bluuebunny/crossref_metadata_2025 huggingface dataset:
HMO Treatment of Photochemical Reactions of Some Purine Derivatives
Authors: Neiman Z.
Published: November 2013

The experimental results of the photochemical transformation of purine, adenine, hypoxanthine and caffeine were tested by using two different sets of parameters in the HMO formalism. Net charges and bond orders are in accord with the photochemical reactivities of caffeine and purine, while for the other cpds. examined the agreement is less satisfactory. The perturbation index ASP (atom ‐self‐polarisability) gives a good estimate of the reaction site, while predictions with Fukui's frontier orbital theory are less adequate.
Grafting of Nylon‐6, 6 on Cellulose Acetate
Authors: Bar‐Ilan A. , Zilkha A.
Published: November 2013

Graft polymers of Nylon‐6, 6 on cellulose acetate were obtained by successive alternate controlled addition of adipoyl chloride followed by 1,6‐hexane diamine to the potassium alkoxide derivative of cellulose diacetate in tetrahydrofuran. The graft polymers were fractionated and isolated from homopolymer fractions. Their Nylon‐6, 6 content increased upon increasing the monomer concentration.
N,N′‐Diarylurea and Amines from Aroylhydroxamic Acids and β‐Propiolactone. Mechanism of a Double Lossen Reaction
Authors: Knobler Y. , Frydman N. , Eliasoff Hanna
Published: November 2013

It has been shown that N,N′‐diphenylurea formation in the reaction of benzohydroxamic acid and β‐propiolactone constitutes a sequence of two rearrangements of the Lossen type. The intermediates, O‐(β‐hydroxypropionyl)benzohydroxamate and O‐(N‐phenylcarbamoyl)benzo‐hydroxamate, have been isolated as products of consecutive steps. Their transformations have been shown independently and along the process leading to N,N′‐diphenylurea. Heating of sodium benzohydroxamate, p‐nitro‐ and p‐methoxy‐benzohydroxamate with β‐propiolactone afforded N, N′‐diphenylurea, p‐nitroaniline and N,N′‐di‐p‐methoxyphenylurea, respectively. Improved procedures for preparation of aroylhydroxamic acids are described.
Exhaustive Proteolysis of Derivatives of Lysozyme
Authors: Sokolovsky M. , Neumann Hava
Published: November 2013

The specificity of pepsin action towards a protein substrate, 8‐carboxymethyllysozyme, was investigated. The complex mixture of peptides obtained after 16hr of digestion was fractionated by high voltage paper electrophoresis. The peptide fragments were identified by a computer program and were fitted along the lysozyme sequence. The peptide bonds attacked were generally those that originate from at least one hydrophobic amino acid side chain, though some bonds involving alanine, threonine, and serine, were also found to be split.
The Synthesis of 22‐Trans‐Cholesta‐5, 22, 25‐Trien‐3β OL
Authors: Ikan R. , Markus A. , Bergmann E. D.
Published: November 2013

22‐Trans‐cholesta‐5,22,25‐trien‐3β‐ol has been synthesized from triphenylphosphine‐2‐methyl‐but‐l‐en‐4‐ylidene and 3‐oxo‐Δ4‐bisnor‐cholenal.
On the Interpretation of Reaction Rates in Concentrated Acid Solutions
Authors: Yagil G.
Published: November 2013

The model of Bascombe and Bell for the indicator acidity of concentrated acid solutions is applied to the analysis of acid catalyzed reactions. A number of well studied reactions are shown to obey the relationship:

magnified image

where Cw is the molar concentration of water not bound to proton (or to hydroxyl OH−). Values of Cw for use in the above correlation are calculated, assuming the existence of the proton in the form suggested by Eigen, H3O(H2 O)3+. The volume fractions of nonbound water are also calculated, this quantity giving even better correlation in some cases. Values of n are obtained which agree, after subtraction of water molecules given up by the proton, with the number of water molecules which can be expected to participate in the formation of the transition state of these reactions.
Applicability of the Brønsted Relation to Reactions of the Hydrated Electron
Authors: Stein G.
Published: November 2013

The hydrated electron, e−aq, reacts with Brønsted acids, BH+, to yield H atoms through a process of proton transfer

magnified image

For a series of Brønsted acids of charge types 1+, 0 and 1−, the rate constant, k, is related to the acid dissociation constant K according to

k/p = GA(qK/p)α, where α = 0.42.

