bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallographic disorder in mixed-valent dioxo-bridged MnIII,IV complexes. [Mn2O2(bpy)4][Ce(NO3)6].5H2O
Authors: Ramalakshmi D. , Rajasekharan M. V.
Published: July 2002

The structure of tetrakis(2,2′-bipyridine)di-μ-oxo-dimanganese(3+) hexanitratocerate(3−) pentahydrate, [Mn2O2(bpy)4][Ce(NO3)6].5H2O, is described; M

r
= 1368.88, monoclinic, C2/c, a = 12.940 (3), b = 18.060 (2), c = 22.54 (1) Å, β = 96.29 (2)°, V = 5237 (3) Å3, T = 132 K, Z = 4, F(000) = 2752, D

x
= 1.736 Mg m−3, λ(Mo Kα) = 0.71073 Å, μ = 1.429 mm−1, R(F
2) = 0.0358, wR(F
2) = 0.0783 for 4877 reflections with I > 2σ(I). The cation does not have crystallographically distinguishable Mn atoms. An analysis of the atomic displacement ellipsoids and Mn—N bond distortions has been used to develop a model for the disorder in this type of mixed-valent complex. The anion, Ce(NO3)_6^{3-}, has a distorted icosahedral geometry.
Disparate atomic displacements in skutterudite-type LaFe3CoSb12, a model for thermoelectric behavior
Authors: Chakoumakos Bryan C. , Sales Brian C. , Mandrus David , Keppens Veerle
Published: July 2002

Mean-square atomic displacements in lanthanum triiron cobalt dodecaantimonide, determined as a function of temperature using single-crystal neutron diffraction, show that the La atom exhibits an anomalously large displacement at room temperature, U
eq = 0.0196 (9) Å2, because it is too small to fill the atomic cage formed by the corner-linked octahedral framework of M
4Sb12, M = Fe, Co. Site-occupancy refinements show 25% vacancies on the La site and an actual Fe:Co ratio of 2.17:1. Analysis of the temperature dependence of the atomic displacements identifies a significant temperature-independent component for the La atom ascribed to static disorder, which amounts to 19% of the room-temperature value. The large-amplitude rattling of the La atom can be effectively linked to the dramatic decrease of the lattice contribution to the thermal conductivity, which is a key factor for improving the thermoelectric behavior of these materials. This structure–property relationship offers a new paradigm for the exploration of thermoelectric materials.
Energetic study of the disordered solvent in the crystal structure of an isoxazole derivative. Erratum
Authors: Pani Marcella , Carnasciali Maria Maddalena , Mugnoli Angelo , Beltrame Paolo , Cadoni Enzo , Gelli Gioanna
Published: July 2002

An error in printing is reported. In the paper by Pani et al. [Acta Cryst. (1998), B54, 872–876] the value of Δρmax is given incorrectly in the last sentence on page 874. The sentence should read `In the last difference Fourier map, the highest Δρ values were found near the Cl atoms (Δρmax +0.32 e Å−3); the final reliability indexes were R
1 = 0.072 over 1762 Fo
> 4σ(Fo
) and wR
2 = 0.228 on 4029 Fo

2 for 245 refined parameters, with a goodness-of-fit of 0.96.'
Absolute configurations of Emycin D, E and F; mimicry of centrosymmetric space groups by mixtures of chiral stereoisomers
Authors: Walker Martina , Pohl Ehmke , Herbst-Irmer Regine , Gerlitz Martin , Rohr Jürgen , Sheldrick George M.
Published: July 2002

The crystal structures of Emycin E (1), di-o-bromobenzoyl-Emycin F (2) and o-bromobenzoyl-Emycin D (3) have been determined by X-ray analysis at low temperature. Emycin E and o-bromobenzoyl-Emycin D both crystallize with two molecules in a triclinic unit cell. These two structures can be solved and refined either in the centrosymmetric space group P\bar 1, with apparent disorder localized at or around the expected chiral centre, or in the non-centrosymmetric space group P1 as mixtures of two diastereomers without disorder. Only the latter interpretation is consistent with the chemical and spectroscopic evidence. Refinements in the centrosymmetric and non-centrosymmetric space groups are compared in this paper and are shown to favour the chemically correct interpretation, more decisively so in the case of the bromo derivative as a result of the anomalous dispersion of bromine. Structures (1) and (3) provide a dramatic warning of the dangers inherent in the conventional wisdom that if a structure can be refined satisfactorarily in both centrosymmetric and non-centrosymmetric space groups, the former should always be chosen. In these two cases, despite apparently acceptable intensity statistics and R factors (5.87 and 3.55%), the choice of the centrosymmetric space group leads to the serious chemical error that the triclinic unit cell contains a racemate rather than two chiral diastereomers! The weakest reflections are shown to be most sensitive to the correct choice of space group, underlining the importance of refining against all data rather than against intensities greater than a specified threshold. The use of similar-distance restraints is shown to be beneficial in both P1 refinements. Di-o-bromobenzoyl-Emycin F crystallizes in the monoclinic space group P21 with one molecule in the asymmetric unit and so does not give rise to these problems of interpretation. The absolute configuration of the two bromo derivatives, and hence the Emycins in general, was determined unambiguously as S at the chiral centre C3.
Structure refinement of Cu8GeS6 using X-ray diffraction data from a multiple-twinned crystal
Authors: Onoda Mitsuko , Chen Xue-An , Kato Katsuo , Sato Akira , Wada Hiroaki
Published: July 2002

