bluuebunny/crossref_metadata_2025 huggingface dataset:
Constitutive Overexpression of Cytosolic Glutamine Synthetase (GS1) Gene in Transgenic Alfalfa Demonstrates That GS1 May Be Regulated at the Level of RNA Stability and Protein Turnover
Authors: Ortega Jose Luis , Temple Stephen J. , Sengupta-Gopalan Champa
Published: July 2002

Glutamine synthetase (GS) catalyzes the ATP-dependent condensation of NH4  + with glutanate to yield glutamine. Gene constructs consisting of the cauliflower mosaic virus (CaMV) 35S promoter driving a cytosolic isoform of GS (GS1) gene have been introduced into alfalfa (Medicago sativa). Although transcripts for the transgene were shown to accumulate to high levels in the leaves, they were undetectable in the nodules. However, significant amounts of β-glucuronidase activity could be detected in nodules of plants containing the CaMV 35S promoter-β-glucuronidase gene construct, suggesting that the transcript for the GS1transgene is not stable in the root nodules. Leaves of alfalfa plants with the CaMV 35S promoter-GS1 gene showed high levels of accumulation of the transcript for the transgene when grown under low-nitrogen conditions and showed a significant drop in the level of GS1 transcripts when fed with high levels of NO3  −. However, no increase in GS activity or polypeptide level was detected in the leaves of transgenic plants. The results suggest that GS1 is regulated at the level of RNA stability and protein turnover.
Reduced Activity of Antioxidant Machinery Is Correlated with Suppression of Totipotency in Plant Protoplasts
Authors: Papadakis Anastasia K. , Siminis Charalambos I. , Roubelakis-Angelakis Kalliopi A.
Published: July 2002

We previously showed that during protoplast isolation, an oxidative burst occurred and the generation of active oxygen species was differentially mediated in tobacco (Nicotiana tabacum) and grapevine (Vitis vinifera), accompanied by significant quantitative differences (A.K. Papadakis, K.A. Roubelakis-Angelakis [1999] Plant Physiol 127: 197–205). We have now further tested if the expression of totipotency in protoplasts is related to the activity of cellular antioxidant machinery during protoplast culture. Totipotent (T) tobacco protoplasts had 2-fold lower contents of intracellular O2  .− and H2O2 and 7-fold lower levels of O2  .− and H2O2 in the culture medium, compared with non-totipotent (NT) tobacco protoplasts. Addition of alkaline dimethylsulfoxide, known to generate O2  .−, resulted in isolation of tobacco protoplasts with reduced viability and cell division potential during subsequent culture. Active oxygen species levels decreased in tobacco and grapevine protoplasts during culturing, although higher contents of O2  .− and H2O2 were still found in NT- compared with T-tobacco protoplasts, after 8 d in culture. In T-tobacco protoplasts, the reduced forms of ascorbate and glutathione predominated, whereas in NT-tobacco and grapevine protoplasts, the oxidized forms predominated. In addition, T-tobacco protoplasts exhibited severalfold lower lipid peroxidation than NT-tobacco and grapevine protoplasts. Furthermore, several antioxidant enzyme activities were increased in T-tobacco protoplasts. Superoxide dismutase activity increased in tobacco, but not in grapevine protoplasts during culturing due to the increased expression of cytoplasmic Cu/Zn-superoxide dismutase. The increase was only sustained in T-tobacco protoplasts for d 8. Together, these results suggest that suppressed expression of totipotency in protoplasts is correlated with reduced activity of the cellular antioxidant machinery.
Flavonoids Act as Negative Regulators of Auxin Transport in Vivo in Arabidopsis
Authors: Brown Dana E. , Rashotte Aaron M. , Murphy Angus S. , Normanly Jennifer , Tague Brian W. , Peer Wendy A. , Taiz Lincoln , Muday Gloria K.
Published: July 2002

Polar transport of the plant hormone auxin controls many aspects of plant growth and development. A number of synthetic compounds have been shown to block the process of auxin transport by inhibition of the auxin efflux carrier complex. These synthetic auxin transport inhibitors may act by mimicking endogenous molecules. Flavonoids, a class of secondary plant metabolic compounds, have been suggested to be auxin transport inhibitors based on their in vitro activity. The hypothesis that flavonoids regulate auxin transport in vivo was tested in Arabidopsis by comparing wild-type (WT) and transparent testa (tt4) plants with a mutation in the gene encoding the first enzyme in flavonoid biosynthesis, chalcone synthase. In a comparison between tt4 and WT plants, phenotypic differences were observed, including three times as many secondary inflorescence stems, reduced plant height, decreased stem diameter, and increased secondary root development. Growth of WT Arabidopsis plants on naringenin, a biosynthetic precursor to those flavonoids with auxin transport inhibitor activity in vitro, leads to a reduction in root growth and gravitropism, similar to the effects of synthetic auxin transport inhibitors. Analyses of auxin transport in the inflorescence and hypocotyl of independent tt4 alleles indicate that auxin transport is elevated in plants with a tt4mutation. In hypocotyls of tt4, this elevated transport is reversed when flavonoids are synthesized by growth of plants on the flavonoid precursor, naringenin. These results are consistent with a role for flavonoids as endogenous regulators of auxin transport.
Use of CrKα radiation to enhance the signal from anomalous scatterers including sulfur
Authors: Kwiatkowski Witek , Noel Joseph P. , Choe Senyon
Published: July 2002

