bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal structure of a protein‐toxin α1‐purothionin at 2.5Å and a comparison with predicted models
Authors: Teeter Martha M. , Ma Xing‐Qi , Rao Usha , Whitlow Marc 
Published: May 2005

Abstractα1‐Purothionin (α1‐P), a wheatgerm protein and lytic toxin, has a secondary and tertiary structure similar to that of crambin as revealed by CD and NMR studies. α1‐P crystallizes in the tetragonal space group I422 with unit cell dimensions: a = b = 53.59 and c = 69.79 Å. X‐ray diffraction data have been measured to 2.5 Å Bragg spacing. The crystal structure has been determined by molecular replacement methods, using an energy‐minimized α1‐P model structure derived from crambin (Whitlow and Teeter: Journal of Biomolecular Structure and Dynamics 2:831–848, 1985, Journal of the American Chemical Society 108:7163–7172, 1986). The energy‐minimized model gives a slightly cleaner rotation solution and better refinement against the x‐ray data than do the crambin or unminimized α1‐P structures. The final crystallographic residual with the data in the 10–2.5 Å resolution range is 0.216. The refined α1‐P structure has a backbone rms difference of 0.74 Å from crambin and 0.55 Å from the energy‐minimized α1‐P model. A low resolution NMR model of α1‐P calculated from metric matrix distance geometry and restrained molecular dynamics differs from crambin's backbone by 2.3 Å rms deviation (Clore et al.: EMBO Journal 5:2729–2735, 1986). Backbone dihedral angles for our predicted model differ from the refined α1‐P structure in only one region (at a turn where there is a deletion relative to crambin). The NMR model had differences in four regions.
Analysis of protein sheet topologies by graph theoretical methods
Authors: Koch Ina , Kaden Frieder , Selbig Joachim 
Published: May 2005

AbstractIn order to find rules for the secondary structure prediction of proteins which describe the (sequentially) long‐range interactions in sheet structures methods of applied graph theory were used. The so called β graph which describes the sheet topology was defined for every protein in the Brookhaven Data Bank containing β sheets. The resemblance of proteins at that topological level is discussed, and four notations and graphic representations of sheets which describe the sequential and topological neighborhoods of the strands were derived. This description level supports the usage of data structures which allow the implementation of efficient algorithms for the analysis and comparison of β structures in proteins. A computer program for the representation and retrieval of bibliographic data and β sheet structures was implemented. Some examples for substructure search illustrate the usefulness of the program. Two graphic catalogues were compiled: one contains all β graphs of PDB proteins and the other all occurring different greek key descriptions.
Primary mutations in calmodulin prevent activation of the Ca+ +‐dependent Na+ channel in Paramecium
Authors: Ling Kit‐Yin , Preston Robin R. , Burns Robert , Kink John A. , Saimi Yoshiro , Kung Ching 
Published: May 2005

AbstractParamecium tetraurelia behavioral mutant cam12 displays a “fast‐2” behavioral phenotype: it fails to respond to Na+ stimuli. Electrophysiologically, it lacks a Ca+ +‐dependent Na+ current. Genetics and DNA sequencing showed the primary defect of cam12 to be in the calmodulin gene (Kink et al., 1990). To correlate calmodulin structure and function in Paramecium, we elucidated the primary structure of cam12 calmodulin. Peptide sequencing confirmed the two point mutations predicted by the DNA sequence: a glycine‐to‐glutamate substitution at position 40 and an aspartate‐to‐asparagine substitution at position 50. Our results further showed that lysine 13 and lysine 115 were methylated normally in cam12. It is likely that the electrophysiological abnormalities of cam12 are a direct reflection of the amino‐acid substitutions, as opposed to improper posttranslational modification.
NMR study of the reconstitution of the β‐sheet of thioredoxin by fragment complementation
Authors: Tasayco María Luisa , Chao Kan 
Published: May 2005

AbstractThe study of complementary protein fragments is thought to be generally useful to identify early folding intermediates. A prerequisite for these studies is the reconstitution of the native‐like structure by fragment complementation. Structural analysis of the complementation of the domain‐sized proteolytic fragments of E. coli thioredoxin, using a combination of H‐exchange and 2D NMR experiments as a fingerprint technique, provide evidence for the extensive reconstitution of a native β‐sheet, with local conformational adjustments near the cleavage site. Remarkably, the antiparallel β‐strand between the fragments shows a native‐like protection of the amide protons to solvent exchange. Our results indicate that these fragments can be useful to study the early events in the still little understood formation of β‐sheets. © 1995 Wiley‐Liss, Inc.
Crystallization and preliminary crystallographic data for class I deoxyribose‐5‐phosphate aldolase fromEscherichia coli: An Application of Reverse Screening
Authors: Stura Enrico A. , Ghosh Sutapa , Garcia‐Junceda Eduardo , Chen Lihren , Wong Chi‐Huey , Wilson Ian A. 
Published: May 2005

