bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Potassium Permanganate Oxidation of Methylated and Unmethylated Humic Acids Extracted from Solonetz, Solod and Chernozem Ah Horizons
Authors: Khan S.U. , Schnitzer M. 
Published: November 2013

AbstractHumic acids were extracted from Ah horizons of a Solonetz, a Solod, and a Chernozem soil. A portion of each extracted humic acid was methylated in order to make it more resistant to attack by electrophilic KMnO4. Both the methylated and unmethylated humic acids were then oxidized with KMnO4. The oxidation products were extracted into ethyl acetate and separated by preparative gas chromatography into relatively pure components, which were then analyzed by mass spectrometry and micro‐infrared spectrophotometry. A matching of the mass and IR spectra and gas chromatographic retention times of the isolated components with those of authentic specimens led to their identification.The most prominent compounds produced by the oxidation of methylated humic acids were 1,3,5‐benzenetricarboxylic acid and a complex phenolic acid, tentatively identified as propanone‐hydroxy‐methyl acetoxy‐benzene‐dicarboxylic acid. These two compounds accounted for between 18 and 23% of the original methylated humic acids. The main products resulting from the oxidation of unmethylated humic acids were benzenetri‐, benzenetetra‐ and benzenepenta‐carboxylic acids, which constituted between 10 and 12% of the weights of the original unmethylated humic acids. The results show that methylation of humic acids prior to oxidation is a useful procedure which substantially increases the yields and types of oxidation products. From the similarities in analytical data and in the quality of the oxidation products, we conclude that the three humic acids have similar chemical structures, yielding benzenecarboxylic and phenolic acids on oxidation. These compounds either originate from more complex structures or they exist in the humic acids in the forms in which they were isolated, held together by hydrogen bonds.
The Molecular and Crystal Structure of Photochemically Formed 1‐H1 : 1,2‐H2‐Trans‐2‐Bromovinyl‐μ‐Bromobis(Tricarbonyliron) (Fe‐Fe) A Carbonyliron‐π‐Complex of the 1‐Ferra‐Allylic System
Authors: Krüger C. , Tsay Y. H. , Grevels F. W. , Von Gustorf E. Koerner 
Published: November 2013

AbstractThe molecular structure of 1‐h1: 1,2‐h2‐trans‐2‐bromovinyl‐μ‐bromo‐bis(tricarbonyliron) (Fe‐Fe), Fe2Br2C8O6H2, has been determined from 1970 absorption‐corrected diffractometer intensity data by Patterson and Fourier methods and refined anisotropically by least‐squares methods to a final R‐value of 6.07%, including anomalous‐dispersion corrections. The molecular framework consists of two distorted octahedral Fe(CO)3 moieties linked together by a slightly asymmetric bromine bridge, an Fe‐Fe bridge (2.525 Å) and a π‐bonded bromovinyl group. The bonding features of the organic ligand suggest the formation of a 1‐ferra‐π‐allyl system. Within the irontricarbonyl fragments, strong trans effects are observed. Cell data are: a = 9.373(4) b = 23.716(12) c = 6.671(4) Å β= 113.96(4)°, Z = 4. Space group Cc (No. 9). A mechanism for the formation of the compound is suggested.
Relative Dipole Moments of Excited Singlet and Triplet States in Molecules
Authors: Coulson C. A. 
Published: November 2013

AbstractThe availability of experimental values of molecular dipole moments in electronically excited states suggests the desirability of establishing some general principles. Three such principles are proposed, as a means of explaining the observed values of the dipole moment in corresponding singlet and triplet states, where the relevant molecular orbitals are very similar. The general conclusion is that we shall usually expect μGS ‐ μT to be larger than μGS ‐ μS, where μGS, μT, μS are the dipole moments in the ground state, the excited triplet and singlet states respectively. The principles are illustrated by specific reference to NF, CO, BeO, formaldehyde, methylene and azulene. Some difficulties arise with larger molecules, and also when configuration interaction plays an unusually important rǒle.
Thione Photochemistry: On Thiobenzophenone Photoannelation
Authors: De Mayo P. , Nicholson A. A. 
Published: November 2013

AbstractThe photochemistry of the reaction of thiobenzophenone with acrylonitrile, following excitation into both the n, π* and π, π* absorption bands, has been examined. The products obtained are different, indicating dual mechanisms. It has been shown that the thietane is not a primary product, but is the result of thermal decomposition of a 1,3‐dithiane which can be isolated at low temperatures. This is the main product at the shorter wavelengths, but at longer wavelengths a 1,4‐dithiane and a thiatetrahydronaphthalene are obtained. A disulphide is also produced as a result of a secondary photochemical attack of thiobenzophenone on the thietane. The mechanistic implications of these results are discussed.
Preliminary Experiments on Solid/Gas Reactions by the Fluidized Bed Method; Preparation of 1,4‐Dicyanobuta‐1,3‐Diene from 2,3‐Dibromo‐1,4‐Dicyanobutane
Authors: Friedman G. , Cohen C. , Wolf D. , Schmidt G. M. J. 
Published: November 2013

