bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Decomposition of RDX Composite Propellants
Authors: Maruizumi H. , Fukuma D. , Shirota K. , Kubota N. 
Published: May 2005

AbstractThe thermal decomposition characteristics of RDX, binders, and RDX composite propellants were studied using thermal analytical techniques. Three kinds of binders were tested to elucidate the role of binder on the burning rate of the propellants. There were no apparent correlations between the thermal decomposition rates of binders and the burning rates of propellants, whereas there was a correlation between the decomposition temperature and the burning rate of the propellants.It is found that the major factor which controls the burning rate is the initial thermal‐decomposition stage of the binders. Thus, the burning rate of nitramine composite propellants appeared to be largely dependent on the physical and chemical properties of binder.
Application of the Robbins‐Monro Method to the Sensitivity Testing of Explosives. I. A computer simulation study
Authors: Schilperoord A. A. , Bijlsma M. , Verweij H. D. , Bruckman H. W. L. 
Published: May 2005

AbstractA computer simulation study of the Robbins‐Monro method is presented. This method can be used to determine percentage points of a distribution function describing the probability of explosion as a function of some stimulus level. Calculations were performed to establish the influence of several parameters involved in the process. It is concluded that the method is suitable for determining 50, 10 and 1 percent points for several distribution functions. The efficiency for a restricted number of experiments and for a reasonable choice of the parameters is similar to that of a situation where experiments are performed at a fixed level, however with the advantage that the desired percentage point is obtained by convergence.
Rapid Methods for Quality Control of Gun Propellants
Authors: Volk F. , Wunsch G. , Müller D. 
Published: May 2005

AbstractSeveral single‐base, double‐base, and triple‐base gun propellants were analyzed by three different methods:

Conventional analytical methods (TL 1376–600)
High‐pressure liquid chromatography (HPLC)
Derivative spectroscopy.
The results obtained by these methods agree well and show a good reproducibility. However, compared with each other, the chromatographic methods are not only more rapid and more flexible than the conventional wet chemical analysis, they enable a quantitative determination of blasting oil mixtures like nitroglycerin or diglycoldinitrate. The same holds for many other explosives, stabilizers and stabilizer reaction products.
On the adhesion between Hydroxyl‐Terminated Polybutadiene Fuel‐Binder and Ammonium Perchlorate. Performance of bonding agents
Authors: Hori K. , Iwama A. , Fukuda T. 
Published: May 2005

AbstractA simple method to evaluate the adhesive force between solid oxidizer and polymeric fuel‐binder is presented. As an illustration, hydroxyl‐terminated polybutadiene (HTPB) sticks including several different bonding agents are bonded on ammonium perchlorate (AP) single crystals, and stress‐strain history until rupture occurs is obtained by applying uniaxial tensile stress perpendicularly to the adhesion surface. Further, whether each bonding agent reacts with AP or not was analysed with pursuing infrared absorption spectra. The hypothesis that the interfacial adhesive force arises from hydrogen bonding force is proposed.
Mechanistic Studies on Self Deflagrating Solids from temperature profile analysis
Authors: Kishore K. , Patil K. C. , Gajapathi D. 
Published: May 2005

AbstractA preliminary investigation has been made to study the mechanism of decomposition of self deflagrating solid (iron oxalate dihydrazinate) using temperature profile technique. A three step decomposition mechanism of two hydrazine losses and subsequent oxidation of anhydrous salt has been proposed. The enthalpy changes for these steps, obtained from the temperature profile measurements agree well with the values calculated using heat of formation data obtained from combustion calorimetry and differential scanning calorimetry.
Combustion of HMX‐CMDB Propellants (I)
Authors: Yano Y. , Kubota N. 
Published: May 2005

AbstractThe combustion wave structure of HMX‐CMDB (composite modified double‐base) propellants was studied in order to elucidate the gas phase reaction mechanism and to understand the burning rate characteristics. Experiments were conducted to determine the thickness of the reaction zone, gaseous products in the dark zone, and the temperature profile in the combustion waves. The reaction rate in the dark zone is increased by the addition of HMX. This is caused by the equivalence ratio of the oxidizer/fuel in the dark zone shifting towards a stoichiometric ratio when HMX is added. However, the reaction rate in the fizz zone and the heat feedback from the gas phase to the burning surface is decreased by the addition of HMX. Thus, the burning rate of HMX‐CMDB propellants decreases when HMX is mixed within double‐base propellants.
A Study of Solid Propellant Containing Titanium Hydride
Authors: Nakahara M. , Yano Y. 
Published: May 2005

