bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the Intrinsic Membrane Proteins of Photosystem II from Spinach
Authors: Irrgang K.‐D. , Hanssum B. , Renger G. , Vater J.
Published: March 2014

The key reactions of photosynthetic water oxidation by visible light take place in photosystem II. Here we report on our recent results about functional studies on a transmembrane pigment‐protein complex of photosystem II. Using O2‐evolving PSII membrane fragments from spinach we isolated the intrinsic membrane proteins and investigated the effect of solubilization with three different non‐ionic detergents, β‐dodecylmaltoside (β‐DM), Triton X‐100 and β‐N‐octylglycopyranoside (β‐NOGP), on two parameters:

77 K fluorescence emission and II. PSII electron transport (DPC → DCIP). The following results were obtained:

All the detergents dramatically modified the 77 K fluorescence emission spectra at/or near their critical micelle concentrations (CMC).

The yield per flash or rate of DCIP‐reduction as an indicator of electron transport activity markedly depended on the type and concentration of the detergent. β‐NOGP caused a decrease of the electron transfer already below its CMC, whereas β‐DM and Triton X‐100 did not reveal a distinct modification at submicellar concentrations. In the case of β‐NOGP the half‐maximum activity is observed at about 20 mM.

On the basis of a simple model assuming an apparent equilibrium between only two stable states (non‐solubilized and β‐NOGP‐solubilized PSII intrinsic membrane proteins) we calculated an apparent equilibrium constant Keq to 48.2 and a free solubilization energy of ΔGsol = −9.6 kJ/mol.

The results are discussed with special emphasis on two questions: a) To what extent have the polypeptide subunits and the pigment and redox group arrangement the same structure and configuration in detergent‐solubilized state as in the thylakoid membrane and PSII membrane fragments, respectively? b) How can we interprete the solubilization properties of the different detergents on the basis of their physical and chemical features and the structural architecture of the PSII membrane fragments?
Reactions of Ba Atoms with NO2, O3 and Cl2: Dynamic Consequences of the Divalent Nature of Barium
Authors: Davis H. Floyd , Suits Arthur G. , Hou Hongtao , Lee Yuan T.
Published: March 2014

The role of the divalent nature of barium atoms in chemical reactivity was explored using crossed molecular beams. Angular and velocity distributions of products from reactions of Ba(1S) with NO2 and O3 indicate the existence of long lived collision intermediates despite very large reaction exothermicities. The existence of these intermediates results from barriers to transfer of the second electron necessary to form ground state products. Although BaO was the dominant product in both reactions, two previously unknown channels were observed: Ba + N02 → BaON + O and Ba + O3 → BaO2 + O. We obtained bond dissociation energies of D0(Ba–ON) = 270 ± 80 kJ/mol and D0(Ba – O2) = 500 ± 80 kJ/mol for these molecules. The dependence of the cross sections for the ion channels, Ba(1P) + Cl2 → Ba+ + Cl−2 and Ba(1P) + Cl2 → BaCl+ + Cl− on Ba(1P) orbital alignment and collision energy was used to probe the course of the reaction through intersections between the ionic and covalent potential energy surfaces.
Theoretical Studies of Collision‐induced Energy Transfer in Electronically Excited States
Authors: Alexander M. H. , Berning A. , Esposti A. Degli , Joerg A. , Kliesch A. , Werner H.‐J.
Published: March 2014

Some recent theoretical studies of collision‐induced energy transfer in electronically excited states are reviewed. Using accurate ab initio electronic wavefunctions potential energy surfaces have been computed for OH(X2Π, A2Σ+) + He and Ar, Li2 (A1Σu+) + Ne, N2+ (X2Σg+, A2Πu) + He, and CN (X2Σ+, A2Π) + He and used in quantum scattering calculations of cross sections and rate coefficients for rotational, vibrational, and electronic energy transfer processes. In cases where comparison with accurate experimental data is possible, the theoretical and experimental data agree within 20–30 percent.
Molecular Reaction Dynamics – Subdoppler and Polarization Spectroscopy –
Authors: Comes F. J.
Published: March 2014

Photofragmentation spectroscopy, – the study of “half‐collisions” with polarized light of subdoppler band width – opens a window to look into the structure of molecules. A pictorial view of the intermediate state is provided by the analysis of fragment vector properties. The forces which make the fragments fly apart or rotate can be “seen” from the line shapes. Information is gained from the stable products of the fragmentation reaction long after the parent has dissociated. – Hydrogenperoxide as a model example is treated and a complete picture of its fragmentation in the uv is given by the discussion of the various vector correlations. The method is further applied to the fragmentation of hydrazoic acid which shows to have a fairly complex dissociation process.
Size Distribution Studies of Sputtered Transition Metal Cluster Ions by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
Authors: Selinger A. , Schnabel P. , Wiese W. , Irion M. P.
Published: March 2014

Mass spectra of various metal cluster ions, mainly of transition metals are presented. These clusters were sputtered by an external 20 keV Xe+ ion source and detected with a Fourier transform mass spectrometer (FT‐MS). Cluster ions could be efficiently trapped in the ion cyclotron resonance cell (ICR‐cell). In the case of indium, for instance, clusters containing more than 100 atoms could be observed. The sensitivity of our instrument was sufficient to even detect Au+85 cluster ions with mass 16745 u. “Magic numbers” are observed in the cluster cation distributions of indium and the d10S1 metals copper, silver and gold.
Nucleophilic Substitution Reactions in Mixed Organic Clusters after Resonant Two Photon Ionization
Authors: Eggert J. , Janes C. , Wassermann B. , Brutschy B. , Baumgärtel H.
Published: March 2014

