bluuebunny/crossref_metadata_2025 huggingface dataset:
Cation Selectivity of Membrane Proteins
Authors: Mezele Martin , Lewitzki Erwin , Ruf Horst , Grell Ernst
Published: March 2014

In order to investigate the high‐affinity K+ binding to proteins, alkali ion binding studies were performed on a fluorescent derivative of membrane‐bound Na,K‐ATPase in buffered aqueous solution at 37°C employing a specially designed automatic spectrofluorometric titration system. The comparison of the obtained apparent stability constants, which reached values for K+ even over 104 M−1 with those of a simpler cyclic peptide, acting as a suitable model compound, provides suggestions concerning the molecular nature of the binding sites involved.
Specific Activation of CH‐ and CC‐Bonds by Bare Transition‐Metal Ions
Authors: Eller Karsten , Karraß Sigurd , Schwarz Helmut
Published: March 2014

Chemists are continuously facing questions and problems as follows: Is it possible to direct the course of a reaction according to one's intentions? Is the activation of specific bonds that are either remote or adjacent to a functional group feasible? What factors dictate the different behaviour of transition‐metal ions in their reactions with organic substrates? Answers to these and other questions are provided by studying the gas‐phase chemistry of “naked” first‐row transition‐metal ions with aliphatic nitriles and some other simple organic substrates. By systematically modifying both the organic molecules and the metal ions, a quite detailed insight is achieved into the mechanisms that are operative, and knowledge is accumulated which permits to specify the conditions that are to be met in order to bring about specific processes. “Remote functionalization”, the generation of ion/dipole intermediates, and the formation of multi‐ligated metal‐ion alkene complexes turn out to be the most important mechanisms in the reactions of aliphatic nitriles with transition‐metal ions in the gas phase. In addition, results will be presented which point to degenerate isomerizations involving metallacycles as intermediates. We will also demonstrate that direct CC bond activation prior to CH bond activation can be achieved, a process for which no analogue exists in solution chemistry. The studies have been performed by using tandem mass spectrometry techniques in a sector‐field mass spectrometer as well as ion/molecule reactions in a Fourier transform ion cyclotron resonance (FTICR) instrument.
Ultrafast Reaction Dynamics
Authors: Gruebele Martin , Zewail Ahmed H.
Published: March 2014

With new laser techniques and with gas phase and molecular beam experiments, ist is now possible to tetermine the ultrafast motion in isolated chemical reactions – chemistry on the 10−13‐second time scale.
Preparation of Single Rotation Vibration States of CH3O (X̃2E) Above the H – CH2O Dissociation Threshold by Stimulated Emission Pumping
Authors: Geers A. , Kappert J. , Temps F. , Wiebrecht J. W.
Published: March 2014

By the technique of Stimulated Emission Pumping (SEP), single high‐lying rotation vibration states of CH3O (X̃2E) with defined total energy Err and total angular momentum J were probed in the regime 3000 cm−1 ≤ Err ≤ 9300 cm−1, up to well above the H – CH2O asymptotic dissociation limit (≈ 6800 cm−1). Observed low resolution SEP spectra exhibit distinctive vibrational band structure. Spectra recorded at high resolution reflect intramolecular dynamical processes occuring on different time scales. The detailed spectroscopic characterization of the level structure of highly excited CH3O provides the basis for critical tests of models for unimolecular reactions.
Quantum Phenomena and Solvent Effects on Addition of Hydrogen Isotopes to Benzene and to Dimethylbutadiene
Authors: Roduner E. , Louwrier P. W. F. , Brinkman G. A. , Garner D. M. , Reid I. D. , Arseneau D. J. , Senba M. , Fleming D. G.
Published: March 2014

Rate constants have been measured for the reaction of the light hydrogen isotope muonium with benzene and 2,3‐dimethylbutadiene‐1,3 in the gas phase and in several solvents. Comparison with H atom data reveals (1) appreciable kinetic isotope effects, (2) a strong contribution of tunnelling for the activated reaction with benzene, (3) encounter controlled reaction for Mu addition to the diene, (4) a mass dependence of the diffusion constant of hydrogen isotopes in solution, and (5) an enhancement of the rate constant in solution over that in the gas phase by a factor, except for water, of the inverse Ostwald solubility coefficient for hydrogen. The isotope‐dependent reduction of the solvent effect in water is tentatively ascribed to the dynamics of the clathrate‐like structure when the hydrogen atom reacts.
FTMS Studies of Sputtered Metal Cluster Ions (III): The Chemistry of Ni+n, Co+n, V+n, Ag+n, Au+n and Fe+n with C2H4, C6H6 or NH3
Authors: Irion Manfred P. , Schnabel P. , Selinger Adrian
Published: March 2014

As previously described in greater detail, diverse transition metal cluster cations are produced in an external source by sputtering with 20 keV Xenon ions and transferred to the ICR cell of a home‐built Fourier transform mass spectrometer. There, they are thermalized by collisions with Neon atoms and stored for up to tens of seconds. They undergo a variety of reactions in the presence of ethene, benzene or ammonia, displaying different size‐specific effects. Depending upon the metal and the actual cluster size, mere physical adsorption or dehydrogenation is prevailing.
The Photodissociation of Jet‐cooled Methyl Thionitrite in the Visible
Authors: Pfab Josef , Wetzel Donna M. , Young Victor M.
Published: March 2014

