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Materials (Basel, Switzerland) Oct 2020Silica has many industrial (i.e., glass formers) and scientific applications. The understanding and prediction of the interesting properties of such materials are...
Study of the Microstructure of Amorphous Silica Nanostructures Using High-Resolution Electron Microscopy, Electron Energy Loss Spectroscopy, X-ray Powder Diffraction, and Electron Pair Distribution Function.
Silica has many industrial (i.e., glass formers) and scientific applications. The understanding and prediction of the interesting properties of such materials are dependent on the knowledge of detailed atomic structures. In this work, amorphous silica subjected to an accelerated alkali silica reaction (ASR) was recorded at different time intervals so as to follow the evolution of the structure by means of high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and electron pair distribution function (e-PDF), combined with X-ray powder diffraction (XRPD). An increase in the size of the amorphous silica nanostructures and nanopores was observed by HRTEM, which was accompanied by the possible formation of Si-OH surface species. All of the studied samples were found to be amorphous, as observed by HRTEM, a fact that was also confirmed by XRPD and e-PDF analysis. A broad diffuse peak observed in the XRPD pattern showed a shift toward higher angles following the higher reaction times of the ASR-treated material. A comparison of the EELS spectra revealed varying spectral features in the peak edges with different reaction times due to the interaction evolution between oxygen and the silicon and OH ions. Solid-state nuclear magnetic resonance (NMR) was also used to elucidate the silica nanostructures.
PubMed: 33019776
DOI: 10.3390/ma13194393 -
Chemical & Pharmaceutical Bulletin 2020A concise spherical granulation method is required to prepare extemporaneously granules remanufactured from oral dosage forms for administration to individuals who...
A concise spherical granulation method is required to prepare extemporaneously granules remanufactured from oral dosage forms for administration to individuals who cannot swallow tablets or capsules. In this study, we determined the feasibility of spherical granulation using a planetary centrifugal mixer. A model formulation, 20% ibuprofen (IBP) granules, was prepared using a lactose/cornstarch (7 : 3, w/w) mixture or D-mannitol as diluents, and changes in granule characteristics (mean diameter (d50), distribution range of granule size (span), and yield) were evaluated according to the amount of water added and the granulation time. The amount of water was assessed using the plastic limit value as measured using a digital force gauge. We successfully produced granules, and larger amounts of water and longer granulation times resulted in larger d50 values and smaller span values. The optimal granulation time was 45 s and the optimal water contents were 70 and 67.5% of the plastic limit value for the lactose/cornstarch mixture and D-mannitol, respectively. When compared to commercial 20% IBP granules, powder X-ray diffraction and differential scanning calorimetry analyses showed that the granulation process did not alter the crystallinity of the drug. Thus, this novel granulation method using a planetary centrifugal mixer may be a promising technique for compounding in pharmacies and in pharmaceutical manufacturing.
Topics: Calorimetry, Differential Scanning; Centrifugation; Ibuprofen; Lactose; Mannitol; Particle Size; Powder Diffraction; Starch; Surface Properties
PubMed: 32115532
DOI: 10.1248/cpb.c19-00888 -
Geoderma Mar 2019X-ray powder diffraction (XRPD) is widely applied for the qualitative and quantitative analysis of soil mineralogy. In recent years, high-throughput XRPD has resulted in...
X-ray powder diffraction (XRPD) is widely applied for the qualitative and quantitative analysis of soil mineralogy. In recent years, high-throughput XRPD has resulted in soil XRPD datasets containing thousands of samples. The efforts required for conventional approaches of soil XRPD data analysis are currently restrictive for such large data sets, resulting in a need for computational methods that can aid in defining soil property - soil mineralogy relationships. Cluster analysis of soil XRPD data represents a rapid method for grouping data into discrete classes based on mineralogical similarities, and thus allows for sets of mineralogically distinct soils to be defined and investigated in greater detail. Effective cluster analysis requires minimisation of sample-independent variation and maximisation of sample-dependent variation, which entails pre-treatment of XRPD data in order to correct for common aberrations associated with data collection. A 2 factorial design was used to investigate the most effective data pre-treatment protocol for the cluster analysis of XRPD data from 12 African soils, each analysed once by five different personnel. Sample-independent effects of displacement error, noise and signal intensity variation were pre-treated using peak alignment, binning and scaling, respectively. The sample-dependent effect of strongly diffracting minerals overwhelming the signal of weakly diffracting minerals was pre-treated using a square-root transformation. Without pre-treatment, the 60 XRPD measurements failed to provide informative clusters. Pre-treatment via peak alignment, square-root transformation, and scaling each resulted in significantly improved partitioning of the groups ( < 0.05). Data pre-treatment via binning reduced the computational demands of cluster analysis, but did not significantly affect the partitioning ( > 0.1). Applying all four pre-treatments proved to be the most suitable protocol for both non-hierarchical and hierarchical cluster analysis. Deducing such a protocol is considered a prerequisite to the wider application of cluster analysis in exploring soil property - soil mineralogy relationships in larger datasets.