The anomalous signals from scatterers such as sulfur (S) and arsenic (As) were compared in diffraction data sets collected from an X-ray source with three different targets, Au, Cu and Cr, on a multi-target rotating anode. HIV-1 integrase crystals served as the test case for this study. The crystalline specimen of HIV-1 integrase contains in each protein molecule two As atoms, each covalently bound to a cysteine S atom, and two additional S atoms derived from methionine. It was found that the CrKα radiation gave the clearest peaks in anomalous difference Fourier maps, although the signal-to-noise ratios of the anomalous signal for the CuKα and CrKα data were similar but better than that for AuLα. This result was in spite of the fourfold higher flux from the Cu anodeversusthe Cr anode. For all three X-ray wavelengths, anomalous difference Fourier maps calculated with bias-removed phases derived from the known atomic model revealed clear peaks at the two As sites. However, only in the map calculated using the CrKα data were both peaks of the expected ellipsoidal shape, enveloping the As atom and the adjacent S atom. None of the S sites was apparent in difference maps calculated using the AuLα data. The ability to enhance the S-derived anomalous signal using CrKα radiation has particularly useful applications in the structure determination of proteins, for example in resolving ambiguities in the chain tracing of a protein with numerous disulfide bonds and in assigning amino acid identities. Additionally, anomalous difference Patterson maps calculated from the CrKα data were sufficiently clear to identify the As-related peaks. These results form the groundwork for in-house phase determination with the multi-wavelength anomalous diffraction method.
Grazing incidence small-angle X-ray scattering from laterally ordered triangular pyramidal Ge islands on Si(111)
Authors: Paniago R. , Metzger H. , Rauscher M. , Kovats Z. , Peisl J. , Schulze J. , Eisele I. , Ferrer S.
Published: July 2002

We present a structural study of nearly perfect triangular pyramidal Ge islands grown on Boron-terminated Si(111). Using atomic force microscopy we show that these islands are strongly ordered in the direction perpendicular to the miscut induced terrace steps of the substrate. We use grazing incidence small-angle X-ray scattering to assess the island shape and size distribution. In this geometry the scattered wave amplitude is composed of four terms, including all combinations of scattering from the islands and reflection from the substrate. We finally show that this technique is able to determine the complete symmetry of arbitrary shaped objects on a substrate.
X-ray structure study of the light-induced metastable states of the spin-crossover compound [Fe(mtz)6](BF4)2
Authors: Kusz Joachim , Spiering Hartmut , Gütlich Philipp
Published: July 2002

Iron(II) complexes exhibiting thermal spin-crossover may be converted from the1A1low-spin (LS) state to the5T2high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST) and from the LS to the HS state by irradiation with red light (reverse LIESST). The lifetime of the metastable LIESST states may be sufficiently long to enable an X-ray diffraction study. The lattice parameters of a single crystal of [Fe(mtz)6](BF4)2(mtz = methyltetrazole) (space groupP21/n) were measured between 300 and 10 K. While one Fe lattice site (A) of the crystal changes from the HS to the LS state near 78 K, the other site (B) remains in the LS state. Using the green light (514 nm) of an argon ion laser the crystal was quantitatively converted to the HS state at 10 K. Irradiation of the crystal at 10 K by red light of a laser diode (820 nm) with siteAin the LS and siteBin the HS state converts siteBalmost completely to the LS state. The lattice parameters of both metastable states were measured up to 50 K, where they start to decay on a minute timescale. At 10 K, a full data set for evaluation of the crystal structure was recorded. The volume change of the crystal per complex molecule accompanying the spin transition is 31.5 Å3at siteAand close to zero [−0.21 (14) Å3] at siteB.
A microspectrophotometer for UV–visible absorption and fluorescence studies of protein crystals
Authors: Bourgeois Dominique , Vernede Xavier , Adam Virgile , Fioravanti Emanuela , Ursby Thomas
Published: July 2002

Absorption microspectrophotometry has been shown to be of considerable help to probe crystalline proteins containing chromophores, metal centres, or coloured substrates/co-factors. Absorption spectra contribute to the proper interpretation of crystallographic structures, especially when transient intermediate states are studied. Here it is shown that fluorescence microspectrophotometry might also be used for such purposes if endogenous fluorophores are present in the macromolecule or when exogenous fluorophores are added and either bind to the protein or reside in the solvent channels. An off-line microspectrophotometer that is able to perform low-temperature absorption and fluorescence spectroscopy on crystals mounted in cryo-loops is described. One-shot steady-state emission spectra of outstanding quality were routinely collected from several samples. In some cases, crystals with optical densities that are too low or too high for absorption studies can still be tackled with fluorescence microspectrophotometry. The technique may be used for simple controls such as checking the presence, absence or redox state of a fluorescent substrate/co-factor. Potential applications in the field of kinetic crystallography are numerous. In addition, the possibility to probe key physico-chemical parameters of the crystal, such as temperature, pH or solvent viscosity, could trigger new studies in protein dynamics.
Lattice-parameter measurements of PbHPO4 single crystals by the ratio method
Authors: Horváth J.
Published: July 2002

Temperature dependences of PbHPO4 single-crystal lattice parameters were measured by the ratio method in the range 158–421 K. Below the ferroelectric phase transition (T

c
= 310 K) lattice parameter b increases non-linearly with decreasing temperature while all others decrease linearly. The ratio method was generalized to the monoclinic crystal system for this purpose.
Buerger precession camera and overall characterization of thin films and flat-plate crystals
Authors: Staudenmann J.-L. , Horning R. D. , Knox R. D.
Published: July 2002