AbstractPreliminary experiments on the fluidized bed reaction of gaseous ammonia with solid 2,3‐dibromo‐1,4‐dicyanobutane to yield 1,4‐dicyanobuta‐1,3‐diene are described.
The Thermal Reaction of Substituted Vinylcyclopropanes with Iron Pentacarbonyl
Authors: Sarel S. , Ben‐Shoshan R. , Kirson B. 
Published: November 2013

AbstractThe thermal reactions of 1‐aryl‐1‐cyclopropylethylenes and 1,1‐dicyclopropylethylene with pentacarbonyliron are investigated. Reactions of the former substrates yield 2‐aryl‐1,3‐pentadiene‐tricarbonyliron complexes via cyclopropane ring opening, hydrogen migration and coordination to iron. Reaction with the latter substrate gives 2‐cyclopropyl‐1,3‐pentadienetricarbonyliron in similar fashion, and, in addition, 3‐(1′‐propenyl)‐cyclohex‐2‐enone tricarbonyliron derived from the opening of the second ring coupled with carbon monoxide insertion. The cyclopropane ring serves as a two π‐electron donor in these reactions, and the vinylcyclopropane system emerges as a novel source of four π‐electrons which are available to coordination in direct analogy to reactions of formal diene systems with iron carbonyls.
The Reduction of Ferricytochrome c Studied by Pulse Radiolysis
Authors: Nilsson Karen 
Published: November 2013

AbstractThe formation of ferrocytochrome c upon pulse radiolysis of aqueous solutions of ferricytochrome c has been studied by following spectral shifts at 550 nm and 700 nm. The reaction between ferricytochrome c and hydrated electrons was studied by following the decay of hydrated electrons as well as the ferrocytochrome c formation. The two processes proceed with the same rate which indicate diffusion‐controlled processes with a second order rate constant of 1.1 × 1011 M−1 sec−1. The reaction between ferricytochrome c and H atoms was studied in a system containing H atoms only and found to be a second order reaction with a rate constant of 1.5 × 1010 M−1 sec−1. The formation of ferrocytochrome c by reaction between ferricytochrome c and OH radicals proceed by a first step with a second order rate constant of 1.4 × 1010 M−1 sec−1 during which OH radicals react with the protein part of ferricytochrome c forming an organic radical. Some of these radicals then undergo intramolecular reduction with a rate constant of 3.1 × 103 sec−1.
Mechanisms of Radiation‐Induced Strand Break Formation in DNA
Authors: Ward J. F. 
Published: November 2013

AbstractThe mechanisms by which γ‐radiation produces strand breaks in DNA were investigated using model systems: breakage of the sugar phosphate bond of deoxynucleotides irradiated in aqueous solution was equated to a reaction which would produce a strand break in DNA. Release of inorganic phosphate from 5′ deoxynucleotides is caused by a radiation‐produced hydroxyl radical abstracting a hydrogen atom from the deoxyribose moiety. Decay of the sugar radical so formed leads to phosphate release. After release of inorganic phosphate from deoxycytidylic acid two products are formed which consist of the cytosine base moiety attached to two or three carbon atoms of the sugar. Radioprotective sulphydryl compounds can repair the sugar radical by donation of a hydrogen atom to the damaged site. In thymidine 3′5′ diphosphate, reaction of OH* radicals with the base moiety as well as with the sugar can lead to inorganic phosphate release, both reactions leading to breakage of both 3′ and 5′ sugar phosphate bonds in the same molecule. When thymidine 3′5′ diphosphate is irradiated in the presence of oxygen, labile phosphate esters are produced in yields which are large compared to the inorganic phosphate yield. Reaction of 5‐bromouracil moieties in DNA with hydrated electrons can also lead to strand break production. Transfer of the electron to 5‐bromouracil from the thymine anion radical was found to be an efficient reaction. Other species such as HCO2−, O2−, and the cytosine anion radical can also donate electrons to 5‐bromouracil. The results and conclusions of these experiments are discussed with reference to reactions which could occur in DNA.
Mechanism of Sensitization to UV Radiation by 5‐Br‐Uracil Substituted DNA
Authors: Lion M. 
Published: November 2013

