bluuebunny/crossref_metadata_2025_split huggingface dataset:
Internal Addition of Ketocarbenes to Conjugated Double Bonds
Authors: Becker D. , Loewenthal H. J. E. 
Published: November 2013

AbstractThe internal, copper‐catalysed, addition of keto‐carbenes (generated from a diazoketone group) to a double bond conjugated either to a ketone or carboxylic ester function has been found to be a feasible preparative reaction in selected cases. This, together with the facile and regiospecific hydrogenolysis of the resulting 1,2‐dicarbonyl cyclopropane intermediate, appear to constitute a convenient route to multifunctional bridged‐ring systems.
Cyclooctatetraene Tetramer
Authors: Hoesch L. , Dreiding A. S. , Oth J.F.M. 
Published: November 2013

AbstractThe constitution of the cyclooctatetraene tetramer, mp 182° (VI), is derived from its spectroscopic properties and from the results of catalytic hydrogenation experiments. The 1H‐NMR spectrum of VI is temperature dependent and indicates the presence of two homotropylidene residues in the molecule, one isomerizing isodynamically, the other anisodynamically. The mass spectrum of VI shows remarkable similarities with those of the cyclooctatetraene dimer, mp 76° (III) and of bullvalene (IX). The tetramer VI is concluded to be the product of a 2 + 4‐cycloaddition reaction between the cyclohexa‐1,3‐diene units of two molecules of III. The tetramer VI appears to be configurationally unique. This is explained and a configuration is proposed on the basis of the stereospecificity of the reaction leading to VI.
The Crystal and Molecular Structure of 11‐Chloro‐3,8‐Methano‐[11] Annulenone
Authors: Beddoes R. L. , Mills O. S. 
Published: November 2013

AbstractThe crystal structure of a benzhomotropone, 11‐chloro‐3,8‐methano‐[11] annulenone, has been solved and refined to R = 4.5%. The crystals are monoclinic, a = 6.854, b = 7.681, c = 19.324 Å, β = 108.54°, spacegroup P21/c. The molecule exhibits alternation of bond lengths with evidence of slight π‐electron delocalisation. Principal bond lengths are CC(mean) 1.344, CC(mean) 1.442, CCl 1.748 and CO 1.231 Å
Topochemistry Part XXXV. The Formation of Mixed Dimers from Solid Solutions of Trans‐Cinnamic Acids and Trans‐Cinnamides
Authors: Hung J. D. , Lahav M. , Luwisch M. , Schmidt G.M.J. 
Published: November 2013

AbstractIrradiation (λ >300 nm) of eight two‐component solid solutions of β‐arylacrylamides, prepared by melting and crystallising equimolar quantities of the amides tr‐ArCH:CHCONE where Ar=C6H5, p‐MeOC6H4, p‐ClC6H4, p‐MeC6H4, and 2‐thienyl, which appeared in the α crystal form, gave three photoproducts for each system studied: two α‐truxillic homodimers, derived from the respective monomers, and an α‐truxillic heterodimer. No other isomers were found. Similarly, two‐component solid solutions were prepared by melting and crystallising ring‐substituted cinnamic acids (tr‐ArCH:CHCO2H, where Ar=C6H5 (α‐form), p—ClC6H4(β), p‐MeC6H4(α), p‐MeOC6H4(γ), o‐ClC6H4(β) and o‐CH3C6H4(γ)) and irradiated. A solid solution of two α‐type acids (each photodimerising in the solid to α‐truxillic acid) behaved like the amides, affording two α‐truxillic homodimers and an α‐truxillic heterodimer. A solid solution of an α‐type acid with a β‐type acid (photodimerising to β‐truxinic acids) gave six photoproducts: three α‐truxillic acid dimers and three β‐truxinic acid dimers (i.e., four homodimers and two heterodimers). Irradiation of a solution of a γ‐type acid (non‐photodimerising in the solid state) with an α‐type acid afforded α‐truxillic dimers (two homodimers and one heterodimer). The above results are consistent with mutual miscibility of the two components which gives rise to mixed crystal formation and subsequent photo‐behaviour within each crystal which is characteristic of the particular lattice type. However, irradiation of the mixed crystals from p‐methoxycinnamic acid (γ‐type) and p‐chlorocinnamic acid (β‐type), which afford two α‐truxillic dimers (methoxy‐homodimer and methoxy, chloro‐heterodimer) and two β‐truxinic dimers (chloro‐homodimer and methoxy, chloro‐heterodimer) indicates that new phases, unobserved for the pure compounds, can also be generated. The new dimers were all characterised by the NMR and mass spectra of their dimethyl ester derivatives and, when possible, by conversion to known compounds.
Molecular Packing Modes. Part X. The Crystal and Molecular Structures of Trans, Trans‐Muconic Acid
Authors: Bernstein J. , Leiserowitz L. 
Published: November 2013