The structure of the orthorhombic room-temperature phase of Cu8GeS6 (copper germanium sulfide), Mr
= 773.27, has been refined on the basis of X-ray diffraction data from a 12-fold twinned crystal applying a six-dimensional twin refinement technique. For 1804 unique reflections measured using Mo Kα radiation, RF
was 0.083 with 77 structure parameters and 12 scale factors. The symmetry operations, the unit cell and other crystal data are (0, 0, 0; ½, ½, 0) + x, y, z; y, x, z; ¼ − x, ¾ − y, ½ + z; ¾ − y, ¼ − x, ½ + z; a = b = 9.9073 (3) Å, c = 9.8703 (4) Å, α = β = 90°, γ = 90.642 (4)°; V = 968.7 (1) Å3, Z = 4, Dx
 = 5.358 Mg m−3, μ = 21.70 mm−1. The standard setting of the space group and the reduced unit cell are Pmn21; a = 7.0445 (3), b = 6.9661 (3), c = 9.8699 (5) Å; Z = 2.
Modulated structures of Cs2HgCl4: the 5a superstructure at 185 K and the 3c superstructure at 176 K
Authors: Bagautdinov Bagautdin , Pilz Katrin , Ludecke Jens , van Smaalen Sander
Published: July 2002

Crystalline dicaesium mercury tetrachloride (Cs2HgCl4) is isomorphous with \beta-K_2SO_4 (space group Pnma, Z = 4) in its normal phase at room temperature. On cooling a sequence of incommensurate and commensurate superstructures occurs, below T = 221 K with modulations parallel to a*, and below 184  K with modulations along c*. The commensurately modulated structures at T = 185 K with {\bf q}= {{1}\over{5}}\bf{a}^* and at T = 176 K with {\bf q} = {{1}\over{3}}\bf{c}^* were determined using X-ray scattering with synchrotron radiation. The structure at T = 185 K has superspace group Pnma(\alpha,0,0)0ss with \alpha = 0.2. Lattice parameters were determined as a = 5\times9.7729\kern2pt(1), b = 7.5276\kern2pt(4) and c = 13.3727\kern2pt(7) Å. Structure refinements converged to R = 0.050 (R = 0.042 for 939 main reflections and R = 0.220 for 307 satellites) for the section t = 0.05 of superspace. The fivefold supercell has space group Pn2_1a. The structure at T = 176 K has superspace group Pnma(0,0,\gamma)0s0 with \gamma = {{1}\over{3}}. Lattice parameters were determined as a = 9.789\kern2pt(3), b = 7.541 \kern2pt(3) and c = 3 \times 13.418\kern2pt(4) Å. Structure refinements converged to R = 0.067 (R = 0.048 for 2130 main reflections, and R = 0.135 for 2382 satellite reflections) for the section t = 0. The threefold supercell has space group P112_1/a. It is shown that the structures of both low-temperature phases can be characterized as different superstructures of the periodic room-temperature structure. The superstructure of the 5a-modulated phase is analysed in terms of displacements of the Cs atoms, and rotations and distortions of HgCl4 tetrahedral groups. In the 3c-modulated phase the distortions of the tetrahedra are relaxed, but they are replaced by translations of the tetrahedral groups in addition to rotations.
Electron density study of KNiF3 by the vacuum-camera-imaging plate method
Authors: Zhurova Elizabeth A. , Zhurov Vladimir V. , Tanaka Kiyoaki
Published: July 2002

The electron density measurements of KNiF3, nickel potassium trifluoride, by the vacuum-camera-imaging plate (VCIP) method and using a four-circle diffractometer with scintillation counter, are performed and compared. In the IP (imaging plate) case evacuation allowed the background around peaks to be reduced 50 times, which significantly increased the accuracy of the data, especially for high-angle reflections. A new VIIPP program for visualizing and integration of IP data was designed to treat the data, in which the correction for oblique incidence was applied. The resulting electron density reproduces all the features of the accurate conventional measurement.
Oligosiloxanediols as building blocks for supramolecular chemistry: hydrogen-bonded adducts with amines form supramolecular structures in zero, one and two dimensions
Authors: O'Leary Brian , Spalding Trevor R. , Ferguson George , Glidewell Christopher
Published: July 2002

The structure of 1,1,3,3,5,5-hexaphenyltrisiloxane-1,5-diol–pyrazine (4/1), (C36H32O4Si3)4·C4H4N2 (1), contains finite centrosymmetric aggregates; the diol units form dimers, by means of O—H...O hydrogen bonds, and pairs of such dimers are linked to the pyrazine by means of O—H...N hydrogen bonds. In 1,1,3,3,5,5-hexaphenyltrisiloxane-1,5-diol–pyridine (2/3), (C36H32O4Si3)2·(C5H5N)3 (2), the diol units are linked into centrosymmetric pairs by means of disordered O—H...O hydrogen bonds: two of the three pyridine molecules are linked to the diol dimer by means of ordered O—H...N hydrogen bonds, while the third pyridine unit, which is disordered across a centre of inversion, links the diol dimers into a C
3
3(9) chain by means of O—H...N and C—H...O hydrogen bonds. In 1,1,3,3-tetraphenyldisiloxane-1,3-diol–hexamethylenetetramine (1/1), (C24H22O3Si2)·C6H12N4 (3), the diol acts as a double donor and the hexamethylenetetramine acts as a double acceptor in ordered O—H...N hydrogen bonds and the structure consists of C
2
2(10) chains of alternating diol and amine units. In 1,1,3,3-tetraphenyldisiloxane-1,3-diol–2,2′-bipyridyl (1/1), C24H22O3Si2·C10H8N2 (4), there are two independent diol molecules, both lying across centres of inversion and therefore both containing linear Si—O—Si groups: each diol acts as a double donor of hydrogen bonds and the unique 2,2′-bipyridyl molecule acts as a double acceptor, thus forming C
2
2(11) chains of alternating diol and amine units. The structural motif in 1,1,3,3-tetraphenyldisiloxane-1,3-diol–pyrazine (2/1), (C24H22O3Si2)2·C4H4N2 (5), is a chain-of-rings: pairs of diol molecules are linked by O—H...O hydrogen bonds into centrosymmetric R
2
2(12) dimers and these dimers are linked into C
2
2(13) chains by means of O—H...N hydrogen bonds to the pyrazine units. 1,1,3,3-Tetraphenyldisiloxane-1,3-diol–pyridine (1/1), C24H22O3Si2·C5H5N (6), and 1,1,3,3-tetraphenyldisiloxane-1,3-diol–pyrimidine (1/1), C24H22O3Si2·C4H4N2 (7), are isomorphous: in each compound the amine unit is disordered across a centre of inversion. The diol molecules form C(6) chains, by means of disordered O—H...O hydrogen bonds, and these chains are linked into two-dimensional nets built from R
6
6(26) rings, by a combination of O—H...N and C—H...O hydrogen bonds.
Anisotropic crystal structure distortion of the monoclinic polymorph of acetaminophen at high hydrostatic pressures
Authors: Boldyreva E. V. , Shakhtshneider T. P. , Vasilchenko M. A.  , Ahsbahs H.  , Uchtmann H. 
Published: July 2002