Substitution reactions in mixed van der Waals aggregates, consisting of halobenzenes and polar molecules are studied by resonant two‐photon ionization (R2PI). From the optical fingerprints in the ion‐yield curves of the product ions we are able to assign their neutral precursors. The ipso substitution reactions have been found to depend both on the number and type of solvent molecules and on the halogen present and are discussed by an addition‐elimination mechanism. Dissociative electron transfer is found to play an important role in the reaction mechanism and in the size dependence of the reactivity.
Model Calculations on Laser Induced Dissociation of Bromine with Control of Electronic Product Excitation
Authors: Hartke B. , Kolba E. , Manz J. , Schor H. H. R.
Published: March 2014

After a short survey of different methods to control electronic product excitations in laser‐induced unimolecular dissociations we develop an alternative strategy, adapted to interfering exit channels with potential energy curve crossings, and implement it for the bromine system. In a reference case with zero potential couplings optimal initial population of the competing dissociative states leads to complete product selectivity. In the real system, however, the electronically excited molecules pass the potential energy curve crossing of the B 3Πo + u and 1Π1u states on their way to dissociation, and Landau‐Zener‐type diabatic transitions establish the final product distribution. For this case we discuss the possibility to refine the electronic product distribution by a second, intense laser pulse applied after the curve crossing. Based on these results inversion of experimental product distribution data may be used to determine the curve crossing parameters, thus extending the short range information obtained from Raman scattering. Simulation of laser controlled dissociation is achieved by FFT (fast Fourier transform) propagation of representative wave packets.
Bond‐selective Photoion Correlations (“Memory Effects”) in Molecules from Site‐Specific 1s Excitation Using Synchrotron Radiation
Authors: Jung Rolf , Staub Ralf , Baiter Hermann , Reiser Georg , Habenicht Wieland , Müller‐Dethlefs Klaus
Published: March 2014

We observe bond‐selective photoion‐photoion correlations in the molecules CF2 = CH2 and CF3–CH3 upon site‐specific C (1s) excitation at either the CF or the CH atom. The observed double photoion correlations can be interpreted as a chemical “memory effect” where the fragmentation process memorizes the initial site of energy deposition. A new “Zero Kinetic Energy Photoelectron”‐photoion‐photoion coincidence technique incorporating a high transmission mass spectrometer and a multi‐stop time‐to‐digital converter is employed. The excitation is carried out by monochromatized X‐ray synchrotron radiation from BESSY.
Critical Examination of the Calculus Convolution Kinetics: The Influence of Nonstationary Diffusion on Excimer Formation with Dissociation
Authors: Vogelsang J. , Hauser M.
Published: March 2014

If time dependent rate coefficients (TDRC) appear in reactions, ordinary rate equations (RE) fail. The calculus convolution kinetics (CK) provides consistent results in these cases, but its appliance is quite unfamiliar. For rate coefficient(s) (RC) that are time‐independent the results of CK are analytically identical with those of RE, though being obtained on a completely different way. – In this paper the failure of the RE method will be briefly demonstrated with an example. Furthermore the concept of CK will be presented in short and applied on excimer formation. On the level of synthesis data a comparison of the result of the rate equations' treatment with √t‐term obtained numerically, the CK result and measuring data will be carried out. For this the time resolved decay curves of “single photon counting” – measurements and synthesis data of both methods convoluted by flash will be graphically laid on top of each other. It turns out that curves from CK represent the measuring graph better than data of the RE calculated with the same parameters. Larger differences appear in the initial part of the curves with both methods. To explain these differences a new mechanism of excimer formation will be brought into discussion, but also the uncompletness of the Smoluchowski approximation for nonstationary diffusion will be taken into account. – The kinetical treatment given below is an example of excited state kinetics [1]; but CK is not limited on this kind of kinetics.
Statistical and Kinetic Approach to Plasmachemical Reactions
Authors: Haberlandt R. , Stiller W.
Published: March 2014

In order to treat reactive and transport processes in dilute and dense gaseous plasmas a quantum‐statistical formalism is given leading to generalized expressions for reaction rate coefficients. For diluted gaseous plasmas with binary collisions the common Boltzmann equation formalism can be derived; for higher order collisions the pair distribution function has to be considered. – In the framework of the Boltzmann equation formalism for multi‐component diluted gaseous plasmas equations for a reactive Lorentz gas are derived. With the help of the calculus electron‐molecule reactions (electron capture) and reactions between small ions and molecules in rare gases can be treated.
Solvent Dynamic in Electron Transfer Reactions: An Application of Kramers Theory to Homogeneous Organic Electron Self Exchange
Authors: Grampp Günter , Harrer W. , Hetz G.
Published: March 2014

Using ESR spectroscopy the rate constants of homogeneous electron self exchange in the TCNQ/TCNQ−., TCNE/TCNE−. and TTF/TTF+.‐couples (TCNQ = tetracyanoquinonedimethane, TCNE = tetracyanoethylene, TTF = tetrathiofulvalene) were measured in 14 different solvents at 293 K. The rate constants were expressed by the preequilibrium encounter model for adiabatic processes applying Kramers theory. “Friction” dependent preexponential factors expressed by the longitudinal relaxation time τL of the solvents are found. The solvent dependence of the rate constant is explained in terms of Marcus theory by using an outer‐sphere reorganization energy for ellipsoidal molecules. From these solvent dependencies the geometric term g(r̄,d′) = 1/r̄‐1/d′ is obtained leading to an experimental reaction distance d between both molecules in the transition state.
Automatic Generation of Reaction Mechanisms for the Description of the Oxidation of Higher Hydrocarbons
Authors: Chevalier C. , Warnatz J. , Melenk H.
Published: March 2014

