bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistical Thermodynamics of Ionic Systems
Authors: Litan Adiel 
Published: November 2013

AbstractA statistical thermodynamical method is presented for calculation of thermodynamic properties of ionic systems. The method has a straightforward formalism for taking into account a variety of physical factors, e.g., making allowance for different finite volumes of different ionic species, treatment of neutral species as thermodynamic components (rather than merely regarding them as a dielectric medium), consideration of dependences of the dielectric constant on solvent composition (in the case of a mixed solvent) and on electric field strength, nonionic interactions, etc. The method is based on an approach of J. L. Jackson [1] whereby a fluctuation state of the system is characterized in terms of a set of functions for the spatial variations of concentrations of the various species. For such a state an appropriate Boltzmann factor is defined and a calculation of a thermodynamic property of the system requires integrations of this factor over function spaces. Two simple applications of the method are worked out by way of illustration and other, more refined, applications are pointed out.
Some Comments Relating to the Physical Chemistry of Polyelectrolytes
Authors: Morawetz Herbert 
Published: November 2013

AbstractThe possible dependence of the “unperturbed dimensions” of ionizable polymer chains on the charge density along the macromolecular chain is discussed in the light of theoretical studies and of experimental evidence. Some experiments on the behavior of dicarboxylic acids are suggested which would provide information useful in the interpretation of the behavior of polycarboxylic acids. A kinetic study of intramolecular reactions of polyions carrying small numbers of randomly spaced reactive and catalytic groups is proposed as a means to characterize chain flexibility. Finally, the advantages are pointed out which result from supplementing data on the ionization equilibrium of polymeric acids with calorimetric data.
Excluded Volume Study of Potassium Polystyrenesulfonate‐Potassium Chloride Solutions
Authors: Raziel Adrian , Eisenberg Henryk 
Published: November 2013

AbstractIntrinsic viscosities [η], sedimentation coefficients s, radii of gyration Rg and second virial coefficients A2, refractive index increments and apparent specific volumes were determined in aqueous solution in theta solvents and over a wide range of concentrations ms of a supporting electrolyte KCl, for five samples of potassium polystyrene sulfonate prepared by sulfonation of narrow molecular weight distribution polystyrenes. Coil expansion coefficients α as well as the Flory coefficient Φ relating [η] to coil dimensions were evaluated. Following a theory of Alexandrowicz, α2 was found to be a linear function of M1/4 m−1/3S; Φ appears to decrease with increase in α. The low values of Φ, characteristic for polyelectrolyte solutions, are consistent with the value determined for the Mandelkern‐Flory parameter β = Φ1/3 P−1.
The Effect of Water Activity on the Dissociation of Weak Ion Exchangers
Authors: Michaeli I. , Kinrot A. 
Published: November 2013

AbstractThe effect of salt on the pH titration curves of weak acid or weak base ion exchangers is discussed, and conditions are formulated for the representation of such titration data by a single master curve. Inspection of experimental data both from the literature and from new measurements reported in this paper shows appreciable deviations from single master curves. These deviations are discussed in terms of the effect of salt on the activity of water. Thermodynamic considerations show that such deviations provide quantitative information on the number of water molecules taken up by the resin following the ionization of the weakly aeidic or basic groups involved. Relatively large changes in hydration are found in some systems; these are especially pronounced in systems undergoing conformational transitions.
Characterization of Charged Membranes During Hyperfiltration: The Transport Numbers
Authors: Kedem O. 
Published: November 2013

AbstractA procedure for the measurement of ionic transport numbers, with the aid of current‐carrying electrodes that are introduced into a hyperfiltration cell is suggested. This procedure is suitable for adsorbed polymer layers and dynamic membranes. For membranes adequately described by the fixed charge model, allowing for ion‐association, a simple relation between transport numbers and salt rejection is derived. This leads to a test for the mechanism of salt rejection.
Phosvitin, A Phosphoglycoprotein
Authors: Perlmann Gertrude E. 
Published: November 2013

AbstractStudies of viscosity, optical rotatory dispersion and circular dichroism on the phosphoglycoprotein phosvitin indicate that this protein resembles a polyelectrolyte. At alkaline pH phosvitin has an unordered conformation, whereas at pH 3.0 to 3.6 some β‐structure is present. When at pH 3.6 an organic solvent is added to a phosvitin solution the protein undergoes a transition from the random conformation to β‐structure. Similarly, if phosvitin interacts with the polybases poly‐L‐lysine and protamine the complexes form a β‐pleated sheet structure.
Fluorescence and Optical Activity of Acridine Dyes Bound to Poly‐A and DNA
Authors: Gafni A. , Schlessinger J. , Steinberg I. Z. 
Published: November 2013

