bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Photochemistry of Solutions of Eu(III) and Eu(II)
Authors: Haas Yehuda , Stein Gabriel , Tenne Reshef 
Published: November 2013

AbstractIrradiation in the CT band of Eu3+ in aqueous solution, in the presence of scavengers for H atoms, gives rise to formation of Eu2+ and evolution of molecular hydrogen. The kinetics of these processes were studied as functions of the concentrations of Eu3+ and scavenger, of pH, and of light intensity. The results are interpreted by means of a complex scheme in which an excited Eu2+ donates an electron to a proton, the resulting H* initiating a series of dark reactions which lead to evolution of H2 and oxidation of the scavenger.
The Crystal and Molecular Structures of Overcrowded Halogenated Compounds VII. 1:10‐Dichloro‐3:8‐Dimethyl4:7‐Phenanthroline
Authors: Herbstein F. H. , Kapon M. , Rabinovich D. 
Published: November 2013

Abstract1,10‐dichloro‐3,8‐dimethyl‐4,7‐phenanthroline crystallizes in the triclinic system with a = 7.651(3), b = 7.792(3), c = 12.301(3)Å, α = 108.48(6), β = 82.74(2), γ = 116.53(4)° space group magnified image, Dm = 1.479 g cm−3, Dc = 1.480(5) g cm−3 for two formula units per cell. The intensities of about 2000 reflections were measured by semi‐automatic Weissenberg diffractometer and supplemented by precession diffractometer measurements. The crystal structure was solved by the SEARCH method (Rabinovich and Schmidt, Nature, 211: 1391 (1968)) and refined by full‐matrix least squares methods, using anisotropic temperature factors for non‐hydrogen atoms. The final R‐factor was 0.067 and the “goodness of fit” 0.94. The molecule has an approximate two‐fold axis of symmetry and is appreciably distorted from planarity, the two chlorines being displaced by +1.12Å and −1.15Å from the mean molecular plane; the non‐bonded ClCl distance is 3.082(3)Å. Bond lengths are close to standard values but there are appreciable distortions in bond angles, torsion angles and fold angles. There is hexagonal close packing of stacks of molecules, with van der Waals binding between stacks. Anti‐parallelism of adjacent molecules in a stack suggests that dipole‐dipole forces are important in the intrastack binding. Comparison of the present molecular structure with that of 2,7‐dibromo‐4,5‐bis‐(2‐pyridyl)phenanthrene‐3,6‐diol (Smith and Barrett, Acta Crystallogr., B27: 419 (1971)) shows that the present molecule is the more highly overcrowded.
The Softness Parameters of Ions. Prediction of the Occurrence of Miscibility Gaps in Molten Salt Mixtures
Authors: Marcus Y. 
Published: November 2013

AbstractSoftness parameters σM for cations and σX for anions, have been calculated as dimensionless quantities for approx. 90 cations and 18 anions. They are given by σM = [σA (Mm+) ‐ σA(H+)]/σA(H+) and σX = [σB(Xa−) ‐ σB(OH−)]/σA(H+) where σA = [σIi(M) + ΔH0h(Mm+)]/m and σB = [‐Ea(X) + ΔH0h(Xa−)]/a are Ahrland's parameters. The new normalized and comparative (to the test ions H+ and OH−) softness parameters are positive for soft ions and negative for hard ones. These parameters, obtained independently, are used with a four‐coefficient equation to calculate coordinate bond energies for metal halides with acceptable accuracy. Considerations of the average coordination in reciprocal molten salt mixture lead to an expression for the metathesis energy change as proportional to the product of the differences in softness parameters of the two cations and the two anions. An empirical one‐coefficient equation involving the softness parameters is proposed to deal with next‐nearest‐neighbor interactions in binary common‐ion molten salt mixtures. These relationships are then used with Blander and Topol's equation to predict the occurrence of irascibility gaps in uni‐univalent reciprocal salt mixtures. The gaps found in other systems are also discussed in terms of the softness of the constituent ions.
Palladium (II) Complexes of Acetylacetone Dioxime
Authors: Ben‐Bassat A. H. I. , Kaszirer F. 
Published: November 2013

AbstractThe formation of a sequence of insoluble Pd(II) compounds was demonstrated by heterometric titration. The species Pd4 AADO (AADO = acetylacetone dioxime), Pd2 AADO and PdAADO were detected and a further compound, Pd(AADO)2 was synthesized. The elemental analysis of Pd2 AADO and Pd(AADOH), is reported. The visible spectrum of Pd/AADO mixtures in solution (at pH = 11) is reported and assigned. IR spectra of Pd2 AADO, Pd(AADO)2 and AADO are recorded and compared, and the structure of the compounds is deduced.
The Water Pressure in the Electrical Double Layer
Authors: Ravina Israela , Zaslavsky Dan 
Published: November 2013