Oxidation mechanisms even for rather simple hydrocarbons like heptane consist due to the occurrence of many isomeric structures of thousands of reactions of hundreds of species. The automatic generation of these reaction mechanisms using artificial intelligence means is described. Results are presented for n‐heptane‐air mixtures, where a hand‐written reaction mechanism tested against experimental data is available.
Determination of the Rate Constant Ratio for the Reactions of the Acetylperoxy Radical with NO and NO2
Authors: Kirchner F. , Zabel F. , Becker K. H.
Published: March 2014

The thermal decomposition of acetyl peroxynitrate was studied in a 420 1 DURAN glass reaction chamber in the presence of different initial [NO2]/[NO] ratios. From an analysis of the rate data, the following rate constant ratios k2/k1 for the reactions of CH3C(O)O2 radicals with NO (k1) and NO2 (k2) were derived at different temperatures and total pressures: 0.45 ± 0.05 (304 K, 1000 mbar), 0.41 ± 0.05 (321 K, 1000 mbar), 0.42 ± 0.02 (313 K, 1000 mbar) 0.39 ± 0.02 (313 K, 300 mbar), 0.28 ± 0.04 (313 K, 100 mbar), 0.25 ± 0.04 (313 K, 30 mbar). Using recent data on k2, a pressure independent rate constant k1 = (2.1 ± 0.5) · 10−11 cm3 molecule−1 s−1 was deduced from these ratios at 313 K.
IR‐Chemiluminescence from the Reactions of Atomic Fluorine with Ethyne and Butyne‐2
Authors: Schwanke U. , Heydtmann H.
Published: March 2014

The reactions F + C2H2 and F + C4H6 (2‐butyne) were studied in a low pressure flow system using the IR‐chemiluminescence technique. The vibrational‐rotational state distributions for the product molecule HF were determined for various conditions. For F + C2H2 only secondary reactions can lead to vibrational excitation of HF; with an excess of F‐atoms HF(ν ≤ 7) was observed. For F + C4H6 the primary abstraction yields the vibrational distribution N1:N2:N3:N4 = 26:36:32:7. With an excess of F atoms ν = 5 and ν = 6 are populated. The possible secondary steps are discussed on the basis of our observations.
1H‐CIDNP During the Reaction of Heavy Carbene Analogues R2M (M = Si, Ge, Sn; R = Me, n‐Bu) with Halides
Authors: Lehnig Manfred , Klaukien Heino , Reininghaus F.
Published: March 2014

During the reaction of photochemically generated silylenes Me2Si: with PhCH2Cl, PhCH2Br, and Ph2CHCl, 1H‐CIDNP is observed in the products of insertion reactions into the C‐X bonds (X = Cl, Br) and in the abstraction products Ms2SiX2 indicating the occurrence of a radical abstraction‐recombination reaction. The silylenes react from singlet states. Me2Si: reacts with CH2 = CHCH2Cl without CIDNP phenomena in a concerted way. (n‐Bu2Sn)6 reacts with EtBr via a radical chain mechanism without the appearance of free stannylenes n‐Bu2Sn: as intermediates.
Electrostatic Processing of Mineral Salt Mixtures: The Selectively‐stimulated Contact Charging of Kieserite (MgSO4 · H2O). An Interpretation
Authors: Ernst Lajos
Published: March 2014

In the electrostatic processing of crude potash salt, a mixture of mainly KCl, NaCl and MgSO4 · H2O, the single salt particles gain an electric charge component‐selectively on contact with each other. This enables the components to be separated in an electric field. The component‐selective stimulation of contact charging can be achieved using a technology developed over many years, where small amounts of certain monocarboxylic acids are added to the salt mixture, while the relative humidity of the ambient air is maintained at some definite value. – Recently a model has been proposed to elucidate the mechanism of stimulated contact charging. It has been applied in the case of NaCl. H2O molecules bonded in surface‐cation‐vacancies of the crystal have an important role in this model, which will be extended in the present work to the case of the stimulated contact charging of kieserite. This enables the interpretation of empirical diagrams characterising the electrostatic salt separation to be made for the first time. Conversely, this may be regarded as a convincing verification of the model itself.
Kinetics of the Corrosion of Iron in Aqueous Electrolytes at Temperatures up to 300°C
Authors: Heusler K. E. , Kusian B. , McPhail D.
Published: March 2014

The corrosion behaviour of iron was investigated in aqueous borate buffer solutions with and without additions of sodium chloride and in quaternary salt brine at temperatures between 150°C and 300°C. A magnetite film grows according to the parabolic rate law. The parabolic rate constant is independent of the pH‐value, increases with the electrode potential and with the chloride concentration, and attains a maximum at about 250°C. The parabolic rate constants are compared to literature data and theoretical calculations. – After some time the corrosion rate drops to a steady state value, if the chloride concentration is not too high and the electrode potential not too positive. The steady state corrosion rate increases with the temperature according to an activation enthalpy of 41 kJ/mol and remains less than 10 μA/cm2 up to 300°C. Above some critical electrode potential becoming more negative with the concentration of chloride, a local corrosion is observed producing flat pits covered by thick oxide layers. At the very high chloride concentration of the quaternary salt brine the whole surface becomes activated and corrosion proceeds rather uniform.
Reduction of Ag+ in Aqueous Polyanion Solution: Some Properties and Reactions of Long‐Lived Oligomeric Silver Clusters and Metallic Silver Particles
Authors: Henglein Arnim , Linnert Thomas , Mulvaney Paul
Published: March 2014

