bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid‐Gas Reactions, Part III. Interaction of Solid Dibenzoylethylenes with Bromine and Iodine Vapours
Authors: Hadjoudis E.
Published: November 2013

The cis and trans isomers of solid 1,2‐dibenzoylethylene, 1,2‐di‐p‐chlorobenzoylethylene and 1,2‐di‐p‐methyl‐benzoylethylene yield, on exposure to bromine vapour at room temperature, the trans‐adducts in quantitative yield except in the case of cis‐1,2‐di‐p‐methyl‐benzoylethylene where isomerisation takes place prior to or during the bromination process yielding the same dibromide as the trans‐isomer. The cis‐trans isomerisation of the three solid cis‐isomers by iodine vapour has been analysed by determining the rate of the reaction from the change in IR transmittance. The isomerisation follows a first‐order mechanism. A plot of ΔH++ against ΔS++ is linear.
Conductance of Polyelectrolyte Solutions: A One—Dimensional Model
Authors: Lifson Shneior
Published: November 2013

An exact derivation of the conductance of parallel double‐layers as a one‐dimensional model of polyelectrolyte solutions is presented. The conductance tends to a finite limit, inversely proportional to the square of the (one‐dimensional) polyelectrolyte concentration, as the polyelectrolyte charge density increases indefinitely. In other words, the conductance tends to zero with the square of the inverse polyelectrolyte concentration in a way independent of the polyelectrolyte charge density. Approaching these limits, the ionic mobility of the counterions predominates over that of the fixed charges. The assumption of superposition of the external and internal electrostatic fields is shown to be inexact even at the limit of very small external fields.
Dichlorocarbene Chlorination of Steroids
Authors: Ikan R. , Markus A. , Goldschmidt Z.
Published: November 2013

Dichlorocarbene, generated from chloroform, aqueous sodium hydroxide and catalytic amount of triethylbenzylammonium chloride, reacts readily with steroids (5α‐stigmastan‐3β‐ol, 5α‐lanost‐8(9)‐en‐3β‐ol‐17‐one and estrone) leading to the corresponding chlorides in fair yields.
Calcium Oxalate Crystallization from Inhibited Solutions
Authors: Sarig Sara , Raphael Micha , Ron Amos
Published: November 2013

The induction periods of calcium oxalate precipitation at high supersaturations were measured and the degrees of inhibition in the presence of different trace quantities of polyphosphates were determined. Crystals were grown from uninhibited and from partially inhibited solutions. The presence of both polyphosphates and of cationic impurities affects the crystal habit very strongly: rod‐like crystals up to 3 mm in length grew from inhibited solutions in a week, whereas very small round particles of 10−2 mm size sprang from the uninhibited solutions. Some previously published mechanisms are reviewed, and a new, comprehensive, heterogeneous nucleation mechanism of growth is proposed to explain the simultaneous inhibition of precipitation and inducement to growth of large crystals.
The Triple Complexes of Copper and its Complexes with the Schiff Bases of Pyridine‐2‐Aldehyde or 2‐Acetyl Pyridine with Aliphatic Diamines
Authors: Kirson B.
Published: November 2013

When alcohol solutions of copper salts are mixed with pyridine‐2‐aldehyde (PyA) and aliphatic diamines (A) (either ethylene diamine or 1,3‐propane diamine) at pH ≤ 6.5, a copper complex containing a molecule of the pyridine derivative and a molecule of the diamine is formed, or a complex containing an additional molecule of the pyridine aldehyde is formed, depending on the PyA concentration in the solution. When the molar concentrations are Cu2+: 2PyA: A, and the pH ≥ 10, the copper (II) ion is reduced to monovalent copper, and a Schiff base of the copper complex is formed. When alcoholic solutions of copper, 2‐acetylpyridine (AcPy), and aliphatic diamines are mixed in concentration ratios of Cu2+: 2AcPy: A, and pH > 9.5, again, the copper ion is reduced and a Schiff base is obtained. At pH = 7.5 a triple complex is obtained only from the copper chloride, containing either or one or two molecules of acetylpyridine, depending on the concentration of the latter in the solution.
Planar and Nonplanar Unsaturation. Preparation, Properties and Molecular‐Orbital Characterization of Some Fluoro‐Derivatives of Anthracene and Anthraquinone
Authors: Meyer A. Y. , Goldblum A.
Published: November 2013