The anisotropy of structural distortion of the monoclinic polymorph of acetaminophen induced by hydrostatic pressure up to 4.0 GPa was studied by single-crystal X-ray diffraction in a Merrill–Bassett diamond anvil cell (DAC). The space group (P21/n) and the general structural pattern remained unchanged with pressure. Despite the overall decrease in the molar volume with pressure, the structure expanded in particular crystallographic directions. One of the linear cell parameters (c) passed through a minimum as the pressure increased. The intramolecular bond lengths changed only slightly with pressure, but the changes in the dihedral and torsion angles were very large. The compressibility of the intermolecular hydrogen bonds NH...O and OH...O was measured. NH...O bonds were shown to be slightly more compressible than OH...O bonds. The anisotropy of structural distortion was analysed in detail in relation to the pressure-induced changes in the molecular conformations, to the compression of the hydrogen-bond network, and to the changes in the orientation of molecules with respect to each other in the pleated sheets in the structure. Dirichlet domains were calculated in order to analyse the relative shifts of the centroids of the hydrogen-bonded cycles and of the centroids of the benzene rings with pressure.
Rigid-body molecular motion in crystals. The centre of libration
Authors: Pawley G. S.
Published: July 2002

It is shown that the concept of the molecular centre of libration in the description of the average rigid-body thermal behaviour of molecules is a useful approximation. A restriction is made on the full theory, making the centre of libration model a constrained version of the complete model. The relationship between the models is discussed. Some examples are chosen to demonstrate the closeness of the approximation. These results show that for data reaching a reliability factor of no better than 7% an analysis using the full theory might yield a meaningless result. Some data of much higher accuracy does, however, show the need for the full theory.
Magnetic symmetry and physical properties
Authors: Krishna Murty T. S. G. , Appalanarasimham V.
Published: July 2002

The number of independent non-vanishing constants required to describe the six known physical properties, involving a polar vector, has been determined by the character method of Bhagavantam & Suryanarayana for each one of the 58 double-coloured point groups.
Molecular statistical theory of nematic liquid crystals
Authors: Chandrasekhar S. , Madhusudana N. V.
Published: July 2002

Assuming a model based on permanent dipole-dipole, dispersion, induction and repulsion forces, the potential energy of a molecule in a nematic liquid crystal is derived as a function of its orientation. Analysis of the temperature variation of the degree of orientational order in p-azoxyanisole (PAA) and p-azoxyphenetole (PAP) indicates that the permanent dipole interactions are relatively unimportant. Making use of a mean field approximation, a statistical theory of long-range orientational order is developed and the thermodynamic properties of the ordered system are derived relative to those of the completely disordered one. Application of the theory to PAA and PAP shows conclusively that a certain degree of short-range orientational order is present in the liquid phase. Using just three parameters for each compound, viz. the two constants of the potential function and a numerical factor to allow for short range order, the following physical properties have been evaluated which are in quantitative agreement with the experimental data: the long-range orientational order parameter, specific heat and compressibility as functions of temperature in the liquid crystalline range, the latent heat and volume change at the nematic-isotropic transition point. The magnetic birefringence of the liquid phase affords an independent estimate of the short range order which supports the previous calculations.
Intermolecular interactions in crystals of carboxylic acids. IV. Empirical interatomic potential functions
Authors: Derissen J. L. , Smit P. H.
Published: July 2002

An intermolecular force field for carboxylic acids has been derived by a least-squares fit of the parameters of non-bonded atom-atom potentials and a hydrogen-bond potential to experimental data. The latter include heats of dimerization and dimer structures of formic, acetic and propionic acid, and heats of sublimation and crystal structures of acetic, α and β-oxalic, α and β-fumaric and isophthalic acid. It was found that (exp - 6 - 1) atom-atom potentials and the Lippincott-Schroeder potential for the hydrogen bonds reproduce fairly well the experimental energies as well as the structures. The transferability of the potentials was studied with respect to the crystal structure of allene dicarboxylic acid and to the crystal structure and the lattice energy of formic acid, and was found to be good. A comparison is made with the results of other authors.
Direct methods and protein crystallography at low resolution
Authors: Gilmore Christopher J.
Published: July 2002

The tools of modern direct methods are examined and their limitations for solving protein structures discussed. Direct methods need atomic resolution data (1.1–1.2 Å) for structures of around 1000 atoms if no heavy atom is present. For low-resolution data, alternative approaches are necessary and these include maximum entropy, symbolic addition, Sayre's equation, group scattering factors and electron microscopy.
Crystallization and preliminary X-ray analysis of the periplasmic receptor (PotF) of the putrescine transport system in Escherichia coli
Authors: Vassylyev Dmitry G. , Kashiwagi Tatsuki , Tomitori Hideyuki , Kashiwagi Keiko , Igarashi Kazuei , Morikawa Kosuke
Published: July 2002