AbstractComplexes of acridine orange (AO) and 9‐aminoacridine (9‐AA) with poly‐A and DNA were studied by absorption and fluorescence spectroscopy, circular dichroism and circular polarization of fluorescence. The nucleotide:dye ratio (P/D) ranged from 20–2. The dye in the AO:poly‐A complex is predominantly in the dimeric form. The optical activity of the monomer dye in the excited state is very small, while that of the dimeric dye is relatively large and its dependence on wavelength and P/D indicates the presence of higher aggregates. At low P/D ratios some transfer of electronic excitation energy from dimer to monomer takes place. The spectral properties of the dye in AO:DNA complexes are different at the P/D ratios of 15 and 3, reflecting different modes of complexing. In contrast to the AO:poly‐A complexes, the optical activity of the AO:DNA complexes in the ground and in the excited states are of comparable magnitude; little change thus seems to take place in the interaction between dye and polymer upon electronic excitation of the dye in AO:DNA. In the 9‐AA:poly‐A complex the dye does not tend to dimerize when in the ground state. Excimer emission was, however, observed; dimers and higher aggregates of high optical activity form upon electronic excitation. In the complex of proflavine:DNA, the bound dye shows appreciable optical activity when in the ground state but is optically inactive when in the excited state. The mode of interaction between this dye and DNA thus changes appreciably upon electronic excitation. The occurrence of two electronic transitions in the last absorption band of acridine dyes and its implication on the interpretation of the corresponding CD spectra is discussed.
Matrix Methods and Normalization Procedures in Chemical Relaxation
Authors: Hayman H. J. G. 
Published: November 2013

AbstractTwo very general methods for dealing with chemical relaxation in solution near equilibrium are developed in detail along parallel lines; in the first of these the normal modes of relaxation are obtained as linear combinations of a set of basic reactions whereas in the second the normal coordinates are obtained as linear combinations of the deviations of the solute concentrations from those at equilibrium. The general procedures described in the literature, differing both in their basic assumptions (some being based on the theory of irreversible thermodynamics, others on kinetic considerations) and also in the concentration units adopted and the normalization procedures used, form special cases of the above two general methods and are considered from this point of view. The two general methods are compared critically and shown to be complementary since each has its own special advantages and disadvantages. In particular, the significance of the normal modes of relaxation corresponding to infinite relaxation times are shown to be entirely different in the two cases; in the first method these modes are “reactionless” and have little significance whereas the “improper” normal modes obtained by the second method show how the concentrations of the various solutes can be changed without disturbing the chemical equilibrium of the system.
Photochemical Processes in Non‐Equilibrated Franck‐Condon States
Authors: Feitelson Jehuda 
Published: November 2013

AbstractSolution reactions which occur in pre‐equilibrium excited states, i.e. before the system has reached the lowest thermalized excited state are discussed. Two examples, the photodissociation of β‐naphtholate into a solvated electron plus radical and the acid dissociation of excited β‐naphthol are dealt with in some detail. It is proposed that in these two cases at least the reactions might take place in a, so called, solvent Franck Condon state, i.e. a state in which the solvent has not yet attained the appropriate excited state orientation.
Proton Transfer in Liquid Ammonia Solutions Containing Water and Hydroxide Ion
Authors: Marks Stephen B. 
Published: November 2013

AbstractThe rate of proton transfer in ammonia solutions containing water and hydroxide ion was determined as a function of temperature and concentration by means of PMR spectroscopy. A first order dependence on hydroxide ion and second order dependence on water concentration was found with a rate constant of k3 = 6.1 ± 1.2 × 103 M−2 sec−1 at 25°C and ΔE‡ = 4.5 ± 0.5 kcal/mole. The value of k3 is in good agreement with that reported by other workers.
The Influence of Vacuum, Carbon Monoxide and Hydrogen on Ceria and Zinc Doped Ceria ‐ Electron Spin Resonance Study
Authors: Gideoni Michael , Steinberg Menachem 
Published: November 2013

