bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Excited State Photoelectrochemical Cell for the Production of O2 Based on Oxidative Quenching of Ru(bpy)2+3
Authors: Dressick Walter J. , Meyer Thomas J. , Durham Bill 
Published: November 2013

AbstractA description is given of an excited state photoelectrochemical cell in which the excited state, Ru(bpy)2+*3 (bpy is 2,2′‐bipyridine) is quenched via irreversible electron transfer to Co(NH35Cl+2 which gives Ru(bpy)3+3. The oxidizing equivalents in Ru(bpy)3+3 are transferred via an external circuit to a second half‐cell in which OH− is oxidized to O2. The variation of photogenerated charge and limiting currents with changes in [Co(NH3)5Cl+2], time, and other variables are presented in the context of a kinetic model for the cell. Conditions are also described for the operation of the cell as an actinometer which is useful for the wavelength range 360 nm ≦ λ ≦ 580 nm and exhibits reproducibility comparable to that observed with conventional chemical actinometers.
The Mechanism of Photocatalysis on Semiconductor Powders in a Liquid Medium. New Experimental Methods and Their Results
Authors: Manassen Joost 
Published: November 2013

AbstractTwo new methods are described for following the reactions occurring on semiconductor powders, when illuminated in a solution of reactants. The reaction between nitroaromatics and hydrazine gives gaseous nitrogen as one of the products, which can be measured manometrically. The rate with CdSe as the catalyst is strongly dependent on the structure of the nitroaromatic, giving faster reactions for the better electron acceptors. The more polar the solvents the lower the yields. The reaction between K4Fe(CN)6 and air in aqueous solution is measured by electrochemical reduction of the product K3Fe(CN)6. Rates are strongly dependent on heat treatments given to the semiconductor before reaction and the dependence of rate on CdSe heat treatment is very similar for both the nitrobenzene/hydrazine reaction in methanol and the K4Fe(CN)6 oxidation in water. Electrochemical measurements with CdSe electrodes in benzene show the current onset to be at a potential similar to the first reduction potential of the nitroaromatics used, which explains the strong rate dependence on the reduction potential of the nitroaromatic. A mechanism is proposed for the n‐type case of a rapid reaction occurring between the minority carriers and hydrazine, by which the powder charges up negatively and the electron transfer from the charged powder to the nitroaromatic in solution is rate determining. With p‐type semiconductors, which give slower rates, the minority carrier reaction with the nitroaromatics is rate determining and only little positive charge accumulates on the particles.
Origin of Thermal Analysis
Authors: Mackenzie R. C. 
Published: November 2013

AbstractInternational acceptance of a definition of “thermal analysis” should enable the originator of studies in this field to be located. A search of the literature suggests that the first to use a technique that could be so classified was Jakob Fredrik Emanuel Rudberg (1800–1839) in Sweden, who observed inverse cooling‐rate phenomena in 1829. He was followed by Moritz Ludwig Frankenheim (1801–1869) in Germany, who determined cooling curves in 1837, by James Ballantyne Hannay (1855–1931) in Scotland, who introduced mass‐change curves in 1877, and by Henry Louis Le Chatelier (1850–1936) in France, who devised quasi‐isothermal heating curves and heating‐rate curves in 1883 and 1887. As all of these studies were probably initially independent of the earlier work, perhaps the honour should be shared.
The Stability of Hydrates of Inorganic Salts in Cooling—Heating Cycles
Authors: Feilchenfeld H. , Fuchs J. , Kahana F. , Sarig S. 
Published: November 2013

AbstractThe stability of calcium chloride hexahydrate with an admixture of nucleating agent was tested during 1000 cooling—heating cycles and was found satisfactory. The experimental set‐up based on computer monitored heating and natural cooling in a cold room is described. Addition of lithium chloride decreases phase transition temperature, but affects the stability.
The Formation of Nickel Ferrite: A Thermo‐magnetic Study
Authors: Tzehoval Hannah , Steinberg Menachem 
Published: November 2013

AbstractThe preparation of NiFe2O4 in the solid‐state has been studied by means of thermo‐magnetic and thermo‐gravimetric continuous measurements and by X‐ray diffraction analysis. The method consists of the preparation of a crystallized organo‐metallic complex (NiFe citrate precursor), which on decomposition at moderate temperatures gave NiFe2O4. The yield of the product depends on the ambient atmosphere during decomposition. Optimal conditions for a high yield of nickel ferrite were pretreatment of NiFe citrate at 250°C in air followed by gradual heating under vacuum to 500°C. This is a relatively low temperature as compared to temperatures previously used in the preparation of NiFe2O4.
An Experimental Review of Thermoanalytical Techniques for the Measurement of the Oxidative Stability of Polyethylene
Authors: Collins L. W. , Wendlandt W. W. 
Published: November 2013