Some acids give rate constants deviating from this relation. These are shown to be ambident reagents with e−aq, one pathway obeying the Brønsted relation, while the other may be nucleophilic addition of e−aq to a reaction center in B. Thus —k(e−aq), the rate of disappearance of e−aq may be greater than +k(H), the rate of formation of H atoms. To account for the results, a molecular model for the structure of e−aq forming a hydrated anion is favored. Its reaction with H+aq is discussed, accounting for recent observations on the rate of the reaction e−aq + H+aq → Haq, which in our view corresponds to proton transfer to fully ordered hydrated electrons, rather than electron addition to H+aq.
Topochemistry. Part XXXIII. The Solid‐State Photochemistry of Some Anthracene Derivatives
Authors: Heller E. , Schmidt G.M.J.
Published: November 2013

The solid‐state photochemistry of several substituted anthracenes has been investigated with particular reference to the behaviour of polymorphic forms of the monomers. A class of 9‐substituted anthracenes (methyl, methoxycarbonyl, chloro, bromo) crystallising in anti‐parallel, sandwich packing arrangements give centrosymmetric dianthracenes in accordance with the topochemical principle, which also operates on light‐stable monomers packing in non‐centrosymmetric space groups having axes > 8 Å (e. g. 9‐methoxy, 9‐ethoxy‐, 1‐cyano‐) and showing no short parallel interplanar contacts. Some but not all monomers, crystallising in the parallel‐stack type with a 4 Å axis, dimerise to the non‐topochemical head‐to‐tail dimer. Two monomers substituted elsewhere than in the 9‐position give the theoretical number of solution dimers but yield only one dimer in the solid state.
The Anomalous Behaviour of 18O‐Labelled Compounds. VII. The Vibrational Spectra of Isotopic Sodium Sulphates
Authors: Pinchas S. , Shamir J.
Published: November 2013

The infrared and Raman spectra of normal and 89.5 atom % 18O‐labelled sodium sulphate have been measured both for the solid salts and for their aqueous solutions. All the fundamentals of S16O2−4 and S18O2−4 have been observed. The observed isotopic frequency ratios of these fundamentals agree excellently with theory.
The Volumetric Determination of Potassium by Heterometric Titration
Authors: Ben‐Bassat A.H.I. , Azrad Anath
Published: November 2013

Heterometric procedures for the volumetric determination of potassium are proposed. The use of direct and reverse titrations, precipitate‐forming ligands as titrants, and the addition of solvents like ethanol make possible the determination of a large number of cations and anions as their insoluble compounds. Two procedures are described: one uses direct heterometric titrations for the formation of the potassium tetraphenylboron precipitate (K‐TPB) for samples of concentrations between 40 and 60 ppm K+; the second uses indirect titrations for the formation of K2Na[Co(NO2)6] in acetic acid ‐ ethanol media, for samples containing 4–10 mg K+. The end point of the heterometric titration is obtained by photometric measurement of the optical absorption of suspensions.
The Synthesis of 8‐Cyclohexyl‐8‐Phosphabicyclo[3.2.1]Oct‐3‐Yl Tropate
Authors: Kashman Y. , Awerbouch O.
Published: November 2013

The preparation and characterization of the phosphorus analogues of cyclohexylnortropine and cyclohexylnorpseudotropine tropates‐ the two C‐3 epimeric 8‐cyclohexyl‐8‐phosphabicyclo[3.2.1] oct‐3‐yl tropates are reported.
Model Experiments Towards Stepwise Degradation of RNA in Dimethylsulphoxide
Authors: Steinschneider A.
Published: November 2013