AbstractThe burning rate characteristics of the propellant containing TiH2 have been examined in order to understand the effect of TiH2 addition on the combustion wave structure. The burning rate increases and the pressure exponent of burning rate decreases as the addition of TiH2 increases. Using very fine thermocouples which were embedded within the propellant samples, the heat transfer process in the combustion wave was determined. The results indicate that the heat flux feedback from the gas phase to the burning surface increases when TiH2 is mixed within the propellants.
Clustering of null mutations in the EcoRI endonuclease
Authors: Yanofsky Stephen D. , Love Robert , McClarin Judith A. , Rosenberg John M. , Boyer Herbert W. , Greene Patricia J. 
Published: May 2005

AbstractEcoRI endonuclease mutants were isolated in a methylase‐deficient background following in vitro hydroxylamine mutagenesis of plasmid pKG2 (Kuhn et al.: Gene 44:253–263, 1986). Mutants which survived high‐level endonuclease expression (IPTG induction) were termed null mutants. Sixtytwo of 121 null mutants tested by Western blot contained normal levels of endonuclease cross‐reacting protein. The complete endonuclease gene was scquenced for 27 null mutants. This group was found to consist of 20 signle base‐change missense mutations, 6 double mutations, and 1 triple mutation. Ten of the 20 signle mutations were clustered between residues 139 and 144. When examined with respect to the structure of the EcoRI‐DNA complex (McClarin et al.: Science 234:1526–1541, 1986), these alterations werre found to fall predominantly into two classes: substitutions at the protein‐DNA interface or substitutions at the protein‐protein (dimer) interface. Protein from several of the mutants was purified and sized by using HPLC. Wild‐type EcoRI endonuclease and protein from three of the DNA interface mutations (A1a139→Thr, Gly140→Ser, Arg203→Gln) appeared to be dimeric, while protein from subunit interface mutations (Glu144→Lys, Glu152→Lys, Gly210→Arg) migrated as monomers.
Stability of wild‐type and mutant RTEM‐1 β‐lactamases: Effect of the disulfide bond
Authors: Schultz Steve C. , Dalbadie‐McFarland Gloria , Neitzel James J. , Richards John H. 
Published: May 2005

AbstractUniquely among class A β‐lactamases, the RTEM‐1 and RTEM‐2 enzymes contain a single disulfide bond between Cys 77 and Cys 123. To study the possible role of this naturally occurring disulfide in stabilizing RTEM‐1 β‐lactamase and its mutants at residue 71, this bond was removed by introducing a Cys 77 → Ser mutation. Both the wild‐type enzyme and the single mutant Cys 77 → Ser confer the same high levels of resistance to ampicillin in vivo to Echerichia coli; at 30°C the specific activity of purified Cys 77 → Ser mutant is also the same as that of the wild‐type enzyme. Also, neither wild‐type enzyme nor the Cys 77 → Ser mutant is inactivated by brief exposure to p‐hydroxymercuri‐benzoate. However, above 40°C the mutant enzyme is less stable than wild‐type enzyme. After introduction of the Cys 77 → Ser mutation, none of the double mutants (containing the second mutations at residue 71) confer resistance to ampicillin in vivo at 37°C; proteins with Ala, Val, Leu, Ile, Met, Pro, His, Cys, and Ser at residue 71 confer low levels of resistance to ampicillin in vivo at 30°C. The use of electrophoretic blots stained with antibodies against β‐lactamase to analyze the relative quantities of mutant proteins in whole‐cell extracts of E. coli suggests that all 19 of the doubly mutant enzymes are proteolyzed much more readily than their singly mutant analogues (at Thr 71) that contain a disulfide bond. Thus, the disulfide bond of the RTEM‐1 β‐lactamase seems able to reduce the destabilizing effect of mutations at Thr 71. These results also emphasize the unique and essential role that Thr 71 performs in the stable folding of RTEM‐1 β‐lactamase and presumably the other class A β‐lactamases.
Functionally acceptable substitutions in two α‐helical regions of λ repressor
Authors: Reidharr‐Olson John F. , Sauer Robert T. 
Published: May 2005