A fast simple and non-destructive method is described to provide qualitative structural information for flat-plate crystals and epitaxically grown films. The technique, based upon the Buerger precession camera, produces an easy-to-interpret photograph of the reciprocal space of all the components at once: substrate, film or buffer layer, and/or superlattice. A wide variety of technologically important examples are used to illustrate the technique: a mixture of CdTe phases on (001) Si, an aluminium layer on a (001) Si substrate, (001) Ge epitaxic layers on (001) Si substrates, three combinations of possible orientations of CdTe epitaxic layers on various substrate types, CdTe/ZnTe and other II–VI superlattices on GaAs substrates. In addition, the precession pictures readily reveal the common [111] face-centered cubic twin fault, or stacking disorder, seen in bulk growth methods. This finding may have severe consequences for the electronic mobility and the feasibility of devices fabricated from these composite systems.
BIRCH, a program for fitting PV data to an Eulerian finite-strain equation of state
Authors: Ross C. R. , Webb S. L.
Published: July 2002

With the recent improvement of high-pressure technology, in particular the diamond-anvil cell, an ever-increasing number of studies are appearing which relate unit-cell parameters (as measured by X-ray diffraction) to the applied pressure.
A microprocessor-controlled multichannel analyser for wavelength determination
Authors: Lange J. , Burzlaff H.
Published: July 2002

The application of an ultrafast analogue-to-digital converter and a high-performance-single board microcomputer permits the construction of a very fast and versatile multichannel analyser (MCA) at low cost. With the powerful instruction set of the microprocessor MC 68000, an intelligent all-round MCA could be realised with useful correction software on the single-board microcomputer. This MCA was used successfully for a data collection by Laue techniques with a four-circle diffractometer.
Indexing of powder diffraction patterns for low-symmetry lattices by the successive dichotomy method
Authors: Boultif A. , Louër D.
Published: July 2002

The dichotomy method for indexing powder diffraction patterns for low-symmetry lattices is studied in terms of an optimization of bound relations used in the comparison of observed data with the calculated patterns generated at each level of the analysis. A rigorous mathematical treatment is presented for monoclinic and triclinic cases. A new program, DICVOL91, has been written, working from the cubic end of the symmetry sequence to triclinic lattices. The search of unit cells is exhaustive within input parameter limits, although a few restrictions for the hkl indices of the first two diffraction lines have been introduced in the study of triclinic symmetry. The efficiency of the method has been checked by means of a large number of accurate powder data, with a very high success rate. Calculation times appeared to be quite reasonable for the majority of examples, down to monoclinic symmetry, but were less predictable for triclinic cases. Applications to all symmetries, including cases with a dominant zone, are discussed.
Double-Bent-Crystal Small-Angle Neutron Scattering Setting and its Applications
Authors: Strunz P. , Saroun J. , Mikula P. , Lukás P. , Eichhorn F.
Published: July 2002

Theoretical relations for optimum adjustments of two arrangements of a double-bent-crystal (DBC) small-angle neutron scattering (SANS) diffractometer are discussed. Results of several experiments demonstrate the applicability of DBC SANS in the investigation of some technologically important materials in the range of scattering-vector sizes 0.0002–0.02 Å−1. Formulas derived for data analysis, which describe the transformation of the SANS cross section to the measured intensity, indicate that water calibration is not required and that the indirect method of data evaluation is the most appropriate.
Interface Evolution in a W/Si Multilayer after Rapid Thermal Annealing Studied by X-ray Reflectivity and Diffuse Scattering
Authors: Jergel M. , Holý V. , Majková E. , Luby S. , Senderák R.
Published: July 2002

An interface study of the effect of rapid thermal annealing (RTA) in the temperature range 523–1273 K for 5–40 s on a nominally [(50 Å Si/10 Å W) × 9] amorphous multilayer (ML) deposited on an Si(100) wafer was performed by X-ray reflectivity and diffuse-scattering measurements at grazing incidence. The results of the X-ray reflectivity and diffuse-scattering measurements were evaluated by Fresnel optical computational code and within the distorted-wave Born approximation, respectively. Up to the 773 K/5 s annealing step, the r.m.s. interface roughness decreases by 30%, which brings about a reflectivity increase of 20% on the first Bragg maximum. There is a small overall increase of the r.m.s. interface roughness across the ML in the as-deposited state and the interface profiles are highly correlated. From the very beginning of RTA, the fractal interface behaviour is gradually lost and the lateral correlation length increases, this process being accompanied by a decrease of the interface conformality. This tendency continues during the 773 K/20 s annealing; however, the r.m.s. roughness evolution is reversed. During the 1023 K/5 s annealing, the interfaces are no longer `seen' by the X-rays and, during the 1273 K/5 s annealing, a total collapse of the ML structure takes place.
The Small-Angle X-ray Scattering Beamline of the Brazilian Synchrotron Light Laboratory
Authors: Kellermann G. , Vicentin F. , Tamura E. , Rocha M. , Tolentino H. , Barbosa A. , Craievich A. , Torriani I.
Published: July 2002

This paper describes the small-angle scattering beamline built at the Brazilian Synchrotron Light Laboratory (LNLS). Vertical focusing of the synchrotron beam is achieved by an elastically bent gold-plated cylindrical mirror. An asymmetric cut curved triangle-shaped silicon single crystal (111 reflection) is used for monochromatization and horizontal focusing. The mirror, monochromator optics and 2θ arm were designed to cover the spectral range between 1.0 and 2.0 Å. Three slit sets, a secondary photon shutter, two beam monitors, filters and absorbers, a multi-sample holder, a vacuum path, a beam-stopper and a set of detectors are the basic components of the workstation. The stepping motors are equipped with specially designed encoders. All mechanical and pneumatic movements and detectors can be remotely controlled using a direct panel or a PC.
A note on mean orientation
Authors: Morawiec A.
Published: July 2002

