bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Use of Synthetic Polyamino Acids for the Detection and Purification of Novel Proteolytic Enzymes
Authors: Yaron Arieh 
Published: November 2013

AbstractPolyamino acids were used as substrates for the detection and purification of new exopeptidases from bacteria. The enzymes, which were obtained in pure form and were characterized, include: aminopeptidase P, clostridial aminopeptidase, dipeptidocarboxypeptidase and a nonspecific dipeptidase. The possible application for sequential hydrolysis by the combined action of the two aminopeptidases was demonstrated by accomplishing complete hydrolysis of a proline‐rich nonapeptide, bradykinin. The dipeptidocarboxypeptidase, which produces dipeptides from the carboxyl end, and the dipeptidase, which then hydrolyses the dipeptides formed, indicate an efficient mechanism by which polypeptides are hydrolyzed from the carboxyl end of the molecule. The unique nature of the peptide bond, in which proline is involved through its nitrogen, is pointed out and the possible role of proline as a residue that protects terminal regions of polypeptides against the hydrolytic action of exopeptidases is discussed.
Phenylacetyl and Phenylpropionyl Amino Acids: Their Inhibitory Effect on Glutamine Synthetase and Their Resistance to Acylase. I
Authors: Lustig N. , Spiegelstein‐Klarfeld H. , Schneider E. , Lichtenstein N. 
Published: November 2013

AbstractThe preparation of a number of phenylacetyl and 3‐phenylpropionyl derivatives of amino acids is described. Derivatives containing more than one aromatic group markedly inhibit ovine brain glutamine synthetase. All phenylacetyl and phenylpropionyl derivatives tested were resistant to hog kidney acylase I.
The Thermal Effects of Nucleation and Crystallization of KBr and KCL Solutions. III. The Heat of Crystallization and the Co‐Precipitation of Lead Ions
Authors: Glasner Abraham , Tassa Menachem 
Published: November 2013

AbstractSalt solutions saturated at 44° C and containing varying amounts of lead ions were allowed to cool to about 29°C in 5.5 h. The total heat, ΔHt, evolved decreased to 2/3 of its highest value with the increase of Pb2+‐concentration, while the amount of salt crystallized, Wc, decreased to nil. The distribution coefficient of Pb2+ between crystals and solution was 10.5 and 9.8 for KBr and KCl respectively. The high lead content improved the perfection of the crystals. The results are consistent with a two‐stage mechanism of crystallization: heterogeneous nucleation by complex ions and growth of crystals by the addition of bloc nuclei.
Boron Phosphate: Preparation in Aqueous Medium; Physical and Chemical Characterization
Authors: Ashboren (Araten) David 
Published: November 2013

AbstractHeating equimolar amounts of pure phosphoric and boric acids in aqueous solution yields, at 130°, a solid boron phosphate of the composition R = P2O5/B2O3 = 1:1.71. Increasing the calcination temperature to 575° increases R to 1:1.29 due to evaporation of boron‐values. Further heating to 850° causes no additional weight losses. The specific surface decreases monotonically with the calcination temperature, from 7.4 to 0.5 m2/g. X‐ray diffraction data indicate that up to 10 min heating at 800°, increased calcination temperature causes a monotonic decrease in the unit cell dimensions, while prolonged heating (48 h) at this temperature reverses this trend.
The Liquid/Solid Alkylation of Alkali Metal Pyrazolates
Authors: Mayer‐Sommer Georg E. , Schmidt Gerhard M. J. 
Published: November 2013

AbstractThe reactions of the lithium, sodium, potassium and cesium derivatives of 3‐methyl‐5‐carbomethoxy‐pyrazole, of 3‐methyl‐5‐ethyl‐pyrazole and of 3‐methyl‐5‐methoxy‐methylene‐pyrazole with methyl iodide, allyl bromide and benzyl chloride were investigated in 1,2‐dimethoxy‐ethane solution and at a liquid/solid interface (suspension of the pyrazole in a 1:1 mixture of n‐hexane and n‐heptane). Comparison of the ratios of the two nitrogen alkylated products formed from the reaction in solution and at the liquid/solid interface, suggests that the latter ratio is determined by the size of the alkali metal cation and by the presence of a coordination centre placed non‐symmetrically with respect to the mirror plane passing through the nitrogen‐nitrogen bond. It is suggested that a “cation in the way” effect is responsible for the liquid/solid‐interface alkylation results.
Ortho Effects. I. The Mechanisms of the H3O and CH3O2 Elimination from the Molecular Ion of N‐Methyl Ortho‐Nitro‐Para‐Toluidine
Authors: Zaretskii Zeev V. I. , Amit Boaz , Patchornik Avraham 
Published: November 2013

