bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Conformation on the Interaction of Macromolecules with Surfaces. The Adsorption of Compact Macromolecules
Authors: Silberberg A. 
Published: November 2013

AbstractThe adsorption of compact macromolecules from solution is considered. A model is developed which permits direct comparison of present results with those for linear flexible structures. It is shown that, under equivalent conditions, size, not conformation, is the determining factor for the amount adsorbed. Size, not conformation, moreover, is responsible for the widespread plateau which is observed as a function of bulk concentration.
Theory of Electrophoresis of Polyelectrolytes
Authors: Imai Nobuhisa , Iwasa Kunihiko 
Published: November 2013

AbstractThe transport of polyions in solutions under an applied electric field is controlled by the three counterion effects: the electrophoresis effect, the field distortion effect and the counterion relaxation effect. Recent experimental and theoretical studies have mainly considered the electrophoresis effect which is a hydrodynamic effect of the medium charged by the counterions. In this paper, the other two effects, which result from the distortion of the counterion atmosphere around the polyion, are evaluated through the strict but simple analysis of the diffusion equations for low molecular ions and the Poisson equation. It was found in this study that these two effects are remarkably important for the system of coiled macroions fairly free‐drained. It was also demonstrated that the applied electric field is strongly depressed near the polyions by the shielding effect of counterions. This result is very different from the various theories which have assumed a constant applied field in the whole space. A cubic free‐volume model was adopted in this theory and the case for infinite dilution of polyion was also discussed as a special case of the free‐volume. The most important factor in our mobility expression is the apparent polyion charge expressed by the counterion activity. The results were compared with the experiments referring to the additivity rule for counterion activity.
Series Arrays of Ion‐Exchange Membranes: Concentration Profiles and Rectification of Electric Current
Authors: Naparstek Avraham , Roy Caplan S. , Katzir‐Katchalsky Aharon 
Published: November 2013

AbstractUsing the nonequilibrium thermodynamic treatment of Kedem and Katchalsky a study has been made of series arrays of ion‐exchange membranes. A rule has been found which identifies certain classes of intermembrane concentrations which vary in the same way with respect to current under different steady‐state conditions. Among these is a set which is independent of the value of the steady‐state current. For the special case of series arrays containing alternately positive and negative fixed charges, with indefinitely large end reservoirs, it is shown that in the steady‐state the array may possess a set of desalinated intermembrane compartments, or a set of salinated intermembrane compartments, but never both simultaneously. This leads to the conclusion, which has been tested experimentally, that a large array of this kind may act as an efficient rectifier. The steady‐state concentration profile across a large array may be radically altered by changing a single membrane in the array, or even adding a single membrane at one end of the array. The approach to the steady‐state has been examined by means of a relaxation calculation, which leads to certain conclusions relating to optimization of flow‐rates in desalination by electrodialysis.
Calcium‐Magnesium Exchange in Aluminum Hydroxide‐Coated Montmorillonite
Authors: Levy Rachel , Tamura Tsuneo 
Published: November 2013

AbstractAluminum hydroxide‐coated montmorillonites have been shown to exhibit exchange properties which differ from those of pure montmorillonites. The direction of change was found to depend on the coating method used and the pH at which the coating is applied. The aluminum hydroxide‐coated montmorillonites were prepared by two different methods at two pH's: (1) reacting aluminum chloride and sodium hydroxide in the presence of the clays (pH 7), and (2) titrating aluminum‐saturated clays with calcium hydroxide to an alkaline pH (∼10). The resulting clay systems were equilibrated with calcium‐magnesium solutions. The first system showed preferential adsorption of calcium over magnesium because the clays contained exchangeable sodium due to the precipitation of aluminum hydroxide in the presence of the clay. The second system showed no preference either for calcium or for magnesium. A distribution coefficient of unity resulted from compensation of exchangeable calcium by magnesium released from the aluminum hydroxide.
A Necessary Simplification of the Kinetics of Carrier Transport
Authors: Stein W. D. , Lieb W. R. 
Published: November 2013