AbstractA method of targeted random mutagenesis has been used in investigate the informational content of 25 residue positions in two α‐helical regions of the N‐terminal domain of λ repressor. Examination of the functionally allowed sequences indicates that there is a wide range in tolerance to amino acid substitution at these position. At position that are buried in the structure, there are severe limitations on the number and type of residues allowed. At most surface positions, many different residues and residue types are tolerated. However, at several surface positions there is a string preference for hydrophilic amino acids, and at one surface position proline is absolutely conserved. The results reveal the high level of degeneracy in the information that specifies a particular protein fold.
Crystal structure of myoglobin form a synthetic gene
Authors: Phillips George N. , Arduini Robert M. , Springer Barry A. , Sligar Stephen G. 
Published: May 2005

AbstractCrystal have been grown of myoglobin produced in Escherichia coli from a synthetic gene, and the structure has been solved to 1.9 Å resolution. The space group of the crystals is P6, which is different from previously solved myoglobin crystal forms. The synthetic myoglobin is essentially identical to myoglobin isolated from sperm whale tissue, except for the retention of the initiator methionine at the N‐terminus and the substitution of asparagine for aspartic acid at position 122. Superposition of the coordinates of native and synthetic sperm whale myoglobins reveals only minor changes in the positions of main chain atoms and roeientation of some surface side chains. Crystals of variant of the “synthetic” myoglobin have also been grown for structural analysis of the role of key amino acid residues in ligand and specificity.
Solvent structure in crystals of trypsin determined by X‐ray and neutron diffraction
Authors: Finer‐Moore Janet S. , Kossiakoff Anthony A. , Hurley James H. , Earnest Thomas , Stroud Robert M. 
Published: May 2005

AbstractThe solvent structure in orthorhombic crystals of bovine trypsin has been independently determined by X‐ray diffraction to 1.35 Å resolution and by neutron diffraction to 2.1 Å resolution. A consensus model of the water molecule positions was obtained using oxygen positions identified in the electron density map determined by X‐ray diffraction, which were verified by comparison to D2OH2O difference neutron scattering density. Six of 184 water molecules in the X‐ray structure, all with B‐factors greater than 50 Å2, were found to be spurious after comparison with neutron results. Roughly two‐thirds of the water of hydration expected from thermodynamic data for proteins was localized by neutron diffraction; approximately one‐half of the water of hydration was located by X‐ray diffraction. Polar regions of the protein are well hydrated, and significant D2OH2O difference density is seen for a small number of water molecules in a second shell of hydration. Hydrogen bond lengths and angles calculated from unconstrained refinement of water positions are distributed about values typically seen in small molecule structures.Solvent models found in seven other bovine trypsin and trypsinogen and rat trypsin structures determined by X‐ray diffraction were compared. Internal water molecules are well conserved in all trypsin structures including anionic rat trypsin, which is 65% homologous to bovine trypsin. Of the 22 conserved waters in trypsin, 19 were also found in trypsinogen, suggesting that they are located in regions of the apoprotein that are structurally conserved in the transition to the mature protein. Seven waters were displaced upon activation of trypsinogen. Water structure at crystal contacts is not generally conserved in different crystal forms. Three groups of integral structural water molecules are highly conserved in all solvent structures, including a spline of water molecules inserted between two β‐strands, which may resemble an intermediate in the formation of β sheets during the folding of a protein.
β‐Sheet coil transitions in a simple polypeptide model
Authors: Yapa Kanthi , Weaver David L. , Karplus Martin 
Published: May 2005

AbstractA simplified model of a polypeptide chain is used to study the dynamics of the β‐sheet–coil transition. Each amino acid residue is treated as a single quasiparticle in an effective potential that approximates the potential of mean force in solution. The model is used to study the equilibrium and dynamic aspects of the sheet–coil transition. Systems studied include ones with both strands free to move (two‐strand sheet), and ones with either strand fixed in position (multistrand sheet). The equilibrium properties examined include sheet–coil equilibrium constants and their dependence on chain position. Dynamic properties are investigated by a stochastic simulation of the Brownian motion of the chain in its solvent surroundings. Time histories of the dihedral angles and residue–residue cross‐strand distances are used to study the behavior of the sheet structure. Auto‐and cross‐correlation functions are calculated from the time histories with relaxation times of tens to hundreds of picoseconds. Sheet–coil rate constants of tens of ns−1 were found for the fixed strand cases.
A method for determining the positions of polar hydrogens added to a protein structure that maximizes protein hydrogen bonding
Authors: Bass Michael B. , Hopkins Derek F. , Jaquysh W. Andrew N. , Ornstein Rick L. 
Published: May 2005