AbstractA review of the use of the classical Boltzmann distribution equation in the Gouy theory indicates that it is only a special case, neglecting important parameters. It is indicated that the present double layer theory needs to be revised to include also the effect of the electrical field on the water as a dielectric. The pressure in the electrical double layer of montmorillonite clay‐water systems is, thus, evaluated. It is shown that the water pressure in the double layer may reach hundreds of atmospheres.
Conformational Studies on Xanthene, Thioxanthene and Acridan
Authors: Aizenshtat Z. , Klein E. , Weiler‐Feilchenfeld H. , Bergmann E. D. 
Published: November 2013

AbstractA study of the dipole moments of xanthone, thioxanthone and their halogeno‐derivatives leads to the conclusion that these molecules are not planar. In the xanthene and thioxanthene series, the dipole moments as well as the NMR spectra can be explained by a planar or a non‐planar but rapidly inverting model. In the acridan series, the NMR spectra of N‐acylacridans show that the molecule is non‐planar and inverts. The barrier is 11.7, 13.1 and 13.1 Kcal/mole for the N‐acetyl‐, N‐chloroacetyl‐ and N‐iodoacetyl derivatives, respectively. Equally, it has been observed that at low temperature the rotation around the XCH2 CO bond in the halogenoacetylacridans is hindered.
Photocyclisation and Photocyclodehydrogenation of Stilbene and Related Compounds
Authors: Bromberg A. , Muszkat K. A. , Fischer E. 
Published: November 2013

AbstractThe reversible photocyclisation of cis‐stilbene analogues to the corresponding dihydrophenanthrenes is not slowed down at high viscosities of the medium. Its attenuation at low temperatures is a true temperature effect. Methylation affects the photocylisation significantly only if it results in strong steric interactions in the cyclisation product. Photocyclodehydrogenation of stilbenes with oxygen to the corresponding phenanthrene analogues passes through the 4a, 4b‐dihydrophenanthrenes, and can be sensitized by various compounds at low concentrations. Photo‐oxidation with iodine probably involves dehydrogenation of ground‐state dihydrophenanthrene with atomic iodine. Electronically excited dihydrophenanthrenes may also be involved in the photo‐oxidation.
Some 9‐Amino‐Acridine Derivatives Containing Silicon
Authors: Osman R. , Gertner D. , Shenhar A. , Zilkha A. 
Published: November 2013

Abstractp‐Tri‐methylsilylphenethylamine and 1‐p‐trimethylsilyphenyl‐1‐amino‐4‐dimethylamino‐butane were reacted with 9‐chloroacridines to give the corresponding N‐substituted 9‐amino acridines, which inhibited the growth of several bacteria but not yeasts.
A Theoretical Study of the Protonation of Purine
Authors: Neiman Z. 
Published: November 2013

AbstractEnergy profiles and molecular binding number (MBN) were calculated for purine and its mono‐protonated forms by the CNDO/2 algorithm. Total energy indicates that the 3,7‐species is the most stable among the protonated isomers, being insignificantly more stable than the 1,7‐analogue. Electronic energy suggests that proton may preferentially be attached to position 3. Charge densities are presented by both Mulliken's population method and CNDO/2.
Metalation Reactions XIII. Effect of the Metalating Agent on the Metalation of Acetylenes
Authors: Becker J. Y. , Brenner S. , Klein J. 
Published: November 2013

AbstractMethyl‐lithium gave with 1‐phenyl‐1‐propyne and 1‐phenyl‐1‐butyne preferentially the products of monometalation although dimetalation of these compounds is faster than monometalation when butyl‐lithium is used. The product of protonation of dilithiophenylbutyne depends on the condition of the reaction. In the presence of starting material, 4‐phenylbut‐2‐yne and in its absence, 1‐phenylbuta‐1,2‐diene is obtained. Alkylation, silylation and protonation of the lithium derivatives was studied.
Chemical Ecology Evidence for Phosphate as the Only Factor Limiting Algal Growth in Lake Kinneret
Authors: Halmann M. 
Published: November 2013