The Dynamics of the photodissociation of jet‐cooled CH3SNO from the S1 (n,π*) state in the visible spectral range has been studied for the first time by pulsed laser photolysis and laser‐induced fluorescence probing of the nascent NO fragment. NO is formed vibrationally cold and rotationally hot confirming that the dissociation is a direct process, and that the structure in the S1 (n,π*) ← S0 absorption does not arise from predissociation. Scalar and some vector properties have been measured, and the fine structure selectivities of the NO fragment have been evaluated. NO is aligned strongly (A(2)0 = +0.75) with the E‐vector of the dissociation light and recoils perpendicularly to the transition dipole μ confirming the symmetry of the S1‐state as A″ and the electronic character as (n,π*). The observed dissociation dynamics of CH3SNO are compared with that of CH3ONO and with recent calculations by Schinke et al.
Investigation of Reaction Barriers in Mixed Organic Aggregates by Two‐Color Resonant Two Photon Ionization
Authors: Awdiew J. , Riehn Ch. , Brutschy B. , Baumgärtel H.
Published: March 2014

We used two‐color resonant two‐photon ionization combined with time‐of‐flight mass spectrometry to study nucleophilic ipso‐substitution reactions with halobenzenes radical cations. Molecular clusters serve as microscopic test tubes to tackle the reactivity problem of solvated radical cations. The reaction paths – van der Waals fragmentation and chemical reaction – could be energetically separated. The substitution reactions turned out to be nearly activationless. The particularities of the excitation process are discussed.
Kinetics of the Reactions of CH2(X̃3B1) with HCl and HBr
Authors: Goldbach A. , Temps F. , Wagner H. Gg.
Published: March 2014

The reactions of CH2(X̃3B1) with HCl (1) and HBr (2) have been studied in an isothermal discharge flow system. CH2 radicals were generated via the reactions of O atoms with a large excess of CH2CO. Their concentration‐versus‐time profiles were measured under pseudo first‐order conditions using Laser Magnetic Resonance (LMR) detection. The rate coefficients of reactions (1) and (2) were found to be kexp1 = (1.7 ± 0.3) · 1012 · exp [–(436 ± 45) K/T] cm3/mol · s in the temperature range 296 K ≤ T ≤ 670 K and k2 = (6.9 ± 1.4) · 1012 cm3/mol · s at T = 296 K. CH3 + Cl or Br, respectively, are suggested to account for the main reaction products.
Adduct Formation of OH Radicals with Benzene, Toluene, and Phenol and Consecutive Reactions of the Adducts with NOx and O2
Authors: Knispel Ralf , Koch Rainald , Siese Manfred , Zetzsch Cornelius
Published: March 2014

The formation of the adducts of OH with benzene, toluene and phenol and consecutive reactions of the adducts with NO, NO2 and O2 are investigated in the temperature range from ∼298–374 K employing the flash photolysis/resonance fluorescence technique in Ar at 133 mbar. Biexponential decays of OH can be observed over at least 2 orders of magnitude in the presence of the aromatics, and the three reaction channels: abstraction of H by OH, addition of OH and unimolecular decomposition of the adduct are distinguished in overlapping temperature ranges. Rate constants and preliminary Arrhenius parameters are obtained for these channels for benzene, toluene, and phenol. The reactions of the adducts with NO are very slow and can be neglected (<10−13 cm3 s−1) in all three cases. Values of ∼3·10−11 cm3 s−1 are obtained for the rate constants of the reactions of the adducts with NO2, almost independent of reactant and temperature. Preliminary determinations of the adduct reactivities against O2 ∼ 2 · 10−16 (benzene‐OH) and ∼5 · 10−16 cm3 s−1 (toluene‐OH) near room temperature indicate that this path predominates under tropospheric conditions. The results for O2 are confirmed by direct observations of the adduct benzene‐OH by the cw UV‐laser longpath absorption technique.
A Study of the Reaction between CH3 and NO at High Temperatures
Authors: Hoffmann A. , Wagner H. Gg. , Wolff Th. , Hwang S. M.
Published: March 2014

The reaction between CH3 and NO was investigated behind incident shock waves at temperatures between 1470 K and 2040 K. Using an Ar‐ion‐laser pumped cw ring dye laser hydroxyl radicals were found to be a primary product of this reaction. The rate constant for the OH forming channel can be expressed by

At temperatures around 2000 K the contribution of the “OH channel” to the total rate constant of the reaction CH3 + NO is about 40%.
High Temperature Reactions of Benzyl Radicals
Authors: Braun‐Unkhoff M. , Frank P. , Just Th.
Published: March 2014

The thermal decomposition of benzyl radicals has been investigated behind reflected shock waves by monitoring the formation of hydrogen atoms. The results reported here have been obtained by using a shock tube in conjunction with atomic resonance absorption spectrometry (ARAS). The temperatures ranged between 1450 and 1700 K at total pressures around 2 bar. The test gas mixtures consisted of argon with relative concentrations of a few ppm benzyliodide, C7H7I. From the measurements of the temporal H‐atom concentrations, in connection with thermochemical restraints, it was deduced that the benzyl decay is preceded by isomerization of benzyl. Due to the low initial concentration of the radical precursor, it was possible to evaluate a first order rate coefficient for the initiation reaction:

magnified image

The heat of formation of the benzyl radical is discussed. A value of ΔH0f, 298 = 215.5 kJ mol−1 fits best to the experimental results.
Measurements of the Second Virial Coefficients of Some New Chlorofluorocarbons and of Their Binary Mixtures at Temperatures in the Range from 296 K to 475 K
Authors: Schramm B. , Hauck J. , Kern L.
Published: March 2014