AbstractA kinetic analysis of facilitated diffusion across cell membranes on the basis of four models is presented. These models are all general in that in no case is symmetry assumed, nor is any particular reaction step considered as rate‐limiting. In one model there is only one form of the free carrier and one form of the bound carrier. In the second model there are two forms of both bound and of free carrier. In the third and fourth models there are two forms of one of these, but only one form of the other. These models fall into two classes: that with one form of the free carrier and that with two forms. Within each class the models give identical predictions for steady‐state fluxes of substrates. It is shown how to distinguish between these two classes using experimental data, and criteria are provided enabling one or other class, or both classes, of model to be rejected. A complete kinetic analysis of a system of either class may be achieved on the basis of a small number of parameters, derived from flux measurements. The significance of these parameters on a molecular level are discussed.
Immobilized Polyelectrolyte Enzyme Systems. Activation of Polyornithylchymotrypsin by the Product of the Enzymic Reaction
Authors: Goldstein Leon 
Published: November 2013

AbstractThe hydrolysis of N‐acetyl‐L‐tyrosine ethyl ester catalyzed by a polycationic derivative of chymotrypsin, polyornithylchymotrypsin (POCH), was studied in the presence of varying concentrations of N‐acetyl‐L‐tyrosine, the product of the enzymic reaction. The values of kcat (lim) and Km (app) for polyornithylchymotrypsin increased hyperbolically with increasing concentrations of N‐acetyl‐L‐tyrosine. Increase in the values of kcat (lim) and Km (app) of polyornithylchymotrypsin was also observed in the presence of other organic anions, e.g. acetate, propionate, benzoate and l‐anilino‐8‐naphthalene sulfonate. The hyperbolic dependence of kcat (lim) and Km (app) of polyornithylchymotrypsin on the concentration of N‐acetyl‐L‐tyrosine suggested that the data could be treated as a saturation phenomenon. The activation of polyornithylchymotrypsin could be attributed to the cancellation of charge resulting from the binding of organic anions to the positively charged side chains of the enzyme derivative.
Resistance and Inductance‐Like Effects in Chemical Reactions: Influence of Time Delays
Authors: Atlan H. , Weisbuch G. 
Published: November 2013

AbstractWithin the framework of network thermodynamics the general form of the constitutive relations between conjugated forces and flows is examined. Since nonequilibrium processes are involved, time delays are assumed to take place between the variation of a concentration — or generalized displacement — and that of its conjugated force — or difference in potential. For example, a certain time is needed in a chemical mixture for the chemical potential X to follow changes in concentration c of a given compound. Thus, the concentration‐potential relationships must be written in the form of retarded functions X(t) = f[c(t — Δt)]. A series expansion of such a function leads to a capacitive term independent of the delay Δt, resistive terms proportional to it, and an inductive term proportional to its square value. When applied to the network analysis of chemical reactions it is apparent, from inspection of the resistive, i.e. dissipative, term, that Δt is identical with the relaxation time of a reaction defined in chemical kinetics. Thus a link between time delays and dissipation is established and can be visualized as an increase in entropy accompanying the redistribution of molecules after any local change in concentration. As to the importance of the inductive terms, it depends upon particular circumstances where longer delays can take place so that second order terms cannot be neglected and inductance‐like effects could, in principle, be observed.
A Raman Spectroscopic Investigation of the Dehydration of Solid Magnesium Nitrate Hexahydrate
Authors: Peleg Mordechai 
Published: November 2013

AbstractA Raman spectroscopic investigation has been carried out on the dehydration products of solid magnesium nitrate hexahydrate. Results are presented for the hexahydrate, dihydrate and anhydrous forms of magnesium nitrate. The splitting of the v1, mode for the anhydrous salt is similar to the correlation field splitting observed for other group II anhydrous alkaline‐earth nitrates suggesting a similar crystal structure. The presence of a metastable hydrated species, probably the tetrahydrate, is observed in polycrystalline mixtures containing less than 6 but more than 4 moles of water.
Interaction Between Montmorillonite and Benzidine in Aqueous Solutions IV. The Color Reaction in the Frozen State
Authors: Lahav N. , Anderson D. M. 
Published: November 2013