The procedure of calculating the mean orientation considered by Humbertet al.[J. Appl. Cryst.(1996),29, 662–666] is reformulated in terms of quaternions of unit magnitude. The problem is reduced to the calculation of an eigenvector of a certain symmetric 4 × 4 matrix.
A cryocooling technique for protein crystals grown by dialysis from volatile solvents
Authors: Fernandez Elias J. , Joachimiak Andrzej , Lolis Elias
Published: July 2002

The transfer of protein crystals from the original crystallization environment to cryoprotectants, heavy-atom solutions, or quartz capillary tubes, exposes crystal droplets to conditions that can cause evaporation of the droplet and damage to the crystal. This problem is particularly acute for crystals grown from volatile solvents or that are otherwise air-sensitive. Here a method that overcomes this problem is applied to crystals of macrophage inflammatory protein II encoded by herpesvirus-8. The method is based on dialysis and makes use of a dialysis adaptor that can be used with 24-well crystallization plates. This method permits the transfer of crystals to cryoprotectant conditions with greater ease and lowers the risk of mechanical damage relative to other available methods.
A study of Li2TiOSiO4 and Li2TiOGeO4 by X-ray powder and electron single-crystal diffraction, 17O MAS NMR and O K-edge and Ti L
2,3-edge EELS
Authors: Bastow T. J. , Botton G. A. , Etheridge J. , Smith M. E. , Whitfield H. J.
Published: July 2002

X-ray powder and electron single-crystal diffraction of crystals of Li2TiOSiO4 and Li2TiOGeO4 showed them to be tetragonal, space group P4/nmm unit-cell parameters a = 6.4379\,(2), c = 4.40032\,(2) Å for Li2TiOSiO4 and a = 6.6110\,(8), c = 4.4372\,(6) Å for Li2TiGeO4. The compounds are isostructural with their sodium analogues but are considerably compressed along the c axis owing to the smaller size of lithium compared with sodium atoms. Square-pyramidal TiO5 groups are joined in these compounds by tetrahedral SiO4 and GeO4 groups, respectively. 17O nuclear magnetic resonance spectra of the two compounds, isotopically enriched with 17O, showed peaks due to the apical titanyl, Ti—O, and basal, bridging, Ti—O—Si or Ti—O—Ge, oxygen atoms of the title compounds. By comparison with reference spectra, oxygen K edges and titanium L
2,3 edges of electron energy-loss spectra were tentatively assigned.
Resonant X-ray diffraction in incommensurately modulated crystals. Symmetry consideration of anisotropic anomalous scattering
Authors: Ovchinnikova E. N. , Dmitrienko V. E.
Published: July 2002

Symmetry restrictions on the intensities and polarization properties of main reflections and their satellites are found for incommensurately modulated crystals in the case of anisotropic anomalous X-ray diffraction near absorption edges. It is shown that the modulation becomes a source of additional anisotropy for each resonant scatterer and induces a modulated behaviour of the susceptibility tensor. The four-dimensional approach is used to calculate the set of possible reflections. It is found that additional (`forbidden') reflections may appear both in the system of main reflections and in the system of satellites. The anisotropy also results in complex azimuthal and polarization properties of each reflection. The displacive modulation is discussed in detail. The ATS reflections corresponding to the resonant X-ray diffraction near the K-edge of iron in pyrrhotite-5.5C are considered.
Real-space Green's-function approach within RHEED
Authors: Derlet P. M. , Smith A. E.
Published: July 2002

Green's-function techniques are used to obtain a real-space series solution for the elastic reflection high-energy electron diffraction (RHEED) from a crystalline surface. A renormalized perturbation expansion due to potential self-scattering is developed for the local real-space Green's function. With the Pt (111) surface as an example, numerical results are obtained for reflection coefficients and intensities. In particular, calculations are performed to obtain the local density of states at and near the surface region. Total density-of-states calculations are also performed. These provide a basis for a discussion of the form of resonant electronic Green's functions that can be used to describe the surface resonance phenomenon within RHEED.
The use of multiple-scattering data to enhance small-angle neutron scattering experiments
Authors: Sabine T. M. , Bertram W. K.
Published: July 2002

Multiple scattering of neutrons by the inhomogeneities responsible for small-angle neutron scattering (SANS) during the passage of the beam through the specimen can be used to provide valuable information about the shape of the objects and the absolute value of the contrast between the scattering particles and the matrix. The neutrons emerging from the specimen are classified into those that have been scattered n times. The index n ranges from zero to infinity. The remnant of the incident beam is the group of neutrons for which n equals zero. Each group contributes separately to the scattering profile. The small-angle scattering cross section is independent of the neutron wavelength for n = 1 only. Thus collection of data as a function of specimen thickness and of neutron wavelength will provide a number of different profiles describing the same physical situation. Simultaneous analysis of these profiles provides absolute values of the cross section for scattering into the small-angle region and of the cross section for removal of neutrons from the small-angle region. So that the method can be used generally, a profile function that is a very good approximation to those in the literature is introduced. The implications for time-of-flight SANS are discussed.
Structures and isomerization in diamminedichloropalladium(II)
Authors: Kirik S. D. , Solovyov L. A. , Blokhin A. I. , Yakimov I. S. , Blokhina M. L.
Published: July 2002