Abstracttrans, trans‐Muconic acid C6H6O4 crystallises in the space group magnified image, with a = 8.982, b = 9.895, c = 3.787 Å, α = 103.68, β=75.27, γ= 101.58°, and two centrosymmetric molecules per unit cell. The structure was solved from 1671 reflections measured by an ω/2θ scan with Mo Kα radiation on an IBM 1800 computer‐controlled Siemens diffractometer, and refined anisotropically (on F2) to R = 0.078. The geometries in the carbon chains of the two independent molecules are essentially identical; their bond lengths match to within 0.003 Å. The carboxyl group of one molecule is statistically disordered (C‐O 1.257, 1.275 Å) whereas in the second molecule the bond lengths differ significantly (1.236, 1.294 Å), indicating a greater degree of order. A careful consideration of the packing mode allows us to interpret the difference between the two molecules.
Multichain Polyproline Coated with Histidyl and Glutamyl Residues — A Potent Synthetic Immunogen
Authors: Shaltiel Shmuel , Mozes Edna , Sela Michael 
Published: November 2013

AbstractA new, water soluble multichain polypeptide coated with short peptides containing histidyl and glutamyl residues was prepared, using the 2,4‐dinitro‐phenyl group for masking the imidazole imino‐nitrogen during synthesis. The polymer obtained after thiolytic deblockage (multi‐poly(L‐histidyl, L‐glutamyl)‐poly‐L‐prolyl – – poly‐L‐lysine) was shown to be a potent synthetic immunogen, capable of provoking a high titer of antibodies in mice already at the primary response, and useful for studying the genetic control of the immune response.
Comments on the Nature of the Oxidized Form of the Nickel Dimethylglyoxime Complex
Authors: Lati J. , Meyerstein D. 
Published: November 2013

AbstractThe pulse radiolytic technique has been used in order to prove that the central nickel atom, in the oxidized form of the nickel‐dimethyl‐glyoxime complex, is in its trivalent oxidation state.
Kinetics of Bromination of Stilbene in Chloroform in the Presence of a Macrocyclic Polyether
Authors: Shchori E. , Jagu‐Grodzinski J. 
Published: November 2013

AbstractThe effect of ethers on the bromination of stilbene in chloroform solutions was investigated spectrophotometrically. In the presence of hydrogen bromide the macrocyclic ether dicyclohexyl‐18‐crown‐6 (DCC) may act as a strong inhibitor, while tetrahydrofuran accelerates the bromination reaction.
The Radiosensitizing Actions of Ketonic Agents and Oxygen in Bacterial Spores Suspended in Aqueous and Non‐Aqueous Milieux
Authors: Tallentire A. , Jones A. B. , Jacobs G. P. 
Published: November 2013

AbstractIncreasing concentrations of the ketonic agents, diacetyl, acetone, acetophenone and p‐nitroacetophenone, cause regular increases in the radiosensitivity of aqueous anoxic spores to an extent that is some 40% of that achieved by O2 alone; no effect on radiosensitivity is observed with agents in the presence of O2. The effectiveness of these agents and O2 as radiosensitizers ranks on a molar basis in the same order as that of their electron affinities, indicating that their modes of action are in some way associated with radiation‐induced electrons. A lack of radiosensitizing action of diacetyl and p‐nitroacetophenone in dried spores and of p‐nitroacetophenone in suspensions of spores in non‐aqueous liquids supports the notion that the origin of their actions is within the water inside the cell.
Electrical Mobility of Counterions in Polyelectrolyte Solutions
Authors: Shavit Nehemia 
Published: November 2013