AbstractThermoanalytical techniques are commonly used to evaluate the oxidative stability of polyolefin resins. The most common technique for this evaluation is the oxidative induction time (OIT) as measured by DSC. This study compares the OIT values for a standard set of polyethylene samples with stability measurements made using other DSC and TG methods as well as a less common photothermal analysis method. The methods were all shown to give comparable results that could be correlated with oxidative stability. Interpretation of the measurements in terms of the resin properties is a significant problem in all thermoanalytical methods.
Estimation of Ca(OH)2 and Mg(OH)2 — Implications in Cement Chemistry
Authors: Ramachandran V.S. 
Published: November 2013

AbstractPortland cement, hydrated Portland cement, magnesium oxychloride, magnesium oxysulphate and plasters are inorganic cementitious systems in which different amounts of MgO, CaO, Ca(OH)2 and Mg(OH)2 are present. Identifying and estimating the Ca‐ and Mg‐oxides and hydroxides by DTA provides information that can, in turn, be used for studying the mechanism of hydration of CaO, reactivity of calcium silicates, the relevance of the autoclave test for determining the unsoundness of cements, interactions occurring in polymer‐impregnated cement, the effect of various admixtures on the hydration kinetics of cement and cement compounds, the contribution of Ca(OH)2 to the physico‐mechanical properties of cement, the composition of the hydrated silicates, mechanism of hydration, chemical activity of blended cements, strength development in magnesium‐oxychloride and magnesium‐oxysulphate cements and causes of failure of gypsum plasters.
Study of Cholesterol—Sitosterol Crystallization Mixtures by DTA
Authors: Karpuj Liliana , Garti Nissim , Sarig Sara 
Published: November 2013

AbstractDTA analysis was used to confirm evidence from X‐ray diffraction studies for the existence of 1:1 mixed sitosterol—cholesterol crystals. The curve of melting point against composition has an inflection point at about 1:1 ratio. The DTA peaks for 1:1 mechanical mixtures and for 1:1 mixed crystals are different with respect to symmetry and width. The curve of the heat of enthalpy against the composition of crystals also changes indicating a change in entropy. This can be attributed to the difference between melting mixed crystals (high order) and solid solution (low order). The solubility curve in the sitosterol—cholesterol—alcohol system has also a region of inflection confirming the previous conclusions.
Helium Diffraction as a Probe of Surface Structure
Authors: Engel Thomas 
Published: November 2013

AbstractThe diffraction of He atoms from solid surfaces has been recently used to determine the electron distribution of electrons at surfaces. From this, the position of underlying atoms can usually be inferred. Recent developments which test the validity of the hard corrugated wall method to calculate diffraction intensities are discussed. Structural studies which have been carried out to date, on various surfaces with He beams, are tabulated.
The Electrostatic Potential Above the 100 Surface Plane of a f.c.c. Ionic Crystal with a Continuous Electron Chargè Distribution
Authors: Ephraim A. Ben , Folman M. 
Published: November 2013

AbstractThe electrostatic potential above the 100 surface plane of a f.c.c. ionic crystal has been calculated using a point charge distribution for the positive nuclei and a continuous charge density distribution for electrons. The continuous electron charge distribution has been obtained from the known results of a Fourier crystal structure analysis. The results for the electric field and its different gradients are compared with those obtained from the Lennard‐Jones and Dent model (point charge distributions for both the positive and negative ions). It has been found that the two models lead to significant differences of the electrostatic potentials and their derivatives.
Electronic Structure of Ion‐Radical Organic Solids and Polyenes
Authors: Soos Zoltán G. 
Published: November 2013

AbstractThe electronic structures of organic ion‐radical salts, molecular conductors, and charge‐transfer complexes are described by solid‐state models with one valence state per site. Similar models occur in π‐electron theories of conjugated molecules or in spin Hamiltonians for magnetic insulators. A localized or valence bond (VB) representation is qualitatively adequate in narrow band systems. Diagrammatic VB methods in finite models yield convenient exact solutions to the resulting configuration interaction (CI) problem as correlated states based on linear combinations of VB diagrams. Also found are exact charges, bond orders, ionicity, correlation functions, transition moments or other properties of correlated electronic states. Particular attention is given to qualitative failures of conventional one‐electron descriptions, which often reflect degeneracies lifted by correlations. Correlated states give the correct ordering of the 21Ag and 11Bu states of trans‐trans octatetraene, clarify the midgap absorption in polyacetylene, rationalize the partial ionicity and electrostatic energy of ion‐radical organic complexes, demonstrate an exactly soluble magnetic analog to the Mott transition, and quantitatively fit the thermodynamics of several random‐exchange Heisenberg antiferromagnets. Correlated states remain central in simultaneously modeling optical, magnetic, and electrical excitations in π‐radical solids.
Molecular Structures of Linear Polypyrrolic Pigments
Authors: Sheldrick W. S. 
Published: November 2013

