bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation Volume for Dimerization Reaction of 2,4,6‐Trimethylnitrosobenzene in Solution
Authors: Yoshimura Y. , Nakahara M.
Published: March 2014

The effect of pressure on the rate and equilibrium constants for the dimerization reaction of 2,4,6‐trimethylnitrosobenzene in acetonitrile was studied up to 196 MPa at 25°C in order to examine whether the dynamical effect on the reaction process in solution can be neglected as assumed in the transition state theory. All the rate constants relevant to the dimerization were determined by the pressure relaxation method. The configurational reaction volume for the dimerization and the activation volume for the dissociation were —17.4 ± 0.7 and + 5.1 ± 0.3 cm3 mol 1 at 98 MPa, respectively. The experimental results were in reasonable agreement with the theoretical ones that were calculated for the model system composed of hard spheres according to the liquid theory and the transition state theory. The dynamical effect on the activation volume was not detected in the present reaction system.
Assoziationsverhalten und Dipolmomente von Tetra(n‐Butyl)‐Ammoniumpertechnetat und Tetra(n‐Butyl)Ammoniumperchlorat in Benzol
Authors: Neck Volker , Maier Ralph , Kanellakopulos Basil
Published: March 2014

At very low concentrations tetra‐n‐butylammonium pertechnetate and tetra‐n‐butylammonium perchlorate form ion pairs in benzene Solutions. At room temperature, formation of dimers and larger aggregates begins to occur at concentrations of 10−5 mol/1. This behaviour has been investigated quantitatively by the determination of the molecular weight in the case of the perchlorate salt, and by the concentration‐dependence of the pertechnetate phase equilibrium between water and benzene. It could be demonstrated that Bu4NClO4‐dimers and larger aggregates have no apparent dipole moment. Knowing the relative concentration of the monomers from the extraction experiments, the dipole moment of 16.6 Debye has been calculated for the ion pair. Applying an extrapolation method, the dipole moment of Bu4NCIO4 was found to be 16.2 Debye. The similarity of the dipole moments is in good agreement with the similar ionic radii of the TcO4− and the ClO4− ions. The charge separation in the ion pairs however, calculated from the dipole moments, is smaller than the sum of cationic and anionic radii.
Untersuchung der Kohlenmonoxidoxidation an polykristallinem Platin bei gleichzeitiger Messung der Sauerstoffaktivität an der Katalysatoroberfläche
Authors: Häfele E. , Lintz H. G.
Published: March 2014

Solid electrolyte potentiometry has been used to measure the oxygen activity at the catalyst surface during the oxidation of carbon monoxide by oxygen and/or nitrogen monoxide on platinum at ambient pressure. The results of the combined kinetic and electrochemical measurements can be interpreted consistently within the accepted concept of elementary steps. The findings of the simultaneous oxidation clearly confirm and explain the high selectivity of the carbon monoxide‐oxygen reaction.
Vector Correlations in the Photodissociation of CH3I, OCS, and Glyoxal
Authors: Hall G. E. , Loo R. Ogorzalek , Harri H.‐P. , Sivakumar N. , Chawla G. K. , Houston P. L. , Chandler D. W. , Hepburn J. W. , Burak I.
Published: March 2014

The use of vector correlations to elucidate the photodissociation dynamics of CH3I, OCS, and glyoxal is discussed. The correlations occur between the vectors Ě, the electric vector of the photolysis light, μ, the transition dipole moment of the parent, v, the relative recoil velocity of the fragments, and J, the angular momentum of one of the fragments. The Ě – μ – v correlation is illustrated by a direct imaging technique in the photodissociation of CH3I; it shows that dissociation takes place by a parallel transition and is rapid compared to parent rotation. The “triple vector correlation”, Ě – μ – (v – J), is used to show that the dissociation of OCS proceeds on two surfaces, one of A″ and one of A′ symmetry in the Cs point group. The v – J correlation in the dissociation of glyoxal illustrates two points, that dissociation of this molecule takes place in a plane and that vector correlations can exist even for dissociations which are slow compared to parent rotation.
Spectroscopy and Photodissociation Dynamics of Highly Vibrationally Excited Molecules
Authors: Likar M. D. , Sinha A. , Ticich T. M. , Vander Wal R. L. , Crim F. F.
Published: March 2014

Vibrationally mediated photodissociation is a technique for studying the spectroscopy and photodissociation dynamics of highly vibrationally excited molecules. One photon prepares a highly vibrationally excited molecule by excitation of a vibrational overtone transition, and a second photon of the same or different wavelength fragments the molecule by excitation to a dissociative electronic state. A third photon from a probe laser interrogates individual quantum states of the fragment by laser induced fluorescence. Applying this technique to hydrogen peroxide and nitric acid provides vibrational overtone excitation spectra in the regions of the 4υOH and 5υOH transitions in HOOH and in the region of the 4υOH transition in HONO2. The photodissociation dynamics arc modified by the participation of the highly vibrationally excited intermediate state. In both HOOH and HONO2, the OH fragment is created with more vibrational energy than in the one‐photon ultraviolet photolysis. In the dissociation of HONO2, a large fraction of the available energy appears in internal excitation of the NO2 fragment, possibly including electronic excitation.
Absorption Spectrum versus Excitation Spectrum of Pyrazine
Authors: Drabe Karel E. , Kommandeur Jan , van Herpen Willy M. , Meerts Leo W.
Published: March 2014

The first ME spectrum of pyrazine was measured as an excitation spectrum. Assuming the quantum yield to be constant over the spectrum it was considered as an absorption spectrum and de‐diagonalisation led to zero order energies and coupling constants of the singlet and triplet states. – By measuring the lifetimes of eight strong ME's we have now shown that the quantum yield varies by as much as a factor of three over the spectrum. With these lifetimes the excitation spectrum can be converted into a real absorption spectrum and a new and now correct set of values for the zero order energies, their widths and the coupling constants was obtained. The most important result is the fact that the zero order singlet and triplets decay non‐radiatively at different rates.
Large Amplitude Motion and its Role in the Relaxation Process
Authors: Ito Mitsuo
Published: March 2014