AbstractElectrical mobilities of counterions in aqueous solutions of potassium polyacrylate, potassium polymethacrylate and sodium polymethacrylate were investigated by moving boundary electrophoresis. At constant polymer concentration, the mobility of counterions decreases with an increase in the degree of neutralization. At a constant degree of neutralization, the mobility increases with an increase in the concentration of the polyelectrolyte. The mobilities of the polyion were derived from the counterion mobility and conductance. The fraction of bound ions increases with the degree of neutralization and reaches a value of about 60%. Osmotic coefficients were evaluated from the mobility data and compared with the values derived from osmotic measurements.
Biopolymer — Small Molecule Interactions. Optical Properties of the System Biliverdin‐Serum Albumin in Aqueous Medium
Authors: Blauer G. , Zvilichovsky B. 
Published: November 2013

AbstractCircular dichroism (CD) and light‐absorption measurements in the wavelength range 300 to 650 nm were carried out for complexes of biliverdin (∼ 2.5 × 10−5 M) with either bovine or human serum albumin (charcoal treated) in aqueous solution (25–27°C) at several protein concentrations and pH values in the range 4 to 10. In all cases investigated, two large ellipticity bands were measured near 385 nm and about 650 nm, respectively, which were of opposite sign. In addition, two smaller bands near 300 and 535 nm were resolved by computer analysis into Gaussian curves of the CD spectrum of biliverdin‐human serum albumin complexes. The main CD bands were inverted in their sign in biliverdin‐bovine serum albumin complexes when compared at pH 5 and 10. Under the conditions used, free biliverdin did not show significant optical activity. The optical activity observed for the complexes is attributed to electric transition dipole coupling of biliverdin with protein transitions and to possible formation of skewed conformations of the biliverdin chromophore upon binding, leading to inherent dissymmetry. Unlike the corresponding bilirubin complexes investigated previously, there appears to be no evidence for substantial band splitting in the small molecule occurring upon binding to the biopolymer. Thus the presence of a center methene bridge instead of an isolating methylene group, the latter allowing internal rotation in the bile pigment, appears largely to determine the mechanism of generation of optical activity. In the case of bilirubin and at excess serum albumin, the observed optical activity is considered to be due mainly to exciton coupling between electric transition dipole moments of the dipyrromethene chromophores within the asymmetrically bound bilirubin. The optical properties investigated may serve as a very sensitive measure of the different types of interaction between the biopolymer and the small conjugated molecule which result from structural and conformational differences of the molecules participating in complex formation.
Polymeric Salicylic Acid Derivatives
Authors: Weiner Ben‐Zion , Zilkha Albert 
Published: November 2013

AbstractThe O‐methacryloyl derivatives of methyl, ethyl and phenyl salicylate, of salicylamide and of salicyl hydrazide were prepared by the reaction of the respective compounds with methacryloyl chloride and were polymerized by heating with azobisisobutyronitrile. Preliminary evaluation of the monomeric and the polymeric compounds for analgetic activity showed that part of the compounds had a longer duration of activity than aspirin.
Synthesis of N‐Alkyl‐α‐Sulfo‐β‐Alanines
Authors: Levi Shalom , Gertner David , Zilkha Albert 
Published: November 2013

AbstractA number of N‐alkyl substituted α‐sulfo‐β‐alanines were synthesized by direct sulfonation of the corresponding N‐alkyl‐β‐alanines.
Kinetics and Equilibria in the System Pyrophosphate‐Nickel (II). Evidence for Two Parallel Reaction Paths; Influence of Ionic Strength on the Ion Pair Constant
Authors: Perlmutter‐Hayman Berta , Secco F. 
Published: November 2013

