bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ion Transport and Oscillatory Phenomena Across Adsorbed Monolayers at the Amalgam/Water and Mercurous Halide/Water Interfaces
Authors: Masters B. , Miller I. R. 
Published: November 2013

AbstractThis paper presents a method for the study of the transport of ions (K+, Na+, Cs+, Cl−, Br−) across adsorbed monolayers at the respective amalgam/water and mercurous halide/water interfaces. The method involves cathodic formation and anodic stripping (inverse polarography) of amalgams and in the reversed order (anodic formation) of mercury halides. Galvanostatic measurements were performed using a stationary mercury drop electrode, a platinum counter electrode and a Ag/AgCl reference electrode. Phase sensitive ac polarography was employed to determine the differential capacity of the electrical double layer in the presence of adsorbed monolayers. Adsorbed monolayers of octadecyltrimethylammonium and of eicosanyltrimethylammonium ions have different permeabilities towards the various cations; cesium ions are the most permeable. The transport of Cl− and Br− was studied across adsorbed monolayers of long chain quaternary ammonia and carboxylic acids and of polyglutamic acid at the mercurous halide/water interface. The anionic permeability depends on the type of anion, the composition of the monolayer, and the charge density of the monolayer and the interface. Ion transport is correlated with the packing in the monolayer. During the anodic stripping of potassium and sodium amalgams in the presence of octadecyltrimethylammonium chloride, and potassium, sodium and cesium amalgams in the presence of eicosanyltrimethylammonium chloride, sustained oscillations of the electrode potential were observed. The frequency varies from about 0.3 to 1.0 Hz, and depends on the current density, the duration of the anodic stripping, the composition of the monolayer, and the temperature. The amplitude of the oscillations varies from 100 to 500 mV. These oscillations involve the following processes: potential build‐up across the monolayer, monolayer rupture (hole formation), followed by hole closure. The oscillations were detected also by instabilities in the measurements of the differential capacity.
Rectifier Characteristics of BaSo4 Precipitation Membranes
Authors: Katzir‐Katchalsky A. , Hirsch‐Ayalon P. , Michaeli I. 
Published: November 2013

AbstractThe behavior of precipitate‐membranes of BaSO4 in cellophane is discussed in terms of the formation process of the system and the known permeability to Ba++, SO=4 and to water components. It is shown that the available information leads to an interpretation in terms of an electrical bipolar model. The specific case of Ba(OH)2 and H2SO4 solutions separated by the above membrane is discussed in detail. The rectification effect and the non‐zero stationary currents observed are discussed in terms of the flows of H+, OH− and the flow of the chemical reaction of water formation. The logarithmic term derived for the voltage current relationship is shown to be directly linked with the depolarizing effect of water formation, and thus quantitatively related to the kinetic constants of water formation and dissociation.
Inorganic Clays as Possible Prebiotic Peptide Templates
Authors: Paecht‐Horowitz Mella 
Published: November 2013

AbstractExperiments on copolymerizations of various pairs of amino acid adenylates in the presence of montmorillonite are described. Only amino acids small enough to be able to enter in between the layers of the clay are able to polymerize. Those amino acids which do so, copolymerize according to certain preferences.
Quantum Mechanical Consistent Force Field (QCFF/PI) Method: Calculations of Energies, Conformations and Vibronic Interactions of Ground and Excited States of Conjugated Molecules
Authors: Warshel A. 
Published: November 2013

AbstractThe extension of the Consistent Force Field approach to π electron systems is outlined. The quantum mechanical energy of π electrons is given as an analytical function of the molecular coordinates. It is shown that with this analytical description one can calculate efficiently equilibrium geometries and vibrational frequencies of ground and excited states of conjugated molecules. Application of the calculated geometry and vibrations to the analysis of vibronic structure is described. A preliminary account of the use of observed vibronic structure for determination of the geometry of excited electronic states is given.
Analysis of Conformations of Amino Acid Residues and Prediction of Backbone Topography in Proteins
Authors: Burgess A. W. , Ponnuswamy P. K. , Scheraga H. A. 
Published: November 2013

