bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectroscopic Investigation of Nitromethane Flames
Authors: Eckl Wilhelm , Weiser Volker , Weindel Martin , Eisenreich Norbert 
Published: May 2005

AbstractNitromethane (CH3NO2) Pool Fire Flames have been investigated analysing both, the radiation emitted from intermediate combustion radicals (diatomic molecules) in the ultraviolet (UV) and visible (VIS) spectral range, and the near infrared spectra dominated by broad water bands. Comparing the UV/VIS spectra to calculated band profiles, rotational and vibrational temperatures (Trot, Tvib) of OH, NH and CN have been determined. At local thermal equilibrium Trot and Tvib must be equal. The determined temperatures show that the OH and NH emissions originate from pure thermal excitation (Trot = Tvib = 2300 K–2380 K) but the CN emissions show additionally a chemical excitation indicated by different vibrational and rotational temperatures in the Boltzman factor (Trot = 2100 K, Tvib = 4300 K). For a more detailed study of the flame, the emission of OH radicals has been investigated more extensively by monitoring a two‐dimensional rotational temperature and emissivity profile. In cooler flame regions, the observed spectra are dominated by the near infrared radiation emitted from stable combustion products like water and carbon dioxide. Therefore, NIR spectra (1000 nm to 2500 nm) have been compared to broad band profiles calculated with a self‐developed code basing on the data of the ‘Handbook of Infrared Radiation of Combustion Gases’. The flame temperatures obtained by this method range from 1800 K to 1900 K. The results are correlated to flames of methane and nitrogen oxide which emit similar spectra indicating similar reaction mechanisms in the gaseous phase.
CL‐20 performance exceeds that of HMX and its sensitivity is moderate
Authors: Simpson R. L. , Urtiew P. A. , Ornellas D. L. , Moody G. L. , Scribner K. J. , Hoffman D. M. 
Published: May 2005

AbstractThe explosive performance of ϵ‐CL‐20 was found to be approximately 14% greater than HMX as determined by cylinder expansion and tantalum plate acceleration experiments. This makes it the most powerful explosive ever tested at small volume expansions of the detonation products. In general CL‐20 is more sensitive than HMX. However, the sensitivity of CL‐20 to one‐dimensional shock loading was found to be similar to HMX.
Relationships Between Electron Structures of Substitutive Ureas and their reactivity in Mannich reaction
Authors: Zhang Yuejun , Yu Mahong , Li Weimin 
Published: May 2005

AbstractThe electron structures of urea, substitutive ureas and N‐methylolamine with special structure and its imine cation were studied by SCF‐MO AM1 computation. The influence of different electronegative substituents on the reactivity of substitutive ureas acting as acid components to react with Mannich reaction intermediates and on the requirement of their reaction conditions were discussed according to the charge density of reaction‐centre atoms. The reactivity of imine cations was also discussed on the basis of Frontier Orbital Theory and Bonding Principle. These results showed that the electronegativity of substituents make effects not only obviously on the nucleophilicity of acid components but also on the requirement of media acidity. As the electron‐withdrawing ability of substituents increases, the nucleophilicity of nitrogen atom which acts as a reaction‐centre in substitutive ureas increases so that they can exist stably in strong acidic media and can condense further with the Mannich intermediate imine cation. These conclusions were confirmed by experimental facts.
Determination of traces of water in liquid dinitrogen tetroxide‐nitric oxide propellant mixtures by Fourier transform proton magnetic resonance spectrometry
Authors: Dove Michael F. A. , Logan Norman , Wood Simon A. 
Published: May 2005

AbstractLiquid dinitrogen tetroxide, N2O4, and mixed oxides of nitrogen as used as rocket propellant oxidizers, contain the products of the reaction of N2O4 with adventitious water. The determination of the total concentration of water and water‐derived species, called the water equivalent content, is essential in view of the effect of the hydrolysis products upon the rate of corrosion of containment metals and the physical state of the corrosion products. High field Fourier transform proton magnetic resonance spectrometry has now been validated for the direct measurement of water equivalent for MON blends up to MON‐3, without prior oxidation. Oxidation does, however, give slightly better precision. The technique is shown to be a reliable, absolute method for the determination of water equivalent contents as low as 0.003 wt% and up to at least 0.2 wt%. The precision of the method in this range is within 5%: it is estimated that the water equivalent content could be determined at levels as low as 0.0001 wt%. Samples of N2O4 prepared for NMR analysis are stable in sealed glass tubes for more than 1 year.
Effects of the polymer matrix density on the shock, bullet impact and high strain‐rate ignition sensitivity of polymer bonded explosives
Authors: Dagley Ian J. , Ho Sook‐Ying , Nanut Victor 
Published: May 2005