Radiolytic reduction of AgClO4 solutions containing a polyanion leads to the formation of long‐lived oligomeric silver clusters which are stabilized on the polymer chains. Under suitable conditions, the accompanying formation of colloidal silver consisting of metallic particles is strongly suppressed and cluster concentrations of several 10−4 M can be produced. In the presence of polyacrylate, the clusters are particularly long‐lived; they have absorption bands at 300 nm, 340 nm, and 370 nm. The bands of the latter two clusters are red‐shifted as compared to the bands of the unstabilized clusters or clusters stabilized by polyphosphate. The Ag24+ cluster, which is formed in the initial stages of Ag+ reduction, absorbs at 275 and 480 nm in the presence of polyacrylate. – The various clusters react at different rates with electron acceptors, such as oxygen, carbon tetrachloride and nitromethane. The clusters also react with complexing agents, such as ammonia, cyanide and hydrogen sulfide anions, to form larger particles of silver and/or larger complexed clusters. The great reactivity of the clusters towards nucleophilic reagents is explained by the high coordinative unsaturation of the silver atoms in the clusters. This also explains the stabilization of the clusters by the anion groups of the polymers used. – These reactivity studies were also complemented by investigating the reactions of larger silver particles, which already have metallic properties, with complexing agents. The oxidative corrosion of such particles is strongly accelerated by the complexing agents. A mechanism for the catalysis of the oxidative corrosion is presented, in which the principle steps are the complexation of silver atoms on the surface with simultaneous electron transfer into the metal interior (“pre‐complexation” or “pre‐oxidation” of surface atoms) followed by pick‐up of the electrons by oxygen.
Electrostatic Interactions of Bodies Bearing Thin Double‐Layers I. General Formulation
Authors: Adamczyk Z. , Belouschek P. , Lorenz D.
Published: March 2014

The modified Poisson‐Boltzmann (PB) equation was formulated for a system of flat dissimilar double‐layers by considering the excluded volume effect. Limiting solutions of the modified PB equation derived for an isolated plate, and for two‐plate system at large and small separations and arbitrary electrolyte composition were discussed. Results obtained for the parallel‐plate geometry were generalized to regularly shaped bodies (either convex or concave around their contact point) bearing thin double‐layers by applying the surface integration procedure analogous to the Derjaguin summation method. The excluded volume effect proved to be important for the dimensionless parameter β larger than 10−2 leading to a considerable increase of the potential difference across double‐layers and to a slight increase of the interaction force between bodies at large separations. At small separations, however, the force remains finite due to the excluded volume effect (in the constant charge model) in contrast to previous results predicting that the force should tend to infinity in this limit. It was also predicted that the presence of trace amount of polyvalente ions (e.g., Al3+ ion) decreased considerably the force between bodies immersed in a 1–1 electrolyte.
Dilute Random Distribution of Small Chiral Ellipsoids in a Chiral Fluid: Optical Properties
Authors: Lakhtakia Akhlesh
Published: March 2014

An integral equation method has been used to derive the polarizabilities of a small chiral ellipsoid immersed in a chiral fluid. These polarizabilities are then used to obtain the effective electromagnetic/optical properties of a dilute random suspension consisting of randomly‐oriented, ellipsoidal, chiral particles in a chiral fluid. The optical rotation and the circular dichroism of the suspension are obtained.
Solvent Induced Intramolecular Electron Exchange Kinetics in 1,3‐Isodisubstituted Aromatic Radical Anions II. Activation Parameters
Authors: Grampp G. , Shohoji M. C. B. L. , Herold B. J. , Steenken S.
Published: March 2014

From the alternant line broadening effect in the ESR‐spectra of the radical anions of 1,3‐dinitrobenzene and benzene‐1,3‐dicarbaldehyde in various protic and aprotic solvents the rates of intramolecular electron exchange were determined in the temperature range 260–340 K. Using Marcus theory and the Rips‐Jortner approach for the uniform adiabatic limit of electron transfer it is shown that the amount of transferred charge ze0 decreases with increasing temperature. This result is explained on the basis of the effect of temperature on the specific asymmetric solvation of the anions. For the 1,3‐dinitrobenzene radical anion in protic solvents the charge transfer number z changes slightly from 0.96 to 0.90 within 250–340 K and in aprotic solvents from 0.55 to 0.32 within 280–340 K. For benzene‐1,3‐dicarbaldehyde radical anion in protic solvents z changes from 0.40 to 0.29 within 260–320 K. From the measured activation parameters for the intramolecular electron exchange the values for the inner sphere reorganization energies λi were estimated, using values for the outer sphere reorganization λ0 as obtained by applying an ellipsoidal cavity model to the measured solvent dependence of the rates. For the 1,3‐dinitrobenzene radical anion λ0 increases with the degree of solvent association (from 18.4 to 106.4 kJ/mol), whereas λi varies much less (82.4–116.0 kJ/mol) for all protic and aprotic solvents investigated. From the difference in λ0 for protic and aprotic solvents, the value for the energy of solvation of the anions by hydrogen bonding is obtained as ≈ 10 kJ/mol.
Determination of Binary Diffusion Coefficients in Liquid Nonelectrolyte Mixtures using the Taylor Dispersion Technique
Authors: Thiel Peter , Paschke Albrecht , Winkelmann Jochen
Published: March 2014

The concentration dependence of mutual diffusion coefficients in four binary systems N,N‐dimethylformamide‐toluene, dimethylsulfoxide‐toluene, sulfolane—toluene and n‐heptane—toluene is determined at 298.15 K using the Taylor dispersion method. To detect the dispersion of the injected sample a flow‐through differential refractometer is applied. The refractometer output signals are recorded at constant time intervalls and a five parameter working equation is fitted to the concentration profile of the sample by a nonlinear least‐square procedure. Diffusion coefficients at infinite dilution were obtained and five empirical correlations for estimating diffusivities at infinite dilution are tested against our results.
Electrochemistry of Colloidal Silver Particles in Aqueous Solution: Deposition of Lead and Indium and Accompanying Optical Effects
Authors: Henglein A. , Mulvaney P. , Holzwarth A. , Sosebee T. E. , Fojtik A.
Published: March 2014