AbstractThe effects of heating in vacuum, carbon monoxide, and hydrogen on cerium (IV) oxide and zinc oxide‐doped cerium (IV) oxide were investigated by ESR, and a difference in the behavior of the signals obtained for the two preparations was observed. The signal decrease g = 1.940 and g = 1.961 was faster and was obtainable at lower temperatures for the doped oxide than for the undoped sample. The effect of oxygen on these samples is reported and a mechanism is proposed.
On the Synthesis of Glutathione in Human Blood Cells In Vitro
Authors: Bondi E. , Levy J. , Ben‐Yoseph Y. , Hochberg A. , Dimant E. 
Published: November 2013

AbstractMature human blood cells depleted of ATP in vitro by preincubation with fluoride, maintain the ability to incorporate glycine into their GSH, presumably by exchange. The incorporation of labelled glycine into GSH, of ATP depleted blood cells, in the presence of added phosphate, is higher than in the nonpoisoned cells. Arsenate accelerates the incorporation of labelled glycine into GSH of ATP depleted blood cells. The inhibitory effect of glucose on the incorporation of labelled glycine into blood cell GSH is thought to be related to the binding of inorganic phosphate. Synthesis of GSH in mature blood cells in vitro was established with labelled cystein and cystine.
Copper (II) Ion Binding in Polyacrylic Acid
Authors: Marinsky J. A. , Imai N. , Lim M. C. 
Published: November 2013

AbstractThe complexing of Cu(II) by polyacrylic acid has been investigated. Potentiometric measurements have been employed to facilitate the experimental program. The stability constant of CuA2, the dominant species observed, has been determined to be approximately 6.5 × 103, a value in good agreement with the formation constant of 4.25 × 103 reported for Cu(acetate)2. The quantitative evaluation of this stability constant is made possible by (1) correcting for complication arising from the large and variable electric field at the surface of the polyelectrolyte in the polymer domain and by (2) expressing the concentration of polymer species in terms of the polymer domain volume.
Determination of Structure and Properties of Acetylacetone Dioxime, Benzoylacetone Dioxime and Bis‐Benzoylacetone Dioximato‐Copper (II): An Ultraviolet Study
Authors: Ben‐Bassat A. H. I. , Adato I. , Sarel S. 
Published: November 2013

AbstractUV spectra of acetylacetone dioxime (2,4‐pentanedione dioxime = AADO), benzoylacetone dioxime (BADO) and bis‐benzoylacetone dioximato‐Cu(II) [Cu‐ (BADO*)2; BADO* = oxidized BADO] are recorded for aqueous and CHCl3 solutions at different pH values and interpreted. pKa values (1st dissociation constant) for AADO and BADO at constant ionic strenths (μ = 0.12) are derived: pKa (AADO) = 10.50; pKa (BADO) = 9.50, and the influence of molecular structure on acid‐base properties is discussed. Diagrams of possible molecular orbital energy‐level transitions for the oxime and the nitroso chromophores are given. The marked influence of acids (HC1) and bases (triethylamine, TEA) on the shape of the UV spectra of Cu‐ (BADO*)2 is discussed and explained in terms of the acid‐base properties of the nitroso and the oxime groups. Additional evidence has been adduced for the presence of nitroso group and of hydrogen bonds in these complexes.
Photodissociation with Polarized Light
Authors: Bersohn Richard 
Published: November 2013

AbstractThis is a review of a small part of the work on photodissociation with polarized light performed by Kent Wilson and his students [1–4] at the University of California at San Diego and the author and his students [5–7] at Columbia. The physics of the experiment has been presented in a recent review by R.N. Zare [8] who was the first to suggest the utility of such work. We comment on the photodissociation of three molecules — I2,Cd(CH3), and α‐iodonaphthalene.
Valence Angles in Group II Dihalide Molecules
Authors: Coulson C. A. 
Published: November 2013

AbstractGroup II A atoms Ca, Sr and Ba form dihalide molecules some of which are linear and others bent. Two general models are considered to account for this. In the first we suppose a purely ionic structure in which the atoms are polarized by the resulting internal electric field. The polarization energy varies with valence angle; but it is shown that if this model were the correct one, all these molecules should be linear. In the second model we consider the valence states that arise from excitations s2 → sp and s2 → sd. The first of these would lead to a linear molecule, the second to a bent one. Considerations of the energies of excitation to these two valence states together with a similar situation for the positive ions show that bent molecules are favored when the central atom is heavy and when the attached halogens are as electronegative as possible. The experimental results are thus completely explained.
Photodissociation and Half‐Collisions — Computational Viewpoint and Boundary Conditions
Authors: Shapiro Moshe 
Published: November 2013