AbstractFour HMX/polymer cast‐cured explosive compositions containing a constant volume percentage (24%) of acrylate polymers ranging in density from 0.93 Mg/m3–1.65 Mg/m3 were evaluated in shock sensitivity, bullet impact sensitivity and high strain‐rate impact ignition tests. It was observed that shock sensitivity and bullet impact sensitivity, measured for flat‐ended projectiles impacting the bare face of elsewhere confined charges, increased with the density of the polymer matrix in the compositions. This correlation between the tests occurs because the detonations observed in the bullet impact test are initiated by shock, with shock initiation presumably occurring more readily when there is less impedance mismatch (i.e. a smaller density difference) at the polymer matrix/HMX crystal interface. In the Hopkinson Bar test a poorer correlation of ignition sensitivity with polymer density was observed because at these lower impact energies other initiation mechanisms such as macroscopic shear and plastic heating, viscous flow, etc. also play an important role.
Studies on 2,4,6‐trinitrophenyl substituted naphthalenes. Part III: Synthesis of nitro‐ and polynitro‐1‐methyl‐4‐(2,4,6‐trinitrophenyl)naphthalenes
Authors: Bergman John S. , Duffin Henry C. , Wells Clifford H. J. 
Published: May 2005

AbstractThe nitration of 1‐methyl‐4‐(2,4,6‐trinitrophenyl)naphthalene (1) and of mono‐ and dinitro‐derivatives of (1) has been studied with a view to obtaining precursors of high energy compounds possessing thermal stability. A number of nitro‐, dinitro‐ and trinitro‐derivatives of (1) have been synthesized. Some of these derivatives have also been synthesized from 4‐bromo‐1‐methylnaphthalene by a combination of nitration and Ullmann reactions.
Study on the Nitrolysis of Hexamethylenetetramine by NMR Spectrometry. Part III: The NMR spectral data of some products and intermediates from the nitrolysis of HA
Authors: Fang Zhijie , Chen Ju , Li Fuping 
Published: May 2005

AbstractThe 1H and 13C chemical shifts of methylene groups in nitric acid are reported for seven products and intermediates involved in the formation of 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX) from the nitrolysis of hexamethylenetetramine (HA). Based on the results, the 1H and 13C chemical shift ranges of the methylene groups in different kinds of methylenenitramines from the nitrolysis liquors of HA were discussed.
Energetics of the structure and chain tilting of antiparallel β‐barrels in proteins
Authors: Chou Kuo‐Chen , Heckel Armin , Némethy George , Rumsey Shirley , Carlacci Louis , Scheraga Harold A. 
Published: May 2005

AbstractThe preferred structural pattern of antiparallel β‐barrels in proteins, described as the right‐handed tilting of the peptide strands with respect to the axis of the barrel, is accounted for in terms of intra‐ and interchain interaction energies. It is related to the preference of β‐sheets for right‐handed twisting. Conformational energy computations have been carried out on three eight‐stranded antiparallel β‐barrels composed of six‐residue strands, in which L‐Val and Gly alternate, and having a right‐handed, a left‐handed, or no tilt. After energy minimization, the relative energies of these structures were 0.0, 8.6, and 46.1 kcal/mol, respectively; i.e., the right‐tilted β‐barrel is favored energetically, in agreement with anti‐parallel β‐barrels observed in proteins. Tilting of the barrel is favored, relative to the nontilted structure, by both intra‐ and interstrand interactions, because tilting allows better packing of the bulky side chains. On the other hand, the energy difference between the left‐ and right‐tilted barrels arises essentially from intrachain interactions. This is a consequence of the preference of β‐sheets for a right‐handed twist. Space limitations inside the barrel are satisfied if there is an alternation of bulky residues and residues with small or no side chain (preferably Gly) in neighboring positions on adjacent strands. Such a pattern is seen frequently in antiparallel β‐barrels of globular proteins. The computations indicate that a structure with Val…Gly pairs can be accommodated in a β‐barrel with no distortion.
Prediction of homologous protein structures based on conformational searches and energetics
Authors: Schiffer Celia A. , Caldwell James W. , Kollman Peter A. , Stroud Robert M. 
Published: May 2005