Colloidal silver particles (ca. 8 nm in diameter) act as microelectrodes in aqueous solution. They are charged via electron transfer from free radicals which are generated radiolytically. The stored electrons reduce adsorbed Pb2+ and In3+ ions. — The first monolayer of lead atoms deposited on the silver particles does not absorb at 215 nm where metallic lead has an absorption band. The Pb atoms cause the 380 nm surface plasmon band of the silver particles to be shifted to shorter wavelengths. This is explained in terms of electron donation from chemisorbed Pb atoms to the silver carrier. The Pb atoms of a submonolayer (which are formed by “under‐potential” deposition) do not react with methyl viologen, MV2+, whereas the lead atoms deposited in subsequent layers (“Nernst potential” deposition) are readily oxidized by MV2+. The absorption spectrum of colloidal lead in water is also discussed (εmax = 3.2 · 104 M−1 cm−1 at 215 nm). — Reduction of In3+ on the silver particles also leads to a blue‐shift of the plasmon band. It is attributed to electron transfer from deposited In atoms. However, as In metal deposition proceeds, In+ is produced by the conproportionation of the indium metal with In3+. When almost all the In3+ ions have been reduced, indium metal is further deposited by In+ reduction. Silver particles carrying a tight indium shell absorb at 225 nm with ε = 3.8 · 104 M−1 cm−1. This ε‐value is somewhat lower than the calculated one, and attributed to a reduction in mean free path for conduction electrons in small In colloids.
Determination of the Rate Constants for the Gas Phase Reactions of NO3 with H, OH and HO2 Radicals at 298 K
Authors: Becker E. , Rahman M. M. , Schindler R. N.
Published: March 2014

The reactions of NO3 with H (1), OH (2) and HO2 (3) radicals have been investigated at 298 K using a discharge flow system equipped with mass spectrometric and fluorescence detectors. The rate constants k(1) and k(2) were determined by numerical modeling of experimental [OH] profiles from reactions (1) and (2). In the reaction of NO3 with HO2 (3) the growth and decay of [OH] as well as the decay of [HO2] were measured. Comparison of these two profiles provided evidence for two different reaction paths (3a) and (3b), for which the rate constants were determined by numerical modeling. Experiments carried out in a wide range of reactant concentrations yielded in units of cm3 molecule−1 s−1 k(1) = (0.94 ± 0.2) · 10−10, k(2) = (1.22 ±0.35) · 10−11, k(3a) = (2.5 ± 0.7) · 10−12, and k(3b) = (1.9 ± 0.8) · 10−12. The results are compared with literature data.
Determination of Rate Constants for the Reactions of the CH2SH Radical with O2, O3, and NO2 at 298 K
Authors: Rahman M. M. , Becker E. , Wille U. , Schindler R. N.
Published: March 2014

CH2SH radicals were produced by the reaction of F atoms with an excess of CH3SH and detected mass spectrometrically at m/e 47 using an electron energy of 9.5 eV. Rate constants for the reactions of CH2SH with the oxidants O2 (k1), O3 (k2) and NO2 (k3) at 298 K were determined by measuring the decay of the radical in the presence of excess oxidants. The following results were obtained: magnified image

The rate constant for the reaction (4) F + CH3SH → products was determined to be k1 = (2.4 ± 0.4)·10−10 cm3 molecule−1 s−1. The branching into the channels (4a) F + CH3SH → CH2SH + HF and (4b) F + CH3SH → CH3S + HF was investigated by using CD3SH, and k4a/k4 = 0.6 ± 0.1 was obtained.
Collisional Deactivation of O2(1Σg+) by Small Polyatomic Molecules
Authors: Schmidt Reinhard
Published: March 2014

Literature data on the collisional deactivation of O2(1Σg+) by small polyatomic molecules in the gas phase are interpreted by a deactivation model which has proven to describe successfully the experimental findings for the collisional deactivation of O2(1Δg) in the liquid phase. Deactivation occurs by electronic to vibrational energy transfer from the excited O2 molecule to peripheral bonds X—Y of the quenching molecule. Using data on Franck‐Condon factors and transition energies for the possible coupled transitions O2(1Σg+, ν = 0 → 1Δg, ν = m) and X—Y (ν' = 0 → ν' = n) experimental rate constants kXYΣ of O2(1Σg+) quenching by X—Y can quite well be reproduced by calculated ones. The only parameter of the model which has to be changed is related with the electronic factor f of the corresponding O2 transition. As ratio of electronic factors of the 1Δg → 1Σg+ singlet‐triplet and 1Σg+ → 1Δg singlet‐singlet transitions fST/fSS = 6 · 10−5 is obtained. Independent measurements of radiative lifetimes of these transitions in an Ar‐matrix yield fST/fSS = 9 · 10−5 confirming our results. Thus for the first time collisional deactivation of O2(1Δg) and O2(1Σg+) by small polyatomic molecules is explained consistently.
An Abnormal Electrocapillary Response Stated by the Drop Time Method in Alkaline Solutions of Hemoglobin
Authors: Kuik Marian , Krassowski Kazimierz
Published: March 2014

In a narrow range of ammonia concentration of the buffer, solutions containing hemoglobin showed an increase instead of a decrease of drop time. The effect is greater in the presence of cobalt(II) ions. In both cases it disappears at higher ammonia concentration. The effect is a complex phenomenon, involving movement of the mercury drop surface, aggregation of hemoglobin, formation of Co(II)‐hemoglobin complexes, and adsorption of hemoglobin, its complexes and aggregates. A scheme explaining the origination of the anomaly is given. The significance of this effect for the determination of electrocapillary curves by the drop‐time method and in precise polarography is pointed out.
Oxirane Formation in the Reaction of NO3 Radicals with Alkenes
Authors: Wille U. , Rahman M. M. , Schindler R. N.
Published: March 2014

Mass spectra of products formed in the reaction between NO3 and cis‐2‐butene, isobutene, 2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene at 298 K and p = 3–10 mbar were obtained, using a fast flow system with molecular beam sampling. The spectra indicate formation of an oxirane in each reaction. Within experimental error the oxirane yields in the reaction of cis‐2‐butene and of 2,3‐dimethyl‐2‐butene were identical (90 ± 10)%. The rate of oxirane formation was found to obey the rate equation for the reaction:

NO3 + alkene → oxirane + NO2.    (1).