AbstractChanges in the color of Na, Ca, and Cu‐bentonite‐benzidine pastes were observed for color changes upon freezing at −5°C, −15°C, and −21°C. At −5°C no color change could be detected. At −15°C and −21°C, when the benzidine/bentonite ratio (W/W) was in the range of approximately 0.0003 to 0.003, the pastes' colors changed from blue or pale blue to green or bluish green. Reflectance measurements of Na‐bentonite‐benzedine paste at −150°C were carried out in a specially designed cell. These measurements show that in addition to the color change, the reflectivity of the frozen paste became higher upon freezing to −150°C, presumably because of the formation of ice crystals. The explanation of the color changes is based on the assumption that the (blue) monovalent and the (yellow) divalent cations coexist in the frozen paste at different zones on the bentonite surface.
Ammonium Chloride Separated into Ammonia and Hydrogen Chloride, with the Aid of Metal Oxides II. Isothermal Operation
Authors: Ashboren (Araten) David , Korob Felix (Efraim) 
Published: November 2013

AbstractAmmonium chloride can be separated into its constituents, ammonia and hydrochloric acid, by treating it with a metal oxide. Whereas earlier it was shown that this separation is feasible for 14 different metals, when effected in two steps at two different temperatures, we now show that isothermal operation is possible, with the driving force consisting of concentration differences of NH4Cl and water vapor, respectively. The experiments with Fe2O3, MgO, NiO and PbO showed that the volatility of FeCl3 interferes when Fe2O3 is used, but the other oxides, which do not have volatile chlorides, serve well at temperatures of about 300°C.
The Arbuzov Reaction in Fused‐Ring Pyrimidines
Authors: Almog J. , Bergmann Ernst D. 
Published: November 2013

Abstract2,4‐Dichloroquinazolines type compounds (I–III) react with trimethyl phosphite preferentially at the 2‐position. In II, the chlorine atoms both at C2 and C4 were replaced practically simultaneously by the —P(=O) (OMe)2 group.
Relaxation and NMR Spectra of Nickel (II) — Purine Complexes
Authors: Karpel Richard L. , Kustin Kenneth , Wolff Michael A. 
Published: November 2013

AbstractThe temperature‐jump and NMR line‐broadening techniques have been used to determine the stability constants, kinetics and binding sites of nickel(II)‐purine complexes in aqueous solution. The temperature‐jump relaxation spectrum consists of two processes, dependent on concentration and pH. Previous evidence has shown that the anionic form of the ligand binds to the metal ion, hence HL, Ni2+ and NiL+ alone are not sufficient to explain the kinetic data. The two most likely systems consistent with the data are: (1) complexes differing in their sites of metal attachment (linkage isomers) and (2) higher order complexes, i.e. and NiL2 complex in addition to the NiL+ complex. Both possibilities fit the temperature‐jump data reasonably well, although neither is entirely satisfactory. The NMR experiments provide additional experimental evidence allowing a choice of mechanisms to be made. The preferred mechanism ismagnified imageThe rate and equilibrium constants for this scheme are calculated. From the temperature‐dependence of the NMR line width, the activation parameter for k−2 and the chemical shift ΔΩNi for H(8) on the bound purine are calculated. The results are consistent with a normal substitution mechanism for aqueous nickel(II) ion.
Thermodynamic Properties of Associated Solutions II. Mixtures of the Type A + B + ABj
Authors: Apelblat Alexander 
Published: November 2013

AbstractThe theory of ideal associated solutions of the type A + B + ABj is investigated. Equations describing the chemical equilibrium, number average molecular weight, activity coefficients and excess thermodynamic functions are given. For the type of association considered, GE is always negative, HE has the same sign as the standard enthalpy of the association reaction, ΔH°, and SE can have positive or negative values. The excess entropy of mixing as a function of composition has a fairly complicated shape, especially in the region where the enthalpy and the free energy term compensate for each other. The extremum properties of the thermodynamic functions are at the stoichiometric mole fraction × = 1/(1 + j), and the functions have an asymmetric parabola‐like form.
Substituent Effects in the Intramolecular Photocyclization of o‐Allylphenols to Cyclic Ethers
Authors: Houry Shlomo , Geresh Shimona , Shani Arnon 
Published: November 2013

AbstractUV irradiation, in benzene or cyclohexane, of substituted ortho‐allylphenols to form cyclic ethers (presumably through an ionic mechanism) does not show any correlation with the pKa of the excited states of the phenols in aqueous solution.
Cyclic Peptides VII. The Synthesis and Characterization of Cyclic Peptides with Repeating Pro‐Gly Sequences
Authors: Deber Charles M. , Blout Elkan R. 
Published: November 2013