Several fluoroanthracenes (I‐III) and fluoroanthraquinones (IV‐VII) were prepared, and their PMR and UV spectra, as well as dipole moments, recorded. These are discussed in terms of molecular‐orbital data, both of the pi‐electronic type (including nonbonding 2p‐orbitals) and of the all‐valence‐electron type. PMR signals can be assigned on the basis of such calculations. The interpretation of UV spectra is straightforward in the case of fluoroanthracenes, but other techniques are required for fluoroanthraquinones. Measured dipole moments are close to the theoretical, except in the case of 1, 4, 5, 8‐tetrafluoroanthraquinone. A distorted structure is proposed for this molecule.
Poly‐p‐Aminostyrene from Polyvinylbenzoic Acid by Schmidt Reaction in Pure Sulphuric Acid
Authors: Cwikel Dory , Eisenberg Henryk
Published: November 2013

Poly‐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

An 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

The 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

The 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

The 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

Chemical 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

Analysis 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

Copper 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

The 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

Problems 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

2‐(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

Differential 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

Reaction 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

The 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

Lithium 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

2,3,7,8‐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

The 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

The 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

Oxygen 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

The 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

In 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

NMR 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

Singlet 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

Methane 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

The 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”.
The Electronic Theory of Photochemical Reactions
Authors: Salem Lionel
Published: November 2013

The four electronic states of diradicals, surface crossings in state correlation diagrams, topicity and avoided surface crossings are shown to be essential components of the electronic theory of photochemical reactions.
Effects of Electronic Excitation on Reaction Rates at the Solid‐Electrolyte Interface
Authors: Gerischer Heinz
Published: November 2013

One 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

Schistosomiasis 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

The 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

Recent 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

The 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.
Chiroptical Properties and Conformation of Dehydrophenylalanine Peptides
Authors: Pieroni Osvaldo , Fissi Adriano , Merlino Stefano , Ciardelli Francesco
Published: November 2013

Some N‐acylated α, β‐unsaturated peptides (dehydropeptides) containing one, two or three dehydrophenylalanine (dehydro‐Phe) residues and a C‐terminal L‐amino acidic residue have been prepared and characterized by NMR, IR and UV absorption. For N‐actyl‐(dehydro‐Phe)2‐L‐Ala the crystal and molecular structure have been determined by X‐ray diffraction analysis. CD spectra of N‐acetyl‐(dehydro‐Phe)‐ϵ‐Cbzo‐L‐Lys and N‐acetyl‐(dehydro‐Phe)2‐ϵ‐Cbzo‐L‐Lys have been measured in different solvents and, of N‐acetyl‐(dehydro‐Phe)2‐L‐Val, in the presence of different amounts of urea. The results have been compared with those for N‐acetyl‐(dehydro‐Phe)‐(dehydro‐Tyr)‐L‐Glu, for the tetrapeptide N‐acetyl‐(dehydro‐Phe)3‐L‐Val, and for analogous compounds already reported [J. Am. Chem. Soc., 97, 5820 (1975)]. Crystalline molecular structure and chiroptical properties are consistent with the hypothesis that the dehydropeptides assume in solution a chiral conformation based on a 4 → 1 hydrogen‐bonded ten‐membered ring, also referred to as β‐turn. The importance of these systems for the understanding of the conformational properties of polypeptides containing D‐L sequences is discussed.
Direct Resolution of Amino Acid Enantiomers by High Pressure Liquid Chromatography
Authors: Lefebvre Bernard , Audebert Roland , Quivoron Claude
Published: November 2013

We have synthetized an optically active macromolecular chromatographic packing from cross‐linked polyacrylamide grafted with an optically active α‐amino acid. This packing, in the form of small beads, slightly swells in water. Its granularity, porosity and rigidity are suitable for high pressure liquid chromatography. Such packings, complexed by a metallic ion, are efficient for the resolution of many underivatized racemic α‐amino acids by elution with water. As an example, on one of these packings, containing Cu++ions, enantiomers of valine, threonine, isoleucine, serine, phenylalanine, tyrosine, tryptophan, and asparagine are completely resolved in less than one hour.
A New Case of Asymmetric Synthesis Using Circularly Polarized Light
Authors: Nicoud J. F. , Kagan H. B.
Published: November 2013