AbstractThe results of X‐ray structural analyses of open‐chain polypyrrolic compounds are reviewed. Particular emphasis is placed on bilirubin and biliverdin derivatives and on the relevance of their observed conformations to the biological function and properties of natural bile pigments. Typical for bilirubin derivatives is a ridge‐tile conformation stabilised by six intramolecular hydrogen bonds, in which the individual pyrromethenone units are Z‐synperiplanar. Macrocyclic helical conformations are adopted by biliverdin derivatives and model bilatrienes‐abc. The bonding pattern and degree of bond delocalisation within the tetrapyrrole skeleton are discussed in comparison to the molecular geometries of model bi‐ and tripyrrolic compounds. The results indicate that the methine bridge at C5 may demonstrate considerable conformational flexibility in bilatrienes‐abc, whereas a marked degree of bond delocalisation is observed for the B, C and D rings. Protonation or metal complexation leads to pronounced changes in the degrees of stretch and widening of the helix and to corresponding changes in the electronic spectrum.
NMR Spectra of Molecules Oriented in Mixtures of Thermotropic Solvents of Opposite Diamagnetic Anisotropies
Authors: Khetrapal C. L. , Kunwar A. C. 
Published: November 2013

AbstractTheory and applications of NMR spectra of molecules oriented in mixed liquid crystals of opposite diamagnetic anisotropies are presented. The theoretical treatment is based on the Landau theory. The applications include a novel method for the determination of chemical shift anisotropy, individual determination of the indirect spin‐spin and direct dipole–dipole couplings, determination of diamagnetic anisotropy of liquid crystals and precise determination of spectral parameters.
Alkyl Chain Flexibility in Liquid Crystals
Authors: Samulski Edward T. 
Published: November 2013

AbstractDeuterium NMR results from labeled chains appended to nematogens and discotigens, chains linking mesogenic units in linear polymeric nematics and simplen‐alkanes and lipids solubilized in a nematic solvent are examined. A phenomenological single chain model is used as a vehicle for contrasting alkyl chain flexibility in various ordered phases. Agreement between the model and experiment suggests a commonality in the behavior of all of these types of alkyl chains originating from a repulsive (steric) constraint that is imposed on the isomerization of the chain by the local ordered environment.
The Reaction of Psoralens and Related Benzofurans with Singlet Oxygen An Account of Current Research
Authors: Berdahl Donald R. , Wasserman Harry H. 
Published: November 2013

AbstractRecent work dealing with the role of singlet oxygen in the biological activity of the psoralens has been reviewed. The reaction of singlet oxygen with benzofurans gives products which result from initially formed dioxetanes. Evidence for dioxetane intermediates was obtained from experiments using diphenyl sulfide as a trapping agent. Psoralen derivatives which contain alkyl or aryl groups on the furan double bond react readily with singlet oxygen to give dioxetane cleavage‐type products. Psoralens which lack furan substituents but possess powerful electrondonating groups in the 5‐ and 8‐positions give rise to peroxidic intermediates which are stable only at low temperature.
Cosensitized Electron‐Transfer Photooxygenation of Epoxides. A New Synthesis of Ozonides
Authors: Schaap A. Paul , Siddiqui Shahabuddin , Balakrishnan P. , Lopez Luigi , Gagnon Steven D. 
Published: November 2013

Abstract9,10‐Dicyanoanthracene (DCA) and biphenyl (BP) cosensitize the electron‐transfer photooxygenation of epoxides in oxygen‐saturated acetonitrile to form ozonides. These epoxides do not measurably quench the fluorescence of DCA and are, therefore, relatively unreactive under standard photooxygenation conditions with only DCA as sensitizer. However, a dramatic increase in the rate of reaction is observed upon the addition of BP as a non‐light‐absorbing cosensitizer. An investigation of the stereochemistry of the reaction with cis‐ and trans‐2,3‐diphenyloxiranes has shown that both epoxides are converted exclusively to the cis‐ozonide. This striking stereochemical result is consistent with a proposed mechanism involving singlet oxygen addition to an intermediate carbonyl ylide.
Activation of Superoxide Ion by Reactions with Protons, Electrophiles, Secondary Amines, Radicals, and Reduced Metal· Ions
Authors: Roberts Julian L. , Sawyer Donald T. 
Published: November 2013