We present measurements of second virial coefficients of the chlorofluorocarbons R12 (CCl2F2), R22 (CHCIF2), R114 (CClF2—CClF2), R134a (CH2F—CF3), R142b (CH3—CClF2), R152a (CH3—CHF2) and of the binary mixtures R12/R22, R22/R114, R22/R142b, R22/R152a, and R134a/R152a in the temperature range from 296 K to 475 K. The data are combined with earlier measurements of the same systems at low temperatures (J. Chem. Thermodyn.23, 281 (1991)) for a critical discussion on the basis of the Stockmayer intermolecular potential model.
Collisional Deactivation of O2(1Δg) by Solvent Molecules. Comparative Experiments with 16O2 and 18O2
Authors: Schmidt Reinhard , Afshari Ebrahim
Published: March 2014

Phosphorescence spectra of natural singlet oxygen 16O2(1Δg) and its heavier isotope 18O2(1Δg) have been recorded in several O2(1Δg) weakly deactivating solvents. Lifetimes of singlet oxygen were determined for both isotopes in 21 solvents. From these data rate constants kXY of deactivation of singlet oxygen by terminal oscillators X—Y of the solvent molecules are calculated revealing a graduated isotope effect of 1.0 ≤ 16kXY/18kXY ≤ 1.9. The unexpectedly low isotope effect points to the important role of overtone excitations of X—Y during O2(1Δg) deactivation. A modified collisional deactivation model including overtone excitation of the energy accepting oscillator reproduces the experimental findings: the tremendeous graduation of kXY of almost 5 orders of magnitude, the heavy atom effect, the O2 isotope effect and the very weak temperature effect on kXY.
Absorption and fluorescence of pyrylium salts
Authors: Haucke Günter , Czerney Peter , Cebulla Frank
Published: March 2014

Absorption and fluorescence of donor‐substituted pyrylium compounds are studied in order to get information of the x‐ and y‐chromophore system and of the role of structural and solvent effects. The experimental results are in accordance with the assumption that the absorption and fluorescence behaviour can be rationalized in terms of intramolecular radiative and non‐radiative charge transfer (charge shift) processes.
Water oxidation at polycrystalline OSX2 electrodes
Authors: Schwarzlose T. , Fiechter S. , Jaegermann W.
Published: March 2014

Polycristalline OsX2 (X = S, Se, Te) powders have been synthesized and electrochemically investigated as pressed discs with respect to water oxidation. Complementary the electrodes were analyzed by ex‐situ X‐ray photoelectron spectroscopy (XPS). OsS2 was identified as oxygen evolution catalyst whereas OsTe2 was completely decomposed. The difference in catalytic behavior is related to differences in the XP valence band spectra and discussed in terms of electronic states involved in charge transfer.
The dynamics of a quantal reservoir coupled to classical modes: A mixed‐mode approach to dissociating molecules
Authors: Yurtsever Ersin , Uzer Turgay
Published: March 2014

We have analyzed a three‐mode model system to study quantum effects in a dissociative process. An algorithm which combines Hamilton's and time‐dependent Schroedinger equations in an SCF manner is applied. Large differences in the qualitative behaviour of trajectories are observed which suggests a chaotic nature. The monitoring of the energy transfer or trajectories themselves by interactive computer graphics can be used to forecast possibilities of dissociation. It is also noted that the initial conditions strongly affect the dissociation process. We compare fully classical calculations with these mixed mode results, and analyze the reasons behind disparities.
Electrical conductivity and thermodynamic properties of liquid Na3+δSb alloys
Authors: Heyer H. , Egan J. J. , Freyland W.
Published: March 2014

The melting point of the intermetallic compound Na3Sb was measured and found to be 1015°C. Partial molar Gibbs energies of Na in liquid NaSb alloys were determined at 1030°C for alloy compositions between xNa = 0.71 and xNa = 0.78 using an emf technique employing CaF2 as a solid electrolyte. A special cell design was used and is described in detail. The electrical conductivity of NaSb alloys was also measured at 1030°C over a composition range from xNa = 0.71 to xNa = 0.77. A sealed cell was used for these measurements where the composition of the alloy is accurately controlled by coulometric titration. Results showed that the alloys are liquid semiconductors. The thermodynamic and electrical properties are quantitatively explained by a model previously proposed by Carl Wagner, and pertinent equations are given. The correspondence with the predictions of electrical transport in disordered liquid semiconductors is discussed.
pH dependent raman spectra of nicotinic acid – spectra of aqueous solutions and surface enhanced raman spectra on silver electrodes
Authors: Barthelmes J. , Pofahl G. , Plieth W.
Published: March 2014

Raman spectra of nicotinic acid have been measured in aqueous solutions in the pH‐range between 1.0 and 12.5. Raman band assignments between 500 cm−1 and 1750 cm−1 are carried out by referring to the compound's solid state Raman spectrum and to spectra of related molecules. Changes of the Raman spectra with solution pH are correlated to the structure change of the nicotinic acid molecule. The surface enhanced Raman spectra (SERS) of nicotinic acid (NA) on a polycrystalline silver electrode are reported in the range 500–1750 cm−1 as a function of pH and applied potential. The results are presented in order to determine the type of adsorbed species (anion, cation, zwitterion). Therefore the SER spectra are compared with the pH dependent solution spectra of NA. These investigations show – in the presence of a non specifically adsorbing electrolyte (0.1 mol l−1 Na2SO4) – the nicotinate anion as the only surface active species detectable within the pH range of 1.4 to 12.5. A detailed analysis of the SER spectra reveals, that the anion exhibits two different molecular orientations towards the metal electrode, a presumably planar alignment dominating at low and medium pH values and a perpendicular one at low proton concentrations. In the intermediate range both orientations exist side by side. The ratio of planar to perpendicular oriented molecules depends on applied potential and increases with growing cathodic polarisation.
Ionic Fragmentation and Ion‐Pair Formation in Chlorine Dioxide
Authors: Rockland U. , Baumgärtel H. , Rühl E. , Lösking O. , Müller H.S.P. , Willner H.
Published: March 2014