Large amplitude motions of aromatic molecules in the ground and excited states and their roles in intramolecular vibrational redistribution and internal conversion will be described with examples mainly obtained in our laboratory.
Studies of Intramolecular Processes by Spectroscopic Techniques
Authors: Ramsay D. A.
Published: March 2014

Spectroscopic techniques are discussed for studying the interactions between the rovibronic levels of the Ã 1A2 states of H2CO and H2CS and the corresponding levels of the ã3A2 and X̃1A1 states.
Can High‐Resolution Molecular Spectroscopy Help to Understand Intramolecular Energy Transfers?
Authors: Graner Georges
Published: March 2014

After a short discussion of the exact meaning of intramolecular processes, a description is given of interactions and perturbations as they are revealed through high resolution molecular spectroscopy. The case of the 3 μm fluorescence of CH3F will be used to illustrate possible pathways for energy flows.
Intramolecular Conversions Over Low Barriers IX: Vibrational Bottle‐Necks at Statistical Equilibrium
Authors: Bauer S. H. , Borchardt D. B. , Chiu N.‐S.
Published: March 2014

The presence of bottle‐necks in IVR rates is indicated by the inverse dependence of a group of bimolecular rate constants on density, at low densities. The previously proposed model for relaxation times of systems in dynamic equilibrium (typical of isomerizations over low barriers) can be extended to make transparent the role of individual vibrational states. A coupling parameter can be explicitly introduced (for each molecular species) which relates the probability for intramolecular energy transfers to the amounts of energy which have to be converted from the non‐involved oscillators to the one (υα) which comprises the reaction coordinate (ζ). The essential function is f(q; E), which is the number of states within the interval E and (E + ΔE) [for a total state density g(E)] which incorporate excitation of any particular v, state. The total energy space is divided into a large number of “bands” between which both collisional and collisionless energy transfers take place. The relaxation time is obtained from the lowest non‐zero root of a large secular determinant.
Eigenstate‐resolved Vibrational State Mixing in Jet‐Cooled 1‐Butyne Near 3333 cm−1
Authors: De Souza A. M. , Kaur Devinder , Perry David S.
Published: March 2014

In the high resolution infrared spectrum of the acetylenic C —H stretch of 1‐butyne, considerable vibrational state mixing is observed. The multiplets of sharp features observed under cooled jet conditions (3 K) are attributed to vibrational state mixing. A dependence of the intramolecular vibrational redistribution (IVR) on the rotational quantum numbers, J and Ka, is found.
Rates of Intramolecular Singlet‐Singlet and Triplet‐Triplet Energy Transfer within One Molecule, an Anti‐Syn‐Bis‐Bimane
Authors: Kosower Edward M. , Giniger Rina
Published: March 2014

The rate constants for intramolecular singlet‐singlet (anti → syn) and triplet‐triplet (also anti → syn) energy transfer in a bis‐bimane, a syn‐anti‐bis‐bimane, in which a dimethylene bridge connects the photophysically active moieties, have been estimated on the basis of radiative rate constants and quantum yields of fluorescence and phosphorescence of syn‐(1) and anti‐(2) bimanes and rate constants of intersystem crossing and photochemical reaction in an anti‐bimane.
An Investigation of Electron Transfer Reactions between Aromatic and Quinoid Systems
Authors: Goez M. , Jaenicke W. , Nickel U.
Published: March 2014

A classical organic redox reaction is the conversion of an aromatic compound from its reduced form R to a semioxidized state S, and further to a totally oxidized (quinoid) species T. Complex redox systems are present in a reaction of quinoid and aromatic forms derived from different parent compounds. In this case, the exchange of one or two electrons in one step between T and R can be distinguished experimentally. These reactions were investigated in a stopped‐flow apparatus with optical detection. In the system N,N,N′,N′‐tetramethyl‐para‐phenylene‐diamine/N,N‐dimethyl‐para‐phenylene‐diamine the rate constants for all elementary reactions have been determined. Protonated, and unprotonated R were found to be reactive. In this system, as well as the others considered, no direct transfer of two electrons between T1and R2takes place. The essential steps of the mechanism have to be seen in a mixed symproportionation yielding S1and S2, and a subsequent fast oxidation of S2by surplus starting material T1. As a generalization, a tangent criterion has been derived to distinguish between one‐ and two‐electron steps in such mixed redox systems.
A Proton Magnetic Resonance and Gravimetric Study of Water and Isopropanol Adsorption on Microcrystalline Rutile. I. Adsorption Sites
Authors: Boddenberg B. , Horstmann W.
Published: March 2014

The adsorption of water and isopropanol on a pure microcrystalline rutile has been studied by means of conventional adsorption isotherm and 1H magnetic resonance intensity measurements. Evidence is obtained that irreversible adsorption of both water and isopropanol is caused by bonding to the coordinatively unsaturated Ti4+ ions of the (110) crystallographic planes which contribute by about 85% to the surface area exposed. On these planes water is displaced by isopropanol such that the amount of alcohol adsorbed is not influenced by preadsorbed water. Reversible isopropanol adsorption is attributed to bonding onto Ti4+ sites of the remaining planes exposed, most likely (100) and (101). It is suggested that isopropanol adsorption can be used to determine the specific surface area of microcrystalline rutile as well as the fraction of it which consists of the (110) crystallographic planes.
Coherence in Disordered Condensed Matter. I: Dissipative Structures in Liquids and Dynamics of Far‐Infrared Absorption
Authors: Chatzidimitriou‐Dreismann C. A. , Brändas E. J.
Published: March 2014