AbstractIn aprotic and aqueous media the proton‐induced disproportionation of superoxide ion (O−2) yields a variety of reactive species (HO2·, H2O2, HO−2, and · OH). In aprotic media O−2 rapidly degrades polychlorinated hydrocarbons (CCl4, HCCl3, and DDT) to oxygenated products (CCl4 →Cl3COO·; HCCl3→ Cl2C: and Cl2C=O). Alkyl halides react more slowly (BuCl →BuOO· and BuOO−). Formation of O−2 in the presence of methyl viologen (MV2+), reduced flavins, esters, and low‐valent transition metal complexes results in the formation of reactive oxygenating agents and reaction mimics for oxygenases [MV+‐OO‐, 4a‐hydroperoxyflavins, RC(O)OO−, and Zn11(O2 ·)+]. Kinetic data for the proton‐induced disproportionation of O−2 in water and the nucleophilic reactions of O−2 in aprotic solvents lead to the conclusion that the latter are probably of little significance for biological oxygenation reactions.
The Radiation Chemistry of Cytochrome c
Authors: Koppenol W. H. , Butler J. 
Published: November 2013

AbstractThe literature on the reaction of cytochrome c with the radiolytically generated radicals \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm e}_{{\rm eq}}^ -,^. {\rm OH,}^{\rm .} {\rm H,CO}_2^ -,{\rm O}_{\rm 2}^ -,{\rm Br}_{\rm 2}^ - $\end{document} and various organic radicals is reviewed. It would appear that negatively charged radicals, aided by the electric field of cytochrome c, react at the exposed haem edge. Uncharged organic radicals also react at this site. \documentclass{article}\pagestyle{empty}\begin{document}$ ^. {\rm H} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ ^. {\rm OH} $\end{document} are likely to reduce the prosthetic group indirectly by a tunnelling mechanism.
On the Use of OH · Scavengers in Biological Systems
Authors: Czapski Gidon 
Published: November 2013

AbstractThe problem of using OH scavengers, with special emphasis on biological systems, is discussed. The problems arising from inhomogeneity and from possible large gradients in scavenger concentrations between the cell and media, or between different parts of the cell, are analysed, and their implications on scavenging efficiency are examined. The possible reactions of secondary radicals and their effect on scavenging and even on possible sensitization are described. The limitations of the usage of OH scavengers in biological systems are discussed.
Nickel‐Catalyzed Addition of Methylmagnesium Bromide to Alkynylsilanes. Stereospecific Synthesis of Tetrasubstituted Alkenes
Authors: Conn Robin S. E. , Karras Michael , Snider Barry B. 
Published: November 2013

AbstractMethylmagnesium bromide adds to trimethylsilyloctyne (1) in the presence of 10 mol% 1:0.67 nickel acetylacetonate‐trimethylaluminum to give a 9:1 mixture of alkenyl Grignard reagents 2a and 3a. This mixture reacts with water, deuterium oxide, formaldehyde, acetaldehyde, carbon dioxide, iodine, vinyl bromide or allyl bromide to give the expected products 2, 3b to 2, 3j. Nickel catalyzed carbometallation of 4 with MeMgBr followed by quenching with formaldehyde and desilylation gives trans, trans‐farnesol (5c). Nickel catalyzed addition of MeMgBr to 6a and 6b proceeds analogously, except that initially formed alkenyl Grignard reagents 7a and 7b isomerize completely to 8a and 8b which are stabilized by chelation. This carbometallation reaction allows the synthesis of both isomers of an allylic alcohol, such as 12 and 13, from a common intermediate 2a.
Catalytically Reactive Ruthenium Intermediates in the Homogeneous Oxidation of Alcohols to Esters
Authors: Blum Yigal , Shvo Youval 
Published: November 2013

AbstractRu(η4‐tetracyclone)(CO)3 and [Ru(η4‐tetracyclone)(CO)2]2 were prepared from Ru3(CO)12 and diphenylacetylene. Their rate of oxidation of PhCH2OH are, respectively, 1.6 and 4.2 times faster than their precursor Ru3(CO)12. Both complexes, as well as others, were also found in the oxidation reaction mixture: PhCH2OH+ Ph2C2 + Ru3(CO)12 which generates benzyl benzoate. Ru(η4‐tetracyclone)(CO)2 is most probably the true catalytic species in the catalytic oxidation of alcohols to esters.
Infrared Multiphoton Absorption by Methanol
Authors: Evans D. K. , Mcalpine Robert D. , Adams H. M. 
Published: November 2013