AbstractExperiments on the growth of the natural populations of algae and of other microorganisms as a function of the supply of various nutrients was carried out for Lake Kinneret water sampled at about 2 week intervals during January‐June 1972. The addition of orthophosphate caused a rapid rise in biomass, which, after several days, increased to 2‐5 times that in untreated water, as measured by the increase in turbidity and protein content. On the other hand, the addition of sodium or potassium nitrate, ammonium chloride, ferrous ethylenediamine sulfate, sodium silicate or vitamin B12 had no noticeable effect. The plot of biomass produced versus the concentration of added phosphate is a steeply rising function in the range of 0.1 to 1.0 μ molar orthophosphate, which levels off at higher phosphate concentrations, reaching saturation above about 2 μ molar phosphate. Thus, in the range of its natural concentration in Lake Kinneret, 0.09‐0.5 μ molar, orthophosphate is the limiting factor. Above 2 μ molar phosphate, nitrate becomes the limiting factor, as was shown by experiments in which both phosphate (>2 μ molar) and nitrate were added, resulting in extremely abundant algal growth. A model of the reduction of nutrient input was achieved by laboratory experiments, in which the lake water was diluted with distilled water (by 1/4), thus resulting in an approximately proportional (to about 1/4) decrease in biomass. The effect of restoring the natural concentration of either nitrate or orthophosphate was then measured. Added nitrate had no effect, while added phosphate caused a rapid increase in biomass, which after 2‐4 weeks came close to that in the natural lake water. These results indicate that during the spring of 1972, phosphorus has been the only element limiting algal growth in the lake.
Polydepsipeptides I. Synthesis and Characterization of Copolymers of α‐Amino and α‐Hydroxy Acids
Authors: Goodman Murray , Gilon Chaim , Kirshenbaum Gerald S. , Knobler Yehuda 
Published: November 2013

AbstractCopolymers of the type magnified image were synthesized and characterized. The syntheses of these copolymers were achieved by copolymerization of an α‐amino acid N‐carboxy anhydride and an α‐hydroxy acid anhydrosulfite in the presence of a catalyst. The copolymers were characterized by spectroscopic methods including infrared, circular dichroism and nuclear magnetic resonance. Specific cleavage of the ester bonds by hydroxylamine in the cold confirmed the A‐B block structure where the A represents the poly(amino acid) segment and the B indicates the polyester segment. Measurements by nmr and viscosity indicate that the blocks consist of short chain lengths.
Evaluation of Spectroscopic Parameters for Cobalt (II) Species Sorbed on Ion Exchangers
Authors: Ben‐Zwi N. , Heitner‐Wirguin C. 
Published: November 2013

AbstractNew spectral data for cobalt (II)‐ligand‐solvent systems is reported and spectroscopic parameters are evaluated for various tetrahedral and octahedral species sorted on ion exchangers.
Complexes of Bromine with Macrocyclic Polyethers
Authors: Shchori E. , Jagur‐Grodzinski J. 
Published: November 2013

AbstractCrystalline complexes of bromine with aromatic macrocyclic polyethers were isolated and the equilibrium constants of complexation of bromine with the aliphatic macrocyclic polyether dicyclohexyl‐18‐ crown −6 and with THF in CCl4‐ethyl bromide solutions were determined by PMR spectroscopy.
Aliphatic, Isoprenoid and Aromatic Acids from an Israeli Shale
Authors: Ikan R. , Bortinger A. 
Published: November 2013

AbstractNormal fatty acids (C9‐C19); isoprenoid acid (C10); aromatic acids (C11‐C13) of the general formula CnH2 n‐8 O2, and two aromatic acids (C11, C12) of the formula CnH2 n‐14 O2, were identified in a bitumen obtained from shale of Nebi Musa (near Jericho), using chromatographic (GLC) and spectroscopic (MS) methods.
Consecutive Radical Reactions and the Role of the Protein in the Pulse Radiolysis Of Enzymes
Authors: Lichtin N. N. 
Published: November 2013

AbstractThe reactions of H atoms, OH radicals and hydrated electrons acting as isolated reagents upon ribonuclease in dilute aqueous solution were studied by the technique of pulse radiolysis‐kinetic spectroscopy. The experiments show that initial action of these reagents upon the protein molecule is followed by intramolecular transformations. Two consecutive intramolecular steps have been observed in the reaction of H atoms, with specific rates of approximately 103 sec−1 and 1 sec−1. Some spectral features can be assigned to specific radical sites. For instance, electron adduct to disulfide is formed by the primary action of H atoms at pH 6.6, by the primary action of hydrated electrons at pH 7.6 and by intramolecular reaction of primary product formed by action of OH at pH 7.
Decay of the HO2 and O−2 Radicals Catalyzed by Superoxide Dismutase. A Pulse Radiolytic Investigation
Authors: Rabani Joseph , Klug Dina , Fridovich Irwin 
Published: November 2013