The Complex Scaling Method (CSM), in connection with Prigogine's Subdynamics predicts the spontaneous emergence of large dissipative (or: coherent) structures in amorphous matter, like liquids. The connection between these structures and the appearance of a large Jordan block (see appendix) with Segré characteristic equal to the dimension or degrees of freedom of the emerged structure, in the CSM‐transformed reduced second order density matrix, is presented and analysed in some detail. The interdependence of the present theoretical considerations with Yang's concept of off‐diagonal long‐range order (ODLRO) is stressed. – The appearance of dissipative structures is accompanied by a quantization condition for the lifetimes of the states contributing to the creation of those structures. The minimum size nmin of a dissipative structure obeys the equation nmin ≅ τrot · (2πkBT/h), where τrot represents the molecular relaxation time that is to be determined by a suitable spectroscopic experiment. – Application to far‐infrared (FIR) absorption spectroscopy is made explicitly. The above formula allows for a surprising interpretation of the well‐known anomalous temperature dependence of the FIR bands from first principles. The “size” of the dissipative structures that contribute to the FIR absorption in liquids is estimated.
Electron Excitation and Chemical Steps during Anodic Decomposition of n‐GaAs Electrodes: A Hole Injection Study
Authors: Vanmaekelbergh D. , Kelly J. J. , Lingier S. , Gomes W. P.
Published: March 2014

The contribution of electron excitation to the anodic dissolution of the n‐GaAs electrode was studied quantitatively by measuring the increase in the anodic blocking current when hole‐injecting agents such as Ce4+ or Fe(CN)3−6 were added to the electrolyte solution. The experimental relationship between the anodic current and the cathodic hole injection current was interpreted on the basis of the anodic decomposition mechanism, including a chemical step, proposed previously to explain stabilization results. This mechanism is complemented by an electrochemical step involving electron excitation from a decomposition intermediate occurring in parallel to the chemical step.
The Pressure Dependence of Self Diffusion in Supercooled Light and Heavy Water
Authors: Prielmeier F. X. , Lang E. W. , Speedy R. J. , Lüdemann H.‐D.
Published: March 2014

Measurements of self‐diffusion coefficients D in H2O and D2O at pressures up to 400 MPa and temperatures down to 200 K are reported. Upon cooling molecular motions are strongly retarded leading to a pronounced non‐Arrhenius temperature dependence of D. In contrast, initial compression of cold water facilitates translational and rotational motions. Unexpectedly, the rates of translational diffusion increase less dramatically than those of rotational diffusion. These results are discussed in relation to the peculiar structure of the hydrogen bond network of cold water. Further all dynamic isotope effects can be removed by shifting all temperature scales by ∼ 7 K in going from H2O to D2O.
Correlation of Second Virial Coefficients of Pure Components and Mixtures
Authors: van Nhu Nguyen , Kohler Friedrich
Published: March 2014

A correlation is given for second virial coefficients on the basis of one‐center Lennard‐Jones potential parameters, which are determined from vapour pressure and orthobaric liquid densities. The anisotropy of the molecules is taken into account via Pitzer's acentric factor. The correlation works well when the preferred orientations are not too different between liquid and gas, i.e. when dipole moments are practically absent and when the acentric factor is smaller than 0.35. For liquid mixtures the unlike interaction is adjusted via the equimolar excess Gibbs energy. This procedure enables the correction for gas phase nonideality in vapour‐liquid equilibria measurements.
Scaling of Shear Viscosity of Nitro‐benzene/Isooctane Mixtures in the Critical Region
Authors: Jaschull G. , Müller‐Kirschbaum Th. , Woermann D.
Published: March 2014

Results of measurements of the temperature dependence of shear viscosity of seven nitro‐benzene/isooctane mixtures of different compositions in the critical region are reported. The analysis of the viscosity data of the mixture of the critical composition in terms of critical exponent gives a value of φη = 0.048 ± 0.001. It is higher by about 20% than the theoretical value based on dynamic renormalization group theory calculations. The shear viscosity data of the non‐critical mixtures are in agreement with the scaling concepts of critical phenomena.
The Electrochemical Behaviour of Iron(II/III) on NAFION Coated Electrodes
Authors: Ye Jianhui , Doblhofer Karl
Published: March 2014

The redox‐system Fe2+/3+ in aqueous H2SO4 electrolytes was investigated with platinum electrodes coated with a perfluorosulfonate polymer (“Nafion”). The partitioning of the redox ions into the membrane‐type coating can be described by a classical ion‐exchange mechanism involving largely electrostatic forces. The apparent heterogeneous charge‐transfer standard rate constant was determined by a transient impedance technique in 0.05 to 0.5 M H2SO4 to be of the order of k0′ ≈ 1 · 10−3 cm s−1. At the lower H2SO4 concentrations the analysis of the charge‐transfer kinetics was not conducted because in this case the redox‐ion transport does not proceed by a simple diffusion mechanism. The diffusion coefficients of the redox ions in the membrane are of the order of 10−7 cm2 s−1. The known phase‐separation phenomena of the considered polymer are not noticeable in the electrochemical behaviour of the coated electrodes in this electrolyte.
Modell zur Berechnung von Kapazitäten bei Bleiakkumulatoren mit festgelegtem Elektrolyten
Authors: Teutsch U. , Böttcher F. , Winsel A.
Published: March 2014

