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UO(2)(C(2)H(3)O(2))(2).2H(2)O reacts with AX or A(C(2)H(3)O(2) or ClO(4)) (where A = Li, Na, K; X = Cl, Br) and crown ethers in HCl or HBr aqueous solutions to give the sandwich-type compounds [K(18-crown-6)](2)[UO(2)Cl(4)] (1), [K(18-crown-6)](2)[UO(2)Br(4)] (2), [Na(15-crown-5)](2)[UO(2)Cl(4)] (3), [Na(15-crown-5)](2)[UO(2)Br(4)] (4), [Li(12-crown-4)](2)[UO(2)Cl(4)] (5), and [Li(12-crown-4)](2)[UO(2)Br(4)] (6). The compounds have been characterized by single-crystal X-ray diffraction, powder diffraction, elemental analysis, IR, and Raman spectroscopy. The [UO(2)X(4)](2-) ions coordinate to two [A(crown)](+) cations through the four halides only (2), through two halides only (3), through the two uranyl oxygens and two halides (3, 4), or through the two uranyl oxygen atoms only (5, 6). Raman spectra reveal nu(U-O) values that correlate with expected trends. The structural trends are discussed within the context of classical principles of hard-soft acid-base theory.
The structure of dilanthanum ruthenium pentoxide was solved by powder neutron diffraction at room temperature and 1.5 K. High-temperature La2RuO5 crystallizes in the monoclinic space group P2(1)/c. Upon cooling, the sample undergoes a phase transition to the triclinic low-temperature form (space group P-1). This transition leads to pronounced changes in the Ru-O-Ru bond distances, resulting in a dimerization of the ruthenium ions.
BACKGROUND: Calcium phosphate manufactured samples, prepared with hydroxyapatite, are used as either spacers or fillers in orthopedic surgery, but these implants have never been used under conditions of mechanical stress. Similar conditions also apply with cements. Many authors have postulated that cements are a useful substitute material when implanted in vivo. The aim of this research is to develop a low cristalline material similar to bone in porosity and cristallinity. METHODS: Commercial hydroxyapatite (HAp) and monetite (M) powders are mixed with water and compacted to produce cylindrical samples. The material is processed at a temperature of 37-120 degrees C in saturated steam to obtain samples that are osteoconductive. The samples are studied by X-ray powder diffraction (XRD), Vickers hardness test (HV), scanning electron microscopy (SEM), and porosity evaluation. RESULTS: The X-ray diffractions of powders from the samples show patterns typical of HAp and M powders. After thermal treatment, no new crystal phase is formed and no increase of the relative intensity of the peaks is obtained. Vicker hardness data do not show any relationship with treatment temperature. The total porosity decreases by 50-60% according to the specific thermal treatment. Scanning electron microscopy of the surfaces of the samples with either HAp 80%-M 20% (c) or Hap 50%-M 50% (f), show cohesion of the powder grains. CONCLUSIONS: The dissolution-reprecipitation process is more intesive in manufactured samples (c) and (f), according to Vickers hardness data. The process occurs in a steam saturated environment between 37 degrees and 120 degrees C. (c) (f) manufactured samples show pore dimension distributions useful to cellular repopulation in living tissues.
Studying the structure of disordered and partially ordered materials is notoriously difficult. Recently, significant advances have been made using the atomic pair distribution function (PDF) analysis of powder diffraction data coupled with the use of advanced X-ray and neutron sources and fast computers. Here we summarize some of the more spectacular successes of this technique in studying the structure of complex materials and compounds. Our purpose is to make the PDF analysis technique familiar to the chemical community by describing its methodologies and highlighting its potential in solving structural characterization problems that are intractable by any other technique available to this community e.g. single crystal diffraction, Rietveld refinement of powder diffraction data and extended X-ray absorption fine structure analysis (EXAFS).
BACKGROUND: The purpose of the present paper was to study the spectrum of stone composition of upper urinary tract calculi by X-ray diffraction crystallography technique, in patients managed at All India Institute of Medical Sciences. METHODS: Between 30 April 1998 and 31 March 2003, a total of 1050 urinary calculi (900 renal, 150 ureteric) were analyzed. The stone fragments were collected after extracorporeal shock-wave lithotripsy, or retrieval by endoscopic (percutaneous nephrolithotomy, ureterorenoscopy), laparoscopic and various open surgical procedures. The structural analysis of the stones was done using X-ray diffraction crystallography. RESULTS: Four types of primary and three secondary X-ray diffraction patterns were obtained. The primary patterns were as follows. Pattern A, well organized crystalline structure; pattern B, moderately organized crystalline structure; pattern C, poorly organized crystalline structure; pattern D, very poorly organized crystalline structure. The three secondary patterns mainly highlighted the mixed variety of stones. These patterns were further analyzed and compared with standard X-ray diffraction (powder) photographs. Of the 1050 stones analyzed, 977 (93.04%) were calcium oxalate stones, out of which 80% were calcium oxalate monohydrate (COM) and 20% were calcium oxalate dihydrate (COD). Fifteen were struvite (1.42%) and 19 were apatite (1.80%). Ten were uric acid stones (0.95%) and the remaining 29 (2.76%) were mixed stones (COM + COD and calcium oxalate + uric acid, calcium oxalate + calcium phosphate, and calcium phosphate + magnesium ammonium phosphate). A total of 89.98% of staghorn stones were made of oxalates (COM/+COD) and only 4.02% were struvite. CONCLUSION: Urinary stone disease in the Indian population is different from that in Western countries, with a larger percentage of patients having calcium oxalate stones, predominantly COM. Also, the majority of staghorn stones (89.98%) were made of oxalates.