AbstractMethods for describing a discrete number of conformational states of amino acid residues in proteins are presented and used to investigate the topography of chain folding. The relative importance of short‐range, medium‐range and long‐range interactions is discussed in the light of an analysis of the conformational states for the different amino acid residues in eight proteins of known structure. A prediction algorithm, which assigns four states to each residue of a protein chain (α‐helix, extended structure, bend, or coil), has been developed from a consideration of both short‐ and medium‐range interactions and applied to thirteen proteins of known three‐dimensional structure. The prediction algorithm is simple to apply, and the assignment of α‐helix and extended structure is considerably better than in most other predictive schemes. The prediction of chain reversal or bend regions was also better than with previous algorithms, but these assignments were not as good as those for α‐helix and extended structure. The motivation for the development of this algorithm is not only to demonstrate the relative importance of short‐ and longer‐range interactions but, more important, to begin to develop procedures for obtaining an approximate starting conformation for subsequent energy minimization to predict the three‐dimensional structure of a protein. This procedure, as well as various other methods for the prediction of the backbone topography and conformational states of residues in proteins from the amino acid sequence, have been reviewed and evaluated by comparing the success of the methods to the success expected from a random assignment of conformational states.
Salicylates Attached to Polymers
Authors: Weiner Ben‐Zion , Havron Abraham , Zilkha Albert 
Published: November 2013

AbstractSeveral salicylate derivatives were attached to low molecular weight polyethylene oxides through an ether or carbonate linkage utilizing the respective halide or chlorocarbonate derivative of the polymers as reactive intermediates. Aspirin and 0‐salicoyl salicylic acid were attached to polyvinyl alcohol and cellulose acetate by ester linkage through melt esterification of the reactants. Preliminary pharmacological evaluation of some of the polymeric salicylates showed that they have a longer duration of antiinflammatory and analgesic activities as compared with aspirin.
Sulfonation of Polyamides
Authors: Vaya Jacob , Zilkha Albert 
Published: November 2013

AbstractThe sulfonation of polyamides (Nylons‐3,6,11 and 6,6) was investigated using fuming sulfuric acid and solutions of SO3 in CCl4. The sulfonated polymers were soluble in water and insoluble in ethanol. Acid hydrolysis of the polymers and quantitative determination of the amino acids in the hydrolysate showed the presence of α‐sulfo amino acids. This showed that sulfonation in the polymer occurred in the active α‐position of the amide group.
Asymmetric Reduction of Ketones with NaBH4 in the Presence of Lecithin
Authors: Doiuchi Tohru , Minoura Yuji 
Published: November 2013

AbstractThe heterogeneous reduction of various water‐insoluble ketones (i.e., alkyl phenyl ketones and alkyl methyl ketones) was carried out with an aqueous NaBH4 solution in the presence of lecithin. It was found that the rate of the reduction reaction from ketone to carbinol was enhanced by lecithin, which is known as an optically active and zwitterionic surface active substance. Furthermore, when the unsymmetric ketones were reduced in this system the carbinols obtained were found to be optically active, though their optical yields were low. From the above results, it was concluded that the reduction reaction proceeds mainly at the micelle–water interface.
Oxygen Exchange Reactions of Cationic Carbonyl Derivatives of Manganese and Rhenium with H218O and Related Processes
Authors: Darensbourg Donald J. 
Published: November 2013

AbstractReactions proposed to involve the intermediacy of metal species containing the hydroxycarbonyl group, [M—COOH], are reviewed. Particular attention is given to reversible reactions of Group VIIb metal carbonyl derivatives with isotopically labelled water, which presumably proceeds via a [M—COOH] intermediate, to afford oxygen labelled metal carbonyl derivatives. The current status of the scope and mechanistic details of this oxygen‐exchange reaction is summarized.
Magnetic Circular Dichroism Spectra of Compounds Containing Quadruple Metal–Metal Bonds. Polarized Single Crystal Absorption Spectra of (n‐Bu4N)2[Re2Br8] at 5 K
Authors: Cowman Charles D. , Trogler William C. , Gray Harry B. 
Published: November 2013

AbstractIt is found that only weak MCD B terms are associated with the 1A1s → 1A2u (δ → δ*) absorption in Re2X2‐8 (X = Cl, Br), Mo2Cl4‐8, and Mo2Cl4[P(C2H5)3]4. At 15K (KBr disk sample), the 585 nm absorption system of Mo2Cl4[P(C2H5)3]4 shows 320 cm−1 vibronic fine structure in a1g (MoMo). By analogy, this sytem is assigned to the spin‐allowed δ → δ* transition. The lowest energy strong MCD signals exhibited by Re2Cl2‐8, Re2Br2‐8, and Mo2Cl4‐8 are A terms at 310, 420, and 270 nm, respectively. These are associated with the 1A1g → 1Eu (X(π) → δ*) transitions. Relatively intense MCD signals at 275 and 380 nm for Re2Cl2‐8 and Re2Br2‐8 and corresponding features in the single crystal polarized absorption spectra are assigned in each case to two overlapping transitions, 1A1g → 1A2u (X(π) → δ*) and 1A1g → 1Eu (X(σ) → δ*). The 440 nm absorption systems of Mo2 (O2CH)4 and Mo2(O2CCF3)4 exhibit strong MCD B terms.
Iron‐Nitrosyl Bond Configuration in Nitrosyl‐Hemoproteins: A Comparative EPR Study of Hemoglobin A and Hemoglobin Kansas
Authors: Chevion M. , Salhany J. M. , Peisach J. , Castillo C. L. , Blumberg W. E. 
Published: November 2013