Ionic fragmentation and ion‐pair formation in chlorine dioxide (OClO) are reported. Photoionization efficiency curves of OClO+, ClO+, O2+, Cl+, O+, as well as of O− and Cl− are measured in the energy regime between 10 eV and 21 eV using monochromatized synchrotron radiation. Appearance potentials are obtained from photoionization efficiency curves which are used to derive photofragmentation mechanisms. These include the formation of electronically excited fragments as well as multiparticle formation. The occurrence of O+2 is interpreted as evidence for rearrangement processes of the chlorine dioxide cation prior to dissociation. This finding is compared to photofragmentation of electronically excited neutral OClO. Ion‐pair formation of photoexcited OClO leads to formation of O− and Cl−. The importance of highly excited Rydberg states and direct processes leading to ion‐pair formation is discussed.
Solute and Solvent Dependencies of Intermolecular Interactions in Different Density Regions in Supercritical Fluids. A Generalization of the Three‐Density‐Region Solvation Mechanism
Authors: Sun Ya‐Ping , Bunker Christopher E.
Published: March 2014

Pyrene, 6‐propionyl‐2‐(N,N‐dimethylamino)naphthalene (PRODAN) and ethyl p‐(N,N‐diethylamino)benzoate (DEAEB) are used as fluorescent probes to study solute‐solvent interactions in supercritical fluoroform, carbon dioxide, and ethane as functions of density and temperature. The Py values, solvatochromic shifts of fluorescence spectra, and dual fluorescence from the locally excited singlet state and twisted intramolecular charge transfer state are strongly fluid density dependent. While the intensities of solvent effects are different for different probes and different fluids, the density dependencies of spectroscopic responses of the probes follow a characteristic pattern. The results are in strong support of the three‐density‐region solvation mechanism.
A Study about the Reactions of NH2 (X̃2B1) Radicals with Unsaturated Hydrocarbons in the Gas Phase
Authors: Hennig G. , Wagner H.G.G.
Published: March 2014

The reactions of NH2(X̃2B1) with the hydrocarbons ethene (1), propene (2) and acetylene (3) were investigated behind incident shock waves at temperatures between 1500 K and 2000 K. The decay of NH2 was measured by laser absorption. NH2 was formed by the thermal decomposition of hydrazine. The following rate constants were obtained for the temperature range mentioned:

These measurements extend the results obtained at low temperatures by Bosco et al. (240 K–460 K) and by Khe and Lesclaux (300 K–500 K) into the range of interest for combustion processes.

The apparent energies of activation correlate well with the ionisation potentials of the unsaturated hydrocarbons and can therefore be used for the extrapolation to the addition reactions of the higher alkenes. For the reaction of propene with NH2 a contribution of an abstraction reaction channel besides electrophilic addition cannot be excluded at high temperatures.
Accurate Calculation of NMR Chemical Shifts
Authors: Gauss Jürgen
Published: March 2014

An overview over currently available methods for the calculation of NMR chemical shifts is given. After a brief discussion of the basis aspects, i.e. definition of the shielding tensor and gauge‐origin problem in the calculation of magnetic properties, recently developed methods for calculating NMR chemical shifts based on electron‐correlated quantum chemical approaches will be discussed. The importance of electron correlation effects for the accurate determination of absolute shielding constants and relative shifts is demonstrated and the accuracy of various approaches assessed by a careful comparison with experiment, before a few representative applications will be presented. In case of the carboranes C2B3H5 and C2B3H7, electron‐correlated calculations were essential to resolve discrepancies between SCF calculations and experiment, while for the vinyl‐substituted vinyl cations CH2 = C+ –CH = CHCH3 correlated NMR chemical shift calculations – but not the SCF calculations – allow the unequivocal assignment of the measured 13C signals to the Z and E isomers formed in superacid solutions. Finally, an outlook with respect to pending problems in the area of NMR chemical shift calculations is given.
Structure Investigations of Liquid Chloroform by Statistical‐Mechanical Calculations and Reverse Monte Carlo Simulation
Authors: Bertagnolli H. , Goller K. , Zweier H.
Published: March 2014

The structure of liquid Chloroform at 298 K is determined with Reverse Monte Carlo simulations. Three independent neutron and one X‐ray scattering experiments are fitted simultaneously to obtain higher evidence in the structural results. The structure is described in form of atom pair correlation and angular distribution functions. Furthermore, the atom pair correlation functions are used to calculate a probability that gives the spatial correlation of atoms of neighbouring molecules around a center molecule. The results are compared with Molecular Dynamics simulations of chloroform from literature and a very good agreement between both methods is found. The aim to reproduce experimental results with statistical mechanical calculations based on site‐site Ornstein Zernike (SSOZ or R1SM) theory in combination with the HNC closure fails. The comparison between statistical mechanical calculations and simulations reveals the unability of the SSOZ theory to describe the short range order of liquid chloroform. SSOZ theory predicts correlations of the hydrogen atom at short distances which clearly are not possible in the real liquid.
Thermodynamic Testing of Equations of State of Dense Simple Liquids
Authors: Randzio Stanisław L. , Deiters Ulrich K.
Published: March 2014