AbstractX‐ray quality crystals of class I deoxyribose‐5‐phosphate aldolase fromEscherichia colihave been obtained for the unliganded enzyme and in complex with its substrate, 2‐deoxyribose‐5‐phosphate. The enzyme catalyzes the reversible cleavage of 2‐deoxyribose‐5‐phosphate to acetaldehyde and D‐glyceraldehyde‐3‐phosphate. The unliganded and complex crystals are prismatic long rods and belong to the orthorhombic space groupP212121with cell dimensionsa= 183.1 Å,b= 61.4 Å,c= 49.3 Å anda= 179.2 Å,b= 60.5, Å,c= 49.1 Å, respectively. Two molecules in the asymmetric unit are related by a noncrystallo‐graphic 2‐fold axis. The crystals are stable in the X‐ray beam and diffract to at least 2.6 Å. A new method, reverse screening, designed to minimize protein utilization during the screening process was used to determine supersaturation and crystallization conditions. © 1995 Wiley‐Liss, Inc.
Characterization of the mycotoxin fumonishin B1: Comparison of thermospray, fast‐atom bombardment and electrospray mass spectrometry
Authors: Korfmacher W. A. , Chiarelli M. P. , Lay J. O. , Boloom J. , Holcomb M. , McManus K. T. 
Published: May 2005

AbstractThe utility of the thermospray mass Spectrometry (TSMS), fast‐atom bombarment mass spectrometry (FABMS), and elctropray mass spectrometry (ESMS) for the analysis of Fumonisin B1 is investigative. In Additional, the analysis of two stanards of Fumonisim B1 as well as an inculated corn culture extract that contained Fumonism B1 is reported. The result of these efforts show that ESMS, as Well as FABMS and a combination of FAB and tandem mass spectrometry (FABMS/MS), provide useful data for the characterization of Fumonisin B1. The detection limit was 50 pg for Fumonism B1 when analyzed by full scan FABMS, and 5 pg when analyzed by single‐reaction monitoring FABMS/MS.
Aromatic hydrocarbon derivatives of fullerences
Authors: Hoke Steven H. , Molstad Jay , Payne Gregory L. , Cotter R. J. , Kahr Bart , Ben‐Amotz Dor , Cooks R. Graham 
Published: May 2005

AbstractThe fullerences C60 and C70 form adducts with toluene, p‐xylene and other aromatic compounds when refluxed in these solvents in the presences of FeCl3. Benzene derivatives are produced only when bromine is also present. Mass spectra of the reaction mixtures indicate the presence of derivatives including 1:1 adducts, as well as products of multiple additions of the aromatic molecules and their dehydrogenation products. Tandem mass spectrometry provides evidence for CC bonds formation between the adducts and fullerences.
The use of electrospray ionization with Fourier transform ion cyclotron resonance mass spectrometry in the analysis of trace impurities in a drug substance
Authors: Haskins Neville J. , Eckers Christine , Organ Andrew J. , Dunk Michael F. , Winger Brian E. 
Published: May 2005

AbstractThe separation of trace impurities in cimetidine drug substance by high pressure liquid chromatography (HPLC) showed a series of minor components. These were analysed using an on‐line electrospray source connected to a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. Working typically with a resolution of 10 000–20 000 accurate mass measurement of the components confirmed their empirical formulae to generally better than 5 ppm accuracy. This work shows that the combination of conventional analytical HPLC using 4.6 mm columns with a low flow rate electrospray source interfaced to an FT‐ICR mass spectrometer enables structural information to be obtained on low levels of low mass components.
Electron ionization mass spectrometry of some substituted, stereoisomeric, partly saturated 1,3‐ and 3,1‐benzoxazino‐1,3‐benzoxazines
Authors: Joutsiniemi Karoliina , Vainiotalo Pirjo , Pihlaja Kalevi , Lázár László , Fülöp Ferenc , Bernáth Gábor 
Published: May 2005

