bluuebunny/crossref_metadata_2025_split huggingface dataset:
Poly‐p‐Aminostyrene from Polyvinylbenzoic Acid by Schmidt Reaction in Pure Sulphuric Acid
Authors: Cwikel Dory , Eisenberg Henryk 
Published: November 2013

AbstractPoly‐p‐vinylbenzoic acid was polymerized from p‐vinylbenzoic acid, and some of its physicochemical properties were studied (infrared and ultraviolet spectrum, solubility, density and refractive index increment in solutions, molecular weight). The polymer was readily transformed to poly‐p‐aminostyrene in a one step reaction by Schmidt transposition, in pure sulphuric acid. Polyampholytes were isolated and characterized at different stages of the reaction.
Polydepsipeptides II: Synthesis and Preliminary Conformational Studies of an Alternating α‐Amino and α‐Hydroxy Acid Polymer
Authors: Goodman Murray , Gilon Chaim , Palumbo Manlio , Ingwall Richard T. 
Published: November 2013

AbstractAn alternating high‐molecular‐weight polymer of L‐valine and L‐lactic acid was synthesized in the solid state. Results from circular dichroism (CD) and nuclear magnetic resonance (NMR) spectra indicate that these polymers are helical in helicogenic solvents such as chloroform and trifluoroethanol (TFE). The conformational analysis is extended to include semi‐empirical energy calculations for alternating α‐amino and α‐hydroxy acid polymers. Preliminary calculations based on depsipeptides from L‐alanine and L‐lactic acid are presented.
Hydrogen‐Deuterium Exchange of Subtilisin Type Carlsberg and Subtilisin Type Novo
Authors: Johansen J. T. , Ottesen M. 
Published: November 2013

AbstractThe hydrogen‐deuterium exchange of diisopropyl phosphate‐inhibited subtilisin (DIP‐subtilisin) Carlsberg type and DIP‐subtilisin Novo type has been measured in the pD interval 2–8. In the pD range 4.5–8 the native DIP‐subtilisins demonstrated closely related exchange properties, especially with respect to the more slowly exchanging fractions of the peptide hydrogens, and this is taken as support for the hypothesis that the two subtilisin molecules have the same internal folding of the peptide chains. The subtilisins exhibit slower exchange rates than any other proteins thus far investigated. The acid denaturation of subtilisin Carlsberg from pD 2–4 is accompanied by the formation of β‐structure. A similar transformation was not observed with subtilisin Novo.
Mapping Toe Active Site of Carboxypeptidase‐A: A Proposed Scheme for Substrate Binding at the Active Site
Authors: Abramowitz‐Kurn Nurith , Schechter Israel 
Published: November 2013

AbstractThe aim of the work presented here was to characterize the active site of carboxypeptidase A. The kinetic constants \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \bar K}_{\rm m} $$\end{document}, kcat and \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C ( = \bar K}_{\rm m} \times {\rm k}_{{\rm cat}} ) $$\end{document} for the enzymatic hydrolysis of the C‐terminal bond in a number of homologous series of peptide substrates were measured. Changes in the kinetic constants due to systematic structural changes in a particular amino acid residue of the substrate are discussed in terms of the interaction of this residue with the corresponding subsite of the enzyme active site. The structural changes included are: (a) elongation of the peptide substrate by one amino acid residue, (b) blocking of the positively‐charged N‐terminal residue by an N‐blocking group, (c) substitution of an L‐amino acid residue by its D‐antipode, and (d) substitution of a particular residue of the substrate from glycyl to alanyl, leucyl, phenylalanyl, cyclohexalanyl or one of the following N‐blocking groups: N‐acetyl, N‐methyloxycarbonyl, N‐phenylpropionyl and N‐benzyloxycarbonyl. The effect of these structural changes in the substrate on the kinetic constants for the hydrolysis of the C‐terminal bond is given by the ratio of the kinetic constants of pairs of homologous substrates differing by a single structural change. Changes in free energy of binding of the substrate‐active site complexes were derived from the ratio of \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \bar K}_{\rm m} $$\end{document} constants of homologous pairs of substrate. Based on the kinetic data presented, the active site of carboxypeptidase A was characterized in terms of (a) length, (b) stereospecificity of the various subsites, and (c). the nature of the interactions between each subsite and the corresponding residue of the substrate, as well as the cooperativity effect of these interactions. Evidence obtained from fitting of model peptide substrate to an atomic model of the active site support the conclusions derived from the kinetic data. In conclusion, we suggest a scheme for binding of peptide substrate to the active site of carboxypeptidase A.
Salt Effects on the Properties of α‐Chymotrypsin: I. Effects on the Enzymic Activity of Chymotrypsin
Authors: Kahana Luna , Shalitin Yechiel 
Published: November 2013