The isobaric thermal expansivities (αp) of n‐hexane and of methane measured over large pressure and temperature ranges have been proposed as a thermodynamic property test for theoretical and semi‐empirical equations of state for simple liquids at high densities. The correlation equations for αp(p, T) and the coordinates of the crossing point of isotherms of αp are given for both substances. A number of selected equations of state with various modifications of the attractive and repulsive contribution to the pressure have been tested with respect to their ability to reproduce the proposed test property. The analysis has revealed that at high densities the equations of state with modified repulsive term reproduce the test property better than the equations with modified attractive term. A reproduction of the most characteristic feature of the test property, the crossing of isotherms of αp can be only obtained with equations in which the repulsion term is made softer than the simple rigid‐sphere term R T/(Vm – b). The best reproduction of the test property was obtained with the soft‐sphere equation constructed on 8–4 Lennard‐Jones intermolecular pair potential. The anisotropy in molecular shape of n‐hexane and methane has only a little influence on the results of testing.
An Ab Initio Study of Alkali Halide Clusters with an Alkali Excess: M13X12, [M13X12]+, [M14X12]+, [M14X12]2+, and [M23X22]+
Authors: Ochsenfeld Christian , Ahlrichs Reinhart
Published: March 2014

The alkali‐excess system [M13X12]+ and the corresponding excess‐electron cluster M13X12 are studied with ab initio methods. Selected reaction energies of cationic alkali‐excess clusters, especially of [M23X22]+, are reported using results for the stoichiometric cluster M10X10 and a comparison between sodium chloride and lithium fluoride is presented. Finally, a fully internal anion defect and an edge defect location are investigated for the clusters [Na14Cl12]2+ and [Na14Cl12]+, to resolve previous discrepancies in the literature.
The High Pressure Range of the Addition of OH to C2H2 and C2H4
Authors: Fulle D. , Hamann H.F. , Hippler H. , Jänsch C.P.
Published: March 2014

The kinetics of the bimolecular reactions OH+C2H2+M ⟺ C2H2OH+M (1) and OH+C2H4+M ⟺ C2H4OH+M (2) have been investigated over an extended pressure (1–130 bar) and temperature (300–800 K) range. The OH radicals have been generated by laser flash photolysis of suited precursors and their decays have been measured by saturated laser‐induced fluorescence (SLIF) under pseudo‐first‐order conditions. The pressure dependences have been analyzed by constructing falloff curves at fixed temperatures leading to reliable extrapolations towards the high pressure limiting rate constants k∞. In the given temperature range these rate constants are represented as k1,∞ = 3.8×10−11 exp (–910 K/T) cm3 molecule−1 s−1 and as k2,∞ = 1.0×10−11 cm3 molecule−1 s−1. At temperatures above 700 K biexponential decay curves have been obtained. The chemical equilibria of reactions (1) and (2) could be determined. By a third law analysis the equilibrium constants have been evaluated with reaction enthalpies for the addition complex C2H2OH of δIHo1 (O K) = ‐(146 ± 10) kJ/mol and for C2H4OH of δIHo2 (O K) = ‐(123 ± 6) kJ/mol, respectively. The two equilibrium constants are given by K1,eq = (5.4±2.2)×10−2 (T/K)−1.7±0.2 exp ((17560±1200) K/T) bar−1 and K2,eq = 2.1 × 10−2 (T/K)−95±0.1 × exp ((14780±720) K/T) bar−1, respectively.
Kinetic Study of the Fe(bpy)2+3 +S2O2−8 Reaction in Solvent Mixtures
Authors: Matamoros‐Fontenla M.S. , Pérez P. , López P. , Prado‐Gotor R. , de la Vega R. , Sánchez F.
Published: March 2014

The kinetics of the oxidation of Fe(bpy)2+3 by S2O2−8 have been studied in water and different water‐cosolvent mixtures. The cosolvents used were methanol t‐butyl alcohol, ethane 1,2‐diol and glycerol. The results are explained assuming an additional component of the reorganization free energy of the solvent in the mixtures, caused by dynamics of the changes in the composition of the (at least) innermost solvation shells of the reactants produced by the electron transfer. A quantitative estimation of this component is attempted.
Vapour Pressures at Eight Temperatures of Mixtures of Di‐n‐Propylether + Ethanol, or +1‐Butanol – Thermodynamic Description of Mixtures of Di‐n‐Propylether + Alkanol According to the ERAS Model
Authors: Garriga R. , Pérez P. , Gracia M.
Published: March 2014

Vapour pressures of di‐n‐propylether with ethanol and with 1‐butanol were measured at eight temperatures between 278.15 and 323.15 K by a static method. Reduction of the vapour pressures to obtain activity coefficients and excess molar Gibbs free energies was carried out by Barker's method. Mixtures containing ethanol show azeotropy with a minimum boiling temperature. GE, HE, and VE, at 298.15 K, of mixtures of di‐n‐propylether + methanol, + ethanol, + 1‐propanol, + 2‐propanol, and + 1‐butanol are compared with predictions of the ERAS model observing that the model reproduces acceptably the experimental behaviour.
Correlation Times and Quadrupole Coupling Constants in Liquid N‐Methylformamide and N‐Methylacetamide
Authors: Seipelt C.G. , Zeidler M.D.
Published: March 2014