The primary receptor (PotF) of the putrescine transport system in E. coli has been crystallized by the hanging-drop vapor-diffusion technique. The crystals belong to the space group P21212 with unit-cell dimensions a = 269.4, b = 82.33 and c = 93.74 Å. The crystals diffract beyond 2.2 Å with a rotating-anode X-ray source. A complete data set from the native crystals has been collected and processed at 2.3 Å resolution. Two heavy-atom derivatives have been prepared from the same Pt compound at 293 and 277 K. The difference Patterson maps revealed completely different major heavy-atom sites between these two derivatives.
1.85 Å Resolution Structure of the ZincII β-Lactamase from Bacillus cereus
Authors: Carfi Andrea , Duée Emile , Galleni Moreno , Frère Jean-Marie , Dideberg Otto
Published: July 2002

Class B \beta-lactamases are wide spectrum enzymes which require bivalent metal ions for activity. The structure of the class B zinc-ion-dependent β-lactamase from Bacillus cereus (BCII) has been refined at 1.85 Å resolution using data collected on cryocooled crystals (100 K). The enzyme from B. cereus has a molecular mass of 24 946 Da and is folded into a \beta-sandwich structure with helices on the external faces. The active site is located in a groove running between the two \beta-sheets [Carfi et al. (1995). EMBO J.
14, 4914–4921]. The 100 K high-resolution BCII structure shows one fully and one partially occupied zinc site. The zinc ion in the fully occupied site (the catalytic zinc) is coordinated by three histidines and one water molecule. The second zinc ion is at 3.7 Å from the first one and is coordinated by one histidine, one cysteine, one aspartate and one unknown molecule (which is most likely to be a carbonate ion). In the B. cereus zinc \beta-lactamase the affinity for the second metal ion is low at the pH of crystallization (Kd
= 25 mM, 293 K; [Baldwin et al. (1978). Biochem. J.
175, 441–447] and the dissociation constant of the second zinc ion thus apparently decreased at the cryogenic temperature. In addition, the structure of the apo enzyme was determined at 2.5 Å resolution. The removal of the zinc ion by chelating agents causes small changes in the active-site environment.
Purification, crystallization and preliminary X-ray diffraction studies on the thermostable catechol 2,3-dioxygenase of Bacillus stearothermophilus expressed in Escherichia coli
Authors: Chen Min-Qin , Yin Chang-Chuan , Zhang Wei , Mao Yu-Min , Zhang Zhi-Hong
Published: July 2002

The thermostable catechol 2,3-dioxygenase of Bacillus stearothermophilus has been crystallized. The crystal is probably in the space group I
222 with unit-cell dimensions of a = 70.87, b = 74.60 and c = 133.69 Å. A native data set has been collected with a completeness of 96% at 2.22 Å resolution and an R
merge value of 0.091.
Static Laue Diffraction Studies on Acetylcholinesterase
Authors: Ravelli Raimond B. G. , Raves Mia L. , Ren Zhong , Bourgeois Dominique , Roth Michel , Kroon Jan , Silman Israel , Sussman Joel L.
Published: July 2002

Acetylcholinesterase (AChE) is one of nature's fastest enzymes, despite the fact that its three-dimensional structure reveals its active site to be deeply sequestered within the molecule. This raises questions with respect to traffic of substrate to, and products from, the active site, which may be investigated by time-resolved crystallography. In order to address one aspect of the feasibility of performing time-resolved studies on AChE, a data set has been collected using the Laue technique on a trigonal crystal of Torpedo californica AChE soaked with the reversible inhibitor edrophonium, using a total X-ray exposure time of 24 ms. Electron-density maps obtained from the Laue data, which are of surprisingly good quality compared with similar maps from monochromatic data, show essentially the same features. They clearly reveal the bound ligand, as well as a structural change in the conformation of the active-site Ser200 induced upon binding.
Structure of the E2 DNA-Binding Domain from Human Papillomavirus Serotype 31 at 2.4 Å
Authors: Bussiere Dirksen E. , Kong Xiangpeng , Egan David A. , Walter Karl , Holzman Thomas F. , Lindh Frank , Robins Terry , Giranda Vincent L.
Published: July 2002

The papillomaviruses are a family of small double-stranded DNA viruses which exclusively infect epithelial cells and stimulate the proliferation of those cells. A key protein within the papillomavirus life-cycle is known as the E2 (Early 2) protein and is responsible for regulating viral transcription from all viral promoters as well as for replication of the papillomavirus genome in tandem with another protein known as E1. The E2 protein itself consists of three functional domains: an N-terminal trans-activation domain, a proline-rich linker, and a C-terminal DNA-binding domain. The first crystal structure of the human papillomavirus, serotype 31 (HPV-31), E2 DNA-binding domain has been determined at 2.4 Å resolution. The HPV DNA-binding domain monomer consists of two β–α–β repeats of approximately equal length and is arranged as to have an anti-parallel β-sheet flanked by the two α-helices. The monomers form the functional in vivo dimer by association of the β-sheets of each monomer so as to form an eight-stranded anti-parallel β-barrel at the center of the dimer, with the α-helices lining the outside of the barrel. The overall structure of HVP-31 E2 DNA-binding domain is similar to both the bovine papillomavirus E2-binding domain and the Epstein–Barr nuclear antigen-1 DNA-binding domain.
Classifying a Protein in the CATH Database of Domain Structures
Authors: Orengo C. A. , Martin A. M. , Hutchinson G. , Jones S. , Jones D. T. , Michie A. D. , Swindells M. B. , Thornton J. M.
Published: July 2002