AbstractThe effects of salts on the activity of α‐chymotrypsin have been studied in detail. In high salt concentration (2 M NaCl) the rate of the enzyme‐catalyzed hydrolysis reactions increased compared to that in low salt. Substrates displayed lower Km and higher kcat values, and with irreversible inhibitors the reaction rate rather than binding was affected in high salt. The activity of chymotrypsin towards specific substrates of trypsin was enhanced by high salt to a larger extent than the activity towards its own specific substrates, and polylysine became a good substrate. Apolar competitive inhibitors exhibited tighter binding in high salt. Analysis of the kinetic data indicated that the acylation step was increased much more than the deacylation step. The effectiveness of different salts in general followed the Hofmeister series. High‐salt‐induced conformational change is considered as a factor affecting the enzymic reaction kinetics.
Modulation of Thermolysin Activity. Reversibility of Inactivation and Superactivation
Authors: Blumberg S. , Holmquist B. , Vallee B. L. 
Published: November 2013

AbstractChemical studies on the mechanism of the action of thermolysin implicate a histidyl residue as essential for catalysis and reveal the existence of another residue which can undergo modification with a concomitant large increase in the activity of the enzyme towards a variety of substrates.
Structural and Functional Interrelationships of Adrenocorticotropin and the Melanotropins
Authors: Ramachandran J. 
Published: November 2013

AbstractAnalysis of the structure‐function relationships of ACTH and the melanotropins of the pituitary gland indicates that a tetrapeptide segment common to the structures of these hormones is involved in eliciting such diverse biological actions as stimulation of adrenal steroidogenesis, lipolysis and melanin dispersion. The structural features of the hormones around the common peptide segment serve to distinguish between receptors in the different target tissues and ensure relative specificity of function of such closely related molecules as ACTH and α‐MSH. Although the mammalian adrenal cortical cell and the amphibian melanocyte appear to be stimulated by the same peptide segment, it can be inferred that there are significant differences in the structural features of the receptors in the two cell types even in the region of interaction with the peptide segment. The evolutionary interrelationships of these hormones as well as their specific receptors are also discussed.
The Copper (II) Complexes of Phenyl‐2 Pyridyl Ketone and the Triple Complexes Obtained by Adding Ethylenediamine
Authors: Kirson B. 
Published: November 2013

AbstractCopper salts of low pH (1.8–2.5) combine with phenyl‐2‐pyridyl ketone to form a ketone complex [(Py–CO–C6H5)2Cu]2+. An electrically uncharged complex is obtained at pH > 9 [(Py–C(OH)(C6H5)O−)2Cu]0, liberating two protons from two molecules of the ligand. The stability constant of this complex is β = 16.05. By mixing the copper salts (except the halide) containing this ligand with ethylenediamine, a charged triple complex is obtained at pH < 7 [Py–C(OH)(C6H5) O–Cu–NH2C2H4NH3+]2+. At pH > 9.5, an uncharged triple complex is obtained: {[(Py–C(OH)(C6H5)O−)2Cu}2 · NH2C2H4NH2}0. The copper halide salts produce only an uncharged triple complex; the halide ions are coordinated with the copper atoms. All of these complexes in their solid state, are bi‐ or polynuclear. As a result, they are magnetically subnormal.
The Oxidative Dehydrogenation of Ethylbenzene. Cobalt Molybdate Catalysts
Authors: Joseph A. , Mednick R. L. , Shorr L. M. , Weller S. W. , Rona P. 
Published: November 2013

AbstractThe role of the catalyst and feed composition in the conversion and product distribution in the oxidative dehydrogenation of ethylbenzene, using a series of cobalt molybdate catalysts, was investigated.
Preparation and Nucleophilic Reactions of β‐Fluoro‐γ‐Alkyl Halides
Authors: Shahak Israel , Ittah Ytzhak , Bergmann E. D. 
Published: November 2013

AbstractProblems related to the preparation of β‐fluoro‐γ‐alkyl halides and the nucleophilic reactions of these compounds are described. These compounds are found to be less reactive than the corresponding halides without the fluorine atom. Nucleophilic reactions of these halides are SN2 reactions, and no allylic rearrangements are observed in any case.
Synthesis of Some Polymer Models of Potentially Biologically Active Compounds
Authors: Tahan Menashe , Calderon Ya'akov , Zilkha Albert 
Published: November 2013