The discharge capacity of a lead‐acid accumulator with immobilized electrolyte is essentially limited by depletion of sulfuric acid in the porous positive electrode. A rather simple macrohomogeneous, one‐dimensional model including consumption, migration and diffusion of sulfuric acid is used to predict discharge capacities as a function of cell parameters, temperature and discharge current density. Calculated capacities agree satisfactorily with experimental data if the final voltage is approximately 350 mV lower than the initial voltage. In addition to these numerical calculations a simple analytical function to approximate discharge capacities is given. The capacity calculations can be completed by another analytical function that gives an estimate of the change of capacity when a different final voltage is applied. The model calculations facilitate the development of new lead‐acid cells designed for special requirements.
Laser Induced Electrical Transients at Semiconductor Electrodes
Authors: Willig F.
Published: March 2014

Laser‐induced electrical transients (LET) are described in a model with two capacitors in series, two current source terms, a measuring resistor, and a resistor for the system. Calculated and experimental LET signals at semiconductor electrodes are shown for characteristic kinetic situations in three different time windows t < τ, t comparable to τ, and t > τ, where τ represents the RC response time of the circuit.
The Underpotential Deposition of Lithium Ions from Acetonitrile Solutions with Small Amounts of Water
Authors: Gerischer H. , Wagner D.
Published: March 2014

Voltammetric and coulometric studies have been performed of the underpotential deposition of Li+ ions from solution in acetonitrile. This process does not result in a Li monolayer if only small amounts of water are present. The deposited lithium reacts with water, primarily forming a LiOH layer. Underneath this layer, further Li+ reduction leads to the formation of a lithium hydride. This hydride with an excess of Li can in parallel form a lithium gold alloy. The reoxidation of the lithium hydride results either in the formation of Li+ ions and hydrogen or Li+ and H+ ions depending on the oxidation potential.
Photoelectrochemical Study on the Ternary Semiconductors AgInS2 and AgInSe2
Authors: Odenweller T. , Grabner E. W.
Published: March 2014

Polycrystalline samples of the ternary semiconductors AgInS2 and AgInSe2 are prepared by melting of the elements in quartz ampoules and characterized by physical and electrochemical methods. A maximum photovoltage of 0.28 V for AgInS2 and a maximum photocurrent of 10 mA/cm2 for AgInSe2 are observed using a light intensity of 34 mW/cm2 (250 W halogene lamp). Action spectra suggest a direct transition to occur in AgInSe2 and an indirect one in AgInS2. A photoelectrochemical cell with AgInSe2 as photoanode, Pt as counter electrode, and I−3/I− in H2SO4 (pH 2) as electrolyte reveals a conversion efficiency of 1.6%.
Impedance Measurements on Illuminated p‐Indiumphosphide During Hydrogen Evolution
Authors: Kühne H.‐M. , Schefold J.
Published: March 2014

Impedance measurements are presented on single crystalline, illuminated p‐type indiumphosphide photoelectrodes. The experiments show a shift of the flatband potentials towards more negative values during photoevolution of hydrogen. This shift amounts, both in acid and alkaline solution, to about −0.7 V at AM1, if no catalyst is deposited on the electrode surface. After platinum deposition, differences in the flatband potential are reduced to less than 100 mV, accompanied by a positive shift of the photocurrent onset for hydrogen evolution. – The results are interpreted in terms of electron trapping at the semiconductor‐electrolyte interface. The rate of charge transfer to the electrolyte (hydrogen evolution) is increased by platinum deposition, resulting in a decrease of the steady state concentration of trapped minority carriers. The model is linking the measured flatband potential shift under illumination to the kinetic overvoltage of multielectron transfer reactions at the semiconductor surface.
Multilayer Adsorption
Authors: Ruiz J. De D. Casquero , Guil J. M. , Masiá A. PÉRez , Paniego A. Ruiz
Published: March 2014

Using an exponential distribution function for the energy of the adsorption sites on a heterogeneous surface, an equation for multilayer adsorption is obtained. The basic assumptions are similar to those of the Frenkel‐Halsey‐Hill model (FHH). The equation deduced here is however somewhat different: a (θ + B)r term appears instead of the FHH θr term, where θ is the coverage, B is a constant related to the parameters of the exponential distribution function, and r is the exponent governing the decrease of energy with increasing distance from the surface. The addition of constant B to θ improves the linearity of the usual logarithmic plot of the equation and increases the value of r as compared with that from the FHH equation. The model is applied to the analysis of adsorption isotherms of N2 at 77 K on SiO2 and Sc2O3. Values obtained for r are close to 3, the theoretical exponent for the interaction due to dispersion forces.
Interrelations Between Thermodynamic Equations of State of Single‐ and Multi‐Component Adsorbates
Authors: Keller J. U.
Published: March 2014

Interrelations of thermodynamic equations of state of adsorbed phases are considered. These relations are consequences of the fact that an adsorbate, assumed to be a thermodynamic system in the sense of Schottky, has a number of degrees of freedom which compared to that of a bulk phase is reduced by one. Depending on the choice of independent variables several forms of these interrelations can be formulated. Here especially relations between the adsorption isotherms of a multi‐component adsorbate, using the partial pressures and the temperature of the surrounding adsorptive as independent variables are considered. By these relations the number of independent parameters included in the isotherms is reduced considerably. This is demonstrated by discussing multi‐component adsorption isotherms of the Langmuir‐Freundlich – and of a generalized BET‐type.
Time Evolution of the Potential Distribution in Earth Alkaline Titanates under de Voltage Stress
Authors: Raith A. , Reijnen P. , Waser R.
Published: March 2014

Earth alkaline titanates which are commonly used as dielectrics in ceramic capacitors may exhibit a long‐term degradation of the insulation resistance under simultaneous dc field and temperature stress. In order to study the nature of this process, it is necessary to detect the time evolution of the potential distribution between anode and cathode. A method is introduced which allows the determination of the potential distribution by the electrostatic deflection of an electron beam close to the edge of a current‐carrying sample. The results are used to evaluate various models which have been proposed to explain the mechanism of the degradation process.
Electrochemical Grafting of Poly‐3‐Methylthiophene on Platinum in Acetonitrile Studied by In‐Situ Ellipsometry and Electrochemistry
Authors: Lang P. , Chao F. , Costa M. , Lheritier E. , Garnier F.
Published: March 2014