Longitudinal 1H, 13C and 15N nmr relaxation rates were measured in the liquid phase for N‐methylformamide (NMF) over the temperature range 228–328 K and for N‐methylacetamide (NMA) over the range 300–378 K. Rotational correlation times were determined for the formyl C‐H and the N‐H bonds. The motion of both molecules is anisotopic, particularly that of N‐methylacetamide. The activation energies are 5.6 kJ/mol for C‐H and 19.7 kJ/mol for N‐H in NMF and 20.4–22.5 kJ/mol for N‐H in NMA. Quadrupole coupling constants were determined by relaxation measurements for the nuclei 14N and 2H. The quadrupole coupling constant for the amide deuteron in NMF is temperature dependent and varies from 193 to 206 kHz. For NMA this quadrupole coupling constant falls into the range 178 to 238 kHz. The quadrupole coupling constant for the formyl 2H in NMF (151–169 kHz) is temperature independet while for the 14N (NMF: 1.85–2.40 MHz; NMA: 1.65–2.45 MHz) it is temperature dependent.
Theoretical Studies of the Relative Cross Sections and Transition State Spectroscopy of Cl+Na2(3 ≤ v″ ≤ 19) → [NaNaCl]‡ *→ NaCl+Na*
Authors: Wang Ming‐Liang , Han Ke‐Li , He Guo‐Zhong , Lou Nan‐Quan
Published: March 2014

Quasiclassical trajectory method (QCT) has been used to investigate the effect of vibrational excitation on the relative cross section for the reaction Cl+Na2(v″). The calculated results are in good agreement with the experimental data, which show the increase of the cross section with increasing vibrational excitation. Furthermore, the spectroscopy of transition state in this reaction has been predicted out using QCT method based on LEPS potential energy surface.
Structure and Electrochemical Properties of the Cathode/Electrolyte Interface in the Planar SOFC
Authors: Kuznecov M. , Otschik P. , Eichler K. , Schaffrath W.
Published: March 2014

The electrochemical behaviour of the cathode/electrolyte interface which is formed between screen printed Lao0.8Sr0.2MNO3‐cathode and ZrO2+8%Y2O3 electrolyte was investigated. The impedance of the cathode/electrolyte interface was calculated as a function of (I) the oxygen exchange velocity between cathode material and atmosphere, (II) interface microstructure and (III) the oxygen vacancies diffusion coefficient. A very good agreement between calculated and measured impedance spectra was achieved. The influence of the porosity of the cathode on the impedance is discussed.
Spectroscopic Anomalies in the 4‐Aryl‐2,2‐Difluoro‐6‐Methyl‐1,3,2‐Dioxaborine Series
Authors: Görlitz Gunter , Hartmann Horst , Kossanyi Jean , Valat Pierre , Wintgens Véronique
Published: March 2014

The spectroscopic properties of 4‐methyl‐6‐phenyl‐2,2‐difluoro‐1,3,2‐dioxaborine 1 and of several of its derivatives 2–5 substituted in para position on the phenyl ring or bearing an alkylene chain between their carbo‐cyclic and heterocyclic rings have been studied in solution of different polarities and in the solid state. In solution, an important intramolecular charge transfer (ICT) process is characterized in the excited state. This charge transfer occurs in a planar configuration of the molecules, as demonstrated by comparison of the data obtained for 1 and 3 with those of the rigid molecules 6 and 7, respectively. The singlet excited state of molecules 1–5 is typical of species having a free rotating substituent and for which the small fluorescence quantum yield and lifetime increase when a planar configuration can be stabilized by electron‐donor substitution. The low fluorescence quantum yield found for molecules 1 and 2, with respect to molecules 3–5, has been attributed to an important deactivation channel resulting from the rapid free rotation of the phenyl moiety of the molecule and not to an efficient intersystem crossing to the triplet excited state, as this process has a quantum yield lower than 0.01. Theoretical calculations lead to a low oscillator strength for molecules 1 and 2 which are more stable with a planar configuration, while a significant higher oscillator strength is calculated for compounds 3 and 4 substituted with electron‐donating groups. The singlet excited state of compounds 4 and 5 might be stabilized by the formation of a twisted species. In the solid state, the molecules are shown by X‐ray analysis to be planar and packed in such a way that two molecules lie head‐to‐tail in two parallel planes separated from each other by ca. 360 pm. As a result, this proximity enables the development of a ground state charge transfer. This charge transfer species has been confirmed by increasing the concentration of compound 2 in dichloromethane solution, giving rise to a new fluorescence band in the long wavelength region.
Curious case of muscle spasm
Authors: Stratemeier Natalie , Kohli Disha , Rastogi Padmashri
Published: March 2014

Key Clinical Message

If no improvement is seen with ongoing treatment for current diagnosis, then diagnosis should be questioned. History taking and physical examination remain essential tools in care of the patient in addition to the current technological advancement.
Neck Circumference Is Not Associated With Subclinical Atherosclerosis in Retired National Football League Players
Authors: Pokharel Yashashwi , Macedo Francisco Y. , Nambi Vijay , Martin Seth S. , Nasir Khurram , Wong Nathan D. , Boone Jeffrey , Roberts Arthur J. , Ballantyne Christie M. , Virani Salim S.
Published: March 2014

Background

Neck circumference (NC) is associated with metabolic syndrome (MetS) in the general population. It is not known if NC is associated with MetS and subclinical atherosclerosis in retired National Football League (NFL) players.

Hypothesis

We hypothesized that NC is associated with MetS and subclinical atherosclerosis (assessed as coronary artery calcium [CAC] and carotid artery plaque [CAP]) in retired NFL players.

Methods

NC was measured midway between the midcervical spine and midanterior neck in 845 retired NFL players. CAC presence was defined as total CAC score >0. CAP was defined as carotid plaque of at least 50% greater than that of the surrounding vessel wall, with a minimal thickness of at least 1.2 mm on carotid ultrasound. Logistic regression analysis was used for the association of NC with CAC or CAP.

