low cadmium concentrations can be found in the zeolitic cavities of iron hexacyanoferrate (Prussian blue), and they start to widen the lattice and facilitate, at higher concentrations, the direct substitution of high-spin iron(III) ions by cadmium ions. In cases of an excess of cadmium, the formation of cadmium hexacyanoferrate with iron(III) ions in the interstitials of the zeolitic structure is observed. These mixed phases show strong charge transfer bands in the visible range and have the appearance of “diluted” Prussian blue. For the first time, this indicates that the charge transfer between the carbon-coordinated low-spin iron(II) ions and the high-spin iron(III) ions can also occur when the latter are situated in the cavities of a host hexacyanoferrate. In Prussian blue the interstitial iron(III) ions are responsible for a very strong charge transfer interaction between the low-spin iron(II) ions and the nitrogen-coordinated high-spin iron(III) ions. Upon substitution of the very small amount of interstitial iron(III) ions in Prussian blue by potassium and cadmium ions the Kubelka-Munk function diminishes by more than 30%, indicating a tremendous decrease in iron(III)-iron(II) interaction.
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  • 4
    ISSN: 1434-601X
    Keywords: 25.55 ; 97.10
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The22Ne(α, γ)26Mg and22Ne(α, n)25Mg reactions were investigated forE α(lab) from 0.71 to 2.25 MeV. Neon gas enriched to 99% in22Ne was recirculated in a differentially pumped gas target system of the extended type. Theγ-ray transitions were observed with Ge(Li) detectors and the neutrons with3He ionization chambers. A previously known resonance at ER(lab)=2.05 MeV was verified and 15 new resonances were found in the energy range covered, with the lowest at ER(lab)=0.83 MeV. Information on resonance energies, widths, strengths,γ-ray branching ratios, as well asJ π assignments, is reported. The energy range investigated corresponds to the important temperature range ofT 9 from 0.3 to 1.4 (109 K), for which the astrophysical rates were determined for both reactions. The results show that the ratios of the rates for22Ne(α, n)25Mg and22Ne(α, γ)26Mg are significantly smaller than the previously adopted values, e.g., by at least a factor of 60 nearT 9=0.65. Thus, the22Ne(α, n)25Mg reaction will likely play a smaller role as a neutron source fors-process nucleosynthesis, than has frequently been assumed.
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  • 5
    ISSN: 1434-601X
    Keywords: 12.40.Qq ; 13.25.+m ; 14.40.Cs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A direct search for theE R =70 keV resonance in17O(p, α)14N was carried out using17O enriched Ta2O5 targets in combination with a 1 mA proton beam and suitable detectors of large solid angle. The observed upper limit for the resonance strength isωγ≤8×10−10 eV.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 162 (1961), S. 28-33 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using the variational method developped in the preceding paper ofDiehl andFlügge, the binding energy and molecular parameters of the muon molecule ppΜ have been calculated. The vibrational amplitudes of the protons turn out to be much larger in comparison to their equilibrium distance than in the electronic molecule H 2 + . The equilibrium distance is about 40% larger than it would have come out from a simple two-center calculation with fixed nuclei. A dissociation energy of 211 ev has been found; this value may be enlarged by something between 10 and 20 ev in consequence of plausible corrections.
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  • 7
    ISSN: 1434-601X
    Keywords: 25.00
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The fusion reactions6Li(p, α)3He,6Li(d, α)4He, and7Li(p, α)4He have been studied over the c.m. energy rangeE=10 to 1450 keV. Each reaction involved the use of hydrogen projectiles and LiF solid targets as well as Li projectiles and hydrogen molecular gas targets. In all cases the effects of electron screening on the low-energy fusion cross sections (exponential enhancement) have been observed; the effects are somewhat stronger in the case of atomicp ord projectiles compared to the case of molecularH 2 orD 2 gas targets. If isotopic effects on electron screening are negligible, all three reactions should exhibit the same enhancements for each set of experimental techniques. The measurements confirmed this expectation to a large extent.
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  • 8
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is generally assumed that there are free electronic carriers associated with the CuO2 planes in high-temperature superconductors. Regarding these carriers as confined to these planes their influence on phonon frequencies is studied within the framework of a shell model of lattice dynamics taking into account the long-range part of the electron-phonon coupling. We find a complete suppression of the LO-TO splitting for modes polarized along the planes by metallic screening and a strong coupling of electronic plasmon and particle-hole excitations especially to some To-phonon branches polarized perpendicular to the conducting planes, particularly pronounced in systems with at least two CuO2 planes per unit cell. Numerical results are presented for YBa2Cu3O7.
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  • 9
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The three-body problem of quantum mechanics has been treated in appropriate co-ordinates. These are, besides those of the center-of-mass, the distances between the three particles and three Eulerian angles, fixing in space the position of the triangle formed by the particles. The Hamiltonian can be simplified by introducing the usual angular momentum operators of a gyrating rigid body. The solution of the wave equation has been discussed. Factorization into an angular part and a part depending on the particle distances only leads to certain linear combinations of such products. The angular parts have the well-known form of the representation coefficientsD MK L of the three-dimensional rotational group. The parts depending on the distances may be derived from a system of differential equations coupling, in two separate sets, either even or odd values ofK for each given value ofL.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 172 (1963), S. 219-223 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is shown that the so-called hypervirial theorems found byHirschfelder and coworkers (Sect. 1) are satisfied for a large class of variational trial functions (Sect. 2). The results are applied to several variational approximations to the eigenfunctions of the H 2 + molecule (Sect. 3).
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