Three forms (cis-, trans-, β-trans-) of [Pd(NH3)2Cl2] were obtained as pure single-phase powder materials. Ab initio structure determinations using X-ray powder diffraction were carried out. The cis-Pd(NH3)2Cl2 [a = 6.3121 (2), b = 6.4984 (2), c = 3.3886 (1) Å, α = 96.604 (4), β = 97.290 (4), γ = 104.691 (2)°, Z = 1, space group P1] and trans-Pd(NH3)2Cl2 [a = 6.5398 (3), b = 6.8571 (4), c = 6.3573 (3) Å, α = 103.311 (5), β = 102.454 (3), γ = 100.609 (4)°, Z = 2, space group P{\bar 1}] phases have a typical layer-column structure, while β-trans-Pd(NH3)2Cl2 [a = 8.1540 (2), b = 8.1482 (2), c = 7.7945 (1) Å, Z = 4, space group Pbca] is described as a parquet-like layer structure. Both trans phases demonstrate the order-disorder phenomenon. The possible ways of phase transitions are discussed. It is noted that the cis phase can transform into trans in the solid state without destroying the crystal body. Further transformation to β-trans follows through a break up of the crystal body.
Octahedral Tilting in Perovskites. I. Geometrical Considerations
Authors: Woodward P. M.
Published: July 2002

The 23 Glazer tilt systems describing octahedral tilting in perovskites have been investigated. It is shown that in tilt systems a
+
a
+
a
−, a
+
b
+
b
−, a
+
a
+
c
−, a
+
b
+
c
−, a
0
b
+
b
− and a
0
b
+
c
− it is not possible to link together a three-dimensional network of perfectly rigid octahedra. In these tilt systems small distortions of the octahedra must occur. The magnitude of the distortions in the a
+
a
+
a
− and a
0
b
+
b
− tilt systems are estimated. A table of predicted space groups for ordered perovskites, A
2
MM′O6, for all 23 tilt systems is also given.
A New Study of the Acid Rhodo Complex Salt [(NH3)5CrOHCr(NH3)5]Cl5.H2O Shows That the Crystals are Orthorhombic
Authors: Harris P. , Birkedal H. , Larsen S. , Güdel H. U.
Published: July 2002

Diffraction data recorded at low temperature with Mo K\alpha from two different crystals have been used in the refinement of the structure of the acid rhodo complex salt, \mu-hydroxo-bis[pentaamminechromium(III)] chloride monohydrate [(NH3)5CrOHCr(NH3)5]Cl5.H2O. Several structural models in two different tetragonal space groups have been investigated before a satisfactory description of the structure was obtained. The compound crystallizes in the orthorhombic space group P212121, with a= 16.155 (3), b = 16.154 (3), c = 14.750 (7) Å and Z = 8. The apparent tetragonal symmetry arises due to rotation twinning of the crystals. The diffraction pattern is further complicated by tetragonal pseudo-symmetry of the chromium sites, which means that reflections with l = 2n + 1 are systematically weak. The two independent dimeric cations are involved in slightly different hydrogen-bond patterns. This observation and the relative orientation of the dimers in the crystal is in accordance with spectral and magnetic measurements.
Charge density study of N-acetyl-L-tyrosine ethyl ester monohydrate derived from CCD area detector data
Authors: Dahaoui S. , Jelsch C. , Howard J. A. K. , Lecomte C.
Published: July 2002

The crystal structure, thermal vibrations and electron density of the peptide N-acetyl-L-tyrosine ethyl ester monohydrate, C13H17NO4.H2O, have been analysed using single-crystal X-ray diffraction data collected at 110 K with Mo Kα radiation to a resolution of (\sin\theta/\lambda)_\max = 1.1 Å−1. A CCD area detector was used to collect 98 393 data during one week. A multipolar atom density model was fitted against the 10 189 unique data with I > 2σ(I) [R(F) = 0.027, wR(F) = 0.020, g.o.f. = 0.65] in order to map the valence electron distribution. These deformation densities compare very well with those obtained from conventional diffractometers equipped with scintillation detectors. This work shows that area detectors permit charge density studies in a more routine way than is possible with conventional diffractometers.
Crystal and molecular structures of 2-[1-(2-aminoethyl)-2-imidazolidinylidene]-2-nitroacetonitrile (C7H11N5O2) and 2,6-diamino-5-hydroxy-3-nitro-4H-pyrazolo[1,5-a]pyrimidin-7-one monohydrate (C6H6N6O4·H2O) from X-ray, synchrotron and neutron powder diffraction data
Authors: Chernyshev V. V. , Fitch A. N. , Sonneveld E. J. , Kurbakov A. I. , Makarov V. A. , Tafeenko V. A.
Published: July 2002

The crystal and molecular structures of 2-[1-(2-aminoethyl)-2-imidazolidinylidene]-2-nitroacetonitrile [C7H11N5O2; space group P21/n; Z = 4; a = 7.4889 (8), b = 17.273 (2), c = 7.4073 (8) Å, β = 111.937 (6)°], (I), and 2,6-diamino-5-hydroxy-3-nitro-4H-pyrazolo[1,5-a]pyrimidin-7-one monohydrate [C6H6N6O4·H2O; space group P21/n; Z = 4; a = 17.576 (3), b = 10.900 (2), c = 4.6738 (6) Å, β = 92.867 (8)°], (II), have been determined from X-ray, synchrotron and neutron powder diffraction data using various methods. The structures were originally solved from Guinier photographs with a grid search procedure and the program MRIA using a priori information from NMR and mass spectra on the possible geometry of the molecules. Because the conformation of molecule (I) changed during the bond-restrained Rietveld refinement, solvent water was found in (II) and, moreover, as both Guinier patterns were corrupted by texture, high-resolution texture-free synchrotron data were collected at the BM16 beamline, ESRF, to confirm the original results. Using the set of |F|
2
values derived from the synchrotron patterns after full-pattern decomposition procedures, the structures of (I) and (II) were solved by direct methods via
SHELXS96, SIRPOW.92 and POWSIM without any preliminary models of the molecules, and by Patterson search methods via
DIRDIF96 and PATSEE with the use of rigid fragments from each of the molecules. The neutron patterns allowed (I) and (II) to be solved using the grid search procedure and correct initial models of the molecules including H atoms. The results obtained from powder patterns measured on different devices demonstrate the high level of reproducibility and reliability of various powder software and equipment, with a certain preference for synchrotron facilities.
Application and comparison of different tests on twinning by merohedry
Authors: Kahlenberg V.
Published: July 2002