Results

Of the participants, 21% had MetS. CAC and CAP were present in 62% and 56%, respectively. Those with MetS had a higher median NC than those without MetS (17 vs 16 inches, P < 0.0001). NC was not associated with the presence of CAC or CAP in an unadjusted model and after adjusting for age, race, and cardiometabolic risk factors (odds ratio [OR]: 1.11, 95% confidence interval [CI]: 0.94–1.31 for CAC; OR: 0.96, 95% CI: 0.82–1.12 for CAP per 1‐standard deviation increase in NC [3.8 inches]). The results were similar when the predictor variable was NC indexed to body mass index.

Conclusions

In retired NFL players with a high prevalence of CAC and CAP, NC was not associated with coronary or carotid subclinical atherosclerosis. NC may not be the most appropriate risk marker for atherosclerosis.
Evaluating monitoring methods to guide adaptive management of a threatened amphibian (Litoria aurea)
Authors: Bower Deborah S. , Pickett Evan J. , Stockwell Michelle P. , Pollard Carla J. , Garnham James I. , Sanders Madeleine R. , Clulow John , Mahony Michael J.
Published: March 2014

Prompt detection of declines in abundance or distribution of populations is critical when managing threatened species that have high population turnover. Population monitoring programs provide the tools necessary to identify and detect decreases in abundance that will threaten the persistence of key populations and should occur in an adaptive management framework which designs monitoring to maximize detection and minimize effort. We monitored a population of Litoria aurea at Sydney Olympic Park over 5 years using mark–recapture, capture encounter, noncapture encounter, auditory, tadpole trapping, and dip‐net surveys. The methods differed in the cost, time, and ability to detect changes in the population. Only capture encounter surveys were able to simultaneously detect a decline in the occupancy, relative abundance, and recruitment of frogs during the surveys. The relative abundance of L. aurea during encounter surveys correlated with the population size obtained from mark–recapture surveys, and the methods were therefore useful for detecting a change in the population. Tadpole trapping and auditory surveys did not predict overall abundance and were therefore not useful in detecting declines. Monitoring regimes should determine optimal survey times to identify periods where populations have the highest detectability. Once this has been achieved, capture encounter surveys provide a cost‐effective method of effectively monitoring trends in occupancy, changes in relative abundance, and detecting recruitment in populations.
Phosphorylated STAT3 and PD‐1 regulate IL‐17 production and IL‐23 receptor expression in Mycobacterium tuberculosis infection
Authors: Bandaru Anuradha , Devalraju Kamakshi P. , Paidipally Padmaja , Dhiman Rohan , Venkatasubramanian Sambasivan , Barnes Peter F. , Vankayalapati Ramakrishna , Valluri Vijayalakshmi
Published: March 2014

We studied the factors that regulate IL‐23 receptor expression and IL‐17 production in human tuberculosis infection. Mycobacterium tuberculosis (M. tb)‐stimulated CD4+ T cells from tuberculosis patients secreted less IL‐17 than did CD4+ T cells from healthy tuberculin reactors (PPD+). M. tb‐cultured monocytes from tuberculosis patients and PPD+ donors expressed equal amounts of IL‐23p19 mRNA and protein, suggesting that reduced IL‐23 production is not responsible for decreased IL‐17 production by tuberculosis patients. Freshly isolated and M. tb‐stimulated CD4+ T cells from tuberculosis patients had reduced IL‐23 receptor and phosphorylated STAT3 (pSTAT3) expression, compared with cells from PPD+ donors. STAT3 siRNA reduced IL‐23 receptor expression and IL‐17 production by CD4+ T cells from PPD+ donors. Tuberculosis patients had increased numbers of PD‐1+ T cells compared with healthy PPD+ individuals. Anti‐PD‐1 antibody enhanced pSTAT3 and IL‐23R expression and IL‐17 production by M. tb‐cultured CD4+ T cells of tuberculosis patients. Anti‐tuberculosis therapy decreased PD‐1 expression, increased IL‐17 and IFN‐γ production and pSTAT3 and IL‐23R expression. These findings demonstrate that increased PD‐1 expression and decreased pSTAT3 expression reduce IL‐23 receptor expression and IL‐17 production by CD4+ T cells of tuberculosis patients.
Alternative splice variants of AID are not stoichiometrically present at the protein level in chronic lymphocytic leukemia
Authors: Rebhandl Stefan , Huemer Michael , Zaborsky Nadja , Gassner Franz Josef , Catakovic Kemal , Felder Thomas Klaus , Greil Richard , Geisberger Roland
Published: March 2014

Activation‐induced deaminase (AID) is a DNA‐mutating enzyme that mediates class‐switch recombination as well as somatic hypermutation of antibody genes in B cells. Due to off‐target activity, AID is implicated in lymphoma development by introducing genome‐wide DNA damage and initiating chromosomal translocations such as c‐myc/IgH. Several alternative splice transcripts of AID have been reported in activated B cells as well as malignant B cells such as chronic lymphocytic leukemia (CLL). As most commercially available antibodies fail to recognize alternative splice variants, their abundance in vivo, and hence their biological significance, has not been determined. In this study, we assessed the protein levels of AID splice isoforms by introducing an AID splice reporter construct into cell lines and primary CLL cells from patients as well as from WT and TCL1tg C57BL/6 mice (where TCL1 is T‐cell leukemia/lymphoma 1). The splice construct is 5′‐fused to a GFP‐tag, which is preserved in all splice isoforms and allows detection of translated protein. Summarizing, we show a thorough quantification of alternatively spliced AID transcripts and demonstrate that the corresponding protein abundances, especially those of splice variants AID‐ivs3 and AID‐ΔE4, are not stoichiometrically equivalent. Our data suggest that enhanced proteasomal degradation of low‐abundance proteins might be causative for this discrepancy.
Human antigen‐specific CD4+CD25+CD134+CD39+ T cells are enriched for regulatory T cells and comprise a substantial proportion of recall responses
Authors: Seddiki Nabila , Cook Laura , Hsu Denise C. , Phetsouphanh Chansavath , Brown Kai , Xu Yin , Kerr Stephen J. , Cooper David A. , Munier C. Mee Ling , Pett Sarah , Ananworanich Jintanat , Zaunders John , Kelleher Anthony D.
Published: March 2014