Abstract2‐(p‐Styryl)‐4‐carboxyquinoline (vinyl cincophen), its 6‐methyl and 6,7‐benzo derivatives, p‐formylstyryl thiosemicarbazone, and p‐vinyl‐DL‐threo‐β‐phenylserine were synthesized and polymerized.
Carnallite Decomposition into Magnesia, Hydrochloric Acid and Potassium Chloride: II. The Phase Diagram KCl–MgO
Authors: Ashboren (Araten) David , Korob Felix (Efraim) 
Published: November 2013

AbstractDifferential thermal analysis and X‐ray diffraction of 12 different compositions in the phase diagram KCl–MgO disclose that there exists an area of solid solution, extending from ca. 30–80 equiv. % of MgO/2 (10–55 wf. % MgO), and, depending on the composition, from ca. 759°–775°. Besides the solid solution solid MgO occurs in this area. No chemical reaction between the components takes place.
Reactions of Organomagnesium Compounds on the Unsaturated β‐Fluoro Compounds
Authors: Shahak Israel , Ytzhak Ittah , Bergmann E.D. 
Published: November 2013

AbstractReaction of α‐fluoroacrylate with both C‐magnesium and N‐magnesium compounds is described. The fluorine atom is stable in these reactions. The fluorotertiary alcohols obtained are surprisingly stable and undergo dehydration only with difficulty.
Inhibition of Strontium Sulfate Precipitation by Soluble Polymers
Authors: Sarig Sara , Tartakovsky Fania 
Published: November 2013

AbstractThe inhibiting effects of vinyl sulfonate (MVS) and polyvinyl sulfonate (PVS) on the precipitation of strontium sulfate were investigated by absorbance measurements of the turbidity formed. The weights of precipitates retained after 3 h of ripening, by a 0.3 μm Millipore filter from unstirred or stirred solutions containing either PVS or MVS, were determined. The results are interpreted by the heterogeneous nucleation mechanism of crystal growth.
The Reaction of Crotonic Acid with Aldehydes Using Lithium Naphthalenide
Authors: Fujita Tsutomu , Watanabe Shoji , Suga Kyoichi , Nagase Tomoyasu 
Published: November 2013

AbstractLithium naphthalenide reacts with crotonic acid in the presence of diethylamine to give an allylic anion of lithium crotonate. The reaction of the anion with various aldehydes gives a mixture of α and γ adducts.
Chlorinated Phenoxaphosphine and 9‐Methylenexanthene
Authors: Granoth Itshak 
Published: November 2013

Abstract2,3,7,8‐Tetrachlorophenoxaphosphine (Ic), 2,3,6,7,11‐pentachloro‐9‐methylenexanthene (Id) and 2,3,6,7‐tetrachloro‐9‐bromomethylenexanthene (If) have been prepared by the aluminium chloride catalysed condensation of 3,4‐dichlorophenyl ether (II) with phosphorus trichloride, chloroacetyl chloride and bromoacetyl chloride, respectively.
Redox Properties of Tetraphenylporphyrin Complexes
Authors: Wolberg Alexander 
Published: November 2013

AbstractThe redox‐properties of tetraphenylporphyrin‐complexes were studied as a function of substituents on the phenyl group. Electron‐withdrawing chlorine substituents cause a rise of approximately 100 mV for the first ligand oxidation and electron‐donating methoxy‐substituents cause a decrease of about the same magnitude. The redox‐properties of the central metal ion are much less sensitive to these substituents. The Fe3+/Fe2+ transition on the other hand, is seen to depend on the anion used. Taking these effects into account a tentative mechanism is proposed for the oxidation‐behaviour of μ‐oxo‐bis (tetraphenyl)porphyrin‐iron(III).
Kinetics of Reduction of Some CoIII(NH3)5 L Complexes by Substituted Pyridinyl Radicals. A Pulse Radiolytic Study
Authors: Cohen H. , Meyerstein D. 
Published: November 2013