Model experiments for stepwise degradation of RNA starting from the 3′OH terminus under anhydrous conditions are described. Using dimethylsulphoxide as the solvent, the cis‐glycol grouping of adenosine 5′‐phosphate is converted to the corresponding dialdehyde when periodic acid is used as the oxidant. Subsequently, the elimination of the phosphoryl residue proceeds instantaneously and quantitatively upon addition of aniline at 45°.
On the Pressure Distribution in Uncharged Membranes During Osmotic Plow
Authors: Banin A. , Low P.F.
Published: November 2013

Experiments indicated that adsorptive forces lower the potential energy of water inside uncharged cellulose acetate membranes. As a result it is postulated that the steady‐state pressure distribution during osmosis is affected. In particular, a sudden rise in pressure should occur across the water‐membrane interface. Thus, in this region, water may flow against a pressure gradient.
Steranes and Triterpanes of Israeli Shale
Authors: Ikan R. , Bortinger A.
Published: November 2013

Steranes (cholestane, stigmastane) and triterpanes (lupane, gammacerane) were identified in a bitumen obtained from a shale of Nebi Musa, near Jericho, using combined gas‐liquid — mass spectroscopic technique.
Spin Polarization in the Photoexcitation of the Triplet State of Phenazine in a Rigid Glass
Authors: Levanon H. , Weissman S. I.
Published: November 2013

Phenazine dissolved in a rigid toluene glass is excited to its triplet state by illumination with a modulated light source. The ESR signal is modulated, the nature of the modulation depending on the kinetics of population and depopulation of the triplet sublevels. Modulation of the ESR signal varies across the spectrum because of the dependence of the kinetics on orientation.
Thermal Isomerization of 1,5‐Dimethyl‐1‐Cyclooctene
Authors: Suga K. , Watanabe S. , Fujita T. , Shimada T.
Published: November 2013

Isoprene is selectively dimerized to 1,5‐dimethyl‐1,5‐cyclooctadiene by the catalyst composed of nickel naphthenate, triethylaluminium and tri‐o‐cresylphosphite. At 500° and atmospheric pressure, 1,5‐dimethyl‐1‐cyclooctene thermally isomerizes to 2,6‐dimethyl‐1,7‐octadiene.
Isolation, Properties and Partial Sequence of the Cytochrome C of the Camel, Camelus Dromedarius
Authors: Schejter A. , Grosman Z. , Sokolovsky M.
Published: November 2013

Cytochrome c was purified from the heart of the camel, Camelus dromedarius. Its chemical properties are typical of eukaryotic cytochrome c. Camel heart cytochrome c consists of a single chain of 104 amino acids, a composition closely related to that of mammalian cytochrome c, and a heme peptide identical to horse cytochrome c. However, its spectrum differs from that of all other cytochrome c in having a 16% lower molar absorbancy of the reduced a band. The possible reason for this difference is discussed.
Penicillin Sensitive Formation of D‐Alanine in a Particulate System from Staphylococcus Aureus
Authors: Oppenheim B. , Burstein Y. , Patchornik A.
Published: November 2013

A cell free system from Staphylococcus aureus 52A5 which incorporates UDPMurNAc‐L‐ala‐D‐isoglu‐L‐lys‐D‐ala‐14C‐D‐ala into lipid intermediates and peptidoglycan is described. During peptidoglycan synthesis, glycine binding to the lipid intermediates and peptidoglycan is also demonstrated as well as release of the terminal D‐alanine from the pentapeptide moiety. This release of D‐alanine is strongly inhibited by penicillin G.
A Physicists View of Crystal‐Structure Determination
Authors: Lipson H.
Published: November 2013

The basic operations of crystal‐structure determination are described in terms of optical imaging: the collection of the diffraction data corresponds to the process of scattering by the object, and Fourier synthesis is the production of the image from the scattered radiation. The “phase problem” expresses our inability to devise an apparatus for exploring the relative phases of diffracted X‐ray beams.
On Interpretation of ESCA Spectra with Application to Thymine and Other Molecules
Authors: Rein Robert , Hartman Aba , Nir Shlomo
Published: November 2013