AbstractThe molecular ion of the N‐methyl ortho‐nitro‐para‐toluidine (I) readily eliminates H3O. The sources of the H atoms lost were proved by deuterium labeling to be an HNCH3 group as well as, probably, the C‐methyl group of the aromatic ring. The interaction between the N‐methyl and nitro groups in I also leads to the expulsion of CH3O2 from the molecular ion.
Molecular Size Effects in the Kinetics of the Electroreduction of Nitroalkanes on Mercury
Authors: Kashti S. , Kirowa‐Eisner E. , Gileadi E. 
Published: November 2013

AbstractThe reduction of nitroalkanes at the dropping mercury electrode in neutral solutions (pH 5.4–7.4) was studied. Careful measurements at the foot of the polarographic wave allow accurate determination of the Tafel slopes to within ± 1 mV, thus the effect of molecular size on the Tafel slope could be determined. The analysis of the results indicates that the adsorbed intermediate, which is a charged species, is situated about halfway between the metal surface and the outer Helmholtz plane. It is also shown that the intermediate is adsorbed with the functional nitro group lying flat on the surface. Only the carbon atoms in the position α and β to the nitrogen atom seem to occupy space on the surface. The importance of employing several members of a homologous series having a common functional group to evaluate the mechanism of electrode reactions is emphasized and the importance of employing the combined isotherm in such analysis is pointed out.
Chemical Approach to Genetics
Authors: Lavie David , Kirson Issac , Abraham Arieh 
Published: November 2013

AbstractThe modifications taking place in the substitution pattern of organic molecules during cross breeding by pollination has been investigated. Through the process of hybridisation of different “chemotypes” of Withania somnifera (Solanaceae), changes have been observed among the substituents present in the steroidal lactones of the withanolide type which are characteristic for this and related species. Several reciprocal cross‐pollinations were performed between the types and the structures of the withanolides produced in the leaves were analysed and determined. These studies led to an understanding of the biogenetic processes leading to specific substitution patterns, and in certain cases enabled a genetic control over the compounds produced in the plant. Compounds not present in natural types could be anticipated to be formed, and indeed were present in the hybrids. Through these studies an insight on the reactions governed by the genetic background of the types taking part in the hybridisation was achieved. Groupings, when found in specific locations of the skeleton could be described as present there due to dominant or recessive genetic characters. These conclusions were reached following analysis of a large number of offsprings for several generations. This method enabled the study of the genetic characters of a plant on the chemical level.
Vibrational Photochemistry
Authors: Bergmann K. , Leone S. R. , Macdonald R. G. , Bradley Moore C. 
Published: November 2013

AbstractThe increase in the rate of chemical reactions with vibrational excitation opens the possibility for selective photochemical processes and isotope enrichment. Recent measurements of chemical reaction rates for vibrationally excited molecules are discussed. A simple kinetic model is used to illustrate some limits on possible process parameters.
Vibrational Electronic Coupling and a Close Look at a Severe Case
Authors: Ross I. G. 
Published: November 2013

AbstractElectronic spectroscopy, at once the oldest and most intricate branch of spectroscopy, has seen intense activity over the past decade. The difference between small‐molecule and large‐molecule spectroscopy is pointed out. The emphasis here is on larger polyatomics. Certain developments of note, especially of the interpretation of unresolved rotational fine structure, are mentioned. No point of principle has remained more tantalizing than the issue of the integrity of an electronic state: to what extent are electronic and nuclear motions really separable, in the Born‐Oppenheimer sense? There is much new theory, yet quantitative applications of theory to real cases are few, especially in polyatomic molecules. A straightforward computational approach to vibronic (= vibrational‐electronic) coupling in molecules such as naphthalene has proved to be quantitatively successful. Physical insight is harder to obtain, however, but a fairly straightforward explanation (based on a polyatomic version of Walsh's rules) can be offered for the presence of exceptionally strong vibronic coupling between two excited electronic states of azulene (C10H8). The effects of this coupling are so profound that the electronic spectrum is highly sensitive to such minor influences as partial deuteration or changes of solvent. These effects can be modelled rather successfully.
Chiral Organotin Compounds
Authors: Gielen Marcel , Simon Serge , Tondeur Yves , van De Steen Michel , Hoogzand Cornelis , van Den Eynde Ivan 
Published: November 2013