The macrophage scavenger receptor CD36 plays a key role in the initiation of atherosclerosis through its ability to bind to and internalize oxidized low-density lipoproteins (oxLDL). Prompted by recent findings that the CD36 receptor also recognizes amyloid fibrils formed by beta-amyloid and apolipoprotein C-II, we investigated whether the oxidation of low-density lipoproteins (LDL) generates characteristic amyloid-like structures and whether these structures serve as CD36 ligands. Our studies demonstrate that LDL oxidized by copper ions, 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH), or ozone react with the diagnostic amyloid dyes thioflavin T and Congo Red and bind to serum amyloid P component (SAP), a universal constituent of physiological amyloid deposits. X-ray powder diffraction patterns for native LDL show a diffuse powder diffraction ring with maximum intensity corresponding to an atomic spacing of approximately 4.7 A, consistent with the spacing between beta-strands in a beta-sheet. Ozone treatment of LDL generates an additional diffuse powder diffraction ring with maximum intensity indicating a spacing of approximately 9.8 A. This distance is consistent with the presence of cross-beta-structure, a defining characteristic of amyloid. Evidence that these cross-beta-amyloid structures in oxLDL are recognized by macrophages is provided by the observation that SAP strongly inhibits the association and internalization of (125)I-labeled copper-oxidized LDL by peritoneal macrophages. The ability of SAP to bind to amyloid-like structures in oxLDL and prevent lipid uptake by macrophages highlights the potential importance of these structures and suggests an important preventative role for SAP in foam cell formation and early-stage atherosclerosis.
The purpose of this research was to develop a rapid chemometrical method based on near-infrared (NIR) spectroscopy to determine indomethacin (IMC) polymorphic content in mixed pharmaceutical powder and tablets. Mixed powder samples with known polymorphic contents of forms alpha and gamma were obtained from physical mixing of 50% of IMC standard polymorphic sample and 50% of excipient mixed powder sample consisting of lactose, corn starch, and hydroxypropylcellulose. The tablets were obtained by compressing the mixed powder at 245 MPa. X-ray powder diffraction profiles and NIR spectra were recorded for 6 kinds of standard materials with various polymorphic contents. The principal component regression analysis was performed based on normalized NIR spectra sets of mixed powder standard samples and tablets. The relationships between the actual and predicted polymorphic contents of form g in the mixed powder measured using x-ray powder diffraction and NIR spectroscopy show a straight line with a slope of 0.960 and 0.995, and correlation coefficient constants of 0.970 and 0.993, respectively. The predicted content values of unknown samples by x-ray powder diffraction and NIR spectroscopy were reproducible and in close agreement, but those by NIR spectroscopy had smaller SDs than those by x-ray powder diffraction. The results suggest that NIR spectroscopy provides a more accurate quantitative analysis of polymorphic content in pharmaceutical mixed powder and tablets than does conventional x-ray powder diffractometry.
This study of the crystal structure, electronic structure, and magnetic properties of the zeta(2)-GaM (M = Cr, Mn or Fe) alloys is motivated by the recent reinvestigation of the crystallographic Al(8)Cr(5) structure type of zeta(2)-GaMn. The isostructural compounds zeta(2)-GaFe and zeta(2)-GaCr have been refined using X-ray powder diffraction as well as neutron powder diffraction for zeta(2)-GaFe. Their structures have been refined using the space group Rm, with cell parameters a = 12.625(8) A and c = 7.785(10) A for zeta(2)-GaCr and a = 12.4368(11) A and c = 7.7642(10) A for zeta(2)-GaFe. Band structure calculations using the self-consistent, spin-polarized TB-LMTO method were performed to understand their electronic structure and magnetic properties. Band calculations show that from GaCr to GaFe the magnetic interactions change from weakly antiferromagnetic coupling to ferromagnetic coupling. Magnetic measurements confirm ferromagnetism for GaFe and show a weak paramagnetic response for GaCr.