AbstractDNA, in which thymine is substituted by 5‐bromouracil is sensitized to the effect of ultraviolet light. Various chemical changes produced in the DNA are described. These include single and double strand breaks, base loss, protein DNA crosslinks as well as the influence of the three dimensional structure of DNA on some of these changes.
The Hydrated Electron, The Hydroxyl Radical, and Hydrogen Peroxide in Radiation Damage in Cells
Authors: Powers E. L. 
Published: November 2013

AbstractSpores of Bacillus megaterium, in suspension, are used to study the biological effects of the three principal products of radiolysis of water, i.e., e−aq, OH and H2 O2. A model is proposed accounting for the action of OH and H2 O2. This model involves two reactions:magnified imagein which RH2 is a “target” molecule, and \documentclass{article}\pagestyle{empty}\begin{document}$ \[ \underline {\rm R} \] $\end{document} is a lethally damaged molecule. Experimental evidence is given supporting this model. These studies of the effects of radiolysis products of water are extended by studies using sensitizers such as biacetyl, NO−3, and Ag+ in varying concentrations. Evidence for a possible relationship between peak sensitivities in anoxic conditions and chemical properties of the sensitizers is discussed. These results are also discussed with regard to the oxygen effect, and the general chemical characteristics of an efficient tumor sensitizer are outlined.
Mechanism of Phage Inactivation by Radiation
Authors: Dewey D. L. 
Published: November 2013

AbstractBacteriophage show two completely different types of response to radiation depending on whether they are irradiated in dilute aqueous solution, where the major lethal event is due to external radicals formed in the water, or whether they are irradiated in nutrient broth or some other radical scavenging medium; under these protected conditions a major lethal event is double strand breaks in the DNA. Single strand breaks do not appear to matter but the contribution of base damage has not yet been directly measured. In dilute solution the most effective radical for phage inactivation is the hydrogen atom followed by the OH radical and the hydrated electron, in that order. The mechanism of inactivation appears to be a radical attack on the phage tail causing a premature release of the DNA from the phage head. It is suggested that the energy for DNA release is stored in the tail and that the hydrogen atom triggers the release of this energy.
A Conductometric Study of Complexation of Macrocyclic Polyethers with Sodium Salts
Authors: Shchori E. , Jagur‐Grodzinski J. 
Published: November 2013

AbstractThe complexation of sodium ions with the macrocyclic polyethers dibenzo‐18‐crown‐6 (DBC), cis‐4,4′‐dinitro‐dibenzo‐18‐crown‐6 (NDBC) and cis‐4,4′‐diamino‐dibenzo‐18‐crown‐6 (AmDBC) has been investigated conductometrically in the temperature range 10–40°C. A computer program based on iteration procedure has been used for the calculation of the equilibrium constants. In DMF, KNDBC < KDBC ≅ KAmDBC (at 30°, KNDBC = 100 M−1, KAmDBC = 580M−1). In dimethoxyethane (DME), values of K's for the complexation of DBC with free sodium ions and with the sodium tetraphenylboron ion pairs have been shown to be nearly identical (at 30° Kf = 4.5 × 103M−1, Kip = 4.2 × 103M−1). The complexation reaction in DME is both entropy and enthalpy driven. Fuoss plots has been used in the calculations of the dissociation constants of the complexed and of the solvated sodium tetraphenylboron in DME at 10–40°C. The apparent ionic radius of the sodium ion complexed with DBC has been found to be about 4.5Å. A significant contribution of the DME molecules to the solvation of sodium ions complexed with DBC seem to be ruled out on the basis of the analysis of the thermodynamic parameters of the system.
Dynamic Patterns in Active Transport
Authors: Blumenthal Robert P. 
Published: November 2013

AbstractA model for active transport is presented based on experiments of sugar uptake across bacterial membranes. The transport proteins in the membrane are assumed to undergo cooperative conformational changes, while mediating the active transport. When the nonlinear active transport flow is kinetically coupled to other flow processes such as passive diffusion or metabolic reactions, the system will exhibit interesting dynamically patterned behavior: multiple steady state transitions, overshoots with respect to the build up of the concentration within the cell resembling action potentials in nerve membranes, and spatial patterns of the transported species along the surface of the membrane. Some consequences of these dynamic processes are discussed.
Unusual Features of the Structure of the Major RNA Component of the Larger Subribosomal Particle of the Rabbit Reticulocyte
Authors: Cox Robert A. , Hüvös Piroska , Godwin Elizabeth A. 
Published: November 2013