Asymmetric photocyclization of N‐methyl N‐aryl enamines by circularly polarized light gives several optically active N‐methyl dihydroindoles. In the synthesis of N‐methyl 2‐phenyl dihydroindole, the optical yield was evaluated to be 0.20%, which is the same order of magnitude as in the asymmetric synthesis of helicenes. The mechanisms of these reactions are discussed.
A Chemical Mass Spectrometric Method for Mapping Short Range Order in Solid‐Solutions Undergoing Topochemical Dimerisation. Application to Some Racemic Mixtures Containing the Chiral Sec‐Butyl Group
Authors: Addadi L. , Gati E. , Lahav M. , Leiserowitz L.
Published: November 2013

A new chemical mass‐spectrometric method for mapping short range order in crystalline solid‐solutions of enantiomers undergoing topochemical reactions is described. We have applied this method to assigning the microstructure of the racemic mixtures of the diacrylates 1 and 2, each one in two dimorphic modifications and which undergo topochemical (2π + 2π) photocyclodimerisation and photocyclopolymerisation. All crystalline phases are disordered with respect to the enantiomeric sec‐butyl group. While the two polymorphs of 1 and polymorph α of 2 form random solid‐solutions, polymorph β of 2 forms partially ordered crystals in which the degree of order depends on the method of crystallization. It could be established that in the latter system the degree of order across the two independent centres of inversion is measurably different. The scope and limitation of this new method are discussed.
Photochemical Asymmetric Synthesis. Irradiation of Ring and Open‐chain Derivatives of L‐Erythritol 1,4‐Dicinnamate
Authors: Green Bernard S. , Hagler Arnold T. , Rabinsohn Yechiel , Rejtõ Miriam
Published: November 2013

The two analogs, (−)‐2,3‐di‐O‐methyl‐L‐erythritol 1,4‐di‐trans‐cinnamate, 1, and (−)‐2,3‐O‐isopropylidene‐L‐erythritol 1,4‐di‐trans‐cinnamate, 2, were irradiated in benzene solution. Intramolecular 2 + 2 photocycloaddition occurs in both derivatives and the stereochemistry of the cyclobutane products, after removal of the L‐erythritol, was established in both cases as β (symmetry m)‐ and δ (symmetry 2)‐truxinate. While the asymmetric induction was 85% in the synthesis of (+)‐dimethyl δ‐truxinate from the open‐chain dimethoxy derivative 1, the more rigid isopropylidene ring derivative led to an asymmetric induction of only 6% and afforded the opposite enantioner, (−)‐dimethyl δ‐truxinate, in excess. Computer simulation of the diastereomeric ground state conformations which are believed to lead to the observed products from 1 was carried out to enable better understanding of the factors which determine the asymmetric synthesis. The simulations afford geometries and relative energies of the product precursor conformations. The results are in qualitative agreement with the experimental observations in predicting an excess of one of the two possible δ‐diastereomers. Since the geometry is also obtained by the simulation, it allows one to predict the absolute configuration of the predominant chiral product.
Studies on Organodisulphides as Metal Ligands. II. The Crystal and Molecular Structure of Re2Br2(CO)6S2Me2, A Compound Containing a Dimethyldisulphide Bridge Across the Two Metals. Comparison Between Solid‐State and Solution Data for Re2Br2(CO)6S2R2(R = Me, Ph)
Authors: Bernal Ivan , Atwood Jerry L. , Calderazzo Fausto , Vitali Dario
Published: November 2013