The first steps of the electropolymerization of methyl‐3‐thiophene on polycrystalline platinum electrode in acetonitrile‐LiClO4 has been analysed, using in‐situ differential ellipsometry and rotating disk voltammetry. The optical method showed that the first step is the formation of oligomers in the solution. These oligomers precipitate onto the electrode surface when they reach a minimum length corresponding to a trimer, forming then nuclei. The polymer chain growths then by coupling with the newly electrogenerated radical cations. The rotating disk electrode study shows the influence of the forced convection on the grafting which under limit conditions, doesn't occur.
Zones of Sparingly Soluble Inorganic Salts with Membrane Properties in Gels
Authors: Choi Jung‐Gyun , Newrzella D. , Woermann D.
Published: March 2014

Polyacrylamide gels containing potassium oxalate (sodium oxalate) are brought into contact with aqueous solutions of Pb(NO3)2, CaCl2, SrCl2 and BaCl2 respectively. The electrolyte concentrations in the gel phase and in the solutions are varied systematically. There exists a system specific characteristic concentration c̃s below which advancing precipitation zones of PbOx, CaOx, SrOx, and BaOx (Ox: oxalate) within the gel are observed. Above c̃s the precipitation zones do not grow after advancing for about 2 mm maximally. Such precipitation zones have membrane properties (e. g. Impermeability to ions forming the precipitate, osmotic property). c̃s corresponds to a supersaturation ratio of the order 103. The experiments indicate that the precipitation zones with membrane properties are generated by homogeneous nucleation. – The kinetics of formation of oxalate precipitates in cellophane skins is studied by measurements of the membrane potential as function of time. In these systems precipitate is formed by interdiffusion of two solutions containing the appropriate ions. A system specific delay time Δtdel is observed after which the precipitation zones acquire membrane properties. It is found that this time is related to the rate of formation of precipitate which is a function of the solubility product and the square of electrolyte concentration. The precipitation zone acquires membrane properties as soon as the local concentration of precipitate has reached a value of the order 10−3 mol cm−3. The existence of the characteristic concentration c̃s and of the delay time Δtdel are interpreted in terms of an absorption charge model proposed by Hirsch‐Ayalon.
Water Desorption Kinetics from Alumina Supported Copper Studied by FTIR Spectroscopy
Authors: Wokaun A. , Jobson E. , Baiker A.
Published: March 2014

The desorption of water from an alumina‐supported copper catalyst has been followed by FTIR spectroscopy. On the catalyst, an exponential decrease of the 2400 cm−1 (O‐D stretching) absorption is observed subsequent to loading of the sample with a D2O pulse. The rates and activation energies of desorption are found to be different in N2 and H2 carrier gases. On the pure alumina support the desorption is non‐exponential, and is well described by a Temkin‐type desorption kinetics: A distribution of sites, which are characterized by different desorption enthalpies, are contributing to the broad O‐D stretching band. This is evidenced by different desorption rates for various parts of the band.
Insights into the Organocatalyzed Synthesis of Urethanes in Supercritical Carbon Dioxide: An In Situ FTIR Spectroscopic Kinetic Study
Authors: Smith Christopher A. , Cramail Henri , Tassaing Thierry
Published: March 2014

The kinetics of urethane (carbamate) formation in supercritical CO2 (scCO2) has been studied by in situ FTIR spectroscopy by using the reaction between n‐butanol and toluene‐2,4‐diisocyanate as a model for the synthesis of polyurethanes. We have evaluated the efficiency of different organocatalysts for this transformation to eliminate the need for potentially toxic organotin compounds. Bicyclic guanidines and amidines (7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene) lead to a significant acceleration of the reaction rate, but we found that their activity in scCO2 is reduced compared to reactions in conventional media because of the formation of guanidinium or amidinium alkylcarbonate salts. In scCO2, these catalysts are also sensitive to the presence of water and can lead to the formation of allophanate or isocyanurate byproducts. On the other hand, we have shown that catalysis with amine N‐oxides (N‐methylmorpholine‐N‐oxide) is suited to the scCO2 medium.
Direct Electrochemical Tyrosinase Biosensor based on Mesoporous Carbon and Co3O4 Nanorods for the Rapid Detection of Phenolic Pollutants
Authors: Wang Xue , Lu Xianbo , Wu Lidong , Chen Jiping
Published: March 2014

A novel tyrosinase (Tyr) biosensor based on a graphitized ordered mesoporous carbon/cobaltosic oxide nanorod (GMC/Co3O4) nanocomposite is developed for the rapid detection of phenolic pollutants. By applying the GMC/Co3O4 nanocomposite as an enzyme immobilization matrix, rapid direct electron transfer between Tyr and the electrode is achieved. The biosensor exhibits a wide linear response for catechol, ranging from 5.0×10−8 to 1.3×10−5 M, with a limit of detection down to 25 nM and a response time of less than 2 s. The sensitivity of the biosensor based on the GMC/Co3O4 nanocomposite (6.4 A M−1 cm−2) is higher than that of the biosensor based on GMC (5.0 A M−1 cm−2) or Co3O4 (3.5 A M−1 cm−2), which can be attributed to the synergistic effect of the GMC/Co3O4 nanocomposite. The biosensor is further used to systematically detect mixed phenolic samples (phenol, catechol, m‐cresol, p‐cresol, and 4‐chlorophenol) and real water samples. The biosensor‐based detection results for river water and tap water samples show outstanding average recovery (92.2–103.3 %) and relative standard deviations (0.9–7.8 %). In comparison with the conventional spectrophotometric method, the biosensor method is more rapid, sensitive, accurate, and convenient. Furthermore, the detection limit of the biosensor method is about 20 times lower than that of the spectrophotometric method. This novel biosensor is proven to be a promising alternative tool for the rapid and on‐site monitoring of environmental phenolic pollutants.
Plant Antimicrobial Peptides Snakin‐1 and Snakin‐2: Chemical Synthesis and Insights into the Disulfide Connectivity
Authors: Harris Paul W. R. , Yang Sung‐Hyun , Molina Antonio , López Gemma , Middleditch Martin , Brimble Margaret A.
Published: March 2014