AbstractThe kinetics of the reaction between Ni2+ and pyrophosphate have been investigated over a wider range of conditions than previously. At 25°, a variation of the ionic strength between 0.02 and 0.20 M (achieved by adding potassium nitrate at appropriate concentrations) showed that the salt effect, though acting on the formation constant of an ion pair rather than on the rate constant of the rate‐determining step, is essentially “classical”. By varying the pH between 4.5 and 7.0, at least two parallel reaction paths were observed, involving Ni2+ and the ions HP2O3−7 and H2P2O2−7. The latter path has a rate constant that is ∼28 times smaller than that of the former and makes an appreciable contribution to the observed rate only at the two lowest pH values. Possible reasons for this difference in reactivity are discussed. The rate constant for the path involving HP2O3−7 was 1.61 × 106M−1 s−1 at 25°, I = 0.1 M. The activation parameters for this path are ΔH≠ = 18.8 Kcal mole−1 and ΔS≠ = 33 e.u. All kinetic experiments were carried out by the T‐jump method. The equilibrium constants necessary for the evaluation of the results were determined by potentiometric titration.
Physical Properties of Alumina Prepared from Machtesh Ramon Ores
Authors: Wolberg A. , Eger I. 
Published: November 2013

AbstractHigh purity alumina is prepared from local ores, containing about 35% alumina, and from low‐grade, 20%, HCl solution. Iron impurities are removed by solvent extraction, and upon pyrolysis, high grade 60% HCl gas is collected. The amorphous alumina obtained at 350°C is transformed to “transition alumina” at 600°C with an increase in surface area; subsequently at 1000–1100°C, high purity crystalline corundum is obtained. The transition‐ and amorphous alumina seem to have promising qualities for desiccant and catalytic use.
Preparation and Crystal Structures of Some Compounds of the A3 BX5 Type (A = Cs, Tl, NH4, B = Mn, Fe, Co, X = Cl, Br)
Authors: Amit M. , Horowitz (Zodkevitz) A. , Ron E. , Makovsky J. 
Published: November 2013

AbstractThe compounds Cs3 FeBr5, Cs3MnBr5,Tl3FeCl5, Tl3CoCl5, (NH4)3FeCl5 and (NH4)3CoCl5 were prepared and their crystal structures determined. Cs3FeBr5, Cs3MnBr5, Tl3FeCl5 and Tl3CoCl5 belong to the tetragonal system, space group 14/mcm, isostructural with Cs3CoCl5 [1]. (NH4)3FeCl5 and (NH4)3CoCl5 belong to the orthorhombic system, space group Pnma, isostructural with (NH4)3ZnCl5 [2].
Unsymmetrical Azoalkanes I. Thermal Decomposition of 1‐Cyano‐1′‐Methoxy‐Azo‐Iso‐Propane
Authors: Malament Donald S. 
Published: November 2013

AbstractThe thermal decomposition of 1‐cyano‐1′‐methoxy‐azo‐iso‐propane (CMA) in decalin, N,N‐dimethylaniline (NNDA) dimethylformamide (DMF), ethylene glycol (EG), and benzonitrile (PhCN) was studied at 54.7° to 69.7°C. A rate enhancement of about four is noted in going from decalin to ethylene glycol, which is the largest solvent effect noted for azoalkane decomposition. This is also the first example of a thermolysis of an azoalkane of type R‐N;NR′ being faster than either of its symmetrical analogs, RNNR or R′NNR′.
Stability of Side‐Chain Protecting Groups in Solid‐Phase Peptide Synthesis
Authors: Erickson Bruce W. , Merrifield R. B. 
Published: November 2013

AbstractThe relative first‐order rates of deprotection of N∈‐benzyloxycarbonyllysine in 2%, 10%, and 50% trifluoroacetic acid in dichloromethane at 20° are 1, 50, and 1000, respectively. The N∈‐2‐chlorobenzyloxycarbonyl group is at least 60 times more stable than the N∈‐benzyloxycarbonyl group under solid‐phase conditions, because no branched peptides (< 0.2 mole%) were formed during synthesis of decalysylvaline using Nα‐tert‐butyloxycarbonyl‐N∈‐2‐chlorobenzyloxycarbonyllysine. Since O‐2‐chlorobenzylserine, Nim‐tosylhistidine, Nim‐2,4‐dinitrophenylhistidine and S‐4‐methylbenzylcysteine were completely stable in 50% trifluoroacetic acid–dichloromethane for over 200 h, these side‐chain protecting groups should be suitable for the solid‐phase synthesis of large peptides.
Conformational Properties of Histidine Related Polymers
Authors: Scoffone E. , Peggion E. 
Published: November 2013