The crystal and molecular structure of the compound having the composition Re2Br2(CO)6S2(CH3)2 was determined from three‐dimensional X‐ray diffraction data collected by automated counter methods. The substrate crystallises in the space group P21/c with cell constants a = 6.798(2), b = 14.493(5), c = 17.028(6) Å and β = 94.70(3)°, V = 1673.0 Å3 and Z = 4 molecules/unit cell for dcalc. 3.161g cm−3; dobe = 3.15(2)g cm−3. The dimeric molecules consist of two hexacoordinated Re(I) cations surrounded by three carbonyl groups in a fac arrangement with one occupying an axial position and two equatorial ones. The other two axial positions of the dimer are occupied by the two sulphur atoms of the bridging dimethyldisulphide ligand. The (OC)2ReBr2(OC)2 fragment is not planar, instead, there is a folding of the molecule along the Br–Br′ vector, such that the two ReBr2 fragments make an angle of 28.0°. The Re–CO fragments are normal and compare well in structural parameters with other studied elsewhere; the same is true of the Re–Br and of the Re–S bonds. The changes introduced in the dimethyldisulphide ligand are principally in the S–S distance, the C–S–S angle and the C–S–S–C torsional angle, which are noticeably affected by bonding to the Re(I) cation.

Spectral data for the Re2Br2(CO)6S2R2 complexes (R=Me, Ph, C6H4–pMe) have been collected in solution. The equilibrium (R = Me, Ph)

Re2Br2(CO)6S2R2 + 2 THF ⇋ Re2Br2(CO)6(THF)2 + S2R2

has been found to be strongly affected by the nature of the group R. In spite of a larger variation of the torsional angle when dimethyldisulfide leaves the coordination sphere of the metal, the displacement of the S2Me2 ligand by tetrahydrofuran is a less favourable process than the corresponding reaction with Re2Br2(CO)6S2Ph2. If solvation effects by THF can be ignored, the conclusion is that the Re2S2Me2 system is inherently stronger than Re2S2Ph2. This conclusion could not easily be drawn from a consideration of solid state parameters alone.
X‐Ray Photoelectron Spectra of Inorganic Molecules. XIX. Thiocyanato and Isothiocyanato Complexes of the Transition Metals: Carbon 1s, Nitrogen 1s and Sulfur 2p Binding Energies and their Possible Correlation with the Mode of Thiocyanate Bonding
Authors: Best S. A. , Walton R. A.
Published: November 2013

The X‐ray photoelectron spectra of a series of thiocyanato and isothiocyanato complexes of the transition metals have been recorded. Carbon 1st, nitrogen 1s and sulfur 2p binding energies were measured in order to establish whether there was any clear correlation with the mode of thiocyanate bonding. Complexes which were studied included those possessing M–NCS, M–SCN and M–NCS–M units. In addition, several species were investigated which contained two different thiocyanate environments within the same molecule. These were the ionic complexes [Cu(tren)(NCS)]SCN and [Cu(trien)(SCN)]SCN, where tren = tris(2‐aminoethyl)amine and trien = triethylenetetramine, and Pd(dppe)(NCS)(SCN), where dppe = 1,2‐bis(diphenylphosphino)ethane. The latter complex contains both N‐ and S‐bound thiocyanate. Within the range of complexes studied, the S 2p energies of M–NCS, M–SCN and SCN− differ at most by a few tenths of an electron volt. This indicates that the XPS technique will not usually permit a ready distinction between these different bonding modes in most transition metal complexes.
Electron Transfer Reactions Induced by Excited State Quenching
Authors: Meyer Thomas J.
Published: November 2013

Electron transfer quenching of excited states can lead to separated redox products for which back electron transfer can be highly favored. Application of flash photolysis leads to a relaxation technique in which a system at equilibrium is perturbed by separate excitation‐quenching steps. The rates of several electron transfer reactions have been studied using the technique based on redox quenching of the CT excited state Ru(bpy)2+−3. Quenching and back electron transfer has also been observed for a series of excited states including examples of CT(Ru(phen)2+3, etc), π ‐ π * (Pd(OEP)), and f‐f(Eu(phen)3+3) states. In recent work, even non‐emitting excited states have been shown to be quenched by electron transfer which suggests that the technique may have broad applicability. In properly designed systems containing more than one redox reagent, the quenching and back electron transfer steps can be separated and reactions have been studied which are driven photocatalytically by excited states like Ru(bpy)2+−3. A modification of the technique has been used to estimate the self‐exchange rate for the Ru(bpy)3+/2+3 couple and to measure rates of electron transfer for a series of systems where the rates measured do not involve a Ru‐couple.
Catalytic Asymmetric Hydrogenation Using Hydridorhodium(I) Diop Complexes [Diop = 2,3‐0‐Isopropylidene‐2,3‐Dihydroxy‐1,4‐Bis (Diphenylphosphino)Butane]
Authors: James Brian R. , Mahajan Devinder
Published: November 2013