AbstractThe electron ionization mass spectra of five substituted, partly saturated 3,1‐benzoxazino‐1,3‐benzoxazines and four substituted 1,3‐benzoxazino‐1,3‐benzoxazines were measured and analysed. The fragmentation pathways were elucidated by metastable ion analysis and exact mass measurement. Although the principal fragmentations were similar for all these compounds, there was an important difference between the two groups as concerns the fragmentation routes. Both routes led to the same fragment ion, but in different ways depending on the ring structure. On the basis of the different fragmentation mechanisms, the 3,1‐benzoxazino‐1,3‐benzoxazines and the 1,3‐benzoxazino‐1,3‐benzoxazines can be distinguished mass spectrometrically. The saturation, the stereochemistry and the substituents all affected the fragmentations, mainly the peak intensities.
High resolution matrix‐assisted laser desorption/ionization time‐of‐flight analysis of single‐stranded DNA of 27 to 68 nucleotides in length
Authors: Christian Noah P. , Colby Steven M. , Giver Lori , Houston Chris T. , Arnold Randy J. , Ellington Andrew D. , Reiily James P. 
Published: May 2005

AbstractMass spectra of single‐stranded DNA oligonucleotides were acquired using matrix‐assisted laser desorption/ ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS). Resolution enhancement using space–velocity correlation focusing allows for facile observation of different oligomers, the direct observation of individual DNA–metal adducts, and investigation of counter ion structure.
The influence of X‐ray‐induced Auger electrons in quantitative electron‐induced Auger spectroscopy
Authors: Cazaux J. , Moutou S. 
Published: May 2005

AbstractThe X‐ray‐induced Auger electron intensities are often neglected in quantitative electron‐induced Auger electron spectroscopy. For the first time, analytical expressions are given for these relative intensities (induced by continuous or characteristic X‐rays). The influence of the operating voltage and the effects of the bulk and surface compositions are also discussed. Some numerical values show that at high operating voltages these intensities can reach several tens of percent of the Auger intensity directly created by the incident electron beam. Such contributions increase the apparent backscattering parameter r, therefore, they cannot be neglected when accurate quantitative analysis is required. Though such influences are troublesome for the analysis of small precipitates in scanning Auger electron microscopy, they can also give additional information on the bulk composition of a sample.
AES and XPS studies of surface films deposited during the plasma etching of silicon dioxide layers
Authors: Tuppen C. G. , Heckingbottom R. , Gill M. , Heslop C. , Davies G. J. 
Published: May 2005

AbstractSurface films deposited during the selective plasma etching of SiO2 on Si by CHF3 have been studied using Auger electron spectroscopy (AES)2 and x‐ray photoelectron spectroscopy (XPS). The films have been subdivided into two types: ‘persistent’ and ‘non‐persistent’. Non‐persistent films could be etched in an oxygen plasma and consisted of a fluorocarbon polymer. The main components of persistent films (unreactive in an oxygen plasma) were oxygen and fluorine compounds of silicon with impregnated metal atoms sputtered from electrodes in the plasma etcher. The thickness of persistent films was found to depend on the electrode spacing and electrode material. This effect has been explained in terms of the ion sputtering inherent within the parallel plate plasma etching system.
Magnetron sputtered gold contacts on n‐GaAs
Authors: Buonaquisti A. D. , Matson R. J. , Russell P. E. , Holloway P. H. 
Published: May 2005

AbstractDC planar magnetron sputtering has been used to deposit gold Schottky barrier electrical contacts on n‐type GaAs. The electrical character of the contact was determined from current‐voltage (I‐V) and electron‐beam‐induced voltage (EBIV) data. These data showed that the Schottky barrier height of magnetron sputter‐deposited contacts was lower than for vapor deposited contacts. The barrier‐height was a function of the deposition rate for electronically isolated substrates, and was dependent upon both the surface treatment prior to contact deposition, and upon doping density and post‐deposition heat treatment. These effects are discussed in terms of particle irradiation of the surface during contact deposition.
Secondary ion mass spectrometric analysis of leaching behaviour of magnesium from chrysotile in oxalic acid solution
Authors: Verlinden J. A. , De Waele J. K. , Swenters I. M. , Adams F. C. 
Published: May 2005