AbstractThe major RNA moiety of the larger subribosomal particle of the rabbit reticulocytes was subjected to partial hydrolysis by RNase T1. The fragments were separated first by gel filtration and then by zonal centrifugation. The fractions so obtained were analysed for molecular weight, nucleotide composition and for “melting” properties (E vs. temperature). The largest fragments (ca. 400,000 daltons) that were obtained had a high G + C content (ca. 78%). Fragments of this size appear to account for most of ca. 78% G·C basepairs which comprises ca. 40% of the intact molecule. Melting properties of reticulocyte RNA were compared with those of rRNA of the larger subribosomal particle Escherichia coli, Bacillus stearothermophilus and Xenopus laevis. The possible evolutionary significance of the unusual distribution of nucleotides within the polynucleotide chain of the RNA moiety of the larger subribosomal particle of reticulocytes is discussed.
Synthesis and Conformational Studies of Model Histones: II Sequential and Random Polypeptides with the Composition L‐Lysyl:L‐Alanyl:L‐Proline
Authors: Cernosek Stanley F. , Wells Margarete , Fasman Gerald D. 
Published: November 2013

AbstractThe sequential polytripeptide (Lys‐Ala‐Pro)n and the random polypeptide (Lys36.2 Ala32.5 Pro31.3)n were synthesized as model histones to be used in studying the structure and interactions of nucleohistone complexes. The CD spectra of (Lys‐Ala‐Pro)n in aqueous solutions, at both pH 7 and 11, as well as in HFIP, TFA, and 1 M SDS (pH 7), indicated that this polytripeptide only assumed the random coil conformation under all these conditions. In aqueous solution, the CD spectra of the random sequence polypeptide indicated that this polymer undergoes a pH‐dependent random coil‐helix transition as the pH is raised from 7 to 11. This polymer was also partially helical in TFE. The observation that the random polymer can assume a regular, asymmetric structure may be due to a clustering of lysyl and alanyl residues at one end of the polymer because of the faster incorporation of Pro than Lys or Ala, as indicated by their respective kinetics of polymerization. The random conformation of the sequential polypeptide, (Lys‐Ala‐Pro)n, is probably determined by the presence of Pro at regular intervals. It is concluded that the sequential polymer (Lys‐Ala‐Pro)n is a plausible model histone for use in studying the influence of amino acid sequence and composition on the structure and interactions of nucleohistone complexes.
Conformational Stability, Partial Specific Volumes and Spectroscopic Properties of Poly‐L‐Proline, Poly‐L‐Hydroxyproline and Some of Its O‐Acyl‐Derivatives in Various Solvent Systems
Authors: Knof Siegward , Engel Jürgen 
Published: November 2013

AbstractCircular dichroism spectra indicate that poly(Pro), poly(Hyp), poly(O‐acetyl Hyp), poly(O‐benzoyl Hyp) and poly(O‐phenacetyl Hyp) form the polyproline‐II‐conformation (all peptide bonds trans) in solvents that form hydrogen bonds with the peptide carbonyl groups. With the exception of poly(Hyp) the I‐helix of these derivatives is stable in more inert solvents like pyridine, di‐ and trichloromethane, dimethylformamide, and N‐methyl‐2‐pyrrolidone. Whereas the CD spectrum of poly (O‐benzoyl Hyp) is governed by large aromatic contributions, poly(O‐pehnacetyl Hyp) shows the same spectrum as poly(O‐acetyl Hyp). This is explained by the high conformational freedom of the phenacetyl groups in contrast to the preferential orientation imposed on the benzoyl groups by steric hindrance. Accurate measurements of partial specific volumes ρdocumentclass{article}ρpagestyle{empty}ρbegin{document}$$ {\rm \bar v} $$ρend{document} were possible in trifluoroethanol and dichloromethane the densities of which are near the reciprocal values of ρdocumentclass{article}ρpagestyle{empty}ρbegin{document}$$ {\rm \bar v} $$ρend{document}. Therefore the usually large errors in polymer concentration have little influence. A remarkable dependence of ρdocumentclass{article}ρpagestyle{empty}ρbegin{document}$$ {\rm \bar v} $$ρend{document} on solvent, large deviations from values calculated from increments, and negative temperature coefficients of ρdocumentclass{article}ρpagestyle{empty}ρbegin{document}$$ {\rm \bar v} $$ρend{document} were observed.
The Acquisition of Functions During Sub‐Unit Assembly of Proteins
Authors: Gutfreund H. 
Published: November 2013