AbstractHemoglobin A and hemoglobin Kansas can exist in alternative forms in which the affinity of heme iron for NO is mediated either by pH or the presence of allosteric modifiers. In this study, we show that the superhyperfine (SHF) pattern observed in the EPR which arises from the heme iron‐NO complex can be correlated with a change in the affinity of the ligated tetrameric protein for NO. When a combination three‐line and nine‐line SHF pattern is observed, the nitrosyl hemoprotein is in a low affinity form while a nine‐line pattern alone is an expression of high affinity. A theory is presented relating SHF patterns to a molecular orbital picture of the nitrosyl heme complex. It is suggested that the change of SHF pattern correlated with an alteration of the affinity state of ligated hemoglobin is related to a structural change of the proximal imidazole ligand to the heme.
IV. Symmetry and its Implications
Authors: Kurki‐Suonio Kaarle 
Published: November 2013

AbstractSignificance of symmetry in representing real‐ and reciprocal‐space properties of a crystal and of its constituents is discussed in terms of symmetry eigenfunctions. The formation of the site‐symmetrized multipole expansion for the 32 crystal point symmetries is shown, and the mutual relations between the real‐ and reciprocal‐space expansions are discussed. The origin of the symmetry‐based phase relations, equivalences and extinction rules of structure amplitudes is pointed out. Distinction is made between the accurate and approximate ones arising from the true space‐group symmetry and from the approximate free‐particle symmetry of the constituents, respectively. Finally, the symmetry imposed by reality of charge density and its violation through anomalous dispersion are discussed in terms of symmetric and antisymmetric contributions of atomic charge densities.
The Influence of Weak Magnetic Fields on Radiationless Processes
Authors: Küttner H. G. , Selzle H. L. , Schlag E. W. 
Published: November 2013

AbstractMagnetic effects on the fluorescence from singlet excited states represent an interesting new method of studying the behaviour of excited states. Here the intersystem crossing in a weak magnetic field in both protonated and deuterated glyoxal was studied. Fluorescence quenching was observed at various pressures with different collision partners as a function of the magnetic field. Time resolved emission and excitation spectra were observed and quenching rate constants were determined with and without magnetic field. The collision free fluorescence lifetime of glyoxal was found to be unaffected by the magnetic field. The magnetic fluorescence quenching effect is only observed in the presence of colliders and is seen as an enhancement of intersystem crossing. In protonated glyoxal all phosphorescence is collision dependent, whereas in the deuterated species there exists zero pressure phosphorescence. The magnetic effect is here interpreted as being due to the interaction of the singlet with the triplet state, which is magnetically sensitive. In particular additional intersystem crossing mechanisms are postulated to be operative in the presence of a magnetic field. A grouptheoretical method predicts which new frequencies must be involved in this new process, and this activity is experimentally confirmed in the emission spectrum.
Some Recent Approaches to the Study of Heterogeneous Redox Kinetics of Metal Complexes. Comparisons with Homogeneous Redox Processes
Authors: Weaver Michael J. 
Published: November 2013

AbstractSome experimental and conceptual aspects of the electrode kinetics of metal complexes are reviewed, with emphasis on the comparison between heterogeneous and homogeneous redox behavior, using cobalt(III)/(II) and chromium(III)/(II) couples as illustrative examples. Experimental methods for determining the position of the heterogeneous reaction sites and for distinguishing between outer‐sphere and ligand‐bridged electrode reactions are examined, along with the interpretation of electrochemical activation parameters for outer‐sphere pathways. The possible roles of bridging ligands in catalyzing electrode reactions are discussed in terms of “intrinsic” and “thermodynamic” contributions to the observed rate constants.
On the Mutual Bonding of Particles of Quantum Systems
Authors: Golden Sidney 
Published: November 2013