AbstractA study was made on the dissolution kinetics of chrysotile asbestos in 0.1 N oxalic acid over the temperature range 0–80°C. After treatment, the fractional release of magnesium from the fibre was measured using secondary ion mass spectrometry. Diffusion coefficients were determined assuming a plane sheet model. It appeared that the Arrhenius relation is obeyed over the entire temperature range, with an activation energy of 72.1 kJ mole−1, in agreement with earlier literature data.
Ion‐bombardment‐induced changes in the surface topography of MBE‐grown silicon on gallium phosphide
Authors: Boudewijn P. R. , Akerboom H. W. P. , Bulle‐Lieuwma C. W. T. , Haisma J. 
Published: May 2005

AbstractIon bombardment of silicon layers grown by molecular beam epitaxy (MBE) or solid phase epitaxy (SPE) on top of GaP(100) substrates results in changes in the surface topography. The influence of the bombardment conditions on such topological features has been studied and the results are interpreted qualititively in terms of the angular dependence of the sputer yield. The consequences of pit formation for the reliability of the results from surface analytical techniques employing ion beam sputtering are discussed. The origin of bombardment‐induced surface roughening is ascribed to the presence of polycrystalline imperfections in the MBE or SPE‐grown silicon layer.
The measurement of the uptake of ions from solution by charged acrylic copolymers using XPS
Authors: Paytner R. W. , Castle J. E. , Gilding D. K. 
Published: May 2005

AbstractXPS has been used to monitor the uptake of Na+ ions by p(acrylic acid/methyl methacrylate) and of Cl− ions by p(dimethylaminoethylmethacrylate/methyl methacrylate) from NaCl solution as a function of time and electrolyte concentration. The resulting changes in both the polymer and the solid/liquid interface are discussed in terms of the performance of these materials in the biological environment.
Characterization of silica‐supported uranium–molybdenum oxide catalysts
Authors: Fierro J. L. G. , Salazar E. , Legarreta J. A. 
Published: May 2005

AbstractThe techniques of X‐ray diffraction, infrared and electron spin resonance spectroscopies, kinetics of reduction by H2, and XPS were used to investigate the chemical species present at the interface in silica‐supported uranium–molybdenum oxide catalysts. In this catalyst series, with constant MoO3 loading (16.7 wt%) and Mo/(Mo + U) atomic ratios ranging between 1 and 0, it was found that the oxidic forms of Mo and U were not well dispersed, MoO3 crystallites being detected on the catalysts with a high Mo/(Mo + U) atomic ratio. In the less‐uranium‐rich catalysts [Mo/(Mo + U) = 0.89] both MoO3 crystallites and a crystalline ‘uranyl molybdate’ phase were present. This catalyst exhibited the highest reduction degree by H2 and the highest ESR signal intensity of Mo5+ ions when reduced under very mild conditions. The information obtained with these techniques was used to explain the promotional effect of U on the MoO3/SiO2 base catalyst for the selective oxidation of isobutene.
Surface analysis of semiconductor‐incorporated polymer systems: 2—Pt‐Nafion and Pt‐CdS‐Nafion
Authors: Kakuta N. , Bard A. J. , Campion A. , Fox M. A. , Webber S. E. , White J. M. 
Published: May 2005

AbstractPt‐Nafion (chemically reduced and sputtered Pt) and Pt‐CdS‐Nafion membranes were studied by x‐ray photoelectron spectroscopy. The chemically deposited Pt was completely reduced to Pt0 and was more concentrated in the surface region than in the interior. The sputtered Pt (100 Å thick) was distributed within the first several hundred Ångstoms of the Nafion, probably involving Pt migration into it, during the RF sputtering process. Changes of the Pt(4f7/2) linewidth indicate interactions between CdS and Pt. The relatively high activity of the 100 Å sputtered Pt‐CdS‐Nafion membrane for the photoassisted production of H2 in aqueous 0.1 M S2− solution is discussed.
Surface treatment of phlogopite particles for composite applications: XPS and DRIFT studies
Authors: Matienzo L. J. , Shah T. K. 
Published: May 2005

AbstractThe use of XPS and diffuse reflectance fourier transform infrared spectroscopy (DRIFT) to characterize mica surfaces modified with a sulfonylazide alkoxysilane coupling agent in the range of 0.2 to 1.0% (w/w) is discussed. XPS and DRIFT provide a description of chemical composition of the surfaces as well as quantitative analysis of the amount of silane present. Both techniques correlate linearly with the amount of surface treatment. However, DRIFT is more sensitive and faster and does not require an ultra high vaccum system.
A comparison of positive and negative ion static SIMS spectra of polymer surfaces
Authors: Brown A. , Vickerman J. C. 
Published: May 2005