Antimicrobial peptides and proteins represent an important class of plant defensive compounds against pathogens and provide a rich source of lead compounds in the field of drug discovery. We describe the effective preparation of the cysteine‐rich snakin‐1 and ‐2 antimicrobial peptides by using a combination of solid‐phase synthesis and native chemical ligation. A subsequent cysteine/cystine mediated oxidative folding to form the six internal disulfide bonds concurrently gave the folded proteins in 40–50 % yield. By comparative evaluation of mass spectrometry, HPLC, biological data and trypsin digest mapping of folded synthetic snakin‐2 compared to natural snakin‐2, we demonstrated that synthetic snakin‐2 possesses full antifungal activity and displayed similar chromatographic behaviour to natural snakin‐2. Trypsin digest analysis allowed tentative assignment of three of the purported six disulfide bonds.
Switching Regioselectivity of β‐Ketothioamides by Means of Iodine Catalysis: Synthesis of Thiazolylidenes and 1,4‐Dithiines
Authors: Wen Li‐Rong , Men Lian‐Bin , He Tao , Ji Guo‐Jing , Li Ming
Published: March 2014

An efficient I2‐catalyzed synthesis of thiazolylidenes and 1,4‐dithiines from β‐ketothioamides (KTAs) has been developed by only controlling the amount of I2 that triggers different cascade reaction sequences by means of [3+2] or [3+3] cyclocondensation in a one‐step process. A possible mechanistic proposal for these transformations is presented.
Metal–Organic Frameworks: From Molecules/Metal Ions to Crystals to Superstructures
Authors: Carné‐Sánchez Arnau , Imaz Inhar , Stylianou Kyriakos C. , Maspoch Daniel
Published: March 2014

Metal–organic frameworks (MOFs) are among the most attractive porous materials known today, exhibiting very high surface areas, tuneable pore sizes and shapes, adjustable surface functionality, and flexible structures. Advances in the formation of MOF crystals, and in their subsequent assembly into more complex and/or composite superstructures, should expand the scope of these materials in many applications (e.g., drug delivery, chemical sensors, selective reactors and removal devices, etc.) and facilitate their integration onto surfaces and into devices. This Concept article aims to showcase recently developed synthetic strategies to control the one‐, two‐ and three‐dimensional (1‐, 2‐ and 3D) organisation of MOF crystals.
Cerium(III/IV) Formamidinate Chemistry, and a Stable Cerium(IV) Diolate
Authors: Werner Daniel , Deacon Glen B. , Junk Peter C. , Anwander Reiner
Published: March 2014

Four new cerium(III) formamidinate complexes comprising [Ce(p‐TolForm)3], [Ce(DFForm)3(thf)2], [Ce(DFForm)3], and [Ce(EtForm)3] were synthesized by protonolysis reactions using [Ce{N(SiMe3)2}3] and formamidines of varying functionality, namely N,N′‐bis(4‐methylphenyl)formamidine (p‐TolFormH), N,N′‐bis(2,6‐difluorophenyl)formamidine (DFFormH), and the sterically more demanding N,N′‐bis(2,6‐diethylphenyl)formamidine (EtFormH). The bimetallic cerium lithium complex [LiCe(DFForm)4] was synthesized by treating a mixture of [Ce{N(SiHMe2)2}3(thf)2] and [Li{N(SiHMe2)2}] with four equivalents of DFFormH in toluene. Oxidation of the trivalent cerium(III) formamidinate complexes by trityl chloride (Ph3CCl) caused dramatic color changes, although the cerium(IV) species appeared transient and reformed cerium(III) complexes and N′‐trityl‐N,N′‐diarylformamidines shortly after oxidation. The first structurally characterized homoleptic cerium(IV) formamidinate complex [Ce(p‐TolForm)4] was obtained through a protonolysis reaction between [Ce{N(SiHMe2)2}4] and four equivalents of p‐TolFormH. [Ce{N(SiHMe2)2}4] was also treated with DFFormH and EtFormH, but the resulting cerium(IV) complexes decomposed before isolation was possible. The new cerium(IV) silylamide complex [Ce{N(SiMe3)2}3(bda)0.5]2 (bda=1,4‐benzenediolato) was synthesized by treatment of [Ce{N(SiMe3)2}3] with half an equivalent of 1,4‐benzoquinone, and showed remarkable resistance towards protonolysis or reduction.
Metal Ion, Light, and Redox Responsive Interaction of Vesicles by a Supramolecular Switch
Authors: Samanta Avik , Ravoo Bart Jan
Published: March 2014