1s binding energies are calculated for nitrogen atoms in thymine, pyrrole, adenine, and pyridine and for carbon atoms in thymine, adenine, pyrrole, and furan, and compared with experimental values. Calculations are performed in the framework of a perturbational model using CNDO molecular wave functions. Interactions of the 1s electron with its own atom are calculated exactly whereas interactions with neighbor atoms are calculated according to two levels of approximation: (1) Point charge approximation. (2) Rigorous calculations of integrals. Magnitudes of the different interactions and integrals are analysed. The questions of assignments of ESCA shifts and the errors inherent in the calculations are discussed.
Photoelectron‐Spectroscopic Assignment of Symmetry Species to the Lower Electronic States of Unsaturated Hydrocarbon Radical Cations
Authors: Heilbronner E.
Published: November 2013

The competitive through‐space and through‐bond interaction of two symmetry‐equivalent, semi‐localized orbitals φa, φb, (= π or lone‐pair orbitals) in a molecule M of Cs or higher symmetry can lead either to the natural order of the corresponding delocalized orbitals, i.e., ψ− ≈︁ (φa ‐ φb)/√2 above ψ+ ≈︁ (φa ‐ φb)/√2 or to the inverted order, i.e., ψ+ above ψ−. It is shown that one can discriminate between these two situations through an analysis of the PE spectrum of a molecule M′ which differs from M only by an additional semi‐localized orbital φc of known symmetry behaviour. The method is exemplified by an investigation of the dependence of the n‐orbital sequence in 3,6‐bridged 1,4‐cyclohexadienes on the dihedral angle between the two CCHCHC moieties.
Interatomic Distances in the Bifluoride Ion
Authors: Carrell H. L. , Donohue Jerry
Published: November 2013

Further refinement has been carried out on the neutron diffraction data for potassium bifluoride. Best agreement was obtained for a physically impossible model which must be rejected on other grounds. Following Ibers, the hydrogen atom is assumed to be centrally located. Combination of spectroscopic and diffraction data from sodium, potassium, and ammonium bifluorides allows a detailed analysis of the thermal motions to be made. The average F ···F distance, after correction, is found to be 2.292 ± 0.004 Å.
Structure Studies on 6a‐Thiathiophthenes and Related Compounds
Authors: Hordvik Asbjørn , Saethre Leif J.
Published: November 2013

The results from structure studies on 6a‐thiathiophthenes show that different substituent groups perturb the bonding in the three‐sulphur sequence to different degrees. Both equal and unequal SS bonds occur in symmetrically as well as in unsymmetrically substituted derivatives.

The specific effect of methyl and phenyl substituents on the sulphur‐sulphur bonding may be described by the results from CNDO/2 calculations on mono‐methyl and mono‐phenyl substituted 6a‐thiathiophthenes. Molecular packing and intermolecular close contacts also seem to affect the SS bonding.

The structures of equally substituted 6a‐thiathiophthene analogues with magnified image and magnified image show, when compared with the equivalent 6a‐thiathiophthene, that magnified image and magnified image cause a pronounced change in the SS bonding, while the perturbation caused by magnified image is negligible.

In symmetrical 6a‐thiathiophthene analogues with magnified image and magnified image, the average bond length in the linear three‐atom sequence is 9 – 12% longer than the respective single bond.
Stevensanaloge, Durch Nickelkomplexe Katalysierte Umlagerung Von Triarylphosphoryliden Und Darstellung Sowie Strukturbestimmung Von Phosphorylid‐Nickeltricarbonylkomplexen
Authors: Heydenreich F. , Mollbach A. , Wilke G. , Dreeskamp H. , Hoffmann E. G. , Schroth G. , Seevogel K. , Stempfle W.
Published: November 2013

The Stevens rearrangement of the triarylphosphorusylids R3 P=CHR′ (III) (R′ = H, CH3, C2 H5) to diarylbenzylphosphines (V) is catalyzed by nickel complexes (e.g., (COD)2 Ni (I)). Attempts to prepare trimesitylphosphine‐methylene result in direct formation of dimesityl (mesitylmethyl) phosphine (XII) — the first recorded direct Stevens rearrangement of a phosphorusylid. Phosphorusylids react with nickeltetracarbonyl without rearrangement to give complexes of the type R3P=CHa · Ni(CO)3 (XIV). The structure of XIV has been established by the IR and NMR spectra and confirmed by an X‐ray structural determination.