AbstractThe rates of reduction of some CoIII pentaamine complexes by HINA·, and , HNA·, radicals were measured. It was found that HNA· is more reactive than HINA·. The redox potential for the couple HINA·/HINA+ was calculated, E° = 0.80 ± 0.02 V. In the presence of large excess of NA, a catalytic enhancement in the reduction of CoIII(NH3)5 NA and CoIII(NH3)5 Pyridine by Eu2+ was observed. The difference in the mechanism of reduction of CoIII(NH3)5 X by Eu2+ where X = NA or INA is discussed. The redox potential of the HNA·/HNA+ couple was estimated, 0.80 < E° < 1.1 V.
An ESR Study of 17O−2 on Cerium (IV) Oxide
Authors: Gideoni Michael , Kaufherr Nurit , Steinberg Menachem 
Published: November 2013

AbstractOxygen was absorbed on cerium (IV) oxide which had been prepared by heating the cerium (III) oxalate at 1173°K in air. In addition to the naturally occurring isotope mixture of oxygen, an enriched 17O2 (67%) was adsorbed. From the enriched mixture it was concluded that the anionic species obtained was O−2. It was also shown that part of the oxygen was adsorbed as a molecular species. On this sample no isotopic exchange took place between the adsorbed (17O 17O)− and (16O 17O)− anion molecules.
The Formation of CrO2+2 in the Reaction of Cr2+ + O2 in Aqueous Acid Solutions
Authors: Ilan Y. A. , Czapski G. , Ardon M. 
Published: November 2013

AbstractThe reduction rate of Cr3+ by eaq was determined, k8 = 1.7 × 1010 M−1 s−1. The reaction of Cr2+ with O2 was studied, k2 = 1.6 × 108 M−1 s−1. The spectrum of CrO2+2 was obtained both with the pulse radiolysis method and by mixing Cr2+ with excess of O2. It was shown that CrO2+2 decays slowly to yield HCrO−4. The results suggest that the reaction of Cr2+ with O2 is a two electron transfer process.
Studies of the Cis, Cis‐Cyclodeca‐1,6‐Diene System
Authors: Shani Arnon 
Published: November 2013

AbstractIn the course of attempting to synthesize cyclodeca‐1,6‐diyne (IIIa) from cis, cis‐cyclodeca‐1,6‐diene (XIX) derivatives by a successive bromination and dehydrobromination, transannular addition of one mole of bromine to the diene system occurred. The reaction products were bicyclic decalin derivatives. New symmetric and unsymmetric derivatives of XIX were prepared. Various approaches towards obtaining [10]annulene‐quinone (XXIX) are reported.
Transannular Aldol Condensation of Cis, Cis‐Cyclodeca‐3,8‐Dien‐1,6‐Dione
Authors: Shani Arnon 
Published: November 2013

AbstractNMR measurements with Eu(DPM)3, as pseudocontact shift reagent, are able to differentiate between the two very unstable cis‐ and trans‐ketols, obtained by transannular aldol condensations of cis, cis‐cyclodeca‐3,8‐dien‐1,6‐dione. Azulenic compounds are the end products of the condensation.
Singlet Molecular Oxygen and Superoxide Radical Anion
Authors: Rosenthal Ionel 
Published: November 2013

AbstractSinglet molecular oxygen generated photochemically by rubrene sensitization or by direct excitation in a microwave‐discharged stream of oxygen at low pressure is physically quenched by superoxide radical ion in aprotic media, with a quenching rate kq = 3.6 ± 0.1 × 107 M−1 s−1.
Slow Combustion of Methane at Elevated Pressures
Authors: Tripathy N. 
Published: November 2013

AbstractMethane was partially oxidized with oxygen in a batch reactor at pressures of 1700 and 3400 atm and temperatures of 270–480°C. Residence times ranged from 0 to 60 min. Water, methanol, formaldehyde, acetone, carbon monoxide and carbon dioxide were produced in every reaction. In addition, ethanol was formed at high temperatures under nonisothermal conditions and formic acid was detected in reactions at 3400 atm. Products analyses were made with a two‐column gas chromatograph.
Molecular Reaction Dynamics: Impact of Theory on Experiment
Authors: Bernstein Richard B. 
Published: November 2013