AbstractBoundary conditions and quantum mechanical numerical methods for evaluating transition probabilities of photodissociation and half‐collisional processes are presented. Direct and indirect dissociation modes are discussed. In each case we write a set of equations tying the particular boundary behaviour of each dissociation mode to the standard scattering boundary conditions. Numerical schemes based on these equations are presented. The case of competing dissociation reactions and exchange is also considered for the indirect case. When interference between these modes is expected to play a significant role, we show how the quantum jump due to photon and electron impact can be incorporated into the set of equations describing the dissociation. Finally we indicate how a numerical construction of potential surfaces from photofragment spectra and absorption spectra in the continuous and predissociation range can be obtained using these numerical schemes.
Fluorination Studies on Glycyrrhetic Acid Derivatives
Authors: Rozen Sh. , Shahak I. , Bergmann E. D. 
Published: November 2013

AbstractAttempts to introduce a fluorine atom directly at the C‐3 position of the triterpenoidal glycyrrhetic acid 1 by reacting the tosylate 2 with KF, or methyl glycyrrhetate 5 with Et2NCF2CHCIF, failed. The ring A olefin 3 and the rearrangement product 4 were obtained. The homoannular diene 7 was treated with NOF, but only nitroso‐fluorine compounds 8, 9 were isolated. Nitrosyl fluoride was also reacted with olefin 3. A difluoro compound 10 and the expected 2‐keto‐3α‐fluoro compound 11 were obtained. The above two olefins were also reacted with bromine fluoride. Although the diene 7 gave only fluorine‐free compounds 13, 14, the expected fluoro‐bromine compound 16 was obtained from 3. When the 2β‐fluoro‐3α‐bromo compound was treated with Bu3SnH, the bromine atom was replaced by hydrogen and the 2β‐fluoro compound 17 was formed.
Polybarbiturates
Authors: Tahan Menashe , Lander Naftali , Zilkha Albert 
Published: November 2013

AbstractSeveral p‐vinylbenzyl malonates were synthesized and condensed with urea to form the corresponding 5‐p‐vinylbenzyl barbiturates, which were polymerized. The gross behavioral changes observed on intraperitoneal (i.p.) administration of the polybarbiturates to mice were compared with those caused by the monomers. The polymers were less toxic but had weaker sedative effects than their respective monomers, and they did not exhibit any prolongation of activity.
Intramolecular Rearrangements in Peptide Derivatives of Anthranilic Acid
Authors: Noguchi Junzo , Kawai Megumi , Hamada Masato 
Published: November 2013

AbstractThe peptidylanthranilic acid ester is stable during the reactions leading to the elongation of peptides. However, when the ester is hydrolyzed, the amide bond of peptidylanthranilic acid is catalytically hydrolyzed at pH 7, owing to the effect of the free carboxyl group of the anthranilic residue, into peptide and anthranilic acid. In this reaction, no decomposition or significant racemization of peptide was observed, and the protected peptide was easily obtained. Only in the case of glycylanthraniloyl derivatives did the rearrangement into peptide and anthranilic acid occur in aqueous solution.
On Lanthionene and Cyclolanthionyl
Authors: Zervas Leonidas , Ferderigos Nicolaos 
Published: November 2013

AbstractThe O,S‐dibenzoyl derivative of N‐carbobenzoxy‐L‐cysteinyl‐L‐serine methyl ester is converted by methanolysis to cyclic products of L‐ and meso‐lanthionine (VI and VIII). This transformation occurs by β‐elimination in the serine moiety followed by addition reactions involving the SH groups and the double bonds thus formed. The structure and configuration of these compounds have been established. The specific rotation of acidic solutions of L‐lanthionine is markedly temperature‐dependent the changes in [α]D being reversible up to 96°. Above this temperature racemization occurs. The above transformation is related to the rearrangements occurring in cystine‐containing proteins treated with alkali and suggests a possible method for synthesis of cyclo‐lanthionyl peptides.
Studies of the Hydrogen Exchange in Aqueous Solutions of Poly‐N5‐(3‐Hydroxypropyl)‐L‐Glutamine
Authors: Hvidt Aase 
Published: November 2013