Chemical, photochemical and electrical stimuli are versatile possibilities to exert external control on self‐assembled materials. Here, a trifunctional molecule that switches between an “adhesive” and a “non‐adhesive” state in response to metal ions, or light, or oxidation is presented. To this end, an azobenzene–ferrocene conjugate with a flexible N,N′‐bis(3‐aminopropyl)ethylenediamine spacer was designed as a multistimuli‐responsive guest molecule that can form inclusion complexes with β‐cyclodextrin. In the absence of any stimulus the guest molecule induces reversible aggregation of host vesicles composed of amphiphilic β‐cyclodextrin due to the formation of intervesicular inclusion complexes. In this case, the guest molecule operates as a noncovalent cross‐linker for the host vesicles. In response to any of three external stimuli (metal ions, UV irradiation, or oxidation), the conformation of the guest molecule changes and its affinity for the host vesicles is strongly reduced, which results in the dissociation of intervesicular complexes. Upon elimination or reversal of the stimuli (sequestration of metal ion, visible irradiation, or reduction) the affinity of the guest molecules for the host vesicles is restored. The reversible cross‐linking and aggregation of the cyclodextrin vesicles in dilute aqueous solution was confirmed by isothermal titration calorimetry (ITC), optical density measurements at 600 nm (OD600), dynamic light scattering (DLS), ζ‐potential measurements and cyclic voltammetry (CV). To the best of our knowledge, a dynamic supramolecular system based on a molecular switch that responds orthogonally to three different stimuli is unprecedented.
Redox Behaviour of Cymantrene Fischer Carbene Complexes in Designing Organometallic Multi‐tags
Authors: Bezuidenhout Daniela I. , van der Westhuizen Belinda , Swarts Pieter J. , Chatturgoon Teshica , Munro Orde Q. , Fernández Israel , Swarts Jannie C.
Published: March 2014

A series of Group 7 Fischer carbene complexes, [Cp(CO)2MnI=C(OEt)Ar] (Cp=cyclopentadienyl, Ar=Th=thienyl (1 a), Ar=Fu=furyl (2 a), Ar=Fc=ferrocenyl (3 a)) and biscarbene complexes, [Cp(CO)2MnC(OEt)Ar′(OEt)CMn(CO)2Cp] (Ar′=Th′=2,5‐thienylene (1 b), Ar′=Fu′=2,5‐furylene (2 b), Ar′=Fc′=1,1′‐ferrocendiyl (3 b)) was synthesized and characterized. Chemical oxidation of [Cp(CO)2MnC(OEt)Fc] (3 a) and isolation of the oxidised species[3 a][PF6]possessing a MnIIcentre proved possible below −30 °C in dichloromethane solution. The ESR spectrum of the transiently stable radical cation,[3 a][PF6], confirmed the presence of a low‐spin MnIIcentre characterized by a rhombicgtensor (gx=1.975,gy=2.007 andgz=2.130) in frozen dichloromethane at 77 K with55 Mn hyperfine coupling constantsA1,A2andA3of 115, 33 and 43 G, respectively. Electrochemical studies demonstrated the influence of the Ar substituent on the oxidation potential. All complexes showed that the redox potentials of carbene double bond reduction and MnIoxidation were dependent on the type of Ar group, but only3 bshowed resolved oxidations for the two MnIcentres. Surprisingly, MnIoxidation occurs at lower potentials than ferrocenyl oxidation. Density functional theory (DFT) calculations were carried out to delineate the nature of the species involved in the oxidation and reduction processes and clearly confirm that oxidation of MnIis favoured over that of ferrocene.
Rational Design of Ni Nanoparticles on N‐Rich Ultrathin Carbon Nanosheets for High‐Performance Supercapacitor Materials: Embedded‐ Versus Anchored‐Type Dispersion
Authors: Yang Mei , Zhong Yiren , Su Liwei , Wei Jinping , Zhou Zhen
Published: March 2014

Highly dispersed Ni nanoparticles (NPs) and abundant functional N‐species were integrated into ultrathin carbon nanosheets by using a facile and economical sol–gel route. Embedded‐ and anchored‐type configurations were achieved for the dispersion of Ni NPs in/on N‐rich carbon nanosheets. The anchored‐type composite exhibited outstanding pseudocapacitance of 2200 F g−1 at 5 A g−1 with unusual rate capability and extraordinary cyclic stability over 20 000 cycles with little capacitance decay. Aqueous asymmetric supercapacitors fabricated with this composite cathode demonstrated a high energy density of 51.3 Wh kg−1 at a relatively large power density of 421.6 W kg−1, along with outstanding cyclic stability. This approach opens an attractive direction for enhancing the electrochemical performances of metal‐based supercapacitors and can be generalized to design high‐performance energy‐storage devices.
Magnesium Complexes as Highly Effective Catalysts for Conjugate Cyanation of α,β‐Unsaturated Amides and Ketones
Authors: Zhang Jinlong , Liu Xihong , Wang Rui
Published: March 2014

Asymmetric cyanation of trimethylsilyl cyanide (TMSCN) with α,β‐unsaturated amides and ketones, respectively, catalyzed by bifunctional mononuclear 1,1′‐bi‐2‐naphthol (BINOL)–Mg and binuclear bis(prophenol)–Mg catalysts was realized. A series of synthetically important 1,4‐cyano products were obtained with good to high enantioselectivities (up to 97 % ee).
Templating the Self‐Assembly of Pristine Carbon Nanostructures in Water
Authors: Mba Miriam , Jiménez Ana I. , Moretto Alessandro
Published: March 2014

The low solubility of carbon nanostructures (CNs) in water and the need of ordered architectures at the nanoscale level are two major challenges for materials chemistry. Here we report that a novel amino acid based low‐molecular‐weight gelator (LMWG) can be used to effectively disperse pristine CNs in water and to drive their ordered self‐assembly into supramolecular hydrogels. A non‐covalent mechanochemical approach has been used, so the π‐extended system of the CNs remains intact. Optical spectroscopy and electron microscopy confirmed the effective dispersion of the CNs in water. Electron microscopy of the hydrogels showed the formation of an ordered, LMWG‐assisted, self‐assembled architecture. Moreover, the very same strategy allows the solubilization and self‐assembly in water of a variety of hydrophobic molecules.
Capsules with Highly Active Pores and Interiors: Versatile Platforms at the Nanoscale
Authors: Müller Achim , Gouzerh Pierre
Published: March 2014