AbstractThe pulse radiolysis technique has been employed in the investigation of the dismutation of superoxide radicals, O−2 and HO2, in the presence of superoxide dismutase in aqueous solutions. The decay of superoxide radicals in the presence of the enzyme was found to be first order in both enzyme and superoxide concentrations. An apparent second order reaction rate constant was found to be about 2 × 109 M−1 sec−1, decreasing slightly as the pH is increased from 5 to 9.5. A mechanism which accounts for all our observations is proposed. It includes two steps: (1) formation of a product (EO−2 or E−) from one enzyme (E) molecule and one O−2 radical ion; (2) regeneration of E by a reaction of this product with an additional O−2 ion radical. The reaction rate constants k = (1.4 ± 0.2) × 109 and k = (1.9 ± 0.6) × 109 M−1 sec−1 were measured at pH = 7 in an oxygenated 0.16 M sodium formate solution.
Radiation Chemistry of Ethylene Glycol, Meso‐Erythritol, 2‐Deoxy‐D‐Ribose and Alkyl Phosphates as DNA Model Compounds
Authors: Schulte‐Frohlinde D. , Von Sonntag C. 
Published: November 2013

AbstractThe γ‐radiolysis of ethylene glycol, meso‐erythritol, 2‐deoxy‐ribose, and alkyl phosphates has been studied in diluted (10−2 M), N2 O‐saturated, deoxygenated aqueous solutions. Products and their G values have been determined. Reaction schemes were derived from complete material balances. In the polyols the primary attack of the radiolytically formed OH radicals and H atoms leads to α, β‐dihydroxyalkyl radicals (A) which eliminate water to give substituted α‐carbonyl‐methyl radicals: (B)magnified imageDisproportionation reactions of the radicals A and B yield products having the structural units COCHOH and COCH2 —. In ethylene glycol a chain reaction is induced, radical B abstracts a hydrogen from ethylene glycol to give acetaldehyde and radical A. In 2‐deoxy‐ribose the major attack is at C‐1. Products from this radical are 2‐deoxy‐ribonic acid and 2,5‐dideoxy‐ribonic acid. In the formation of the latter a rearrangement is involved. With trimethyl phosphate, the reaction of the solvated electron is only small (2 × 10s 1/mole sec), as shown by pulse radiolysis. Dimethyl and methyl phosphates do not react with the solvated electron to a measurable extent. The attack of the OH radical apparently leads to a cleavage of the alkyl phosphate linkage.
Radiation‐Induced Hydrogen Transfer in Nucleic Acids and Proteins in the Solid State
Authors: Riesz Peter , Smitherman Thomas C. 
Published: November 2013

AbstractA radiation‐induced transfer of hydrogen from exchangeable to carbon‐bound sites occurs in nucleic acids, proteins and their constituents. The G‐values for this process are similar within a factor of 2–3 to the G‐values for the initial production of stable radicals measured by ESR at room temperature. Unlike the production of radicals, hydrogen transfer in ribonuclease, DNA, and thymine is a linear function of dose in the 0–30 Megarad region. The tritium distributions obtained in proteins by hydrogen transfer are not a measure of the distribution of the “secondary” radicals. From the studies of the effect of temperature, of various scavengers (particularly nitric oxide) and of the dose dependence in the low dose region, it was inferred that for ribonuclease most of the hydrogen transfer takes place during the conversion of the radicals stable at 195°K to the radicals stable at room temperature. The same mechanism also appears to predominate in DNA.
Radiation‐Induced Strand Scissions in Bacterial DNA and their Enzymatic Repair
Authors: Kaplan Henry S. 
Published: November 2013

AbstractAbundant evidence indicates that lesions induced in DNA, unless they are repaired, may lead to death of cells exposed to ionizing radiations. Although sugar and base damage undoubtedly occur, the lesions which have been most readily quantifiable by biophysical methods and which, if unrepaired, correlate most closely with lethality are single‐strand and especially double‐strand chain breaks. Evidence is presented for the existence of several different systems for the repair of single‐strand breaks, and some of the relevant enzymes are tentatively identified. Chemical inhibitors of these repair processes have been demonstrated. Since these inhibitors act after irradiation and since the consequence of their action is to enhance lethality, they comprise a new class of radiosensitizers.
Variations in the Composition of Bromine Water During Oxidation Reactions
Authors: Ziderman I. 
Published: November 2013