AbstractA “knowledge‐based” method of predicting the unknown structure of a protein from a homologous known structure using energetics to determine a sidechain conformation is proposed. The method consists of exchangin the residues in the known structure for the sequence of the unknown protein. Then a conformational search with molecular mechanics energy minimization is done on the exchanged residues. The lowest energy conformer is the one picked to be the predicted structure. In the structure of bovine trypsin, the importance of including a solvation energy term in the search is demonstrated for solvent accessible residues, while molecular mechanics alone is enough to correctly predict the conformation of internal residues. The correctness of the model is assessed by a volume error overlap of the predicted structure compared to the crystal structure. Finally, the structure of rat trypsin is predicted from the crystal structure of bovine trypsin. The sequences of these two proteins are 74% identical and all of the significant changes between them are on external residues. Thus, the inclusion of solvation energy in the conformational search is necessary to accurately predict the structure of the exchanged residues.
Conformational flexibility of a scorpion toxin active on mammals and insects: A circular dichroism study
Authors: Loret Erwann P. , Sampieri François , Roussel Alain , Granier Claude , Rochat Hervé 
Published: May 2005

AbstractThree scorpion toxins have been analyzed by circular dichroism in water and in 2,2,2‐trifluoroethanol (TFE) solutions. These toxins were chosen because they are representative of three kinds of pharmacological activities: (1) toxin AaH IT2, an antiinsect toxin purified from the venom of Androctonus australis Hector, which is able to bind to insect nervous system preparation, (2) toxin Css II, from the venom of Centruroides suffusus suffusus, which is a β‐type antimammal toxin capable of binding to mammal nervous system preparation, and (3) the toxin Ts VII from the venom of Tityus serrulatus, which is able to bind to both types of nervous systems. In order to minimize bias, CD data were analyzed by a predictive algorithm to assess secondary structure content. Among the three molecules, Ts VII presented the most unordered secondary structure in water, but it gained in ordered forms when solubilized in TFE. These results indicated that the Ts VII backbone is the most flexible, which might result in a more pronounced tendency for this toxin molecule to undergo conformational changes. This is consistent with the fact that it competes with both antiinsect and β‐type antimammal toxins for the binding to the sodium channel.
Substrate‐enzyme interactions and catalytic mechanism in phospholipase C: A molecular modeling study using the GRID program
Authors: Byberg Jette R. , Jørgensen Flemming S. , Hansen Sissel , Hough Edward 
Published: May 2005

AbstractBased on the high‐resolution X‐ray crystallographic structure of phospholipase C from Bacillus cereus, the orientation of the phosphatidylcholine substrate in the active site of the enzyme is proposed. The proposal is based on extensive calculations using the GRID program and molecular mechanics geometry relaxations. The substrate model has been constructed by successively placing phosphate, choline and diacylglycerol moieties in the positions indicated from GRID calculations. On the basis of the resulting orientation of a complete phosphatidylcholine molecule, we propose a mechanism for the hydrolysis of the substrate.
Molecular dynamics simulation of hydration in myoglobin
Authors: Gu Wei , Schoenborn Benno P. 
Published: May 2005

AbstractThis study was carried out to evaluate the stability of the 89 bound water molecules that were observed in the neutron diffraction study of CO myoglobin. The myoglobin structure derived from the neutron analysis was used as the starting point in the molecular dynamics simulation using the software package CHARMM. After solvation of the protein, energy minimization and equilibration of the system, 50 ps of Newtonian dynamics was performed. This data showed that only 4 water molecules are continously bound during the length of this simulation while the other solvent molecules exhibit considerable mobility and are breaking and reforming hydrogen bonds with the protein. At any instant during the simulation, 73 of the hydration sites observed in the neutron structure are occupied by water. © 1995 Wiley‐Liss, Inc.
Crystallization and preliminary diffraction studies of thioesterase II from rat mammary gland
Authors: Buchbinder Jenny L. , Witkowski Andrzej , Smith Stuart , Fletterick Robert J. 
Published: May 2005

AbstractThioesterase II from rat mammary gland has been crystallized in the presence of decanoic acid by the vapor diffusion method. The crystals belong to the orthorhombic space group P212121, and have cell dimensions, a = 52.7 Å, b = 78.0 Å, and c = 133.6 Å. The asymmetric unit likely consists of two protein monomers based on predictions from its calculated Matthews coefficient. Crystals typically diffract to at least 2.5 Å resolution and are suitable for X‐ray crystallographic analysis. © 1995 Wiley‐Liss, Inc.
The mass spectrum of mercury/cesium complex clusters (Hg)n Cs+ ranging up to m/z = 118 000
Authors: Sakurai T. , Ito H. , Matsuo T. , Katakuse I. , Costello C. E. 
Published: May 2005