Good agreement was obtained for the rate constants of reaction (1) determined from the rate of oxirane formation and those determined in earlier works from the consumption of reactants.
Surface plasmon resonance as a technique to study adsorption to aluminum oxide surfaces
Authors: Miller C. E. , Meyer W. H. , Knoll W. , Wegner G.
Published: March 2014

The adaptation of the Surface Plasmon Resonance (SPR) method to the study of aluminum oxide surface interactions with organic and polymeric molecules is achieved through the preparation of a thin‐layer of Al2O3 on the silver layer in which the plasmon is generated. Extensive analyses of this system indicate that it is not ideal, but adequate for SPR surface studies. The use of this system for specific Al2O3 surface analyses, including equilibrium and kinetic adsorption analyses, is demonstrated.
1H‐NMR studies on thermochromism Ni(ii) complexes with N,N‐diethylethylenediamine
Authors: Ghosh Ashutosh , Nakamura The Late Daiyu , Ikeda Ryuichi
Published: March 2014

The temperature dependence of the second moment (M2) of 1H NMR absorptions was measured in solid thermochromic bis(N,N‐diethylethylenediamine)Ni(II) complexes. Perchlorate and tetrafluoroborate having a thermochromic phase transition at Ttr = 383 and 367 K, respectively, showed a discontinuous M2 change at Ttr indicating that a marked change of the chelate‐ring motions takes place at the transition. A small M2 value of ca. 8 G2 observed above the respective Ttr could be explained by the excitation of the chelate‐ring puckering together with a large‐amplitude librations of the whole complex ions. A gradual M2 decrease upon heating from 100 to 400 K was observed in bromide and iodide exhibiting continuous thermochromism. These M2 changes and the reported visible electron absorption maxima showed a quite analogous temperature dependence. This suggests that some kind of chelate‐ring motion such as the puckering also takes place in the continuous thermochromism complexes.
Tailoring magnetic interactions of organic solids: Modification of triphenylverdazyl
Authors: Dormann E. , Winter H. , Dyakonow W. , Gotschy B. , Lang A. , Naarmann H. , Walker N.
Published: March 2014

The synthesis of the free radicals 1‐(4'‐bromophenyl)‐3,5‐diphenyl‐verdazyl (Br‐TPV), 1‐(4'‐isopropyl‐phenyl)‐3,5‐diphenyl‐verdazyl (IP‐TPV), 1,3,5,6‐tetraphenyl‐verdazyl (Ph‐TPV), 6‐(1′‐naphthyl)‐1,3,5‐tri‐phenyl‐verdazyl (1N‐TPV), 6‐(2′‐naphthyl)‐1,3,5‐triphenyl‐verdazyl (2N‐TPV), 6‐(4′‐bromophenyl)‐1,3,5‐triphenyl‐verdazyl (BrPh‐TPV) and 1,3,5,6,6‐pentaphenyl‐verdazyl (PhPh‐TPV) is described. Their magnetic properties (static magnetic susceptibility, ESR) are reported for crystalline samples. They are compared with those of 1,3,5‐triphenyl‐verdazyl (TPV) which behaves as a quasi‐onedimensional antiferromagnet in the crystalline form. Exchange interaction is increased by a factor larger than 3 compared with TPV by the introduction of the additional ring in Ph‐TPV. For Ph‐TPV and PhPh‐TPV also the crystal structure was derived by X‐ray analysis. These results are discussed with special emphasis on their meaning for the tailoring of magnetic interactions in organic solids.
Effect of high pressure on the infrared spectra of solid nitro‐ and nitrito‐cobalt(iii) ammine complexes
Authors: Boldyreva E. V. , Burleva L. P. , Burgina E. B. , Baltachinov V. P. , Ahsbahs H. , Uchtmann H. , Doulepov V. E.
Published: March 2014

IR‐absorption spectra of Co(III) ammine complexes [Co(NH3)5NO2]XY and [Co(NH3)5ONO]XY (XY = Cl2, Br2, I2, (NO3)2, Cl · NO3) were studied at static pressures up to 20 kbar in a diamond anvil cell. The measured pressure induced shifts of valence (symmetric and asymmetric) and deformational frequencies of the NO2‐group were compared with a normal coordinate analysis of [Co(NH3)5NO2]2+ and [Co(NH3)5ONO]2+ models to determine the influence of kinematic factors on IR‐vibrational frequencies. The experimentally observed frequency shifts induced by pressure were interpreted on the basis of theoretical simulation of the spectra. The blue shift of both δ(NO2) and νas(ONO) vibrational frequencies in the complexes with nitro (via nitrogen) coordination can be explained by a decrease in N‐O bond lengths. The blue shift of νs(ONO) and the red shift of νas(ONO) frequencies in the solid complexes with nitrito (via oxygen) coordination can be explained by a decrease of the O‐N‐O bond angle with increasing pressure. For comparison, the pressure induced shifts of νs(ONO) and νas(ONO) for two Cr(III)‐ammine complexes [Cr(NH3)5ONO]XY (XY = Cl2, (NO3)2) were also measured. Whereas the pressure dependence of νs is similar to the corresponding Co‐compounds, νas is only slightly pressure dependent.
Thermodynamics of liquid cesium‐cesium hydride mixtures at high pressures and temperatures
Authors: Szafranski A. W. , Keller E. , Franck E. U.
Published: March 2014