AbstractFour cyclic peptides of the type cyclo (Pro‐Gly)n were synthesized and characterized. The peptides are cyclo (L‐Pro‐Gly)2, cyclo (L‐Pro‐Gly)3, cyclo (L‐Pro‐Gly)4, and cyclo (D‐Pro‐Gly‐L‐Pro‐Gly). Aspects of the cyclization reactions leading to these peptides are discussed, particularly with respect to the choice of sequence of linear precursor peptides and effects of elevated temperatures. The cyclic octapeptide, cyclo (L‐Pro‐Gly)4, was isolated as a crystalline complex with sodium thiocyanate. Experimental details of the syntheses are provided.
Nonaqueous Determination of the Tert‐Butyloxycarbonyl Group in Amino Acid and Peptide Derivatives
Authors: Ehrlich‐Rogozinski Sarah 
Published: November 2013

AbstractThe tert‐butyloxycarbonyl group is quantitatively cleaved from N‐blocked amino acids and peptides by applying a known excess of perchloric acid solution in acetic acid to yield protonated amino groups and free perchloric acid. Back titration of the latter with sodium methylate permits accurate determination of the tert‐butyloxycarbonylderivative. The method is rapid and simple since the same reagent serves for both cleavage and determination of the tert‐butyloxycarbonyl group.
Photosensitive Protecting Groups — A Review
Authors: Amit B. , Zehavi U. , Patchornik A. 
Published: November 2013

AbstractA review of recent work utilizing photosensitive protecting groups is presented, (literature to September 1973 is reviewed). Although still in the developmental stage, the application of groups such as 2‐nitrobenzyl, 3‐nitrophenyl, 3,5‐dimethoxybenzyl, 2,4‐dinitrobenzenesulfenyl and 3,5‐dimethoxybenzoinyl in synthetic chemistry shows great promise for the future.
Infrared Studies on the Backbone Conformation of Nucleic Acids
Authors: Brahms S. , Brahms J. , Pilet J. 
Published: November 2013

AbstractThe presence and assignment of low frequency infrared bands characteristic of the A, B and C forms of DNA (Salmon Sperm and Micrococcus Lysodeikticus) and of synthetic poly (dA‐T): (dA‐T) and of polyribonucleotides‐A form are considered. The vibrational modes that may arise from the phosphate diester stretch of DNA backbone are investigated in the region of 750 cm−1–900 cm−1. The proposed assignment of the IR bands occurring at about 837 cm−1 to the vibrations of the phosphate diester C–O–P–O–C chain in a specific conformation allow characterization of the backbone geometry in the B and C forms. The bands situated at 812 cm−1 and 860 cm−1 are undoubtedly characteristic of the backbone phosphodiester chain of the A form. The possibility of other contributions to the 812 cm−1 band is also discussed.
The Circular Dichroism Spectrum and Structure of Unordered Polypeptides and Proteins
Authors: Krimm S. , Tiffany M. Lois 
Published: November 2013

AbstractThe evidence bearing on our revision of the early assignment of the circular dichroism spectrum of the maximally unordered polypeptide chain is reviewed. Our initial, as well as subsequent, studies are believed to support the proposed revision in assignment. This conclusion need not be modified in the light of recent work on water‐soluble, non‐ionizable polymers.
On the Statistical Mechanical Theories of Helix‐Coil Transition in Polypeptides, and the Structure and Structural Stability of Proteins
Authors: Lifson S. , Lotan N. 
Published: November 2013

AbstractThe theoretical and experimental study of the helix‐coil transition of synthetic polypeptides has significantly deepened our understanding of the phenomena of nucleation and cooperativity in the equilibrium transition between the native and the denatured states of proteins. Proteins differ, however, from synthetic copolymers by being neither regular nor random, their sequence having been determined by natural selection. Therefore, the quantitative results of the theoretical analysis of synthetic polypeptides should not be indiscriminately transferred to the study of proteins. However, these results provide important information for a rational analysis of the conformation and conformational stability of proteins.
Cooperative Multisite Binding to DNA
Authors: Schellman John A. 
Published: November 2013