AbstractSeveral classes of organotin compounds are configurationally stable within the NMR time‐scale and are even optically stable for weeks. Optically active tetraorganotin compounds, triorganotin hydrides and an optically active (triorganogermyl)triorganotin compound have been synthesized. Two reactions transforming optically active triorganotin hydrides into optically active tetraorganotin compounds are described.
Optical Activity and Lifetime Measurements of Tris‐(2,2′‐Bipyridine) Ruthenium (II) Bromide: Evidence for some Singlet‐Singlet Emission
Authors: Gafni Ari , Steinberg Izchak Z. 
Published: November 2013

AbstractEvidence for some emission from the first excited singlet state of tris‐(2,2′‐bipyridine) ruthenium (II) bromide is presented based on circular dichroism, circular polarization of luminescence and fluorescence decay measurements. The anisotropy factors in absorption and emission assume very similar values in the wavelength region where these two spectra overlap. Moreover, the two anisotropy factors change markedly in this wavelength range indicating the existence of a second emission band at the short wavelength edge of the main phosphorescence band of the chelate. This observation is further supported by fluorescence decay measurements which reveal biexponential decay kinetics with a fast decaying component at the short wavelength edge of the emission.
Steric Demands of Tertiary Phosphine Ligands
Authors: Clark Howard C. 
Published: November 2013

AbstractThe concept of Cone Angle as defined by Tolman provides a useful measure of relative sizes of phosphine ligands. In attempting to arrive at better descriptions of absolute sizes, the importance of ligand intermeshing is illustrated, and recent calculations of the steric demands of phosphine ligands are reviewed. The effect of steric compression of the ligand, and the effect of possible variations in the metal‐phosphorus distance are also considered.
The Isolation of Stable Platinum(II) σ‐Allylic Derivatives
Authors: Pearson Ralph G. , Laurent Michel 
Published: November 2013

AbstractThe isolation of some stable platinum(II)‐σ‐allylic complexes is reported. The complexes, trans‐Pt(σ‐all)X(PEt3)2:(X = CI, all = allyl, crotyl; X = Br, all = allyl) are synthesized by the oxidative addition of allylic halide to Pt(PEt3)4 in hexane at room temperature. They were characterized by infrared, 1H NMR and 13C NMR spectroscopy.
A Biomimetic Synthesis of Benzo[c]Phenanthridine Alkaloid Nitidine
Authors: Kametani Tetsuji , Takemura Makoto , Ihara Masataka , Fukumoto Keiichiro , Takahashi Keiichi 
Published: November 2013

AbstractOxidation of 1,2,3,4‐tetrahydro‐7‐hydroxy‐6‐methoxy‐3‐(4,5‐dimethoxy‐2‐vinylphenyl)‐2‐methylisoquinoline (10), derived from the corresponding berbine methiodide (8), with lead tetraacetate, followed by acidic treatments, gave 5,6‐dihydro‐8‐hydroxy‐2,3,9‐trimethoxy‐5‐methylbenzo[c]phenenthridine (20). By a similar procedure, 1,2,3,4‐tetrahydro‐7‐hydroxy‐6‐methoxy‐3‐(4,5‐methylenedioxy‐2‐vinylphenyl)‐2‐methylisoquinoline (11) was converted to cis‐8‐acetoxy‐4b,5,6,10b‐tetrahydro‐9‐methoxy‐5‐methyl‐2,3‐methylenedioxybenzo[c]phenanthridine (17), whose hydrolysis with hydrochloric acid followed by methylation with diazomethane furnished dihydronitidine (22).
Synthesis of a Steroidal Dicarbamate Related to Meprobamate from 3‐Ketobisnorcholenal
Authors: Golander Yechiel , Breuer Eli , Sarel Shalom 
Published: November 2013

AbstractCondensation of 3‐ketobisnorcholenal (1) with malononitrile could be directed selectively to the aldehyde group to afford dicyanomethylene ketone 3. Ketalization of 3 with ethylene glycol followed by alkaline hydrolysis gave the aldehydo dioxolane 5, which served as starting material for the syntheses of 1,3‐propanediol derivatives 7 and 10 and their respective dicarbamates 9 and 11.
III. Total X‐ray Scattering and Two‐Electron Density Functions
Authors: Stewart Robert F. 
Published: November 2013