AbstractThe mass spectrum of mercury/cesium complex clusters (Hg)nCs+ is observed up to m/z=118 000 (n = 590). Singly charged clusters are produced by Cs+ ion bombardment. The presence of an alkali metal in the ionization process yields cluster ions of the form (Hg)nX+. The clusters are analysed using the grand‐scale mass spectrometer, GEMMY, at Osaka University. The mass resolution of the instrument is high enough to resolve each cluster up to m/z=70 000. From the pattern of cluster distribution, the structrues of the large clusters can be studied. The number of Hg groups in metastable decay increases with the cluster size n. The ion intensities of the mercury/cesium clusters are much stronger than that from CsI (used for mass calibration). The mass spectrum of the clusters can therefore easily be utilized for direct mass calibration up to m/z=70 000.
Determination of the glycosidic linkage in peracetylated disaccharides comprised of d‐glucopyranose units by use ofr desorption electron‐ionization mass spectrometry
Authors: Peltier John M. , MacLean David B. , Szarek Walter A. 
Published: May 2005

AbstractAn oxonium ion at m/z 317 is present in the desorption electron ionization and ammonia desorption chemical ionization mass spectra of peracetylated disaccharides, comprised of glucopyranose units linked (1 → 2), (1 → 3), (1 → 4) and (1 → 6), but is absent in the spectra of the (1 → 1)‐linked isomer. The ion aat m/z 317, which is derived from the reducing moiety, has an O‐formyl group at the position of linkage to the non‐reducing moiety, and O‐acetyl groups at each of the remaining positions. The iosmeric monoformyl, triacetyl oxonium ions (at m/z 317), derived from the (1 → 2)‐, (1 → 3)‐, (1 → 4)‐ and (1 → 6)‐linked disaccharides, give distinctly different mass‐analysed ion kinetic energy spectra, thereby enabling the linkage position to be assigned unambiguously.
Simple physical models for coulomb‐induced frequency shifts and coulomb‐induced inhomogenous broadening for like and unlike ions in fourier transform ion cyclotron resonance mass spectrometry
Authors: Chen Shu‐Ping , Comisarow Melvin B. 
Published: May 2005

AbstractTwo simple models which Correspond more closely to physical reality than some prior models are proposed to account for the Coulomb‐induced frequency shifts to lower frequency, Which have been observed in Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry. The first model consists of two different‐mass point charges which undergo cyclotron orbits with the same orbit centers at their respective cyclotron frequencies. The model predicts that each excited cyclotron motion should induce a negative frequency shift in the other's cyclotron motion. The model predicts a zero frequency shift for ions of the same mass. The physical basis for the Coulomb‐induced shift is most easily seen in a coordinate frame which rotates at the cyclotron motion of the ion whose frequency is shifted. It is noted that a prior model for Coulomb‐induced frequency shifts is more appropriate for scanning ICR than FT‐ICR and the reason is described for the correctness of the predictions of this less appropriate model. A second model, the line model, is created by extension of the point model. The line model gives rise to a position‐dependent frequency shift which is synonymous with inhomogeneous Coulomb broadening. When a non‐quadrupolar electrostatic trapping field is included in the model, ‘like’ ions become ‘unlike’ and Coulomb‐shifting and Coulomb‐broadening apply, as for ‘like’ ions. The analysis predicts that ICR cells which are designed to have negligible trapping fields over most of their volume will be less sensitive to Coulomb shifting/broadening than ordinary ICR cells.
Electron‐pair ion coincidence (EPIC) techniques for spectrometry and state‐selective chemistry of doubly charged ions
Authors: Eland J. H. D. , Mathur D. , Brenton A. G. 
Published: May 2005

AbstractMultiple‐coincidence techniques involving detection of two near‐threshold electrons in coincidence with each other and with product ions are proposed to measure spectra of doubly charged ions and the decay of their energy‐selected states. The new techniques are demonstrated by laboratory experiments on double photoionization of CO2 and SO2.
Electron ionization mass spectra of the diterpenoid isomers atractyligenine, atractyliretine, 2‐ß‐hydroxy‐15‐oxo‐atractylan‐4‐carboxylic acid and of some related nor‐kaurane derivatives
Authors: Camarda Lorenzo , Ceraulo Leopoldo , Ferrugia Mirella , Sprio Vincenzo 
Published: May 2005