AbstractAn automated method for the optimal placement of polar hydrogens in a protein structure is described. This method treats the polar, side chain hydrogens of lysine, serine, threonine, and tyrosine and the amino terminus of a protein. The program, called NETWORK, divides the potential hydrogen‐bonding pairs of a protein into groups of interacting donors and acceptors. A search is conducted on each of the local groups to find an arrangement which forms the most hydrogen bonds. If two or more arrangements have the same number of hydrogen bonds, the arrangement with the shortest set of hydrogen bonds is selected. The polar hydrogens of the histidyl side chain are specifically treated, and the ionization state of this residue is allowed to change, if this change results in additional hydrogen bonds for the local group. The program will accept Protein Data Bank as well as Biosym‐format coordinate files. Input and output routines can be easily modified to accept other coordinate file formats. The predictions from this method are compared to known hydrogen positions for bovine pancreatic trypsin inhibitor, insulin, RNase‐A, and trypsin for which the neutron diffraction structures have been determined. The usefulness of this program is further demonstrated by a comparison of molecular dynamics simulations for the enzyme cytochrome P‐450cam with and without using NETWORK.
Comparison of the hemocyanin β‐barrel with other greek key β‐barrels: Possible importance of the “β‐zipper” in protein structure and folding
Authors: Hazes Bart , Hol Wim G. J. 
Published: May 2005

AbstractThe Greek key β‐barrel topology is a folding motif observed in many proteins of widespread evolutionary origin. The arthropodan hemocyanins also have such a Greek key β‐barrel, which forms the core of the third domain of this protein. The hemocyanin β‐barrel was found to be structurally very similar to the β‐barrels of the immunoglobulin domains, Cu,Zn‐superoxide dismutase and the chromophore carrying antitumor proteins. The structural similarity within this group of protein families is not accompanied by an evolutionary or functional relationship. It is therefore possible to study structure–sequence relations without bias from nonstructural constraints. The present study reports a conserved pattern of features in these Greek key β‐barrels that is strongly suggestive of a folding nucleation site. This proposed nucleation site, which we call a “β‐zipper,” shows a pattern of well‐conserved, large hydrophobic residues on two sequential β‐strands joined by a short loop. Each β‐zipper strand is near the center of one of the β‐sheets, so that the two strands face each other from opposite sides of the barrel and interact through their hydrophobic side chains, rather than forming a hydrogen‐bonded β‐hairpin. Other protein families with Greek key β‐barrels that do not as strongly resemble the immunoglobulin fold—such as the azurins, plastocyanins, crystallins, and prealbumins—also contain the β‐zipper pattern, which might therefore be a universal feature of Greek key β‐barrel proteins.
Long timestep dynamics of peptides by the dynamics driver approach
Authors: Derreumaux Philippe , Schlick Tamar 
Published: May 2005

AbstractPrevious experience with the Langevin/implicit‐Euler scheme for dynamics (“LI”) on model systems (butane, water) has shown that LI is numerically stable for timesteps in the 5–20 fs range but quenches high‐frequency modes. To explore applications to polypeptides, we apply LI to model systems (several dipeptides, a tetrapeptide, and a 13‐residue oligoalanine) and also develop a new dynamics driver approach (“DA”). The DA scheme, based on LI, addresses the important issue of proper sampling, which is unlikely to be solved by small‐time step integration methods or implicit methods with intrinsic damping at room temperature, such as LI. Equilibrium averages, time‐dependent molecular properties, and sampling trends at room temperature are reported for both LI and DA dynamics simulations, which are then compared to those generated by a standard explicit discretization of the Langevin equation with a 1 fs timestep. We find that LI's quenching effects are severe on both the fast and slow (due to vibrational coupling) frequency modes of all‐atom polypeptides and lead to more restricted dynamics at moderate timesteps (40 fs). The DA approach empirically counteracts these damping effects by adding random atomic perturbations to the coordinates at each step (before the minimization of a dynamics function). By restricting the energetic fluctuations and controlling the kinetic energy, we are able with a 60 fs timestep to generate continuous trajectories that sample more of the relevant conformational space and also reproduce reasonably Boltzmann statistics. Although the timescale for transition may be accelerated by the DA approach, the transitional. information obtained for the alanine dipeptide and the tetrapeptide is consistent with that obtained by several other theoretical approaches that focus specifically on the determination of pathways. While the trajectory for oligoalanine by the explicit scheme over the nanosecond timeframe remains in the vicinity of the full αR‐helix starting structure, and a high‐temperature (6000°K) MD trajectory departs slowly from the a helical structure, the DA‐generated trajectory for the same CPU time exhibits unfolding and refolding and reveals a range of conformations with an intermediate helix content. Significantly, this range of states is more consistent with spectroscopic experiments on small peptides, as well as the cooperative two‐state model for helix–coil transition. The good, near‐Boltzmann statistics reported for the smaller systems above, in combination with the interesting oligoalanine results, suggest that DA is a promising tool for efficiently exploring conformational spaces of biomolecules and exploring folding/unfolding processes of polypeptides. © 1995 Wiley‐Liss, Inc.
A lipoamide dehydrogenase from Neisseria meningitidis has a lipoyl domain
Authors: Bringas Ricardo , Fernandez Julio 
Published: May 2005