B. L. Barnett and C. Krüger, J. Cryst. Mol. Struct., im Druck.

The ylid is bonded to the nickel through the C‐atom with resulting hybridization from sp2 towards sp3.
A New X‐Ray Method for the Determination of the Quaternary Structure of Protein Complexes
Authors: Hoppe W.
Published: November 2013

The determination of the spatial arrangement of subunits in protein complexes is possible by an application of a new method. After appropriate labelling of the subunits with heavy atoms the distances between the subunits can be found from X‐ray experiments. Theoretical and experimental considerations allow us to deduce these distances and to find the relative positions of the subunits within the protein complex.
Photochemical Behaviour of Cyclopropa[c]Chromenes in Alcohols
Authors: Jackson B. , Hug R. , Hansen H.‐J. , Schmid H.
Published: November 2013

Cyclopropa[c] chromenes (VI, VII, VIII, IX) on irradiation with a mercury high‐pressure or low‐pressure lamp in alcoholic solutions (MeOH, EtOH, i‐PrOH) are transformed into the corresponding 2‐(1′‐alkoxy‐but‐3′‐enyl)‐phenols (cf. X, XI, trans. and cis‐XII). Possible mechanisms of this photoreaction are discussed.
Spectroscopic Studies of d‐Pilocarpine and Some Quaternary Derivatives
Authors: Ben‐Bassat A. , Lavie D.
Published: November 2013

Detailed spectroscopic studies have been carried out on the alkaloid d‐pilocarpine as free base and after quaternization. Characteristic changes in the NMR, IR and UV spectroscopic properties have been established following quaternization. The respective mass spectra have been analysed, and characteristic fragmentation patterns are described. The amidic nature of d‐pilocarpinehydroxamic acid has been confirmed by IR, NMR and mass spectrometric measurement.
Polymeric Conductors and Semiconductors
Authors: Mark H.
Published: November 2013

Polymeric conductors up to conductivities of about 102 – 103 ohm cm can be made either by copolymerizing monomers which contain tetracyanoquinolines with monomers which have pronounced salt character or by introducing metal atoms or ions into highly conjugated systems such as polyenes, polyynes or pyropolymers. Both ways are also successful in preparing semiconductors with room temperature conductivities around 10−1 ohm cm and with activation energies of several millivolts.
Fulvenes and Thermochromic Ethylenes. Part 70 Syntheses in the Dibiphenylene‐Ethene (Bifluorenylidene) Series
Authors: Gosnay Ian , Bergmann Ernst D. , Rabinovitz M. , Agranat I.
Published: November 2013

In order to obtain a better insight into the fine‐structure of dibiphenylene‐ethene, the 1,1′‐difluoro‐, 1,1′‐dichloro, 1,1′‐ and 2,2′‐dimethyl derivatives have been prepared using a variety of methods. The attempted preparation of the pure 1,1′‐dibromo‐derivative failed.
Solid‐State Photolysis of Azobis‐3‐Phenyl‐3‐Pentane. Crystal‐Lattice Control of the Stereochemistry of Radical Disproportionation
Authors: Skinner Karen J. , Blaskiewicz Robert J. , Michael McBride J.
Published: November 2013