Three different tests on twinning by merohedry from the literature have been applied to single-crystal data sets of five different inorganic crystal structures. Although the three test procedures differ significantly with regard to their efficiency, in both detecting the existence of twinning and estimating the volume fractions of the twin individuals, they represent useful tools in the early stages of a structure analysis and should be applied routinely in the preliminary stage of a structure determination whenever a twinning by merohedry is possible.
Crystallization and preliminary crystallographic analysis of glyceraldehyde 3-phosphate dehydrogenase from Sacchromyces cerevisiae (baker's yeast)
Authors: Gilboa Rotem , Bauer Alan Joseph , Shoham Gil
Published: July 2002

Two related and not thoroughly resolved issues in biochemistry concern the role, if any, of enzyme surfaces in routine metabolism and the method by which metabolic intermediates move between enzyme active sites during multi-step degradation or synthesis. An important enzyme for which a detailed three-dimensional structural analysis has been initiated is yeast glyceraldehyde 3-phosphate dehydrogenase (yGAP-DH). This enzyme is active as a tetramer of total molecular weight of 145 kDa and requires nicotinamide adenine dinucleotide (NAD+) as cofactor. In this report, the crystallization and preliminary crystallographic characterization of several crystal forms of yGAP-DH are described. Of the five distinct crystal forms, the most suitable was found to contain the holo-enzyme, and the crystals were grown by the vapor-diffusion method using polyethylene glycol 6000 as precipitant, sodium acetate as buffer (pH 4.6), and NAD+ and dithiothreitol as additives. The crystals belong to the orthorhombic space group P21212, with cell dimensions of a = 87.33, b = 96.11 and c = 115.34 Å. These crystals are mechanically strong, relatively stable in the X-ray beam and diffract X-rays (from a normal rotating-anode radiation source) to better than 2 Å resolution. A full 2.1 Å resolution diffraction data set (98% completion) has been measured. The three-dimensional structures of related GAP-DH enzymes from several other sources have been determined and reported, and are available for a molecular replacement structure solution.
Biochemical and Crystallographic Characterization of Homologous Non-peptidic Thrombin Inhibitors Having Alternate Binding Modes
Authors: Strickland Corey L. , Fevig John. M. , Galemmo Robert A. , Wells Brian L. , Kettner Charles A. , Weber Patricia C.
Published: July 2002

The X-ray crystallographic structure of [N-(3-phenylpropionyl)-N-(phenethyl)]-Gly-boroLys-OH (HPBK, Ki
 = 0.42 nM, crystallographic R factor to 1.8 Å resolution, 19.6%) complexed with human α-thrombin shows that the boron adopts a tetrahedral geometry and is covalently bonded to the active serine, Ser195. The HPBK phenethyl aromatic ring forms an edge-to-face interaction with the indole side chain of Trp215. Four HPBK analogs containing either electron-withdrawing or electron-donating substitutents at the 3′ position of the phenethyl ring were synthesized in an attempt to modulate ligand affinity by inductive stabilization of the edge-to-face interaction. Refined crystallographic structures of the trifluoromethyl (Ki
= 0.37 nM, crystallographic R factor to 2.0 Å resolution = 18.7%), fluoro (Ki
= 0.60; R factor to 2.3 Å resolution = 18.4%), methoxy (Ki
= 0.91 nM, R factor to 2.2 Å resolution = 19.8%) and methyl (Ki
= 0.20 nM, R factor to 2.5 Å resolution = 16.9%) HPBK analogs complexed with thrombin revealed two binding modes for the closely related com-pounds. A less than 1.5-fold variation in affinity was observed for analogs (trifluoromethyl-HPBK and fluoro-HPBK) binding with the edge-to-face interaction. The slight inductive modulation is consistent with the overall weak nature of the edge-to-face interaction. Owing to an unexpected rotation of the phenethyl aromatic ring, the 3′ substituent of two analogs, methoxy-HPBK and methyl-HPBK, made direct contact with the Trp215 indole side chain. Increased affinity of the 3′ methyl analog is attributed to favorable interactions between the methyl group and the Trp215 indole ring. Differences in inhibitor, thrombin and solvent structure are discussed in detail. These results demonstrate the subtle interplay of weak forces that determine the equilibrium binding orientation of inhibitor, solvent and protein.
Purification and preliminary X-ray crystallographic studies of recombinant 7,8-diaminopelargonic acid synthase from Escherichia coli
Authors: Käck Helena , Gibson Katharine J. , Gatenby Anthony A. , Schneider Gunter , Lindqvist Ylva
Published: July 2002

Recombinant 7,8-diaminopelargonic acid synthase from Escherichia coli, a pyridoxal-phosphate-dependent aminotransferase, has been crystallized in space groups P21 and C2. Both crystal forms were obtained at pH 7.3 with 21% polyethylene glycol and 10% 2-propanol as precipitants. The cell dimensions were a = 130, b = 57.5, c = 117 Å, β = 110° for the C2 crystals, and a = 58.4, b = 55.6, c = 121 Å, β = 96.9° for the P21 crystals, which diffract to at least 2.6 and 2.0 Å resolution, respectively.
Metal Complex Geometries in Small-Molecule Crystals
Authors: Orpen A. Guy
Published: July 2002