AbstractThe multiphoton absorption of CO2 laser 9 μm P(18), P(20) and P(34) lines by methanol has been studied for fluences from 10−3 to ∼ 20 J/cm2, pulse widths of 6 and 60 ns FWHM and methanol pressures from 0.067 to 13.3 kPa. The absorption depends on laser fluence, laser line and gas pressure but not on laser beam intensity. For each line studied the results can be expressed as a function of fluence and the product of pressure with pulse width. Absorption by a Q‐branch transition (9P(34) pumping) shows a faster relaxation and a stronger absorption than R‐branch transitions (9P(18) and 9P(20) pumping). The results obtained here are compared to multiphoton absorption data for an HF laser pumping the OH stretch vibration.
Nonlinear Multi‐Photon Excitation and Dissociation in Intense Laser Fields: Recent Developments in Floquet Theory and Quasi‐Energy Methods
Authors: Chu Shih‐I , Ho Tak‐San 
Published: November 2013

AbstractA short account of several recent developments in semiclassical Floquet theory and quasi‐energy (QE) methods for nonperturbative treatments of intense field multiphoton excitation (MPE) and dissociation (MPD) processes is given. Topics discussed include (a) non‐Hermitian Floquet theory and complex QE method for MPD, (b) MPE quantum dynamics in intense laser and static electric fields, (c) nonadiabatic approach for resonant infrared (IR) multiphoton absorption spectroscopy, (d) IR MPE/MPD of triatomic molecules — most probable path approach, and (e) many‐mode Floquet theory. Also presented are new methods and results for nonlinear MPE of finite level systems in linearly and circularly polarized bichromatic fields.
Stepwise Excitation Processes in Photodissociation and Detection
Authors: Reisler H. , Radhakrishnan G. , Sumida D. , Pfab J. , Chou J. S. , Nadler I. , Wittig C. 
Published: November 2013

AbstractTwo‐photon processes in which stationary intermediates are involved in the excitation are discussed, and three processes are described in detail: (a) stepwise 2‐photon laser induced dissociation of NCNO at wavelengths 600–800 nm, followed by detection of the CN fragment via laser induced fluorescence (LIF); (b) detection of HONO via a 2‐frequency scheme, in which dissociation is induced at 355 nm and is followed by LIF detection of the OH fragment; (c) stepwise 2‐frequency 2‐photon ionization detection of nascent PO produced via the collision free IR photolysis of aliphatic phosphonates and phosphites. Absorption throughout the B2Σ+‐X2 system of PO is followed by ionization using 266 nm radiation.
An Artificial Channel Type Ionophore
Authors: Nolte R. J. M. , van Beijnen A. J. M. , Neevel J. G. , Zwikker J. W. , Verkley A. J. , Drenth W. 
Published: November 2013

AbstractA polymer of an isocyanide (R–N=C<)n has been synthesized in which R contains a benzo‐18‐crown‐6 group. The crown ether rings are on top of each other and form channels which bind metal ions. The channel compound can be incorporated in vesicles and is able to transport ions across the bilayer membrane.
Conformational Versatility of Open‐Chain Polyethers: Crystal and Molecular Structures of the Ba(SCN)2 Complexes of Two Heptaethyleneglycol Diaryl Ethers
Authors: Hilgenfeld R. , Hirayama F. , Bhagwat V. , Saenger W. , Weber G. , Sheldrick G. M. , Sieger H. , Vögtle F. 
Published: November 2013

AbstractThe crystal structures of the Ba(SCN)2 complexes of two linear octaethers, heptaethyleneglycol diphenylether (HGPE; 1,20‐bis(phenyloxy)‐3,6,9,12,15,18‐hexaoxaicosane) and heptaethyleneglycol dinaphthylether (HGNE; 1,20‐bis(naphthyloxy)‐3,6,9,12,15,18‐hexaoxaicosane), are reported. In spite of their close similarity, the ligands adopt quite different conformations in their Ba(SCN)2 complexes. HGPE wraps around the metal ion in a discontinuous helix providing seven of its eight ether oxygens for coordination. 10‐fold coordination of Ba2+ is completed by the nitrogens of the SCN− ions and by a water molecule for which an occupancy of 0.37(5) was determined. In contrast, HGNE behaves as a hexadentate only. The barium ion is 9‐fold coordinated to six ether oxygens, to a water molecule, to one SCN− ion via its nitrogen atom and to a symmetry‐related thiocyanate ion via its sulphur atom. The second SCN− ion does not contact the metal ion but is hydrogen‐bonded to two symmetry‐generated water molecules. HGNE displays some unusual conformational features never found before for open‐chain polyethers.