AbstractConceptual, logical and dynamical restrictions on the criteria characterizing the mutual bonding of particles are examined. In accord with these restrictions, observables consisting of fixed linear combinations of the particles' position and conjugate momentum are used to construct appropriate “boundedness” criteria. As a result, comparable localization of relative position and relative momentum are obtained for mutually bound particles; neither excessively compact nor excessively diffuse localization can result for bonding to occur.
A Theoretical Aspect of the Formation and Breaking of Chemical Bonds in Reactions
Authors: Fujimoto Hiroshi , Fukui Kenichi 
Published: November 2013

AbstractA partitioning analysis of the electron reorganization in chemical reactions is presented. The mechanisms of the formation and breaking of chemical bonds, the rehybridization of the reaction sites and shift of electronic charges have been discussed in terms of the exchange, delocalization and polarization interactions. The specific roles of these interactions in causing the rearrangements of the constituent nuclei of the composite reacting system along a reaction pathway have been elucidated. The effective collaboration between the delocalization interaction and the polarization interaction has been suggested to be of key importance in promoting the progress of chemical reactions.
The Conformations of Cyclononane Dynamic Nuclear Magnetic Resonance and Force‐Field Calculations
Authors: Anet Frank A. L. , Krane Jostein 
Published: November 2013

AbstractIterative force‐field calculations for cyclononane are reported for four conformations and five transition states for conformational interconversions. The strain energies (in kcal/mol) relative to the [333] conformation are as follows: energy minima, [333], 0; [144], 1.2; [225], 1.7; [234], 3.2; conformational transition states, [1323], 4.4; [1224], 6.0; [1233], 7.0; [18], 8.3; [1134], 9.9. The 13C NMR spectrum of cyclononane shows two dynamic NMR effects at low temperatures and reveals the presence of three different conformations. At – 173.°C, the major conformation (≃ 95%) is [333] and the minor conformation (≃ 5%) is [225]. The third conformation, [144], is present in a very small amount (≃ 1% at – 95°C) and is only barely detectable by its broadening effect near – 95°C. The [225] has an entropy which is 3.5 eu greater than that of the [333], mainly because of the high symmetry of the latter conformation. As a result of the entropy difference, ΔG0 for the [333] to [225] equilibrium is quite temperature dependent and the equilibrium constant is very strongly temperature dependent. It is estimated that at room temperature there are roughly 40% of the [333], 50% of the [225], and 10% of the [144] in cyclononane.
Additions of Chlorosulfonyl Isocyanate to 6‐Substituted Benzonorbornadienes
Authors: Mazzocchi Paul H. , Harrison Aline M. 
Published: November 2013

AbstractThe addition of chlorosulfonyl isocyanate (CSI) to 6‐substituted benzonorbornadienes gives pairs of isomeric syn and anti β‐lactam products. Previously published molecular orbital calculations indicate that the benzonorbornadiene π‐bond is not polarized. Relative rate data are inconsistent with either a concerted addition process or a process which proceeds by the direct formation of a carbenium ion intermediate. A mechanism proceeding through the initial formation of a benzonorbornadiene‐CSI π‐complex which decays to a carbenium ion in a product determining step is suggested.
Energy Transfer at 1.5 K in Some Photosynthetic Bacteria Monitored by Microwave‐Induced Fluorescence (MIF) Spectra
Authors: Hoff A. J. , De Vries H. Gorter 
Published: November 2013

AbstractWith an optically detected magnetic resonance technique, Microwave Induced Fluorescence difference (MIF) spectra have been recorded at 1.5 K for a number of photosynthetic bacteria under reducing conditions. It is found that the MIF spectra coincide with the longest wavelength fluorescence band. A relation for energy transfer at very low temperature is derived, leading to a (r0R)−3 dependence of the rate of energy transfer on the distance r0 of closest approach of donor and acceptor pigment and the diameter 2R of the antenna complex. It is tentatively concluded that the photochemical trap in the photosynthetic reaction center has a distribution of 0‐0 transitions similar to that of the antenna pigments.
Homogeneous Catalysis of the Photoreduction of Water by Visible Light. 3. Mediation by Polypyridine Complexes of Ruthenium(II) and Cobalt(II)
Authors: Krishnan C. V. , Creutz Carol , Mahajan Devinder , Schwarz Harold A. , Sutin Norman 
Published: November 2013