AbstractA cubic equation has been derived that permits calculation of the composition of aqueous bromine solutions in terms of HOBr, BrO−, Br2, Br−3 and Br− as a continuous function of the pH, the initial oxidant concentration and the mole fraction of oxidant consumed. The calculations were performed by computer for the pH range 0–14 at bromine concentrations (c0) of 10−1 to 10−7 M. Throughout the course of an oxidation at pH 0 and c0= 10−4, bromine water is pure Br2. No Br−3 exists at c0 < 10−3. In the pH range 4–6, dilute bromine solutions are pure HOBr (+ equimolar Br−). For pH > 10, bromine water is pure BrO−, while at pH < 7, no BrO− is present. These conditions are unchanged during oxidant consumption.
Photoionization of Ferrocyanide at Various Wavelengths in Polar Glasses at 77°K
Authors: Moan Johan , Shirom Miriam , Weiss Matitia 
Published: November 2013

AbstractSolutions of potassium ferrocyanide in 10 N NaOH glass and in ethylene‐glycol/water (3/1) glass at 77°K were irradiated with UV‐light. The ratio of the yields of radicals in the two solvents, as well as the scavenging efficiency of an election scavenger (acrylamide) in 10 N NaOH, were found to change with the irradiation wavelength. From the experiments the conclusion is drawn that the ejection of electrons may occur from different electronic levels depending on the excitation wavelength and that the electrons ejected from a charge‐transfer‐to‐solvent state have higher reactivity with a scavenger than electrons ejected from intramolecular singlet states.
The Role of Cations in Some Inorganic Hydrolysis Reactions
Authors: Perlmutter‐Hayman B. , Wieder H. , Wolff Michael A. 
Published: November 2013

AbstractCations which shift certain equilibria from left to right by forming a compound with one of the reaction products were investigated with respect to their kinetic role in the process. Silver ions have no influence on the rate of the hydrolysis of cyanogen iodide. Similarly, cations which form sparingly soluble carbonates do not influence the rate of hydration of carbon dioxide. On the other hand, the hydrolysis of chlorine is accelerated by Ag+ and, to a lesser extent, by Cd2+ and Fe(III). It is shown that the effect is not due simply to a bimolecular reaction between chlorine and the cation. In the case of Ag+, heterogeneous catalysis may play some role, in analogy with the solvolysis of organic halides. In the case of Cd2+, there is spectrophotometric evidence for compounds between Cl2 and HOCl on the one hand, and the cation on the other. It is suggested that these compounds interconvert more rapidly than do the parent substances. A similar mechanism may be operative in the case of Fe(III), and, possibly, also in the case of Ag+.
The Reaction of α,β‐Unsaturated Ethyl Esters with Vinylmagnesium Chloride
Authors: Watanabe Shoji , Suga Kyoichi , Fujita Tsutomu 
Published: November 2013

AbstractWhile the reaction of linear α,β‐unsaturated ethyl esters with vinylmagnesium chloride yields vinyl ketones as the main product, the reaction of substituted α,β‐unsaturated ethyl esters yields triethylenic carbinols.
Computer Simulation of Cooperative Systems
Authors: Alexandrowicz Z. 
Published: November 2013

AbstractComputer simulation of cooperative, many particle systems (eg. real gas, Ising lattice) encounters a difficulty inherent to the ensemble theory. Under given conditions, the typical configurations constitute a vanishingly small fraction of all possible particle arrangements. Moreover, near to certain phase transitions, the typical configurations abruptly acquire pronounced long range order. Hence a computer method (like Metropolis Monte‐Carlo), which is not explicitly oriented towards discovery of such extremely rare arrangements, will almost certainly become inadequate. An attempt is made to formulate quantitatively these elementary observations, with the view of deriving a unified search for methods, that will enable to simulate the emergence of long range order in random systems.
Energy Parameters in Polypeptides. VI. Conformational Energy Analysis of the N‐Acetyl N′‐Methyl Amides of the Twenty Naturally Occurring Amino Acids
Authors: Lewis Peter N. , Momany Frank A. , Scheraga Harold A. 
Published: November 2013

AbstractThe conformational space accessible to the N‐acetyl N′‐methyl amides of the 20 naturally occurring amino acids has been explored extensively with the aid of empirical energy functions, and many minima have been located. The statistical weights for all minima with energy ≤ 3 kcal above the lowest for each residue have been calculated. In numerous cases, the conformation of lowest energy does not possess the highest statistical weight, thereby emphasizing the importance of considering the conformational librations when comparing theoretical and experimental results. The calculated minimum‐energy conformations, as well as those of highest statistical weight, are for the most part in good agreement with experimental results from studies of these compounds in solution and in the crystalline state.