The origins, scope and utility of compilations of metal–ligand and intraligand bond lengths based on the Cambridge Structural Database are discussed. The limitations on the apparent uncertainty of metal–ligand bond lengths derived from crystallographic data and recent evidence of metal-assisted hydrogen bonding involving ligands are reviewed in the light of the transferability of bond-length values from one crystal structure determination.
Overproduction, purification, crystallization and preliminary X-ray diffraction studies of the human spliceosomal protein U5-15kD
Authors: Reuter Klaus , Ficner Ralf
Published: July 2002

The gene coding for the human spliceosomal U5 snRNP-specific 15 kDa protein (U5-15kD) was overexpressed in Escherichia coli, its product purified to homogeneity and crystallized. Well diffracting single crystals were obtained by the vapour-diffusion method in hanging drops and subsequent macroseeding. The crystals belong to the orthorhombic space group P21212 with a = 62.3, b = 65.7, c = 37.1 Å. They diffract to at least 3.0 Å and contain one molecule in the asymmetric unit. A selenomethionine derivative of the protein was prepared and crystallized for multiwavelength anomalous diffraction (MAD) data collection.
Detection and treatment of twinning: an improvement and new results
Authors: Dumas P. , Ennifar E. , Walter P.
Published: July 2002

This work deals with two aspects of the twinning problem. Firstly, an improvement of a known statistical test aimed at detecting twinning is presented and, secondly, a new parametrization of twinning is described, as well as a new method to obtain an accurate estimate of the degreee of twinning. During work on crystals of the dimerization-initiation site of the HIV-1 genomic RNA, perfectly twinned crystals were obtained which were not immediately recognized as such by use of a known statistical method. This method, reminiscent of Wilson tests for the detection of centrosymmetric space groups, relies on the calculation of 〈F^{2}〉/〈F〉2 or, equivalently, of 〈I
2〉/〈I〉2. It is shown that overlooking experimental errors may lead to erroneously large values of this index and, in turn, to ambiguous or incorrect conclusions. An immediate solution to this problem is presented. Independently, an alternative parametrization which expresses both the effect of twinning on intensities and the operation of untwinning to recover the correct intensities is proposed. A new method for estimating the degree of twinning is also presented. It is based upon maximization of the cross-correlation coefficients between intensities of all available data sets, and yields a fully analytical solution. Tests made with experimental data are quite satisfactory. It is suggested that the latter results could be used efficiently within the MIR method by allowing refinement, through one additional parameter only, of the twinning ratios of all data sets considered for phasing. Finally, the new parametrization of twinning has striking consequences in this correlation-based twinning determination: very unexpectedly, it yields a novel estimate of the `twinning ratio' of a potentially twinned crystal which is fully independent of the data set used for the comparison.
The CXXC motif: crystal structure of an active-site variant of Escherichia coli thioredoxin
Authors: Schultz L. Wayne , Chivers Peter T. , Raines Ronald T.
Published: July 2002

The 2.2 Å crystalline structure of an oxidized active-site variant of Escherichia coli thioredoxin (Trx) has been solved. Trx is a 12 kDa enzyme which catalyzes the oxidation of dithiols and the reduction and isomerization of disulfides in other proteins. Its active site contains the common structural motif CXXC. Protein-disulfide isomerase (PDI), a 57 kDa homolog of Trx, contains four Trx-like domains. The three-dimensional structure of PDI is unknown. PDI-deficient Saccharomyces cerevisiae are inviable. An active-site variant of Trx which complements PDI-deficient yeast has the active-site sequence Cys32-Val33-Trp34-Cys35 (CVWC). The reduction potential of oxidized CVWC Trx (E°′ = −0.230 V) is altered significantly from that of the wild-type enzyme (E°′ = −0.270 V). However, the structure of the oxidized CVWC enzyme is almost identical to that of wild-type Trx. The addition of valine and tryptophan in the active site is likely to increase the reduction potential, largely by decreasing the pKa
of the Cys32 thiol in the reduced enzyme. Unlike in wild-type Trx, significant protein–protein contacts occur in the crystal. Protein molecules related by a crystallographic twofold axis form a dimer in the crystal. The dimer forms as an extension of the twisted mixed β-sheet which composes the backbone of each Trx structure.
Crystallization and preliminary X-ray analyses of catabolite control protein A, free and in complex with its DNA-binding site
Authors: Tebbe Jan , Orth Peter , Küster-Schöck Elke , Hillen Wolfgang , Saenger Wolfram , Hinrichs Winfried
Published: July 2002

The catabolite control protein (CcpA) from Bacillus megaterium is a member of the bacterial repressor protein family GalR/LacI. CcpA with an N-terminal His-tag was used for crystallization. Crystals of free CcpA and of CcpA in complex with the putative operator sequence (catabolite responsive elements, CRE) were obtained by vapour-diffusion techniques at 291 K using the hanging-drop method. CcpA crystals grown in the presence of polyethylene glycol 8000 belong to the hexagonal space group P6122 or P6522, with unit-cell parameters a = 74.4, c = 238.8 Å. These crystals diffract X-rays to 2.55 Å resolution and contain one monomer of the homodimeric protein per asymmetric unit. Crystals of the CcpA–CRE complex were obtained with ammonium sulfate as precipitant and belong to the tetragonal space group I4122, with unit-cell parameters a = 125, c = 400 Å and one complex per asymmetric unit. Although these co-crystals grew to a sufficient size, X-ray diffraction was limited to 8 Å resolution.
Multi-component fitting XAFS analysis of molybdate species during catalyst preparation by the molten salt method
Authors: Matsubayashi Nobuyuki , Sato Koichi , Imamura Motoyasu , Shimada Hiromichi , Afanasiev Pavel , Geantet Christophe
Published: July 2002