AbstractA protein of molecular weight of 64 kDa (p64k) found in the outer membrane of Neisseria meningitidis shows a high degree of homology with both the lipoyl domain of the acetyltransferase and the entire sequence of the lipoamide dehydrogenase, the E2 and E3 components of the dehydrogenase multienzyme complexes, respectively. The alignment of the p64k with lipoyl domains and lipoamide dehydrogenases from different species is presented. The possible implications of this protein in binding protein‐dependent transport are discussed. This is the first lipoamide dehydrogenase reported to have a lipoyl domain. © 1995 Wiley‐Liss, Inc.
Effect of chlorimuron‐ethyl on Bradyrhizobium japonicum and its symbiosis with soybean
Authors: Zawoznik Myriam S , Tomaro María L 
Published: May 2005

AbstractPossible side‐effects of the acetolactate synthase (ALS)‐inhibiting herbicide chlorimuron‐ethyl on Bradyrhizobium japonicum (Kirchner & Jordan) in pure culture and on inoculated soybean plants growing under controlled conditions were investigated. Growth of B japonicum strain E109 was not affected by this herbicide even when exposed to concentrations 150 times higher than recommended field doses. However, nodulation of soybean plants treated 5 days after emergence with chlorimuron‐ethyl at standard application rates was impaired: a 38% decrease in the number of nodules per plant was observed four weeks after treatment. Despite nodule number decrease, no changes in shoot nitrogen content could be detected. Total fresh biomass was diminished by 25% in herbicide‐treated plants. Leghemoglobin content in nodules did not vary; nevertheless total nodule protein was diminished by 40% in the herbicide‐treated group. ALS activity in different soybean tissues and their relative sensitivity to chlorimuron‐ethyl were also investigated. Roots and bacteroids had the greatest specific ALS activities. On a fresh weight basis, the bacteroid fraction displayed the highest ALS activity and was also the most tolerant to in vitro chlorimuron addition: 72% of its activity was retained after including 10 µM chlorimuron‐ethyl in the reaction mixture. These results indicate that standard application rates of chlorimuron‐ethyl will have limited incidence on B japonicum survival, and effects on nodulation may have little long‐term consequences on soybean nitrogen fixation potential. The differences found among soybean tissues not only in intrinsic ALS activity but also in their relative sensitivity to this herbicide suggests that, in leguminous plants living in symbiosis with rhizobia, nodules may contribute to an enhanced tolerance to ALS inhibitors. Copyright © 2005 Society of Chemical Industry
Kinetics of matrix/sample interactions in fast‐atom bombardment
Authors: Vékey Kàroly , Colombo Luigi , Zerilli Luigi F. , Székely Györgyi 
Published: May 2005

AbstractAddition of a hydroxy‐containing matrix to an aldehyde was observed in fast‐atom bombardment (FAB). This FAB‐induced interference reaction, observed in the case of a microbial alkaline protease inhibitor, shows a characteristic time behaviour. This can be explained by a first‐order reaction kinetics scheme which leads to quilibrium, for which rate and equilibrium constants were also determined. These data suggest that in situ reaction kinetics can be studied by FAB mass spectrometry.