AbstractNegative ion static SIMS spectra are presented for several polymers whose positive ion spectra have been well characterized previously. The negative cluster ions present in the spectra of poly‐methyl methacrylate, poly‐hydroxy ethylmethacrylate and poly‐ethylene terephthalate provide detailed information on polymer side chain and back‐bone structure complementing and clarifying the information previously only obtainable from positive ion emission. The detection and optimization of structurally informative negative cluster ions is discussed in relation to experimental parameters and the role of surface potential.
Electron channelling induced effects in grain boundary AES measurements
Authors: Bennett B. , Viefhaus H. 
Published: May 2005

AbstractThe influence of incident electron beam angle on the Auger peak height and peak height ratios was studied for clean and surface enriched iron single crystal samples and for grain boundary segregation on polycrystalline samples. The AES measurements were supplemented by observing electron channelling patterns (ECP) for the same samples within a SEM. Auger electron peaks for segregated species Aseg are normalized with respect to the iron substrate Auger peak, AFe, at 651 eV. A considerable change of the Auger peak height ratio Aseg/AFe was observed for surface segregation single crystal planes depending on the incident electron beam angle. The main contribution of the observed changes comes from variations of the iron substrate Auger peak AFe and is attributed to electron channelling effects. The same is true for AES measurements on grain boundaries of polycrystalline samples, if the incident electron beam is nearly parallel to a low index crystallographic pole. Some recommendations are given for performing quantitative AES measurements on grain boundary surfaces.
Surface microstructure investigation of calcined θ‐Al2O3‐supported molybdena catalyst
Authors: Zaki M. I. , Ismail H. M. , Fahim R. B. 
Published: May 2005

AbstractSamples of θ‐ and α‐Al2O3‐supported molybdena catalyst of various loading levels (0.5–16 wt% MoO3) were prepared by impregnation of the support from a dilute aqueous solution (at pH 6) of ammonium paramolybdate. After drying at 80°C, they were calcined at 550°C for 16 h. The effect of support nature and Mo loading level on surface microstructural characteristics, namely physicochemical identity of the supported Mo‐O species and consequent textural modifications of the calcination products thus yielded, were investigated by means of differential thermal and thermogravimetric analyses, x‐ray diffraction, infrared spectroscopy, scanning electron microscopy and N2 adsorption. The results obtained show that during the thermal treatment of the impregnated samples the adsorbed paramolybdate anions interact preferentially with the thermally most stable surface OH groups (relatively most basic) which reside at the interior and/or entrances of fine pores of the support. They further show that α‐Al2O3 stabilizes the molybdates loaded at up to 12% level in monolayer‐like structures, however α‐Al2O3 does not do likewise giving way to the formation of Al2(MoO4)3 and bulk MoO3 at a loading level as low as 4%.
XPS study on the thermal degradation of poly‐N,N′/4,4′‐diphenylether/pyromellitimide
Authors: Tóth A. , Bertóti I. , Székely T. , Sazanov J. N. , Antonova T. A. , Shchukarev A. V. , Gribanov A. V. 
Published: May 2005

AbstractThin foil samples of the title polymer preheated in vacuo up to different temperatures with the highest one reaching 1200 K were analysed by XPS. On heat treatment the surface content of oxygen decreased and that of carbon increased monotonously, while that of nitrogen passed over a local maximum at c. 800 K. Ether‐type oxygens proved to be more heat resistant than carbonyl type ones. From the change of the N 1s peak the probable mechanism of decomposition up to c. 800 K was inferred to be a decarboxylation to give CHN type structures. At higher temperatures decarbonylation of the imide groups appeared to become predominant, resulting in the formation of amide functionalities. The development of a conductive (polyaromatic) structure was deduced from the gradual decrease in the charge shift with the increase of the temperature of pretreatment.
X‐Ray diffraction investigations on ultra‐thin gold films
Authors: Häupl K. , Lang M. , Wissmann P. 
Published: May 2005

AbstractThe structure of epitaxially grown ultra‐thin gold films is investigated by x‐ray diffraction, texture analysis and LEED/Auger techniques. High sensitivity of the x‐ray diffraction analyzer has been achieved by means of a step scanning unit and an impulse height discriminator. The resolving power is then sufficient for the detection of the reflections of films as thin as 1 nm. It is concluded that the particle size broadening is the limiting factor for a further extension of the investigation range towards smaller thicknesses.