The hydridorhodium(I) phosphine complex HRh[(+)‐diop]2, [(+)‐diop = (+)‐2,3,‐0‐isopropylidene‐2,3‐dihydroxy‐1,4‐bis(diphenylphosphino)butane] has been studied for catalytic hydrogenation of a number of olefinic substrates. Certain prochiral olefinic carboxylic acids have been reduced to products with up to about 60% enantiomeric excess. Rate data show the importance of the degree of substitution at the olefinic bond in terms of steric effects, and the ‐COOH function of the substrate likely plays a role. Kinetic and spectrophotometric studies on the hydrogenation of itaconic acid in n‐butanol‐toluene (2:1) solutions under mild conditions are best interpreted in terms of a mechanism involving formation of a metal alkyl via coordination of the olefinic substrate, followed by reaction with H2 to give saturated product and the starting catalyst complex. The actual catalyst is thought to be HRh(diop)(diop*), where diop* represents a monodentate diop with one dangling ‐CH2PPh2 moiety.

The catalyst systems are somewhat complicated by the occurrence of slower side‐reactions, the extent of these varying from negligible for the more rapidly reducing substrates, to possibly of prime importance in the slow hydrogenations. The initial hydride catalyst, for example, is slowly decomposed to the cationic [Rh(diop)2]+ complex by protons from the olefinic substrate. Under H2, the cation reversibly forms a dihydride. The cation is also formed from a reaction that appears to involve an intermediate alkyl complex and the butanol.
Simultaneous Asymmetric Hydrogenation and Hydroformylation by Chiral Platinum Complexes
Authors: Consiglio Giambattista , Pino Piero
Published: November 2013

An asymmetric induction of 37.6% has been obtained in the asymmetric hydrogenation of α‐ethylstyrene with the [(−)‐DIOP]‐PtCl2/SnCl2 catalytic system. When carbon monoxide is present, both hydrogenation and hydroformylation of the substrate occur. The prevailing antipode arises from the opposite prochiral face of the olefin in hydrogenation and hydroformylation respectively.
Iridium and Rhodium Nitrosyl o‐Catecholato Metal Complexes
Authors: Ghedini Mauro , Denti Gianfranco , Dolcetti Giuliano
Published: November 2013

The synthesis and characterization of several novel tetra and pentacoordinate catecholato metal nitrosyl complexes of the type Ir(NO)(1,2‐O2C6H3‐3 or 4‐R)‐P(C6H5)3): 3‐R = iso C3H7; 4‐R = COOH, H, CH3, terC4H9; and M(NO)(1,2‐O2C6H3‐4‐R)(P(C6H5)3): M = Ir and Rh; R = NO2, CHO, COOCH3; M = Rh; R = H; are reported together with their IR spectra. Two different classes of cathecolato complexes are obtained, tetracoordinate and pentacoordinate. The pentacoordinate complexes achieve tetracoordination, in solution, by spontaneous and reversible release of a phosphine molecule. The separation of the crystalline species seems to be determined either by the electron withdrawing or releasing power of the cathecolato ring substituents rather than by the solubility of the single species in our preparative conditions. The possibility for the pentacoordinate complexes to have a packed trigonal bipyramid geometry with axial bent nitrosyl NO− and axial equatorial catechol ligand is supported by the easy phosphine dissociation to form the tetracoordinate, which has been observed both in solution and in field desorption mass spectra measurements. For the tetracoordinate complexes a square planar geometry with linear nitrosyl, NO+, is proposed.
Chemical Analysis of Hybrids of Withania somnifera L. (Dun.). 1. Chemotypes III (Israel) by Indian I (Delhi)
Authors: Kirson Isaac , Abraham Arieh , Lavie David
Published: November 2013

