Numerical simulation of nonadiabatic electron excitation in the strong field regime. 2. Linear polyene cations

Time-dependent Hartree-Fock theory has been used to study the electronic optical response of a series of linear polyene cations (+1 and +2) in strong laser fields. The interaction of ethylene, butadiene, and hexatriene, with pulsed and CW fields corresponding to 8.75 x 10(13) W/cm(2) and 760 nm, have been calculated using the 6-31G(d,p) basis set. Nonadiabatic processes including nonlinear response of the dipole moment to the field and non-resonant energy deposition into excited states were more pronounced for the monocations in comparison with dications. For a given charge state and geometry, the nonadiabatic effects in the charge distribution and instantaneous dipole increased with the length of the polyene. For pulsed fields, the instantaneous dipole continued to oscillate after the field returned to zero and corresponded to a non-resonant electronic excitation involving primarily the lowest electronic transition. For a given molecule and fixed charge state, the degree of nonadiabatic coupling and excitation was greater for geometries with lower excitation energies.     

A calcium-selective optrode based on fluorimetric measurement of membrane potential

An ion-selective optrode for the continuous determination of calcium ions is presented. It is based on measurement of the fluorescence intensity of a potential-sensitive dye (the C-18 ester of rhodamine B) incorporated into a lipid membrane constructed by the Langmuir-Blodgett film technique. The membrane potential depends on the calcium ion concentration in the sample solution, when a calcium-selective ionophore (ETH 1001) is incorporated into the lipid membrane. The fluorescence of the potential-sensitive dye is reduced with increasing calcium ion concentrations. Interferences by other cations can be compensated for by using a reference optrode. The relation between the negative logarithm of the calcium ion concentration and the decrease in relative fluorescence is linear over the range 0.1–10 mM calcium and can be described by an optical “Nernst” equation. The selectivity factors over magnesium, sodium and potassium are better than 1×10⁵ when the reference optrode is used. The maximal signal change caused by 10 mM calcium ion is ?8%. The membranes are stable for more than six months when stored in the dark. The analytical data are compared with those obtained with potassium- and sodium-selective optrodes, and the photophysical principles underlying the selective and unselective responses are discussed.     

Synthesis,Characterization, and Crystal Structure of a New Coordination Polymer of Lead(II) Containing 2,6‐Pyridinedicarboxylic Acid

The reaction of solution 2,6‐pyridinedicarboxylic acid ( 1 ) and 2,2′‐Bipyridine with Pb(NO₃)₂ led to the coordination polymer [Pb(pydc)]_n ( 2 ) (pydcH₂ is 2,6‐pyridinedicarboxylic acid). This complex was characterized by elemental analysis, IR spectroscopy and single‐crystal structure of 2 . Crystal data for 2 at ?80 °C: monoclinic, space group P2₁/n, a = 977.2(1), b = 554.0(1), c = 1425.3(2) pm, β = 104.75(1)°, Z = 4, R₁= 0.0261. The units [Pb(pydc)] form infinite chains along [010].     

[Li7(CHPMe2NSiMe3)3(OSiMe2nBu)]2, ein Gemischtligand-Li14-Cluster mit dem Carbdianion (CHPMe2NSiMe3)2−

[Li₇(CHPMe₂NSiMe₃)₃(OSiMe₂ⁿBu)]₂, a Mixed-Ligand-Li₁₄ Cluster with the Carbdianion (CHPMe₂NSiMe₃)^2? The title compound is formed as colourless moisture and oxygen sensitive crystals by the reaction of [LiCH₂PMe₂NSiMe₃]₄ with zinc or cobalt chloride in a toluene suspension in the presence of silicongrease (–OSiMe₂–)_n and n-butyllithium. It is characterized by multinucleus NMR spectroscopy and by crystal structure determinations of two different crystal individuals. 1. Space group P1 , Z = 1, lattice dimensions at ?70 °C: a = 1272.0, b = 1392.6, c = 1417.6 pm, α = 115.33°, β = 96.75°, σ = 106.81°; R = 0.042. 2. Space group P2₁/n, Z = 2, lattice dimensions at ?50 °C: a = 1424.8, b = 1457.1, c = 1997.0 pm, β = 90.32, R = 0.069.     

Metallic behavior of the Zintl phase EuGe2: combined structural studies, property measurements, and electronic structure calculations

The Zintl compound EuGe₂ crystallizes in the trigonal space group (No. 164) with the CeCd₂-structure type. Its structure can be formally derived from the hexagonal AlB₂-structure type by a strong puckering of the hexagonal layers. The chemical bonding in EuGe₂ can be rationalized according to the Zintl concept as (Eu²⁺)(Ge¹⁻)₂, since the europium atoms are divalent and each germanium atom receives one additional valence electron. In that sense, EuGe₂ is expected to be a closed-shell compound with semiconducting behavior. However, temperature dependent resistivity measurements show EuGe₂ to be metallic. Subsequently, detailed crystallographic studies revealed the structure and the composition of EuGe₂ to be free of defects and impurities, which, along with the confirmed divalent oxidation state of the europium atoms by means of magnetic measurements, make EuGe₂ another example of a metallic Zintl phase. These results are in good agreement with the results of electronic structure calculations such as TB-LMTO-ASA (LDA) and FLAPW (GGA), which reveal non-zero DOS at the Fermi level.     