The CATH database of protein domain structures classifies structures according to their (C)lass, (A)rchitecture, (T)opology or fold and (H)omologous family (http://www.biochem.ucl.ac.uk/bsm/cath). Although the protocol used is mostly automatic, manual inspection is used to check assignments at some critical stages, such as the detection of very distantly related homologues and anologues and the assignment of novel architectures. Described in this article is a recently established facility to search the database with the coordinates of a newly determined structure. The CATH server first locates domain boundaries and then uses automatic sequence and structure comparison methods to assign this new structure to one or more of the domain families within CATH. Diagnostic reports are generated, together with multiple structural alignments for close relatives. The Server can be accessed over the World Wide Web (WWW) and mirror sites are planned to improve access.
Crystallization and preliminary X-ray diffraction data of the complex of recombinant tick anticoagulant peptide (rTAP) and bovine factor Xa
Authors: Wei Anzhi , Smallwood Angela , Alexander Richard S. , Duke Jodie , Ross Harold , Rosenfeld Stuart A. , Chang Chong-Hwan
Published: July 2002

The complex of bovine factor Xa and recombinant tick anticoagulant peptide (rTAP) was crystallized in two different crystal forms using polyethylene glycol as a precipitant. Form I belongs to space group P42212 with unit-cell dimensions a = b = 133.1, c = 68.8 Å. It contains one complex per asymmetric unit and diffracts to 3.0 Å resolution. Form II belongs to P41212 (or P43212) with dimensions a = b = 126.5, c = 146.7 Å; it contains two complexes per asymmetric unit and diffracts to 2.5 Å. The crystals of both forms consist of factor Xa (MW
 = 45.3 kDa) and rTAP (MW
= 6.7 kDa).
Structure of basic winged-bean lectin and a comparison with its saccharide-bound form
Authors: Manoj N. , Srinivas V. R. , Suguna K.
Published: July 2002

The crystal structure of the saccharide-free form of the basic form of winged-bean agglutinin (WBAI) has been solved by the molecular-replacement method and refined at 2.3 Å resolution. The final R factor is 19.7% for all data in the resolution range 8.0–2.3 Å. The asymmetric unit contains two half-dimers, each located on a crystallographic twofold axis. The structure of the saccharide-free form is compared with that of the complex of WBAI with methyl-α-D-galactoside. The complex is composed of two dimers in the asymmetric unit. The intersubunit interactions in the dimer are nearly identical in the two structures. The binding site of the saccharide-free structure contains three ordered water molecules at positions similar to those of the hydroxyl groups of the carbohydrate which are hydrogen bonded to the protein. Superposition of the saccharide-binding sites of the two structures shows that the major changes involve expulsion of these ordered water molecules and a shift of about 0.6 Å of the main-chain atoms of the variable loop.
Macromolecular crystal annealing: evaluation of techniques and variables
Authors: Harp Joel M. , Hanson B. Leif , Timm David E. , Bunick Gerard J.
Published: July 2002

Additional examples of successful application of macromolecular crystal annealing are presented. A qualitative evaluation of variables related to the annealing process was conducted using a variety of macromolecular crystals to determine in which cases parameters may be varied and in which cases the original macromolecular crystal annealing protocol is preferred. A hypothesis is presented relating the solvent content of the crystal to the specific protocol necessary for the successful application of annealing.
How RhoGDI binds Rho
Authors: Longenecker Kenton , Read Paul , Derewenda Urszula , Dauter Zbigniew , Liu Xiaopu , Garrard Sarah , Walker Lori , Somlyo Avril V. , Nakamoto Robert K. , Somlyo Andrew P. , Derewenda Zygmunt S.
Published: July 2002

Like all Rho (Ras homology) GTPases, RhoA functions as a molecular switch in cell signaling, alternating between GTP- and GDP-bound states, with its biologically inactive GDP-bound form maintained as a cytosolic complex with RhoGDI (guanine nucleotide-exchange inhibitor). The crystal structures of RhoA–GDP and of the C-terminal immunoglobulin-like domain of RhoGDI (residues 67–203) are known, but the mechanism by which the two proteins interact is not known. The functional human RhoA–RhoGDI complex has been expressed in yeast and crystallized (P6522, unit-cell parameters a = b = 139, c = 253 Å, two complexes in the asymmetric unit). Although diffraction from these crystals extends to 3.5 Å and is highly anisotropic, the experimentally phased (MAD plus MIR) electron-density map was adequate to reveal the mutual disposition of the two molecules. The result was validated by molecular-replacement calculations when data were corrected for anisotropy. Furthermore, the N-terminus of RhoGDI (the region involved in inhibition of nucleotide exchange) can be identified in the electron-density map: it is bound to the switch I and switch II regions of RhoA, occluding an epitope which binds Dbl-like nucleotide-exchange factors. The entrance of the hydrophobic pocket of RhoGDI is 25 Å from the last residue in the RhoA model, with its C-terminus oriented to accommodate the geranylgeranyl group without conformational change in RhoA.
Expression, purification, crystallization and preliminary X-ray data of Escherichia coli galactoside acetyltransferase
Authors: Wang Xing-Guo , Roderick Steven L.
Published: July 2002

Crystals of galactoside acetyltransferase from Escherichia coli have been prepared from solutions of ammonium sulfate containing acetyl-CoA. These crystals diffract to at least 2.7 Å resolution, belong to space group C2221 and contain one copy of the trimeric enzyme in the asymmetric unit.
Precision wavelength measurement of the 14.4 keV Mössbauer photon
Authors: Xiaowei Zhang , Yoda Yoshitaka , Imai Yasuhiko
Published: July 2002

The wavelength of the 14.4 keV Mössbauer photon has been determined by using undulator radiation and diffraction of FZ silicon crystals. For the wavelength determination a goniometer equipped with a laser rotary encoder and a sine-bar angle optical interferometer was developed; a temperature-monitoring system and X-ray optics related to the experiment were also developed. The mean wavelength was 0.08602557 nm with an uncertainty of 0.6 p.p.m., derived from 16 measurements of three pieces of FZ Si(840) crystals.
Fourth-generation X-ray sources: some possible applications to biology
Authors: Doniach Sebastian
Published: July 2002