AbstractWithin the Waller–Hartree theory it is possible to map out the interelectron density function (the diagonal elements of the intracule matrix) from an analysis of total X‐ray scattering intensities. Theoretical studies of He and H2 show that electron correlation effects substantially influence total X‐ray scattering intensities, but do not appreciably alter the elastic X‐ray scattering intensity. On the other hand, theoretical studies of Be(1S), Ne(1S) and CO(1Σ*) indicate that electron correlation influences both total and elastic X‐ray scattering intensities by comparable amounts (∼ 1–2%), but at differing regions of the scattering vector variable.
XVIII. On the Relation Between the Spatial Electron Density and the Conformational Properties of Molecular Systems
Authors: Hagler A. T. 
Published: November 2013

AbstractThe increasing power of computer simulation experiments for molecular systems is discussed. These include such apparently disparate calculations as Monte Carlo simulation of solvent structure in biological systems, conformational analysis and folding of oligopeptide chains, and lattice‐energy calculations and the effect of lattice forces on molecular geometry. All such calculations have in common the requirement of an analytic expression of the energy of the system as a function of the inter‐ and intramolecular coordinates of interest.The nature and derivation of these force fields and their relation to the spatial electron densities in relevant molecular systems is reviewed. The method of the derivation of intermolecular force fields from crystal data of amides is outlined. It is shown that information which may be obtained from ab‐initio molecular orbital or X‐ray diffraction studies, population analysis, and total and difference electron density maps, may be used in conjunction with the crystal data both to verify (or test) assumptions made in the derivation and to help in the formulation of the models on which the analytical expressions for the energy are based. Finally, the relation between intramolecular forces and the electron distribution as represented in difference electron density maps is discussed. Several examples involving carbonyl compounds are presented, in which changes in the molecular geometry, intramolecular forces and vibrational frequencies on protonation and substitution are discussed both in terms of “valence or Urey—Bradley” type interactions and the changes which occur in the difference electron density maps.
Resonant and Near‐Resonant Rayleigh and Raman Scattering for a Diatomic Molecule
Authors: Berg J. O. , Robinson G. W. 
Published: November 2013

AbstractUsing the results of a unified theory of scattering in the time‐independent (narrow exciting line) limit, excitation profiles for Rayleigh and Raman cross sections have been calculated for an actual diatomic molecule from over 8000 cm−1 off resonance into the resonance region. Three interference effects, a “vibrational level interference”, an “on‐resonance Franck—Cordon interference”, and “off‐resonance interference,” are discussed.
Application of Orbital Correspondence Analysis in Maximum Symmetry (OCAMS) to Spin‐Forbidden Processes
Authors: Halevi E. A. , Trindle Carl 
Published: November 2013

AbstractOrbital Correspondence Analysis in Maximum Symmetry (OCAMS) is extended to deal with thermal reactions in which spin multiplicity changes. Only minor revisions are required in the theoretical foundation previously established for OCAMS. For reactions in which triplets may be interconverted with singlets, the use of geminals rather than one‐electron wave functions allows us to provide a symmetry criterion for determining whether spin‐orbit coupling can induce the interconversion and—if so—which component of the triplet state would participate in it.A number of examples illustrate the analysis, including: intersystem crossing between 1A1 and 3B1 CH2; the direct production of 3CH2 by thermolysis of singlet diazomethane; and the stereospecific trapping of 3CH2 by ethylene. We also analyze the intriguing reactions of Dewar‐benzene and 1,2‐dioxetanes, described as “photochemistry without light”, and clarify the complex manifold of thermolysis reactions of methylenepyrazoline.
Mass Spectral Studies of Amaryllidaceae Alkaloids
Authors: Onyiriuka O. S. , Jackson A. H. 
Published: November 2013

AbstractAmaryllidaceae alkaloids have been isolated from the bulbs of Crinum ornatum and Crinum natans and studied by a combination of mass spectral techniques including EI, CI, FD and GLC/EI mass spectrometry. In addition to the abundant lycorine present in both species three new alkaloids have been obtained in crystalline form from C. ornatum and one new crystalline alkaloid from C. natans. Several other new alkaloids were also shown to be present by GLC/MS and FD/MS. Tentative structures are proposed for the new alkaloids from C. ornatum based on mass and NMR spectral evidence.
Ionization Potential, Oxidation Potential Comparisons for Compounds Containing Amino Nitrogen
Authors: Nelsen Stephen F. 
Published: November 2013