The room-temperature crystal structure of the B-site ordered complex perovskite strontium ytterbium niobate, Sr(Yb(0.5)Nb(0.5))O(3) [monoclinic, Z = 2, P2(1)/n (set 2), a = 5.79095 (8), b = 5.82210 (7), c = 8.20358 (12) Å, beta = 90.126 (1) degrees, with final R(wp) = 0.0595, R(Bragg) = 0.0203 for the neutron profile and R(wp) = 0.0832, R(Bragg) = 0.0193 for the X-ray profile, respectively], was determined by X-ray powder diffraction, high-resolution neutron powder diffraction and transmission electron microscopy. This compound shows a slight triclinic distortion from the prototype doubled cubic perovskite cell as a result of an a(-)a(-)c(+)-type oxygen octahedral tilting distortion. It is also shown that the site ordering of the different species of B-site cations, Yb(3+) and Nb(5+), inherently leads to a difference between the volumes of the YbO(6) and NbO(6) octahedra. This volume difference is shown to inevitably inhibit the rigid rotation of octahedra.
The structure of strontium niobium dioxygen nitride, SrNbO2N, has been solved by powder neutron diffraction at room temperature and 1.5 K. SrNbO2N crystallizes in the tetragonal space group I4/mcm, with a = 5.7056 (4) and c = 8.1002 (9) A at room temperature, and a = 5.6938 (4) and c = 8.0974 (8) A at 1.5 K. The crystal structure is derived from the cubic perovskite archetype by a slight rotation of the Nb(O,N)6 octahedra with respect to the tetragonal axis. A partially ordered distribution of oxygen and nitrogen on the anionic sites was found.
We have examined a sample of 3000 year old Antarctic ice, collected at the Kohnen Station, by time-of-flight powder neutron diffraction to test the hypothesis of Fukazawa et al. [e.g., Ann. Glaciol. 31, 247 (2000)] that such ice may be partially proton ordered. Great care was taken to keep our sample below the proposed ordering temperature (237 K) at all times, but we did not observe any evidence of proton ordering.
The effects of heat-treatment on the structure of the strontium ion-exchanged titanosilicate ETS-4 have been studied by Rietveld analysis of powder neutron diffraction data and by FT-Raman spectroscopy. Hydrous Sr-ETS-4 (space group Cmmm), upon heat-treatment under inert atmosphere at temperatures between 423 and 573 K, exhibits framework contraction as evinced by the decrease in the unit cell dimensions. The effects of heat-treatment on the dimensions of the transport-controlling eight-membered ring (8MR) are elucidated by Rietveld analysis. It is also found that during heat-treatment: (a) the double three membered rings (D3MRs) in ETS-4 are sites of structural instability, (b) the titania chains running along [010] exhibit a large degree of disorder in the bridging oxygen atoms, and (c) significant relocations of the strontium cations take place, which may affect the separation properties of the heat-treated materials. Raman spectra of heat-treated ETS-4 crystals exhibit strong cation-framework interaction effects. Vibrational modes involving the atoms in the titania chains show progressive frequency shifts and loss of intensity with increasing heat-treatment temperature, in a manner consistent with the crystallographic results. The study indicates the potential for continuously varying the effective pore dimension of ETS-4 by combining heat-treatment with appropriate ion-exchange procedures.
Hemoglobin digestion in the intraerythrocytic trophozoite stages of the malaria parasite releases large quantities of heme, which is then detoxified by crystallization into regular crystallites, which are subsequently secreted into the host vascular network as malaria pigment. This crystalline product is isostructural with the synthetic phase b-hematin, and its structure, solved from its powder diffraction pattern, (Pagola et al., 2000), corresponds to a hydrogen bonded chain of propionate linked dimers, Figure 1. This is an example where the crystalline phase is the macromolecule of direct biological interest, particularly in light of the currently accepted hypothesis for the quinoline antimalarial drug action being the inhibition of b-hematin formation and biosynthesis. A surprisingly array of spectroscopically similar closely related phases can also form during the reactions which are used to synthesize b-hematin. Scanning electron microscopy and X-ray powder diffraction have been used to characterize these materials. Taken together these results indicate that infrared spectroscopy, in itself, is insufficient to identify synthetic analogs to malaria pigment and that a combination of electronmicroscopy and powder diffraction are required to unambiguously characterize these heme aggregates.
An oral hematinic marketed as "Niferex," the active component of which is a polysaccharide-iron complex (PIC), has recently been recharacterized. PIC is synthesized by the neutralization of an FeCl3 carbohydrate solution. Original characterization of this complex by Mössbauer spectroscopy and X-ray powder diffraction suggested that the iron-rich core was similar in structure to the mineral ferrihydrite. Higher precision X-ray powder diffraction now indicates that the core has a long-range order more similar to the mineral akaganéite, beta-FeOOH, than to ferrihydrite. This structure has been found for other similar ferric iron-carbohydrate polymers, especially those synthesized by the hydrolysis of FeCl3. Also discussed are the variable temperature (24-295 K) Mössbauer spectroscopic data for PIC. The first example of EXAFS data for polysaccharide iron complexes confirms that the iron is in an octahedral environment, coordinated to oxygen, with a short-range order similar to that for ferritin. The second iron shells in the PIC samples are less ordered than the second shell in ferritin. The size of the PIC core was found to be approximately 5 nm by X-ray powder diffraction, and is of the same order of magnitude as the ferritin core.