The term `fourth generation X-ray sources' has come to mean X-ray free-electron lasers which use multi-GeV electron beams from linear accelerators to generate X-rays by self-amplified stimulated emission when fired into long undulators. Properties of the radiation expected from such sources are reviewed briefly and two possible applications of the resulting pulsed highly collimated X-radiation to problems in biology are discussed: use of X-ray photon correlation spectroscopy to measure time correlations of atoms in protein crystals, and use of Mössbauer radiation extracted from the photon beams by resonant Bragg diffraction from ^{57}Fe-containing crystals, for MAD phasing of very large unit-cell biomolecular crystals and possibly for photon echo measurements.
A multiwire proportional counter for XAS fluorescence experiments
Authors: Barrea Raúl A. , Tamura E. , Tolentino H. C. N.
Published: July 2002

A multiwire proportional counter was used in fluorescence X-ray absorption measurements and a comparison to a Si(Li) and NaI(Tl) detectors was done. The main features of the mutiwire proportional counter are its high counting rate capability (107 counts s−1) and large active area (6 × 6 cm2). It was shown that the MWPC is suitable for fluorescence absorption. Although the maximum capability was not reached in the present experiments, it was found that as the counting rate increase the MWPC performance became better than Si(Li) detectors and shows a similar response to the scintillator counter at medium counting rates (up to 105 counts s−1).
Determination of dissociation energy for ligand exchange reaction from EXAFS
Authors: Miyanaga T. , Sakane H. , Watanabe I.
Published: July 2002

EXAFS (extended X-ray absorption fine structure) experiments were performed at several different temperatures for a series of 3d transition metal ions (Cr3+, Fe3+, Fe2+, Ni2+, Co2+, Zn2+) in aqueous solutions. Anharmonic EXAFS analyses, which include up to third order cumulant, were carried out to study on the metal-oxygen bonding potential. According to the model in which the dissociation process is dominant for the ligand-water exchange reaction, the dissociation energy has been first evaluated from EXAFS in solution phase.
Thermal decomposition of (NH4)2[PdCl6] studied by in situ X-ray absorption spectroscopy
Authors: Rumpf Holger , Modrow Hartwig , Hormes Josef , Amann Peter , Möller Angela , Meyer Gerd
Published: July 2002

In situ X-ray absorption near edge structure (XANES) investigations were carried out at chlorine K edge and palladium L
3 edge to study the mechanism of the thermal decomposition of ammonium hexachloropalladate. The spectra show a characteristic feature for the initial step that might be explained as the formation of the precursor via ligand exchange (Cl ⇒ NH3). Multiple scattering calculations (Feff 8) for the Cl K, Pd and Rh L
3 edges were successful in simulating the XANES spectra of the precursor as well as the reference compounds (NH4)2[PdCl4] and (NH4)3[RhCl6].
In situ XAS characterization of the electrochemical insertion of copper in polypyrrole films
Authors: Alves M. C. M. , Watanabe N. , Ramos A. Y. , Tolentino H. C. N.
Published: July 2002

We report the electrochemical insertion of copper in polypyrrole films followed by XAS spectroscopy. Depending on the applied potential the copper remains as an ionic form like Cu+n
-(OSO3
−)
n
. For more reductive potentials metal particles are synthesized. Small particles with an estimated average diameter of 20 Å were obtained.
Local structure of liquid and solid silver halides probed by XAFS
Authors: Di Cicco Andrea , Taglienti Marco , Minicucci Marco , Filipponi Adriano
Published: July 2002

Investigation of the local structure of the high-temperature liquid and solid phases in the 300-725 K range of AgBr has been performed using the x-ray absorption spectroscopy (XAS). Structural results are compared with existing diffraction studies and computer simulations demonstrating the reliability of the XAS technique in determining the short-range structure. Present results on solid AgBr are in agreement with known thermal expansion data. The short-range g(r) of liquid AgBr is reconstructed showing the unique insight provided by the XAS technique in measuring short-range atom-atom correlations in liquids.
In situ XAFS study on cathodic materials for lithium-ion batteries
Authors: Nonaka Takamasa , Okuda Chikaaki , Ukyo Yoshio , Okamoto Tokuhiko
Published: July 2002

Ni and Co K-edge X-ray absorption spectra of LiNi0.8Co0.2O2 have been collected using in situ coin cells. To investigate the electronic and structural changes accompanied by the capacity fading during electrochemical cycling and keeping batteries at high temperatures, the cells with different cycling states and keeping conditions (temperature, time) were prepared. Upon charging the cell, the Ni and Co K absorption edge shifted towards higher energy, and the good correlation between the range of chemical shifts upon charging and the capacity of the cell was observed. From quantitative analysis of EXAFS data, it was revealed that the capacity fading is closely related to the Jahn-Teller distortion of the NiO6 octahedron.
Spin-resolved NEXAFS from resonant X-ray scattering (RXS)
Authors: Dräger G. , Kirchner Th. , Bocharov S. , Kao C.-C.
Published: July 2002