AbstractPlots of solution oxidation potential (Eo′, V vs sce in acetonitrile) versus vapor phase vertical ionization potential (IPv, eV) are discussed for several types of compounds containing amino nitrogen, including tetraalkylhydrazines, tetraalkyl‐2‐tetrazenes, bicyclic diamines, and ortho and para‐substituted phenylenediamines. All amino compounds fall considerably below the polycyclic aromatic hydrocarbon line in an Eo′ vs IPv plot, and there is not a linear correlation of Eo′ vs IPv for amino compounds. Reasons for the non‐linearity, and the information that can be gained by comparison of the ease of electron removal in the vapor and solution phases are discussed.
Electrode Kinetics of Solvated Electrons in Liquid Ammonia
Authors: Harima Y. , Aoyagui S. 
Published: November 2013

AbstractElectrode reaction of ammoniated electrons was investigated with voltammetry, potentiometry and chronoamperometry. Experiments were conducted on Pt, Au and W electrodes in 0.5 M LiI, NaI, KI, CsI and KBr solutions of liq. NH3. The results in dilute solutions (< 10<−4 M) do not reflect the differences in alkali metal, electrode metal and supporting electrolyte and are explained by a simple one‐electron transfer process whose transferring species is a free solvated electron and its ion‐pair with a metal cation in a rapid equilibrium. The formal standard potential is −2.155 ± 0.005 V vs. Pb/Pb(NO3)2 (0.05 M) at −40°C in liq. NH3 involving 0.5 M alkali metal iodide. The lower limit of the averaged diffusion coefficient is 0.7 × 10−4 cm2 s−1. At higher metal concentrations (> 10−2 M), a two‐electron transfer process tends to prevail, which is explained by considering the dimer of ion‐pairs as the diffusing species.
Effect of Crystal and Molecular Structure on the Thermochromism and Photochromism of some Salicylidene‐2‐Aminopyridines
Authors: Hadjoudis E. , Moustakali‐Mavridis I. , Xexakis J. 
Published: November 2013

AbstractCrystalline salicylidene‐2‐aminopyridine and its derivatives exhibit thermochromic phenomena, i.e. they show a reversible colour change as a result of variation in temperature. Photochromism, reversible colour change on ultraviolet irradiation, is not observed in this class of compounds. The appearance of the thermochromic phenomen and its generality depend upon the crystal structure and the molecular orientation of the compounds. In fluid solution, where the orientation of the molecules is random, the compounds exhibit photochromic phenomena. The process is so fast that it can be followed only by flash photolysis techniques or at liquid nitrogen temperature. The results and mechanisms of thermochromism and photochromism are compared with findings on salicylideneanilines.
Low Energy Electron Diffraction Studies of Organic Monolayers on Metal Surfaces
Authors: Firment L. E. , Somorjai G. A. 
Published: November 2013

AbstractThe structures of monolayers of organic molecules adsorbed at metal single crystal surfaces are conveniently studied using Low Energy Electron Diffraction (LEED). Analysis of LEED intensity data determined the structures formed on adsorption of acetylene on Pt(1 1 1). Structures within monolayers can be reliably inferred from LEED data without extensive analysis of the diffracted beam intensities if supplementary information, i.e. spectroscopic data, is available. Structures obtained in this way are discussed and several general features of the adsorption of organic molecules are presented. Weakly adsorbed molecules form close‐packed monolayers. Strongly adsorbed molecules adsorb in specific sites on the metal surface. The nature of the adsorption can be determined from observation of the monolayer registry with the metal lattice. The structure and bonding of organic molecules at metal surfaces depends strongly on temperature.
Circular Fluorescence Polarization of Achiral Molecules in Cholesteric Liquid Crystals
Authors: Stegemeyer H. , Stille W. , Pollmann P. 
Published: November 2013

AbstractIn liquid crystalline matrices the molecular axes of solute molecules adopt an orientation which is given by the director of the liquid crystal. Consequently, the physical properties of the solute become anisotropic, governed by the director distribution within the matrix. An example of this general effect is the circularly polarized fluorescence emission of achiral molecules dissolved in cholesteric liquid crystals. The degree of circular polarization (CPF), given by a dissymmetry factor ge = (IL ‐ IR)/1/2(IL + IR), is rather high (IL, IR intensity of left or right circularly polarized fluorescence, respectively). The sign of ge was found to depend (i) on the screw sense of the cholesteric helical structure, and (ii) on the direction of the electric transition moment within the emitting molecule. The absolute value of ge is a function of the helical pitch p. The CPF can be understood as an ensemble effect of helically orientated emitting chromophores (e.g. perylene, pyrene, azulene, diphenylhexatriene). Based on the theory of Mauguin and de Vries relations have been derived describing quantitatively the dependence of CPF on the structure of the emitting molecules as well as on the helix structure of the cholesteric solvent.