The hydrogen pressure in equilibrium with liquid phases of the system cesium‐cesium hydride has been measured between 575 and 750°C at pressures between 30 and 600 bar. The results support the discussion of metal‐nonmetal transition in this system. Apparatus and procedure have been described earlier. An autoclave was used with an outer and an inner compartment with equilibrated hydrogen pressures. A critical solution point was found at 665°C, 157 bar and a mole fraction x(CsH) = 0.68. Below this temperature two liquid phases coexist. Nine isotherms of hydrogen pressure in dependence of cesium‐cesium hydride composition have been determined at sub‐ and supercritical temperatures. The melting temperature of pure cesium hydride has been redetermined to 522°C at nearly 30 bar. A monotectic point exists at 519°C. The width of the two phase region in terms of mole fraction difference, Δx, as a function of subcritical temperature gives a “classical” critical exponent β = 0.5. A careful calculation suggests a “bulge” of the two phase equilibrium boundary curve near x(CsH) = 0.85; this is the region of prominent metal‐nonmetal transition. Activity coefficients and excess functions of Gibbs energy, enthalpy and entropy are presented.
High pressure vapour‐liquid equilibria in binary mixtures of carbon dioxide and benzaldehyde, bromobenzene, chlorobenzene, 1,2‐dichlorobenzene and 2‐chloro‐1‐methylbenzene at temperatures between 313 and 393 k and pressures up to 22 MPa
Authors: Walther D. , Maurer G.
Published: March 2014

The high‐pressure vapour‐liquid equilibrium in binary mixtures of carbon dioxide and five aromatic compounds (benzaldehyde, bromobenzene, chlorobenzene, 1,2‐dichlorobenzene and 2‐chloro‐1‐methyl‐benzene) has been investigated by a flow technique at temperatures between 313 and 393 K at pressures up to about 22 MPa. For none of these mixtures – with the exception of CO2 + benzaldehyde – experimental results have been reported before. The experimental arrangement is described. The results of the measurements are reported, discussed and correlated by a recently developed generalized Bender equation of state.
Electrochemical preparation of semipermeable polymer membranes on carbon fiber microelectrodes for selective amperometric detection of cations
Authors: Potje‐Kamloth Karin , Josowicz Mira
Published: March 2014

An electrochemical procedure is presented for in situ preparation and subsequent deposition of semipermeable membranes on ultramicroelectrodes. The membranes are based on a matrix of poly(oxyphenylene) bearing carboxyl and sulfonic groups, i.e. poly(1,2‐oxyphenylene‐4‐sulfonic acid) or poly(1,2‐oxyphenylene‐3‐carboxylic acid). These membranes exhibit a cation exchange behavior whereas the transport of anions is inhibited. The diffusion coefficients of Ru(NH3)6·3+ within the semipermeable membranes could be estimated by means of chronoamperometric and steady‐state measurements. The values obtained are in the range of 1.0–6.9 · 10−7 cm2/s. The permeability of the cation through the membranes is high. Therefore, no distortion of the voltammetric response due to the attached membrane is observed. It is shown that the transport rate can be modulated by copolymerization of the functionalized phenolic monomer with varying amounts of a cross‐linking agent. The ultramicroelectrodes modified with the above membranes can be used as amperometric sensors displaying a linear current/concentration relationship.
A high‐temperature study of defect‐induced optical absorption in nickel oxide, Ni1−δO
Authors: Becker K. D. , Rau F.
Published: March 2014

UV‐VIS‐NIR absorption spectra of single crystalline nickel oxide, Ni1−δO, have been measured at high temperatures (up to 1200°C) as a function of oxygen partial pressure, pO2. The observed pO2‐dependence of the spectra is discussed in the context of the point defect chemistry of the compound. From its dependence on oxygen partial pressure and temperature, and from its spectral shape it is concluded that the pO2‐dependent contribution to absorption is due to singly charged cation vacancies, V'Ni. The microscopic model of the optical process is discussed in the framework of light‐induced charge transfer processes involving ions in the neighbourhood of the cation vacancy.
Solvent and isotope effects on addition of atomic hydrogen to benzene in aqueous solution
Authors: Roduner E. , Bartels D. M.
Published: March 2014

Pulsed ESR has been used to measure rate constants for the addition of hydrogen atoms to benzene as a function of temperature in aqueous solution. At 298 K we obtain kH(aq) = (1.1 ± 0.1) · 109 M−1 s−1. The average Arrhenius activation energy, Ea = 19.1(6) kJ · mol−1, is essentially the same in solution as in the gas phase, but the frequency factor, represented by log(A/M−1 s−1) = 12.34(9), is 54 times higher than in the gas. This may be explained in terms of solvation of reactants and transition state, with most of the enhancement attributed to H atom solvation. In a 90% D2O/10% H2O mix, H atoms react at the same rate, but deuterium atoms react more slowly than H atoms by a factor of 1.4. The much smaller solvent enhancement previously demonstrated for the light muonium isotope is tentatively attributed to incomplete hydration of the transition state in that case.
Dispersion of mean molecular dipole polarizability and second density virial coefficients of 1,3‐butadiene
Authors: Hohm Uwe , Trümper Ulf
Published: March 2014