AbstractThe H‐D exchange of the peptide groups of poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine (PHPG) in D2O solution was studied by an infrared spectrophotometric method. The exchange of the peptide groups of the side chains of the polymer follows simple first‐order kinetics, with exchange rates 3–4 times slower than those of N‐methylacetamide. The kinetics of the exchange of the peptide groups of the polypeptide chain is more complicated and suggests that these molecules are less motile than other polypeptides studied by the exchange method. The observation that the exchange rates measured in solutions of PHPG, as a whole, are much faster than the exchange rates typical of protein solutions is taken as experimental evidence of the shortcoming of PHPG as a model of a protein molecule.
Conformational Behaviour of Non‐Ionizable Polypeptides in Gem‐Diol: Water Solvent Systems
Authors: Lotan Noah , Chen K. , Roche R. S. 
Published: November 2013

AbstractThe conformation of poly‐N5‐(2‐hydroxyethyl)‐L‐glutamine (PHEG) has been investigated in hexafluoropropan‐2,2‐diol‐water mixtures. In spite of the similarity of the circular dichroism spectra obtained in some of these mixtures and in water, NMR and hydrodynamic measurements revealed that macromolecular conformations of various degrees of rigidity are present in the different solvents considered. Homologue polymers of PHEG behave in a similar manner.
Factors Contributing to the Absorption and Fluorescence Characteristics of Pyridoxal Phosphate in Glycogen Phosphorylase b
Authors: Veinberg Shlomit , Shaltiel Shmuel , Steinberg Izchak Z. 
Published: November 2013

AbstractThe Schiff base formed between salicylaldehyde and n‐hexylamine has absorption bands peaked at 255 and 317 nm in non‐polar solvents. In a polar solvent (ethanol) an additional band appears at 405 nm and a shoulder is resolved at 275 nm. The fluorescence band has a peak at 535 nm in non‐polar solvents (with the exception of CCl4) which is blue shifted to 505 nm in ethanol. These spectral data are similar to those of Schiff bases formed between pyridoxal phosphate and aliphatic amines. On the other hand, the spectral properties of the Schiff base of o‐methoxybenzaldehyde with n‐hexylamine are very different. It may thus be concluded that the nitrogen atom of the aromatic ring does not have to be invoked in explaining the spectral properties of pyridoxal phosphate Schiff bases and of pyridoxal phosphate in glycogen phosphorylase. The hydroxyl group seems however to play an important role in determining the spectral properties of Schiff bases of o‐hydroxyaldehydes. The optical rotatory power of the pyridoxal phosphate in phosphorylase is of comparable magnitude for the chromophore in the ground state or the electronically excited state, indicating similarity of mode of binding of the chromophore to the protein in the two electronic states. Measurements of circular dichroism indicate that the “deformer” imidazole citrate affects the interaction of the pyridoxal phosphate with the protein when the cofactor Schiff base is in the ketoenamine form but not when in the enolimine form.
The Active Site of Pancreatic Porcine Elastase: Specificity, Size and Stereospecificity
Authors: Atlas Daphne 
Published: November 2013

AbstractThe kinetic parameters of pancreatic‐porcine‐elastase catalyzed hydrolysis of peptides and peptide esters were determined. The most efficient and specific cleavage occurred at the Ala‐Lys bond of the S‐peptide (RNAse P1–20), RNAse P1–8 octapeptide and the synthetic heptapeptide Ala5‐Lys‐Phe. The active site is extended over eight subsites (about 29 Å) and consists of five subsites from the cleaved bond toward the N‐terminal end and three subsites from the scissil bond toward the C‐terminal end of the substrate. The size of the active center was deduced by comparing the kinetic parameters of the appropriate diastereomers of peptides (of the general formula Ala4‐Lys‐Phe and Alas‐Lys‐Phe), and p‐nitrobenzyl esters of tri‐ tetra‐ and penta‐alanine peptides. Specific local interactions of the various subsites, and their stereospecificity were determined by comparative study of the steady‐state kinetic parameters of the appropriate group‐pairs of substrates. Alignment of the substrate Ala5‐Lys‐Phe‐Ala at the active site was determined by constructing the CPK (space filling model) of elastase, based on its known coordinates, determined at 2.5 Å resolution.
Fluorescent Probes in the Study of the Extended Sites of Proteinases
Authors: Fruton Joseph S. 
Published: November 2013

AbstractStudies on the kinetics of the cleavage of oligopeptide substrates by pepsin, together with the examination of the changes in fluorescence of dansyl or mansyl peptides upon interaction with pepsin or pepsinogen, give further evidence of the importance of secondary interactions of such substrates with the extended active site of the enzyme and indicate considerable conformational flexibility at the active site of pepsin in response to enzyme–substrate interaction.