The goal of the present study was to elucidate the formation mechanisms of highly dispersed catalysts by the molten salt method. For this purpose, multi-component fitting Mo K-edge EXAFS analysis was applied to the structure of molybdate catalysts prepared in KNO3 and NaNO3. The analysis revealed that MoO3 dissolved in molten salts was at first transformed into polymolybdate anions and finally into MoO4
2- anions. The transformation into MoO4
2- anions took place at a lower temperature when NaNO3 was used as molten salt than KNO3. In contrast, polymolybdate anions were stable even at higher temperature when ZrO2 was added as a support of molybdate.
Ho–Fe–Garnet soft XMCD measurements below and above the compensation temperature
Authors: Goering E. , Gold S. , Schütz G.
Published: July 2002

We have investigated the magnetism of Holmium-Iron-Garnet (Ho3Fe5O12) at the Ho M4,5- the Fe L2,3- and the O K - edges. As expected switching of the sub-lattice magnetization is observed at the compensation temperature. We will give detailed analysis of the Ho and Fe XMCD signals, using sum rules. Fe dichroism is analyzed in terms of 3d ground state moments and compared to Gadolinium-Iron-Garnet (Gd3Fe5O12). Contributions of octahedral and tetrahedral Fe sites could be separated and analyzed quantitatively. At the oxygen K edge two different structures are observable. Those structures show different temperature dependencies. Therefore we address these features separately to Fe and Rare Earth contributions.
[TcCl(CS)(dppe)2]·C6H6
Authors: Bryan Jeffrey C. , Burrell Anthony K. , Kubas Gregory J.
Published: July 2002

The title compound, chlorobis[1,2-ethanediylbis(diphenylphosphine)-P,P′](thiocarbonyl-C)technetium benzene solvate, [TcCl(C46H42P4)(CS)]·C6H6, was obtained as one of two Tc-containing products isolated from the reaction between CS2and the electron-deficient complex [TcCl(dppe)2], where dppe is 1,2-ethanediylbis(diphenylphosphine). The structure exhibits an unusually short Tc—C distance [1.819 (6) Å], suggesting some multiple-bond character.
Inverse problems of determining the unknown shape of oscillating airfoils in compressible 2D unsteady flow via variational technique
Authors: He Ji‐Huan
Published: July 2002

A generalized variational principle of 2D unsteady compressible flow around oscillating airfoils is established directly from the governing equations and boundary/initial conditions via the semi‐inverse method proposed by He. In this method, an energy integral with an unknown F is used as a trial‐functional. The identification of the unknown F is similar to the identification of the Lagrange multiplier. Based on the variational theory with variable domain, a variational principle for the inverse problem (given as the time‐averaged pressure over the airfoil contour, while the corresponding airfoil shape is unknown) is constructed, and all the boundary/initial conditions are converted into natural ones, leading to well‐posedness and the unique solution of the inverse problems.
Anodizing of aluminium alloys
Authors: Thompson G.E. , Habazaki H. , Shimizu K. , Sakairi M. , Skeldon P. , Zhou X. , Wood G.C.
Published: July 2002

Anodizing is used widely in the surface treatment of aluminium alloys for aerospace applications. Considers recent advances in understanding of the influences of alloying elements in anodizing of aluminium alloys and, in particular, their applicability to second phase particles during anodizing of commercial alloys. Through more precise knowledge of the response of second phase materials to anodic polarization, improved anodizing and related surface treatment processes may be developed in order to enhance the performance of aluminium alloys.
Efficient quaternary ammonium salt as corrosion inhibitor for steel pickling in sulphuric acid media
Authors: El Dahan H.A. , Mohamed T.Y.S. , Abo El‐Enin S.A.
Published: July 2002

A study is carried out on the resistance to corrosion of mild steel in 5 per cent H2SO4 solutions at temperatures between 30 and 60°C. The effectiveness of quaternary ammonium salt used as corrosion inhibitor under the same experimental conditions was also investigated. Weight loss results and electrochemical data showed the good inhibiting action of the inhibitor, acting as anodic type. Thermodynamic parameters for adsorption of the compound are calculated using the Temkin adsorption isotherm.
Crambe oil ‐ a potential new hydraulic oil and quenchant
Authors: Lazzeri Luca , De Mattei Franca , Bucelli Fiorenzo , Palmieri Sandro
Published: July 2002

The technical properties of Crambe abyssinica oil prompted the co‐operation between a research institute and a lubricant producer to determine some possible industrial applications. The results confirm the special physico‐chemical characteristics of crambe oil which, compared with some vegetable or synthetic oils, shows a higher heat removal capability and interesting lubrication characteristics. The research establishes that crambe oil could be a good hydraulic fluid. These findings led to the cultivation of a suitable area with Crambe abyssinica to obtain a sufficient amount of oil for lubricant formulation on a commercial scale.
Oil analysis cost‐effective machine condition monitoring technique
Authors: Newell Gary E.
Published: July 2002

This paper describes the development of the use of lubricant analytical programmes and trend analysis to optimise oil change intervals and to predict equipment failure. The various analytical methods are covered, as are the most frequently occurring lubricant applications where such condition monitoring programmes are most appropriate.