AbstractThe 75eV electron ionization mass spectra of eight nor‐kaurane compounds related to atractyligenine were investigated. The different fragmentation pathways and ion intensities from isomeric compounds are indicated.
Electron ionization mass spectra of some substituted stereoisomeric 1,6,7,11b‐tetrahydro‐2h,4H[1,3]oxazino[4,3‐a]‐isoquinolines and 1,6,7,11b‐tetrahydro‐2H[1,3]oxazino [4,3‐a]‐isoquinolin‐4‐ones1
Authors: Joutsiniemi Karoliina , Vainiotalo Pirjo , Lázár László , Fülöp Ferenc , Bernáth Gábor 
Published: May 2005

AbstractThe mass spectra often substituted oxazino[4,3‐a]isoquinolines, two isoquino[2,1‐c][1,3]benzoxazines and seven substituted oxazino[4,3‐a]isoquinolin‐4‐ones were recorded under electron impact ionization. Fragmentations were examined by metastable ion analysis, collision induced dissociation and exact mass measurement. The oxazinoisoquinolines and oxazinoisoquinolin‐4‐ones behaved similarly, although there were a few differences in the fragmentation and especially in the peak intensities. The most important fragmentation began with the opening of the oxazole ring. The substituents affected the fragmentation of the isomeric compounds, whereas the spectra of the stereoisomeric compounds were identical. The two isoquinobenzoxazines differed noticeably from the other compounds in their fragmentation behaviour; the additional phenyl ring prompted entirely new fragmentations unique to this structure.
Tryptic mapping of human chorionic gonadotropin by matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Laidler Paul , Hider Robert C. , Cowan David A. , Kicman Andrew T. , Keane Anita 
Published: May 2005

AbstractThe potential of matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI)(I‐TOF) mass spectrometry for use in the identification of human chorionic gonadotropin (hCG) seized by law enforcement agencies is investigated. Analysis of untreated hCG revealed signals corresponding to the molecular ions of the intact hCG heterodimer and both its non‐covalently linked subunits. Unfortunately, due to carbohydrate heterogeneity, the peaks are broad which makes accurate mass assignment, and consequently identification, difficult. Peptide mapping by MALDI‐TOF following‐tryptic digestion gave sequence coverage of 59% and 52% for the α and b̃‐subunits respectively. Nevertheless, the tryptic map was considered to provide unambiguous identification of hCG. This was confirmed by searching peptide‐mass databases with the experimentally determined masses. Our data suggest that peptide mapping by proteolytic digestion followed by MALDI‐TOF mass spectrometry is a suitable analytical technique for the identification of hCG seized by the legal authorities.
Ion exchange and purification of carbohydrates on a Nafion® membrane as a new sample pretreatment for matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Börnsen K. Olaf , Mohr Martin D. , Widmer H. Michael 
Published: May 2005

AbstractA Nafion membrane was tested as a new tool for a fast and easy sample pretreatment for matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) measurements. This membrane material was used for ion exchange and carbohydrate purification with minimal quantities of sample solution. An ion exchange method for carbohydrates was developed and demonstrated on a Dextran sample. The cations of the original sample were replaced within minutes by potassium or cesium ions. Another feature of this membrane was the fact that proteins and peptides adsorb on the acid surface. This behavior was investigated as a purification step for carbohydrates with high peptide and protein impurity concentrations. It was found that oligosaccharide libraries from rat‐ and mouse IgG mass spectra can be obtained clearly in the presence of high peptide impurities.
Static SIMS for applied surface analysis
Authors: Brown A. , Vickerman J. C. 
Published: May 2005

AbstractA review is presented of the use of static secondary ion mass spectrometry (SSIMS) and fast atom bombardment mass spectrometry (FABMS) in applied surface analysis. Some common criticisms of SIMS are discussed first, and then the experimental apparatus required is described briefly. Four main areas of application have been chosen: catalysts, polymers, glasses and metals, to illustrate the power of SSIMS/FABMS in characterising the chemical state of material surfaces. Finally the very new technique of SSIMS imaging has been described and some preliminary results presented, to indicate its potential in obtaining chemical state information at high spatial resolution.