Spherical porous capsules offer new exciting approaches in chemistry, materials sciences, and in context of physical and biological phenomena. The underlying concepts are reported with particular emphasis on metal oxide based capsules of the {M132} Keplerate type which display—due to their exceptional structural features and easy variation/derivatization as well as exchange of building units—an unmatched range of properties and offer unique opportunities for investigating a variety of basic aspects of nanoscience, including the discovery of some new phenomena, especially those related to hydrophobicity issues that are of significance for everyday life. This relies in particular on the existence of a large number of flexible crown ether type pores/channels and the possibility of changing the interior from completely hydrophilic to completely hydrophobic due to the presence of numerous easily exchangeable internal ligands/functionalities; the capsules can even be constructed so that they enclose a large number of highly active Lewis and Brønsted acid sites. The manifold of possible applications/uses are outlined as subtitles with reference to results as well as possible future studies. There are, among many others, options to control passing cations under different internal frames allowing also their separations, to conduct studies about hydrophobic recognitions and clustering of biological interest in water, controlled internal ion transport, nanoscale dewetting, and to carry out basic as well as new types of reactions under confined conditions.
Halometallate Complexes of Germanium(II) and (IV): Probing the Role of Cation, Oxidation State and Halide on the Structural and Electrochemical Properties
Authors: Bartlett Philip N. , Cummings Charles Y. , Levason William , Pugh David , Reid Gillian
Published: March 2014

The GeIV chlorometallate complexes, [EMIM]2[GeCl6], [EDMIM]2[GeCl6] and [PYRR]2[GeCl6] (EMIM=1‐ethyl‐3‐methylimidazolium; EDMIM=2,3‐dimethyl‐1‐ethylimidazolium; PYRR=N‐butyl‐N‐methylpyrrolidinium) have been synthesised and fully characterised; the first two also by single‐crystal X‐ray diffraction. The imidazolium chlorometallates exhibited significant CH⋅⋅⋅Cl hydrogen bonds, resulting in extended supramolecular assemblies in the solid state. Solution 1H NMR data also showed cation–anion association. The synthesis and characterisation of GeII halometallate salts [EMIM][GeX3] (X=Cl, Br, I) and [PYRR][GeCl3], including single‐crystal X‐ray analyses for the homologous series of imidazolium salts, are reported. In these complexes, the intermolecular interactions are much weaker in the solid state and they appear not to be significantly associated in solution. Cyclic‐voltammetry experiments on the GeIV species in CH2Cl2 solution showed two distinct, irreversible reduction waves attributed to GeIV–GeII and GeII–Ge0, whereas the GeII species exhibited one irreversible reduction wave. The potential for the GeII–Ge0 reduction was unaffected by changing the cation, although altering the oxidation state of the precursor from GeIV to GeII does have an effect; for a given cation, reduction from the [GeCl3]− salts occurred at a less cathodic potential. The nature of the halide co‐ligand also has a marked influence on the reduction potential for the GeII–Ge0 couple, such that the reduction potentials for the [GeX3]− salts become significantly less cathodic when the halide (X) is changed Cl→Br→I.
Stereostructural Implication by the Differential Bond Polarizability: ROA Intensity Study of Chiral S 2‐Amino 1‐Propanol
Authors: Wu Guozhen , Wang Peijie
Published: March 2014

The bond polarizability and differential bond polarizability are introduced to interpret the Raman and Raman optical activity (ROA) intensities, calculated by the ab initio method. Chiral S 2‐amino 1‐propanol is taken as a model molecule. Through these bond polarizabilities, we observe that symmetric and antisymmetric coordinates are, respectively, more significant in Raman and ROA. It is noted that in S 2‐amino 1‐propanol those bonds lying on a common plane share the same differential bond polarizability sign while that of the asymmetric C‐H bond which protrudes out of the plane possesses the opposite sign. We conclude that ROA can offer more stereostructural implications than Raman and that the differential bond polarizability is potentially the appropriate parameter in interpreting the 3D configuration of a molecule. Chirality 26:255–259, 2014. © 2014 Wiley Periodicals, Inc.
Electrically Assisted Liquid‐Phase Microextraction Combined With Capillary Electrophoresis for Quantification of Propranolol Enantiomers in Human Body Fluids
Authors: Tabani Hadi , Fakhari Ali Reza , Shahsavani Abolfath , Gharari Alibabaou Hossein
Published: March 2014

In this study, electromembrane extraction (EME) combined with cyclodextrin (CD)‐modified capillary electrophoresis (CE) was applied for the extraction, separation, and quantification of propranolol (PRO) enantiomers from biological samples. The PRO enantiomers were extracted from aqueous donor solutions, through a supported liquid membrane (SLM) consisting of 2‐nitrophenyl octyl ether (NPOE) impregnated on the wall of the hollow fiber, and into a 20‐μL acidic aqueous acceptor solution into the lumen of hollow fiber. Important parameters affecting EME efficiency such as extraction voltage, extraction time, pH of the donor and acceptor solutions were optimized using a Box‐Behnken design (BBD). Then, under these optimized conditions, the acceptor solution was analyzed using an optimized CD‐modified CE. Several types of CD were evaluated and best results were obtained using a fused‐silica capillary with ammonium acetate (80 mM, pH 2.5) containing 8 mM hydroxypropyl‐β‐CD as a chiral selector, applied voltage of 18 kV, and temperature of 20°C. The relative recoveries were obtained in the range of 78–95%. Finally, the performance of the present method was evaluated for the extraction and determination of PRO enantiomers in real biological samples. Chirality 26:260–267, 2014. © 2014 Wiley Periodicals, Inc.