The 3‐phenyl‐3‐pentyl radicals from photolysis of azobis‐3‐phenyl‐3‐pentane (APP) in solution give 3,4‐diethyl‐3,4‐diphenylhexane and a photolabile product assumed to arise by para coupling. Photolysis of APP as a crystalline solid at −78° gives the disproportionation products 3‐phenylpentane (PPH) and 3‐phenyl‐2‐pentene (PP) as a 3:1 mixture of the E and Z isomers. This stereoisomeric ratio is surprising in terms of the solid‐state molecular conformations, for which a topochemical scheme predicts predominance of the Z isomer. Isotopic distributions in PPH, Z‐PP and E‐PP from photolysis of solid APP which was 82% deuterated in its methylene groups shows: (1) that Z‐PP is formed under strong lattice control; (2) that E‐PP is formed in a process with greater, but not complete, molecular freedom; and (3) that there is often a dynamic competition for hydrogen‐atom donation between the two radicals involved in disproportionation.
Application of Electron Microscopy to the Study of Photochemical Reactions in Organic Solids
Authors: Thomas J. M.
Published: November 2013

Currently available electron microscopic techniques are discussed and illustrated with specific reference to some of the unsolved problems in the photochemistry of organic solids. New techniques, such as dynamical electron diffraction, are outlined and some future prospects are assessed.
A CNDO/2 Study of Dimerization of Methylene
Authors: Tantardini Gian Franco , Simonetta Massimo
Published: November 2013

The CNDO/2 Molecular Orbital method has been used to investigate the energetically favoured path in the dimerization of methylene in the singlet state.
Mechanisms of Photochemical Reactions in Solution. LXXIV. The Photochemistry of 3‐Methyl‐1‐Phenoxybut‐2‐Ene.,
Authors: Carroll Felix A. , Hammond George S.
Published: November 2013

The photochemical reactions of 3‐methyl‐1‐phenoxybut‐2‐ene (γ,γ‐dimethylallyl phenyl ether), I, were investigated in solution and in the gas phase. Irradiation of I resulted in the formation of phenol, II, 3‐methyl‐3‐phenoxybutene, III, 1‐(2‐hydroxyphenyl)‐3‐methylbut‐2‐ene, IV, 1‐(4‐hydroxyphenyl)‐3‐methylbut‐2‐ene, V, 3‐(2‐hydroxyphenyl)‐3‐methylbutene, VI, and 3‐(4‐hydroxyphenyl)‐3‐methylbutene, VII. Formation of III ‐ VII in the gas phase was efficiently quenched by nitric oxide. The results suggest that all products were formed by a dissociation ‐ radical recombination mechanism and that none were formed by concerted processes. The absorption spectrum of I and its quantum yields for fluorescence and photochemical reaction were used to estimate the rates of the processes which deactivate its lowest‐lying excited singlet state. The results suggest that OC bond homolysis need not occur via intersystem crossing from an S1 (π, π*) to a 3σ (CO) state. Fragmentation to radicals, and perhaps rapid non‐radiative decay without chemical reaction, probably involve internal conversion with population of high vibrational levels of the CO bond. Weak electronic interaction between the aromatic nucleus and the olefinic chromophore may also be important.
Crystal Structure of Rb2CoCl4 and Rb3Mn2Cl7
Authors: Amit M. , Horowitz (Zodkevitz) A. , Makovsky J.
Published: November 2013

Previously published cell dimensions of Rb3Mn2Cl7 are confirmed and atomic positions are given. The crystal structure of low temperature Rb2CoCl4 is reported. The material was found to belong to the orthorhombic system, space group Pnma with a = 9.272 ± 0.006 Å, b = 7.283 ± 0.004, c = 12.723 ± 0.006 Å and Z = 2.
Studies on the Specificity of the Interaction Between Peptidyl‐tRNA and E. Coli Ribosomes, Initiation and Elongation Factors
Authors: Degroot N. , Panet A. , Lapidot Y.
Published: November 2013

Several aspects of the binding of peptidyl‐tRNA to E. coli ribosomes were studied. The E. coli binding factor (EF1) does not increase the rate of peptidyl‐tRNA binding. From the results obtained it was concluded that two molecules of Gly2 Phe‐tRNA can bind to one and the same ribosome, but no new peptide bond was formed. Gly, Phe‐tRNA at the A site inhibited the puromycin reaction of Gly2 Phe‐tRNA at the P site of the same ribosome. The binding of peptidyl‐tRNA at the P site activates the adjacent A site for aminoacyl‐tRNA binding.
N,O‐Diarylation of N‐Hydroxycarbamates. Rearrangement and Cleavage Reactions of the Intermediate N,O‐Diarylhydroxylamines
Authors: Sheradsky Tuvia , Salemnick Gad
Published: November 2013