AbstractThe field of molecular reaction dynamics deals with the microscopic, molecular‐level mechanism of elementary chemical reactions [1]. The experimental methods which have provided the most insight at this “micro‐level” have been the molecular beam scattering [2] and chemiluminescence techniques [3] (and their derivatives). It has been possible to measure the polarization [4] as well as the angular [5], velocity [6] and internal state [7] distribution of the nascent products of a bimolecular collision as a function of the relative translational [8] and internal energy [9] (and mutual orientation [10]) of the reactants. In addition to detailed cross section measurements for direct‐mode reactions [11], there have been significant new observations on complex‐mode reactions [12], i.e., the (bimolecular) formation and (uni‐molecular) decay of long‐lived intermediate complexes. Theory [13] has provided the conceptual framework upon which to “hang” the experimental data, the means to analyze the observations, and frequently the very incentive for attempting the difficult, micro‐level, experiments. The key concept of the potential energy hypersurface and the basic molecular collision theory underlying elementary chemical reactions have been known since the early days of quantum mechanics. Only recently, however, has quantum chemistry begun to provide ab initio surfaces [14] and computationally feasible procedures [15] to predict the entire course of a reactive collision. The path [16] has nearly been traversed: from Coulomb's law, via the Schrödinger equation, to the scattering cross sections [17], and ultimately the reaction rate constant [18]. The great impact of theory upon experiment in the field of molecular reaction dynamics is illustrated by a few selected “case histories”.
Effects of Electronic Excitation on Reaction Rates at the Solid‐Electrolyte Interface
Authors: Gerischer Heinz 
Published: November 2013

AbstractOne of the central problems of electrochemistry is the understanding of charge transfer reactions at the solid‐electrolyte interface. In such reactions, electronic interactions are altered and chemical bonds are changed or modified. It is obvious that electronic excitation of the involved species which is usually obtained by light absorption will effect the reaction rate or even the reaction products. The excitation of electronic states, present at the interface between a solid and an electrolyte can effect electron transfer processes as well as ion transfer steps. The efficiency depends on the lifetime of the excited states and on the rate of the reactions. Due to the high rate of electron transfer, such a process is much more frequently accelerated by electronic excitation than ion transfer. Examples are discussed for both cases with excitation at the interface either on the side of the solid (metals, semiconductors, or insulators) or of the electrolyte. In the solid, effects caused by excited electrons or excited holes can be distinguished. Excitation in the electrolyte serves as a model for a mechanism of spectral sensitization. The generation of photo‐voltages at a semiconductor/electrolyte interface could possibly be used for energy conversion.
Progress and Prospects in the Conquest of Schistosomiasis
Authors: Werbel Leslie M. 
Published: November 2013

AbstractSchistosomiasis is a waterborne, snail mediated parasitic infection which afflicts over 200 million people. The disease has persisted since ancient times, and if anything is thriving in the shadow of technological progress. Some 50 years after the introduction of organoantimonials for treatment of the disease no entirely satisfactory curative, nontoxic agent for schistosomiasis exists. Recent progress with two novel types of extremely potent schistosomicidal agents, the nitrothiazolines and the 2H‐[1] benzothiopyrano‐[4,3,2‐cd] indazoles will be discussed. In particular the dissociation of toxic side effects from antischistosome activity via structure modification will be emphasized. Clinical evaluation of these agents will determine whether we have succeeded in this battle against one of the developing world's most pressing human health problems.
Materials Chemistry in the Development of Thermonuclear Fusion Energy
Authors: Gruen Dieter M. 
Published: November 2013

AbstractThe promise of thermonuclear fusion energy ultimately to provide a relatively clean, cheap, dependable and potentially inexhaustible energy source, justifies the increasing world‐wide effort which is being directed to the achievement of this goal. Although the major effort in this field must still be devoted to reaching the Lawson criterion, the problems associated with the construction and operation of fusion power reactors are so challenging as to require serious attention even today. The discussion of the role of materials chemistry in the development of fusion reactors will focus on some of the major problem areas such as tritium breeding, recovery and permeation; chemical effects of thermonuclear plasma interactions with first wall materials; and the solid state chemistry of high performance insulating as well as superconducting materials.
Chemical Storage of Solar Energy and Photochemical Fuel Formation
Authors: Stein G. 
Published: November 2013

AbstractRecent advances in the quantum utilization of solar energy will be surveyed. The efficiency of photovoltaic devices in combination with electrical storage will be compared with photogalvanic and photochemical systems. Photochemical formation of fuel (including hydrogen) in homogeneous and heterogeneous devices will be discussed in detail.
An Epistemological Note on Chirality
Authors: Mislow Kurt , Bickart Paul 
Published: November 2013

AbstractThe terms “chiral” and “achiral” are sharply defined when applied to geometric figures or models. The same terms are also commonly used to refer to the real systems to which these models have been adjoined, e.g., molecules, solvents, or reagents. Here, the terms are not sharply defined but depend upon conditions of measurement. The contrast between the geometric and operational usages is discussed in detail.