Resonantly excited metal K core line spectra of NiO, MnO, CoO and other compounds have been investigated at the beamlines X21 (NSLS/BNL), BW1 and W1.1 (HASYLAB/DESY). From analysis of spectral data we have drawn the following conclusions: -spin conservation is valid in the scattering process, for excitations below the absorption threshold as well as above it, -the absorption thresholds are different for spin-up and spin-down components of resonantly scattered spectra, -quadrupole transitions are very important or even crucial in the excitation process. Provided that these conclusions are true, a novel technique for quantitative resolution of NEXAFS spectra into spin-up and spin-down components has been developed. Since the method employs spin conservation and local spin references, it needs no circularly polarized radiation and no sample magnetization for taking both the RXS and NEXAFS spectra. Hence antiferromagnetic and paramagnetic materials can be investigated as well. Utilizing linear dichroism by angular-dependent measurements on single-crystal samples additional resolution of NEXAFS spectra is possible with respect to the orbital symmetry. Application of the method to paramagnetic MnO, for the first time, provides new and unambiguous experimental results confirming modern (LSDA+U) calculations: The metal K pre-edge XAS of MnO has predominantly 3d(t2g and eg) spin-down character. On the other hand, the delocalized p-like states, arising from the p-d band effect hybridization have spin-up character.
Valence selective DAFS measurements of Mn in La1/3Ca2/3MnO3
Authors: Ravel Bruce , Grenier Stéphane , Renevier Hubert , Eom Chang-Beom
Published: July 2002

The manganese perovskite system La1-x
Ca
x
MnO3 displays a complex phase diagram of structural, magnetic, and transport properties with varying Ca concentration. At x = 2/3 and at low temperature, the system is antiferromagnetic with Mn4+ and Mn3+ ions occupying special positions in a charge-ordered supperlattice. The charge ordering transition at about 260 K is characterized by the appearance of satellite peaks around certain strong normal lattice reflections. The normal lattice reflections are due to scattering from planes containing Mn4+ and Mn3+ ions in nearly stoichiometric proportion, however the superlattice reflections are due to scattering from planes containing only Mn4+ ions. By measuring Diffraction Anomalous Fine-Structure spectra on a superlattice reflection and its associated normal lattice reflection, it is possible to isolate absorption-like spectra for the two Mn sites. Due to the weak intensity of these superlattice reflections, we were unable to obtain high quality near-edge spectra for the superlattice reflection measured. However, the data offer useful information about the local electronic structures of the two Mn ions.
Linear dichroism in 3d transition metal NEXAFS of correlated materials
Authors: Dräger Guenter , Bocharov Sergey , Kirchner Thomas , Kirchner Nadejda
Published: July 2002

Investigations of 3d transition metal (TM) compounds by means of linear dichroism in TM K-NEXAFS will be reported. At this, the decomposition of the angular-dependent NEXAFS into orbital projected components are important problems. A survey is given on methods how to extract information on the geometrical, electronic and magnetic structure from linearly polarized NEXAFS and EXAFS spectra. New results on CuO and CuPc (Copper Phthalocyanine) are reported. A reference is given to the novel method for spin-resolving of NEXAFS by analysis of resonantly scattered X-ray core lines.
XAFS studies of the formation of cobalt silicide on (31/2 by 31/2) SiC(0001)
Authors: Platow W. , Wood D. E. , Burnette J. E. , Nemanich R. J. , Sayers D. E.
Published: July 2002

Thin Co films (1-8 nm) were directly, sequentially, and co-deposited with Si (3.6-29.2 nm) on the (31/2 × 31/2)-R30° reconstruction of 6H-SiC(0001). The films were annealed over a temperature range of 823-1373K and investigated with XAFS, XPS, AES and AFM. After annealing up to 1373K directly deposited Co films do not transform entirely to cobalt disilicide and C segregation is observed on the surface of the films. On the other hand, sequentially and co-deposited films do form cobalt disilicide after annealing at 823K, but also show islanding after annealing at 923K.
Development of a multilayer Fresnel zone plate for high-energy synchrotron radiation X-rays by DC sputtering deposition
Authors: Tamura S. , Yasumoto M. , Kamijo N. , Suzuki Y. , Awaji M. , Takeuchi A. , Takano H. , Handa K.
Published: July 2002

Hard X-ray microscopy with high spatial resolution (≤0.1 µm) using a high-energy and high-brilliance X-ray microprobe is expected to be a promising technology for various types of analysis, imaging etc. in materials science, biology and medicine. A multilayer Fresnel zone plate (FZP) could be a promising approach to focusing optics in the high-energy X-ray region (≥20 keV) because a large thickness (aspect ratio) can be available. Various types of multilayer FZPs have been fabricated by DC sputtering deposition. Their focusing characteristics have been evaluated at the high-brilliance undulator beamline BL47XU of SPring-8. An optical system using a Cu/Al multilayer FZP (with an outermost zone width of 0.25 µm) as the focusing optics fabricated by the optimum deposition condition with precise film (zone) thickness control has attained an almost diffraction-limited microbeam of 0.3–0.35 µm at 8.9 keV. A line-and-space resolution test pattern has been observed: fine structures up to 0.2 µm were clearly observed in the measured image. This FZP has been working since 1995, keeping good focusing characteristics. It can be said from these results that a spatial resolution better than 0.1 µm in the high-energy X-ray region is in prospect by the development of a multilayer FZP with a narrower outermost zone width in the near future.
High-Throughput Asymmetric Double-Crystal Monochromator of the SAXS Beamline at ELETTRA
Authors: Bernstorff S. , Amenitsch H. , Laggner P.
Published: July 2002

A new high-flux wiggler beamline for fast time-resolved small-angle X-ray scattering (SAXS) based on double-focusing optics has recently commenced operation at the 2 GeV third-generation storage ring ELETTRA at Trieste, Italy. Its non-dispersive double-crystal monochromator contains three pairs of interchangeable asymmetrically cut flat Si(111)-crystal pairs, each of which is optimized for high throughput at one of the three fixed energies 5.4, 8 and 16 keV. To cope with the severe thermal power load produced by a 57-pole wiggler on the first crystal of each pair (up to 5.4 W mm−2 and 700 W under normal incidence, for 400 mA), grazing angles of 2° and optimized back-cooling have been chosen. This solution allows simultaneously a gain of 2.5–3.0 in throughput and, accordingly, in flux density. Finite-element analysis as well as commissioning tests showed that the cooling layout functions very satisfactorily, and that up to 5 × 1012 photons s−1 are available at the sample (at 8 keV and 250 mA), as predicted.
Magnetism in Nickel and Synchrotron Beam Polarization Studied by X-ray Diffraction
Authors: Laundy D. , Brown S. , Cooper M. J. , Bowyer D. , Thompson P. , Paul D. F. , Stirling W. G.
Published: July 2002