The reactions of benzyl N‐hydroxycarbamate with 2‐ and 4‐nitrofluorobenzene yielded the corresponding benzyl N‐(nitrophenoxy)carbamates. Their reaction with nitrofluorobenzenes yielded derivatives of biphenyl and of diphenyl ether. The formation of these products has been rationalized by assuming the existence of N,O‐diphenylhydroxylamines as intermediates which undergo rearrangement analogous to the benzidine rearrangement.
Synthetic Aspects of Selective Ion Exchangers
Authors: Goldstein S. , Gulko A. , Schmuckler G.
Published: November 2013

New anion exchange resins were prepared by the interaction of sulfonated and chloromethylated crosslinked polystyrene with hexamine, ethylene diamine, and thiourea. The conditions of preparation were based on existing information concerning the analogous monomers and were adapted to the special case of the polymeric matrix.
Raman Study of Mixed Cyanide‐Iodide Complexes of Cadmium in Aqueous Solution
Authors: Yellin N. , Marcus Y.
Published: November 2013

The formation of the mixed iodo‐cyano cadmate (II) complexes at coordination level four in aqueous solutions was examined by Raman spectrophotometry. The existence of the species CdI3CN2− was definitely proven, while the existence of the other species CdI2 (CN)2 2− and CdI(CN)3 2− could not be established.
Thermally Stable Polymers Derived from Itaconic Acid
Authors: Avny Yair , Saghian Nasser , Zilkha Albert
Published: November 2013

Thermally stable polyamides were prepared by reaction of aromatic diamines with pyrrolidone dicarboxylic acids obtained by reaction of itaconic acid with aromatic diamines. The reaction was carried out either by melt poly‐condensation or by converting the diacids to their active mixed anhydrides and reacting them with the diamines. Polybenzimidazoles were prepared by melt polymerization of the pyrrolidone dicarboxylic acids with 3,3′‐diamino‐benzidine. All the polymers were soluble in concentrated sulfuric acid and part of them were also partially soluble in DMF or DMSO. DTA and TGA measurements in air showed that the polyamides were stable up to about 400° and the polybenzimidazoles were stable to 500°.
The Determination of Lithium in Dead Sea Water by Atomic Absorption Spectrophotometry
Authors: Ben‐Zwi N.
Published: November 2013

An atomic absorption spectrometric method is described for the determination of lithium in highly salted solutions, employing the addition method.
Electrochemical Synthesis of Cis‐3, 4‐Dicarbomethoxycyclobutene
Authors: Leftin J. H. , Redpath D. , Pines A. , Gil‐Av E.
Published: November 2013

Anodic oxidation of cis, trans, cis‐3, 4‐dicarbomethoxy‐1, 2‐cyclobutanedicarboxylic acid (I) yields 65% of the title compound (II), which on heating isomerizes stereoselectively into the cis, trans‐muconate III.
The Effect of Conformation on the Interaction of Macromolecules with Surfaces. The Adsorption of Compact Macromolecules
Authors: Silberberg A.
Published: November 2013

The 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

The 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

Using 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

Aluminum 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

A 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

The 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.
Systems, Circuits and Thermodynamics
Authors: Oster George F. , Perelson Alan S.
Published: November 2013

The fundamentals of equilibrium and nonequilibrium thermodynamics are reviewed in the context of dynamical systems and network theory. The resulting mathematical structure forms an appropriate framework in which to discuss complex nonlinear phenomena encountered in biophysics and chemistry.
Resistance and Inductance‐Like Effects in Chemical Reactions: Influence of Time Delays
Authors: Atlan H. , Weisbuch G.
Published: November 2013

Within 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

A 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

Changes 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

Ammonium 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

2,4‐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

The 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 is

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The 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

The 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

UV 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

Four 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

The 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

A 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

The 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

The 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

The 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

The 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

Rhodanese (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.