For the first time, measurements of the gas‐phase refractive index of 1,3‐butadiene are performed in the ranges of temperature 295 K < T < 365 K, pressure 0 < p < 1.7 · 105 Pa, and wavelength 325 nm < λ < 633 nm, respectively. Precise values of the dispersion of the mean dipole polarizability α0(λ, T) with an uncertainty of Δα0/α0 < 0.25% are obtained. Moreover, second density virial coefficients B(T) are estimated with error bounds of 10cm3mol−1 from the interferometric measurements.
Thermal Diffusion in Crystalline Binary Compounds with Narrow Range of Homogeneity – II. Stationary Thermal Diffusion in β‐Ag2+δS
Authors: Janek J. , Korte C.
Published: March 2014

The experimental determination of the (reduced) heat of transport of silver, Q*Ag, in β‐Ag2+δS by the direct measurement of the silver flux in a given temperature gradient, under the condition of equal composition at the ends of the crystalline sample, is reported. The measurement is based on the application of galvanic cells for the simultaneous control and measurement of both the silver flux and composition. A set of data for the heat of transport of silver is determined for 210°C<T<270°C and 0.96·10−3<δ< 1.7·10−3.

The measured values for the heat of transport, Q*Ag, are positive and nearly independent of the composition of β‐Ag2+δS. Thus, a flux of silver metal which is induced by a temperature gradient is directed towards the low temperature side of the crystal. In addition, a strong temperature dependence of Q*Ag was observed.
Surface Diffusion on Heterogeneous Surfaces: The Effect of Steps
Authors: Uebing Christian
Published: March 2014

Monte Carlo modeling was utilized for determining the tracer and chemical surface diffusion coefficients of adsorbates. Simulations were carried out on a square array of 64×64 lattice sites applying periodic boundary conditions. In order to analyze the effects of steps on surface diffusion different atomistic models of steps were introduced. For the simplest model steps were assumed to affect the site energies of a single row of lattice sites located on the down‐side of the step. Another set of simulations was performed for steps affecting the site energies on the up‐side of the step as well. For attractive interactions between adsorbates and step sites surface diffusion is slowed down with respect to the noninteracting Langmuir gas on a plain surface. Steps cause diffusion to be anisotropic as crossing of steps costs an extra activation energy. Additional calculations are performed in order to analyze the effect of the saddle points of the periodic potential on surface diffusion.
Profiles of Voltage and of Channel Density in a Planar Membrane Cable on Micromachined Silicon
Authors: Klingler Jürgen , Fromherz Peter
Published: March 2014

A lipid bilayer of glycerolmonoleate is spanned over a microscopic shallow groove etched into the 110 surface of a silicon wafer and insulated by thermal oxidation. The conductance of the bimolecular membrane is modulated by gramicidin. The voltage profile in the groove is recorded by a set of Ag/AgCl electrodes which are integrated into the bottom of the groove. It is used to determine the distribution of ion channels along the membrane on the basis of Kelvin's cable equation.
Relationship Between Phase Transition Temperature and Protonation Degree of Dipalmitoylphosphatidylcholine in Liposomes
Authors: Fernández Marta S.
Published: March 2014

The relationship between the gel‐liquid ctystal phase transition temperature (tm) of dipalmitoylphosphatidylcholine (DPPC) liposomes and the protonation degree of the lecithin phosphodiester moiety, has been studied. A linear function is obtained when the phase transition temperatures of liposomes determined by 90° light scattering variation at different bulk pH values, are plotted against the corresponding protonation degrees calculated either as described previously from the potentiality for tm elevation of DPPC liposomes using stearylamine as a probe [Ber. Bunsenges. Phys. Chem. 95, 1669 (1991)] or from combination of Boltzmann, Henderson‐Hasselbach and Gouy‐Chapman equations, by assuming an interfacial intrinsic pK of 4 for the phosphodiester group and an average cross section molecular area of 45 or 65 Å2 for the phospholipid. The approach described here, which supplements the above‐mentioned previous work, allows to predict that the tm of fully protonated DPPC in liposomes should be in the range from 59.2 to 62.9°C, the variation being dependent on the procedure used to calculate the protonation degree.
Thermodynamic Properties of Pd‐Nd Alloys
Authors: Hennemann K. , Schaller Hans‐Jürgen
Published: March 2014

A complete set of thermodynamic functions was determined for the palladium‐rich solid solution and for the intermetallic compounds Pd5Nd, Pd3Nd, Pd2Nd, Pd4Nd3, and PdNd from electromotive force measurements between 700 and 800°C. A CaF2 single crystal was employed as the solid electrolyte. The activity of Nd in Pd‐rich alloys shows pronounced negative deviations from Raoult's law with a relative partial excess Gibbs energy of Nd at infinite dilution of −305 kJ/mol. Two effects are discussed to account for the non‐ideal properties of the solid solution: the transfer of the valence electrons of Nd to the electron gas of the alloy and the lattice distortion brought about by the size difference of the components. Remarkably exothermic values were obtained for the heats of formation of the intermetallic compounds. The results are compared with predictions of the Miedema model.
Investigation of the Redox Couple Benzophenone/Benzophenone Anion Radical in Acetonitrile and N,N‐Dimethylformamide by Electrochemical and Spectroelectrochemical Methods
Authors: Walczyk K.R. , Popkirov G.S. , Schindler R.N.
Published: March 2014

Diffusion layer imaging (DLI), time‐resolved spectroelectrochemical methods and electrochemical impedance spectroscopy (EIS) were applied to determine the influence of the solvent and the supporting electrolyte on reaction parameters for the benzophenone/benzophenone radical anion redox couple (BP/BP*−) formed at a Hg‐covered Au wire in aprotic solvents.

Results are reported for the solvents acetonitrile (AN) and N,N‐dimethylformamide (DMF) using two different tetraalkylammonium salts as supporting electrolytes. Heterogeneous rate constants for the electron transfer reaction and diffusion coefficients of the neutral BP and the radical anion BP*− obtained with the different methods are discussed and compared.