The ratio of the magnetic to the charge form factors of nickel has been determined by white-beam X-ray diffraction. The measurements were made on the new UK magnetic scattering beamline (XMaS) on a dipole source at the ESRF. The data comprise the three (h,h,0) reflections (4,4,0), (6,6,0) and (8,8,0) and the seven high-order (h,0,0) reflections (6,0,0) to (18,0,0), which doubles the range of wavevectors compared to previous studies. The data have been analysed using Hartree–Fock free-ion wave functions and core electron polarization effects were included. The results support the interpretation of neutron data obtained at lower momentum transfer for the e

g
and t
2g
orbital occupancies. The polarization of the dipole source is deduced to vary from 99.88 to 99.83% between 5 and 15 keV, respectively. This high value makes it an extremely suitable source for studies of ferromagnetism.
Multiple solutions in data fitting: a trap in EXAFS structural analysis and some ideas to avoid it
Authors: Michalowicz Alain , Vlaic Gilberto
Published: July 2002

A possible source of error on interatomic distance determination in EXAFS multishell data analysis is described on the basis of fitting a simulated signal for a cluster of Rh atoms with an interaction of O atoms; a fit of an experimental signal is also presented. The origin of this type of mistake is briefly discussed.
A low-profile monolithic multi-element Ge detector for X-ray fluorescence applications
Authors: Derbyshire Gareth , Cheung Kan-Cheung , Sangsingkeow Pat , Hasnain S. Samar
Published: July 2002

A highly compact and rapid-count-rate multi-element solid-state detector has been designed, built and recently commissioned on the oldest XAFS station of the SRS, station 7.1, which has undergone major refurbishment. The low profile of the detector has been achieved by using the monolithic solution where nine elements with a combined active area of 370 mm2 have been fabricated on Ge of diameter 21.8 mm. A typical energy resolution of 170 eV with a semi-Gaussian shaping time of 0.5 µs has been achieved with X-rays of energy 5.9 keV. The low profile of the detector makes it ideal for several synchrotron radiation applications as it can be easily incorporated into complicated experimental set-ups. These include XAFS of single crystals and samples generated in a stopped flow system, protein crystallography (fluorescence XAFS for MAD or for on-line monitoring), microprobe fluorescence imaging and trace-element analysis.
Combining CXMD and XSW to study magnetic and geometric properties of thin films: Gd/Fe(100)
Authors: Treusch R. , Drube W. , Materlik G.
Published: July 2002

The magnetic and geometric structure of 1–5 monolayers (ML) of Gd on Fe(100) single crystals has been investigated using synchrotron X-rays between 4 and 8 keV. Choosing a high-flux wiggler beamline made it possible to analyse the magnetic properties by studying the circular X-ray magnetic dichroism (CXMD) and, in addition, to apply the X-ray standing-wave (XSW) technique to elucidate the geometric structure of the overlayers. CXMD reveals that Gd couples antiferromagnetically to the Fe substrate and that 2 ML Gd at 243 K yield a magnetization of ∼22% with respect to the saturation value of a thick Gd foil at 123 K. A magnetic polarization of the Gd pertains even at 308 K. While LEED investigations do not show any long-range lateral order of the Gd film, XSW measurements reveal an ordering of Gd perpendicular to the (100) surface of Fe.
Bis[N,N-bis(2-hydroxyethyl)dithiocarbamato-S,S′]diphenyltin(IV)
Authors: Farina Yang , Othman A. Hamid , Razak Ibrahim Abdul , Fun Hoong-Kun , Ng Seik Weng , Baba Ibrahim
Published: July 2002

The Sn atom in the title compound, [Sn(C6H5)2(C5H10NO2S2)2], is six-coordinate in acis-C2SnS4octahedral environment.
Why knowledge management is here to stay
Authors: Bagshaw Mike
Published: July 2002

Knowledge is at the basis of wealth – more so than tangible assets. Being invisible, it is not always recognised as an asset at all, but business success depends on its good management. It is important to distinguish between information, an ingredient of knowledge, and knowledge itself. Knowledge is the result of sifting, reviewing, disseminating, sharing and discussing information. Instead of volumes of data, you get mental models that can be used to advance the business. Mental models can deal with the dynamics of change, as well as the situation frozen at the time of data collection. They can also take into account alternative scenarios. Computers bring mechanistic results far more quickly, but these results are purely rational, without insight, intuition or creativity.
Accrediting Prior Learning
Authors: Hamill John , Sutherland John
Published: July 2002

Describes the nature of accrediting prior learning (APL). Examines its
potential from the perspectives of professional bodies, such as the IPM
and the Government. As a prelude to examining a case study evaluation of
a “Portfolio Exercise” used to detect non‐standard entrants to a suite of
programmes in higher education discusses some problems of putting its
principles into practice.
Absence and return to work: towards a research agenda
Authors: Cunningham Ian , James Philip
Published: July 2002

Notes that the present human resource literature on absence pays relatively little attention to the management of genuine injury and illness. Seeks to partially address this lacuna in the literature through the findings of an exploratory study of the arrangements used to facilitate the return to work of ill and injured employees in 77 organisations. Finds that larger organisations and those which recognised trade unions offered the most extensive range of assistance to workers. Also finds the presence of return to work policies to be associated with favourable trends in absence. Suggests that the impact of return to work activities on absence merits further study and goes on to identify issues that should be addressed in future research.