Reciprocal crossbreeding between Withania somnifera chemotype III (Israel) and chemotype Indian I (Delhi) were performed. The F1 offspring of this cross was characterized by significant changes in the main steroidal lactone constituents of the parent plants. From the withaferin A (9) and the withanone (2) both present as major constituents in the parent Indian I, the former had disappeared in the hybrid and was replaced by withanolide D (10), whereas the latter was still present, though in about one third of the original quantity. It was accompanied by 17‐deoxy‐20‐hydroxy withanone (2) and by withanolide T (1); the enzymatic system leading to hydroxylation at C20 (20αF‐OH) has a dominant character. Two new withanolides have been isolated from this F1 offspring, namely withanolide T (1) (20αF‐hydroxy withanone) and withanolide U (5) (4β‐hydroxy‐withanolide G). The structures assigned to these two new compounds are based on spectral evidence (NMR, IR and UV) and analysis of their fragmentation under electron impact.
The Flavonoids: Indispensable Additions to a Recent Coverage
Authors: Gottlieb Otto R.
Published: November 2013

While the flavonoids are biosynthetically and constitutionally a homogeneous group of compounds, the neoflavonoids, as presently defined, may be biosynthetically and are constitutionally a heterogeneous group. Biogenetic considerations which lead to these conclusions and reviews on occurrence, structural elucidation and synthesis are presented for 1,3‐diarylpropanes and flavans (flavonoids), as well as for cinnamylphenols and 2‐aryl‐3‐methylbenzofurans (neoflavonoids), with the purpose of providing addenda to the 1975 monograph, The Flavonoids, edited by Harborne, Mabry and Mabry for Chapman and Hall, London.
Techniques for Signal Assignment in 13C‐NMR Spectroscopy of Naturally Occurring Aromatic Compounds
Authors: Gottlieb Hugo E.
Published: November 2013

Techniques of signal assignment of 13C‐NMR spectra of organic compounds, and in particular those of natural origin, are reviewed. They include symmetry, chemical shift considerations, spin‐spin coupling (both one‐bond and long‐range), spin relaxation (T1, NOE), isotopic enrichment and complexing agents. Special emphasis is given to the effects of oxygenated substituents on aromatic rings.
VIII. What Systems Can Be Studied, Have Been Studied, and Should Be Studied?
Authors: Coppens Philip
Published: November 2013

The status of charge density studies is reviewed with special emphasis on factors limiting its potential, on a priori estimates of position‐dependent standard deviations and on present and possible future applications of the method.
XIII. Charge Deformation and Vibrational Smearing
Authors: Hirshfeld F. L.
Published: November 2013

A tractable model for treating the vibrational smearing is provided by the convolution approximation, which divides the molecular charge into fragments that are assumed to move rigidly with the atomic nuclei. This model is of questionable validity for internal vibrations, the required charge decomposition is largely arbitrary, the atomic vibration amplitudes may not be well determined and rotational motion introduces special difficulties. These deficiencies are especially severe if we attempt, by means of a charge deformation model and least‐squares refinement, to derive static charge density maps from the X‐ray data. The greatest uncertainty occurs at the nuclear positions, around hydrogen atoms, or in groups undergoing large librational motion. Yet with suitable caution and a well tested deformation model, least‐squares refinement can yield more detailed and dependable charge‐density information than can Fourier methods.
XIV. Static Versus Dynamic Densities
Authors: Coppens Philip , Stevens Edwin D.
Published: November 2013

Experimental density maps are affected by both thermal smearing and limited resolution. The two effects commute and have to be introduced in theoretical density maps for a quantitative comparison between theory and experiment. An appropriate procedure is discussed and some applications are given. The error expression for the thermally smeared multipolar density is given. No error analysis exists for the thermally deconvoluted “at rest” density at infinite resolution, which corresponds to an extrapolation beyond the limit of experimental information.
XVII. Spatial Partitioning of Charge Density
Authors: Hirshfeld F. L.
Published: November 2013

Quantitative indices of a molecular charge distribution are provided by the values of volume integrals of the deformation density times a set of appropriate sampling functions. These integrals may, for example, represent the net charges in particular atomic or bond regions. A sharing function derived from the promolecule density defines a general partitioning of any molecule into bonded‐atom fragments, whose net charges and multipole moments determine the electrostatic properties of the molecule. Expressions are available for estimating the experimental accuracy of such indices but they are not easy to evaluate nor very reliable.