AbstractIrradiation of polypyridineruthenium(II) complexes (RuL2+3) in aqueous solutions containing ascorbate (HAs−) and Lî (2,2′‐bipyridine or other polypyridines) with visible light yields reduced polypyridine LîH2 and H2. The quantum yield of H2 is increased greatly when cobalt(II) is also present and is optimal, Φ = 0.13, with L = bpy, Lî = 4,4′‐(CH3)2bpy (2 × 10−3 M), [Co(II)] = 0.01 M, [HAs−] = 0.7 M at pH 4.5–5.5. The quantum yield of LîH2 is ≧ 0.01 when Lî = bpy at ≧ 10−3 M, [HAs−] = 0.7 M at pH ∼ 5 but diminishes greatly at pH ≧ 6 or when cobalt(II) is present. The photochemical experiments and pulse‐radiolysis studies indicate that the quantum yields reflect the relative rates of some twenty elementary reactions. The rate constant for the first, quenching of *RuL2+3 by HAs− to give RuL+3 and ascorbate radical, spans the range 0.2 × 107 M−1 s−1 (L = 4,4‐(CH3)2bpy) to 1.1 × 109 M−1 s−1 (L = 5‐(Cl)phen). In the absence of Co(II), RuL+3 reduces LîH+ and formation of LîH2 (in competition with oxidation of LîH by ascorbate radical) ensues. When Co(II) is present, Co(Lî)2+n complexes are reduced by RuL+3 to cobalt(I) complexes Co(Lî)+n. These may react with H+ to form cobalt hydride complexes which undergo further reaction with H2O, H+ or Co(Lî)2H2+ to produce H2. At high pH, however, these reactions are too slow to compete with oxidation of cobalt(I) (k ∼ 1010 M−1 s−1) and the hydride complexes by ascorbate radical. By contrast, at pH < 4 the H2 yield drops because of oxidation of Co1(Lî)+n (or its hydride) by LîH+.
Dehydration Energy of the Exchangeable Cations in Montmorillonite — a DTA Study
Authors: Poinsignon C. , Yvon J. , Mercier R. 
Published: November 2013

AbstractHomoionic montmorillonites, with exchangeable alkaline and alkaline earth cations, have been studied by means of DTA. The activation energy of dehydration of cations was deduced by applying kinetic considerations to thermograms, obtained experimentally. The results are in good agreement with the literature.
The Effects of Thermal Treatment on Associations between Fatty Acids and Montmorillonite
Authors: Yariv S. , Shoval S. 
Published: November 2013

AbstractThe sorption from CCl4 solutions of acetic, lauric and stearic acids by montmorillonites saturated with H, Li, Na, K, Cs, Ca, Mg, Cu, Al and Fe, was studied by IR and X‐ray methods combined with various thermal treatments. Two distinct species were detected in the clay phase, the carboxylic acid (RCOOH) and the carboxylate anion (RCOO−). The ratios of the two sorbed species were found to be dependent both on the nature of the exchangeable cation and on the chain length of the acid. In Al−, Fe− and Cu—montmorillonites, the ionic species predominates whereas in Cs—montmorillonite the acidic species predominates. Stearic acid shows the highest tendency to dissociate. The following associations were identified as occurring in the interlayer space: (I) and (II) — linkages between COOH group and oxygen sheet of silicate layer or with hydrophobic structured water; (III) — linkage between a COOH group and an exchangeable cation through a “water bridge”; (IV) — direct linkage between a COOH group and an exchangeable cation; (V) — linkage between a COO− group and an exchangeable cation through a “water bridge” and (VI) — direct linkage between a COO− group and an exchangeable cation. Although several types of associations are associated with every homoionic montmorillonite, some are more predominant. Thus, with Cs, association (I) predominates. With Li, Ca and Mg, association (III) predominates and is transformed to (IV) after thermal dehydration; whereas with Na and K association (IV) appears in freshly prepared sample. Al, Fe and Cu—montmorillonites mainly produce association (V). This structure is transformed into (VI) in the case of Al—montmorillonite by stearic and lauric acids, only. In the case of Cu—montmorillonite, all the three acids are transformed into (VI), but at 200°C decarboxylation of lauric and stearic acids occur.
Scattering of Low Energy Atoms by Surfaces: The Helium—Copper Systems
Authors: Armand G. , Lapujoulade J. , Manson J. R. , Perreau J. , Salanon B. 
Published: November 2013

AbstractA number of experimental results for the diffraction of low energy helium by closely packed and stepped copper surfaces is presented. Observation of selective adsorption resonances shows that the surface average of the interaction potential is the same for all crystal faces. The thermal attenuation of the scattered intensities is given by a modified Debye—Waller factor. These results are interpreted in terms of interaction potentials with a soft exponential repulsion and an attractive well using an exact method based on Neumann iteration of the transition matrix equation. Good agreement with experiment is obtained in several systems over a large range of scattering energies.