AbstractThe method of sequence generating functions is applied to the binding of substrates to a linear array of binding sites such as is encountered in DNA. Cooperativity parameters are introduced for contact between bound ligands and for the extension of interaction over one or two empty binding units. By allowing these parameters to have values less than or greater than one, a large variety of anticooperative and cooperative situations can be developed. These and other parameters are systematically built into the sequence generating function as markers which are useful for statistical averages even in the absence of cooperativity. The resulting equations are applied to a system of highly cooperative binding, resulting in predicted behavior that simulates many features of the binding of T4 gene 32 protein to DNA. A model for the intercalation of dyes in DNA is also proposed which is based on two anticooperativity parameters: one for intercalating dyes in adjacent sites, the other for dyes separated by one empty site. The method of sequence generating functions not only permits the prediction of binding isotherms for systems like those described above, but also provides statistical distributions for any type of binding event to which a statistical weight can be attached. The only limitation is that the chains must be sufficiently long that end effects are negligible.
The Structure of Rhodanese at 4Å Resolution. The Conformation of the Polypeptide Chain
Authors: Smit J. D. G. , Ploegman J. H. , Pierrot M. , Kalk K. H. , Jansonius J. N. , Drenth J. 
Published: November 2013

AbstractRhodanese (thiosulfate: cyanide sulfurtransferase, EC 2.8.1.1), a dimeric enzyme of MW 37,000 was crystallized from an ammonium sulfate solution. The crystals belong to space group C2 with a = 156.1 ± 0.2Å, b = 49.0 ± 0.05Å, c = 42.2 ± 0.1Å and β = 98.50 ± 0.05°. Three dimensional X‐ray data to a resolution of 3.9Å were collected from crystals of the native protein, a mercury‐, and a platinum‐containing heavy atom derivative. The phases of the protein reflexions were determined by the isomorphous replacement method, including anomalous scattering data. In the resulting electron‐density map the course of the polypeptide chain could be followed in both monomers. Six short helices and what seems to be a three strand, parallel twisted pleated sheet are found in each. The monomers are related by a pseudo‐dyad or near‐dyad, which, however, is not obeyed by the chain ends. The carboxyl terminus of one monomer and the amino terminus of the other one are in close contact and obviously form a salt bridge. A correlation with the presently available data of the amino acid sequence cannot yet be made.
Dinitrophenylation and Thiolysis as a Tool in Protein Chemistry
Authors: Shaltiel Shmuel 
Published: November 2013

AbstractThe thiolytic cleavage of 2,4 dinitrophenyl derivatives of sulfhydryls, imidazole imino‐nitrogens, and phenolic hydroxyls converts dinitrophenylation into a reversible method for masking or labeling these functional groups. The merits of this method are illustrated in the synthesis of peptides and polyamino acids (including a potent synthetic immunogen), in sharpening the specificity of dinitrophenylation, in masking “super reactive” nucleophiles in proteins while labeling “buried” functional groups, and in the probing and three‐dimensional mapping of enzyme active sites. Analytical techniques for monitoring the rate and extent of the thiolysis step are described.
Some Stereochemical Implications of the Molecular Conformation of Collagen
Authors: Traub Wolfie 
Published: November 2013

AbstractA space‐filling model of collagen has been constructed in accordance with the conformation found for (Gly.Pro.Pro)n. The model shows that leucyl and phenylalanyl residues can be easily accommodated at position X of the collagen tripeptide sequence Gly.X.Y, but are severely constrained by steric hindrance at position Y. Examination of the model has also led to the suggestion that hydrogen bonding of hydroxyproline OH through a water molecule to glycyl CO on the same polypeptide chain might account for the stabilisation of the triple helix conformation by hydroxyproline.
Chemistry of Parathyroid Hormone
Authors: Potts John T. 
Published: November 2013

AbstractAdvances in newer techniques for high sensitivity sequence analysis of polypeptides coupled with improvements in solid phase synthesis procedures have led to systematic analyses of structure‐activity relations in parathyroid hormone. Twenty‐five amino acids at the amino terminus of the 84 amino acid peptide suffice for biological expression of hormonal actions on kidney and bone in vivo and in vitro.
Uranyl Halide Species Sorbed on Ion Exchangers
Authors: Heitner‐Wirguin C. , Gantz M. 
Published: November 2013

AbstractUranyl ions were sorbed on a cation and anion exchanger from fluoride, chloride, and bromide solutions. The visible and IR spectra of the sorbed species were recorded. The species identified were UO2F−3, UO2Cl+, UO2Cl−3 and UO2Cl2−4, UO2Br+ and UO2Br2−4. Analysis of the spectra obtained made possible the determination of the coordination number and the symmetry of the species, i.e., the cationic species have the coordination number six, while the anionic species have the coordination number four.