AbstractIn briefly reviewing the results of conformational studies on histidine‐related polymers, two main problems appear to be unsolved at the present time, namely, the conformations to be assigned to poly‐(1‐benzyl)‐L‐histidine · HClO4 in trifluoroethanol and to charge‐free poly‐L‐histidine (PLH) in water. In both cases the right‐handed α‐helical form must be ruled out. The optical rotatory properties are of little help in solving the problem unambiguosly, because of the complication of the side‐chain chromophores. By slow neutralization of PLH hydrochloride solutions, solid samples could be obtained in which the polymer molecules should have the same conformation as in solution. Similarly, slow addition of HClO4 to a concentrated solution of poly‐(1‐benzyl)‐L‐histidine (PBLH) causes precipitation of PBLH · HClO4 in which the same conformation as in solution should be maintained. X‐ray diffraction studies on polymer samples obtained in such a way should provide more information for the conformation of PBLH · HClO4 and of deprotonated PLH in water.
p‐Azido‐L‐Phenylalanine Peptides. I: Synthesis of Peptide Ligands for Chymotrypsin and Aminopeptidases
Authors: Escher Emanuel , Jost Rolf , Zuber Herbert , Schwyzer Robert 
Published: November 2013

Abstractp‐Azido‐L‐phenylalanine peptides as ligands for α‐chymotrypsin and aminopeptidases were synthesized in two ways: (i) by direct incorporation of f‐butoxycarbonyl‐p‐azido‐L‐phenylalanine or its active esters, or (ii) by conversion of the nitro groups of the corresponding p‐nitrophenylalanine‐containing peptides into azido functions. Both procedures yielded O‐t‐butylthreonyl‐p‐azidophenylalanylproline (L, L, L) which, like its parent tripeptide O‐t‐butylthreonyl‐phenylalanylproline (L, L, L), acted as a competitive inhibitor for leucine aminopeptidase (Ki ≈ 7 to 8 × 10−6 M). The two peptides p‐azidophenylalanylphenylalanine (L, L) and p‐azido‐phenylalanylphenylalanylproline (L, L, L) proved to be substrates for leucine aminopeptidase and for both aminopeptidases I and II from Bacillus stearothermophilus. Acetyl‐p‐azidophenylalanine ethyl ester (L) is a substrate of α‐chymotrypsin with Km ≈ 6 × 10−4 M, closely resembling that of N‐acetyltyrosine ethyl ester (L), Km ≈ 5.4 × 10−4 M, but with an approximately 100‐fold reduced maximum velocity of hydrolysis (Vm ≈ 1.3 s−1 versus 211 s−1). The results obtained with photo‐affinity labelling will be described in a forthcoming paper.
Structure and Substrate Specificity in the Serine Enzymes
Authors: Blow D. M. 
Published: November 2013

AbstractAvailable data on the primary and secondary specificities of chymotrypsin, trypsin, elastase and subtilisin are reviewed in relation to their structures. For chymotrypsin and trypsin, proper binding in the main specificity pocket S1 is sufficient to ensure almost perfect orientation of the substrate for hydrolysis. For these enzymes further binding at S2 and S3 increases the binding energy slightly but has little effect on kcat. For subtilisin and elastase, binding at S2–S4 is important to maintain the correct orientation of the hydrolyzed bond. The mechanism proposed for subtilisin, whereby movements of 1 Å at P′1 stabilize the transition state of the reaction, seems unlikely to occur in chymotrypsin. For all these enzymes, proper orientation of the leaving group at S1 can have a further significant effect on kcat. Slight differences between the secondary specificities of trypsin and chymotrypsin are likely, owing to the presence of tyrosine at residue 151 and the deletion of residue 218 in trypsin.
Binding of d‐Amino Acid Residues to the Aromatic Binding Sites of α‐Chymotrypsin, Subtilisin Novo and Subtilisin Carlsberg
Authors: Bosshard Hans Rudolf 
Published: November 2013