Human Ag‐specific CD4+ T cells can be detected by their dual expression of CD134 (OX40) and CD25 after a 44 hours stimulation with cognate Ag. We show that surface expression of CD39 on Ag‐specific cells consistently identifies a substantial population of CD4+CD25+CD134+CD39+ T cells that have a Treg‐cell‐like phenotype and mostly originate from bulk memory CD4+CD45RO+CD127lowCD25highCD39+ Treg cells. Viable, Ag‐specific CD25+CD134+CD39+ T cells could be expanded in vitro as cell lines and clones, and retained high Forkhead Box Protein 3, CTLA‐4 and CD39 expression, suppressive activity and Ag specificity. We also utilised this combination of cell surface markers to measure HIV‐Gag responses in HIV+ patients before and after anti‐retroviral therapy (ART). Interestingly, we found that the percentage of CD39− cells within baseline CD4+ T‐cell responses to HIV‐Gag was negatively correlated with HIV viral load pre‐ART and positively correlated with CD4+ T‐cell recovery over 96 weeks of ART. Collectively, our data show that Ag‐specific CD4+CD25+CD134+CD39+ T cells are highly enriched for Treg cells, form a large component of recall responses and maintain a Treg‐cell‐like phenotype upon in vitro expansion. Identification and isolation of these cells enables the role of Treg cells in memory responses to be further defined and provides a development pathway for novel therapeutics.
Airflow and aeolian sediment transport patterns within a coastal trough blowout during lateral wind conditions
Authors: Smyth Thomas Andrew George , Jackson Derek , Cooper Andrew
Published: March 2014

Blowouts are depressions that occur on coastal dunes, deserts and grasslands. The absence of vegetation in blowouts permits high speed winds to entrain and remove sediment. Whereas much research has examined patterns of wind flow and sediment transport on the stoss slopes and lee of sand dunes, no study has yet investigated the connections between secondary air‐flow structures and sediment transport in a blowout where zones of streamline compression, expansion and steering are less clearly delineated. In this study we investigated the variability of sediment flux and its relation to near‐surface wind speed and turbulence within a trough blowout during wind flow that was oblique to the axis of the blowout. Wind flow was measured using six, three‐dimensional (3D) ultrasonic anemometers while sediment flux by eight sand traps, all operating at 25 Hz.

Results demonstrated that sediment flux rates were highly variable throughout the blowout deflation basin, even over short distances (< 0.5 m). Where flow was steadiest, flux was greatest. Consequently the highest rates of sediment transport were recorded on the erosional wall crest where flow was compressed and accelerated. The strength of correlation between sediment flux and wind parameter improved with an increase in averaging interval, from 10 seconds to 1 minute. At an interval of 10 seconds, however, wind speed correlated best with flux at seven of eight traps, whereas at an interval of one minute Turbulent Kinetic Energy (TKE) provided the best correlation with flux at six of the eight traps. Correlation between sediment flux and wind parameters was best in the centre of the blowout and poorest on the erosional wall crest. The evidence from this paper suggests, for the first time, that TKE may be a better predictor of sediment transport at minute scale averaging intervals, particularly over landforms where wind flow is highly turbulent. Copyright © 2014 John Wiley & Sons, Ltd.
Cholinesterase activity of muscle tissue from freshwater fishes: Characterization and sensitivity analysis to the organophosphate methyl-paraoxon
Authors: Lopes Renato Matos , Filho Moacelio Veranio Silva , de Salles João Bosco , Bastos Vera Lúcia Freire Cunha , Bastos Jayme Cunha
Published: March 2014

The biochemical characterization of cholinesterases (ChE) from different teleost species has been a critical step in ensuring the proper use of ChE activity levels as biomarkers in environmental monitoring programs. In the present study, ChE from Oreochromis niloticus, Piaractus mesopotamicus, Leporinus macrocephalus, and Prochilodus lineatus was biochemically characterized by specific substrates and inhibitors. Moreover, muscle tissue ChE sensitivity to the organophosphate pesticide methyl-paraoxon was evaluated by determining the inhibition kinetic constants for its progressive irreversible inhibition by methyl-paraoxon as well as the 50% inhibitory concentration (IC50) for 30 min for each species. The present results indicate that acetylcholinesterase (AChE) must be present in the muscle from P. mesopotamicus, L. macrocephalus, and P. lineatus and that O. niloticus possesses an atypical cholinesterase or AChE and butyrylcholinesterase (BChE). Furthermore, there is a large difference regarding the sensitivity of these enzymes to methyl-paraoxon. The determined IC50 values for 30 min were 70 nM (O. niloticus), 258 nM (P. lineatus), 319 nM (L. macrocephalus), and 1578 nM (P. mesopotamicus). The results of the present study also indicate that the use of efficient methods for extracting these enzymes, their kinetic characterization, and determination of sensitivity differences between AChE and BChE to organophosphate compounds are essential for the determination of accurate ChE activity levels for environmental monitoring programs. Environ Toxicol Chem 2014;33:1331–1336. © 2014 SETAC