Thermal spraying of composites—Manufacturing and post treatment

Composites are materials with an increasing importance for the industry. A newly developed method for fabrication of fibre-reinforced metal matrix composites permits the production of composites with metal or ceramic fibres by thermal spraying. An improvement of coatings properties and the removal of flaws by post treatment is possible. This paper presents the thermal treatment by laser beam, electron beam and hot isostatic pressing (HIP) process and the mechanical treatment by shot peening.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Reaktionen von Diorganogallium(indium)fluoriden. Die Kristallstruktur von Mes2InF

Reaction of Diorganogallium(indium) Fluorides. The Crystal Structure of Mes₂InF Mes₂GaF ( 1 ) reacts with t-BuNH₂ at 20°C to the amine adduct [Mes₂Ga(F)(t-BuNH₂)] ( 2 ). Treatment of 1 with H₂S gives after a redox reaction γ-S₈-Sulfur (Muthmanns' Sulfur) ( 3 ) as the only isolated product. When i-Pr₂InF ( 4 ) is reacted with [SnCl₂(dioxane)] in toluene at 70°C one yields after workup [i-PrInCl₂(dioxane)] ( 5 ), which is formed after ligand exchange and reaction with dioxane. 2 and 5 were investigated by NMR-, IR- and MS-techniques. In addition, 2 · 2,5 THF, 3, 5 and Mes₂InF were characterized by an X-ray structure determination. According to that 2 · 2,5 THF contains dimeres, associated by hydrogen brigdes, while 5 possesses a polymeric structure with bridging dioxane molecules. 3 forms eightmembered rings with C ₂-symmetry. Me₂InF is a trimer in the solid state with an In₃F₃-backbone.     

BLUE LIGHT PHOTORECEPTION IN Neurospora ORCADIAN RHYTHM: EVIDENCE FOR INVOLVEMENT OF THE FLAVIN TRIPLET STATE

The mechanism of the photoreceptor acting on the circadian conidiation rhythm of Neurospora crassa was studied, with the following results: (1) the efficiency of 8-haloflavins as sensitizers increased with their triplet yields. (2) Phase shifts were not abolished by removal of oxygen prior to illumination. (3) Oxygen inhibited phase shifts when introduced into the cultures after light treatment. It is proposed that the blue light photoreceptor for the circadian clock of Neurospora crassa acts (1) from its triplet state, but (2) not via singlet oxygen; (3) signal transduction involves (an) oxygen-sensitive intermediate(s).     

Correlation of free radical yields with strand break yields produced in plasmid DNA by the direct effect of ionizing radiation

The purpose of this study was to determine how free radical formation (fr) correlates with single strand break (ssb) and double strand break (dsb) formation in DNA exposed to the direct effects of ionizing radiation. Chemical yields have been determined of (i) total radicals trapped on DNA at 4 K, G(Sigmafr), (ii) radicals trapped on the DNA sugar, Gsugar(fr), (iii) prompt single strand breaks, Gprompt(ssb), (iv) total single strand breaks, Gtotal(ssb), and (v) double strand breaks, G(dsb). These measurements make it possible, for the first time, to quantitatively test the premise that free radicals are the primary precursors to strand breaks. G(fr) were measured by EPR applied to films of pEC (10,810 bp) and pUC18 (2686 bp) plasmids hydrated to Gamma = 22 mol of water/nucleotide and X-irradiated at 4 K. Using these same samples warmed to room temperature, strand breaks were measured by gel electrophoresis. The respective values for pEC and pUC18 were G(fr) = 0.71 +/- 0.02 and 0.61 +/- 0.01 micromol/J, Gtotal(ssb) = 0.09 +/- 0.01 and 0.14 +/- 0.01 micromol/J, G(dsb) = 0.010 +/- 0.001 and 0.006 +/- 0.001 micromol/J, and Gtota)(ssb)/G(dsb) approximately 9 and approximately 20. Surprisingly, Gsugar(fr) approximately 0.06 mumol/J for pUC18 films, less than half of Gtotal(ssb). This indicates that a significant fraction of strand breaks are derived from precursors other than trapped DNA radicals. To explain this disparity, various mechanisms were considered, including one that entails two one-electron oxidations of a single deoxyribose carbon.