AbstractInhibition of CT†, S. Novo and S. Carlsberg by peptides (virtual substrates) of the structure Z‐L‐Ala‐L‐Ala‐L(or D)P1‡ and Ac‐L(or D)‐P1 has been studied. P1 stands for a variety of amino acids. Standard free energies of binding, ΔF°, were determined from inhibition experiments with ester substrates. The differences between standard free energies of binding of configurational isomers to CT are similar (ΔΔF° = −0.5 to −0.8 kcal/mole) regardless of the structure of the side chain of P1. Binding of both isomers is governed by the same pKa, 7.3. These findings are interpreted as follows: LLD tripeptides as compared to LLL tripeptides differ in the interaction of the carboxyl group and the Ca‐proton of P1 with subsite S1 of CT. Acetyl‐D‐amino acids as compared to the L‐enantiomers differ in the positioning of the carboxyl and the acetyl group on the enzyme. All inhibitors preserve the hydrophobic S1‐P1 interaction irrespective of the configuration of P1. In contrast, ΔΔF°‐values for inhibitor binding to S. Novo and S. Carlsberg scatter between −0.2 and −1.6 kcal/mole indicating grossly different, and probably multiple binding modes for the individual inhibitors. The impact of the latter finding on the mapping technique is discussed.
Comparative Studies of the Active Site Region of Lysozymes from Eleven Different Sources
Authors: Sharon Nathan , Eshdat Yuval , Maoz Ilana , Bernstein Yael , Prager Ellen M. , Wilson Allan C. 
Published: November 2013

AbstractLysozymes from 11 different sources were examined for their ability to react with the affinity label 2′,3′‐epoxypropyl β‐glycoside of di‐(N‐acetyl‐D‐glucosamine) and in some cases with the corresponding derivative of tri‐(N‐acetyl‐D‐glucosamine). Their fluorescence spectra, in the presence or absence of tri‐(N‐acetyl‐D‐glucosamine), and their transglycosylase activity were also examined. The results obtained suggest that these lysozymes can be classified into two groups: Group I includes the lysozymes derived from the egg‐whites of bobwhite quail, chachalaca, duck, hen, Japanese quail, ring‐necked pheasant and turkey, and from human leukemic urine; Group II includes the lysozymes from bacteriophage T4, goose egg‐white and papaya latex. The lysozymes of group I are irreversibly inactivated by the epoxypropyl β‐glycosides and exhibit similar fluorescence spectra which shift to the blue upon the addition of tri‐(N‐acetyl‐D‐glucosamine). Moreover, they catalyse the transfer of disaccharide residues from the bacterial cell wall tetra saccharide to N‐acetyl‐D‐glucosamine, D‐glucose, D‐mannose and L‐fucose, at rates which are similar for the different enzymes. It is concluded that the active sites of the enzymes of Group I are all similar, and that they differ from those of the other three lysozymes.
The Thermal Effects of Nucleation and Crystallization of KBr and KCl Solutions. II. The Heat Of Nucleation and the Supersaturated Solution
Authors: Glasner Abraham , Tassa Menachem 
Published: November 2013

AbstractIt is shown that the induction period commonly observed in the crystallization of salts from aqueous solutions is due to a heterogeneous nucleation process made apparent by the release of heat. The metastable supersaturated solution is therefore a solution of particles, and the supersaturation limit can be extended by the addition of a good nucleator. In the case of KBr and KCl the halogenoplumbate complex ions are good nucleators. The heat evolved during the nucleation process is proportional to the concentration of the lead ions and the supersaturation limit is a kinetic function of the concentration of the lead ions. The size of the fine particles that can be held in a supersaturated solution and σ, “the crystal‐liquid surface tension”, were determined by the use of the Ostwald‐Freundlich equation. The thermal effects can thus be quantitatively accounted for.
The Redox Potential of the O2–O−2 System in Aqueous Media
Authors: Ilan Yael A. , Meisel Dan , Czapski Gidon 
Published: November 2013

AbstractO−2 radicals were formed in the presence of 2,5‐ dimethyl benzoquinone (DMBQ). The equilibrium constant of the electron transfer reaction DMBQ + O−2 ⇌ DMBQ− + O2 was determined. From this value and from E0(DMBQ/DMBQ−) we calculated the redox potential of the couple O2/O−2, as E0 (O2/O−2) = −0.33 V.