AbstractThe self assembly of subunits of enzymes is an important feature in the evolution of a number of their capabilities. Many oligomeric enzymes have identical subunits that act quite independently. In such cases the quaternary structure appears to act principally to stabilize the correct conformation of the subunit. They offer an interesting field of study of the factors that control the correct folding of enzymes. In enzyme systems where the quaternary structure serves to add control functions, the study of subunit association gives information about the changes in interaction responsible for information transfer. Some examples are given of each of the two fields of investigation and the outstanding problems are discussed.
Color, Conformation, and Catalysis
Authors: Bernhard Sidney A. , Malhotra O. P. 
Published: November 2013

AbstractThe spectra of active‐site specific chromophoric acyl enzymes are discussed in terms of both the chemical (electronic) nature of the acyl‐enzyme bond and the protein conformation. The evidence presented demonstrates the following: (1) The acyl‐enzyme bond is perturbed with regard to both reactivity and electronic spectrum. (2) The perturbation is intimately related to the native enzyme conformation. (3) Such extreme perturbation, although a ubiquitous property of native monomeric acyl enzymes, is lacking in an oligomeric enzyme (glyceraldehyde‐3‐PO4 dehydrogenase). (4) In the presence of a positive effector (NAD+), the same perturbation is evident. (5) NADH, the reverse reactant, is also an effector. Noncovalent binding of NADH results in a new electronic configuration for the acyl enzyme which can undergo hydrogen transfer. This configuration of the thiol ester is nonexistent in the absence of an effector.
Studies on the Mechanism of Action of Collagenase: Inhibition by Cysteine and Other Chelating Agents
Authors: Harper Elvin , Seifter Sam 
Published: November 2013

AbstractUnder specific conditions cysteine inhibits collagenase (Clostridiopeptidase A and B (EC 3.4.4.19)) irreversibly. Neither collagenase A or B contains cysteinyl or cystinyl residues, so that the inhibition cannot proceed either by disulfide reduction, formation, or exchange. By use of [35S]cysteine, cysteine has been shown to bind to collagenase A in the ratio of about two moles to one mole of protein, and to collagenase B in the ratio of approximately one mole to one mole of protein. After cysteine binds to the enzyme, the sulfhydryl group can no longer be titrated with p‐mercuribenzoate or 5,5′‐dithiobis‐(2‐nitrobenzoic acid). Cysteine inhibits the low‐temperature binding of collagenase to a collagen substrate (ichthyocol). Histidine inhibits the activity of collagenases A and B, but this inhibition, in contrast to that produced by cysteine, is readily reversible by dialysis against water or passage through a DEAE cellulose column. 2,3‐Dimercaptopropanol also inhibits both collagenases. The order of the inhibitor efficacy on collagenase by cysteine, histidine, imidazole and 2,3‐dimercaptopropanol appears to be consistent with the order of stability constants of these chelating agents with zinc. The suggestion made previously that zinc may be an intrinsic component of collagenase is thereby reinforced. Indeed preliminary experiments are reported in which the incorporation of 65Zn into collagenases A and B is demonstrated.
An Enzyme with Collagenolytic Activity from Dog Pancreatic Juice
Authors: Takahashi Shizuko , Seifter Sam 
Published: November 2013

AbstractA purified collagenase has been isolated from the pancreatic juice of dogs prepared with pancreatic fistulae and stimulated to secrete the enzyme by injection of high quality pancreozymin. The purification steps included the use of affinity chromatography employing a Sepharose‐collagen column. The isolated enzyme had relatively high specific activity, was able to digest extracted, undenatured collagen to peptides of relatively small size, and could act on so‐called insoluble beef tendon collagen. Unlike clostridial collagenases, and most tissue collagenases, but resembling the collagenase of the hepatopancreases of crab and crayfish, the canine pancreatic collagenase was inhibited by diisopropylphosphorofluoridate, albeit in relatively high concentrations. Resembling the bacterial collagenase and tissue collagenases, but differing from the collagenase of crab hepatopancreas, the canine pancreatic collagenase was inhibited by cysteine. Resembling other pancreatic proteases, the pancreatic collagenase was inhibited by glycoproteins, human serum, or to a small extent by soy bean trypsin inhibitor. Apparently, just as carnivorous mammals have evolved with a specific elastase homologous with trypsin and chymotrypsin, they also have evolved in some instances with a specific collagenase; its homology with the other serine proteases is not yet established, although it appears to have properties intermediate between those of a serine protease and those of most tissue collagenases. The latter group of enzymes have been considered to be metallo‐enzymes. One may speculate that non‐carnivores would not have had selective pressure to evolve with a digestive collagenase, and that even the selective pressure to develop with a digestive collagenase in non‐carnivores would not be so great since the other serine proteases can digest denatured collagen. Finally, a new radioactive method of assay for collagenases is described.