PubMed: 30828102
DOI: 10.1016/j.geoderma.2018.09.044 -
Frontiers in Chemistry 2018The Rietveld analysis of X-ray powder diffraction patterns is used widely for obtaining the structural information of clay minerals. However, the complex hydration...
The Rietveld analysis of X-ray powder diffraction patterns is used widely for obtaining the structural information of clay minerals. However, the complex hydration behavior and the variability of interlayer contents are often considered difficult to be described correctly by a simple structure model. In the present work, the use of Cu-triethylenetetramine (Cu-trien)-exchanged nontronites has been proposed to simplify the interlayer structure. This method provides a potential to obtain the structural information of nontronites, for example, the layer charge density, occupancies of -octahedral sites, and the iron content by the Rietveld analysis from the X-ray powder diffraction patterns. The approach was demonstrated on three Cu-trien-exchanged nontronite samples. The Rietveld refinements were carried out first on the purified samples and the results showed a good peak fitting between measured and calculated patterns. The refined iron content and the occupancies of -octahedral sites are in general agreement with the reference data, which have been obtained from chemical and thermal analyses. The refinement of layer charge density showed lower values compared with the reference. It may be due to the assumption of temperature factor of Cu-trien in the interlayer. A raw sample with natural impurities was chosen to test the applicability of this method. The refinement pattern of the raw sample led to good agreement with the observed data. The results of the iron content and the occupancies of -octahedral sites showed the same tendency as purified samples. This study showed that this approach allows for obtaining some structural details of nontronites directly from X-ray powder diffraction patterns of Cu-trien-exchanged samples.
PubMed: 30515377
DOI: 10.3389/fchem.2018.00558 -
Acta Crystallographica. Section E,... Feb 2016The crystal structure of sodium potassium hydrogen citrate has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density...
The crystal structure of sodium potassium hydrogen citrate has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional theory techniques. The Na(+) cation is six-coordinate, with a bond-valence sum of 1.17. The K(+) cation is also six-coordinate, with a bond-valence sum of 1.08. The distorted [NaO6] octahedra share edges, forming chains along the a axis. The likewise distorted [KO6] octahedra share edges with the [NaO6] octahedra on either side of the chain, and share corners with other [KO6] octahedra, resulting in triple chains along the a axis. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds; the O⋯O distances are 2.414 and 2.400 Å. The Mulliken overlap populations in these hydrogen bonds are 0.138 and 0.142 e, which correspond to hydrogen-bond energies of 20.3 and 20.6 kcal mol(-1).
PubMed: 26958380
DOI: 10.1107/S2056989016000232 -
Acta Crystallographica. Section E,... Oct 2020The crystal structures of disodium hydrogen citrate monohydrate, NaHCHO(HO), and di-ammonium sodium citrate, (NH)NaCHO, have been solved and refined using laboratory...
The crystal structures of disodium hydrogen citrate monohydrate, NaHCHO(HO), and di-ammonium sodium citrate, (NH)NaCHO, have been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. In NaHCHO(HO), the NaO coordination polyhedra share edges, forming zigzag layers lying parallel to the plane. The hydro-phobic methyl-ene groups occupy the inter-layer spaces. The carb-oxy-lic acid group makes a strong charge-assisted hydrogen bond to the central carboxyl-ate group. The hydroxyl group makes an intra-molecular hydrogen bond to an ionized terminal carboxyl-ate oxygen atom. Each hydrogen atom of the water mol-ecule acts as a donor, to a terminal carboxyl-ate and the hydroxyl group. Both the Na substructure and the hydrogen bonding differ from those of the known phase NaHCHO(HO). In (NH)NaCHO, the NaO coordination octa-hedra share corners, making double zigzag chains propagating along the -axis direction. Each hydrogen atom of the ammonium ions acts as a donor in a discrete N-H⋯O hydrogen bond. The hydroxyl group forms an intra-molecular O-H⋯O hydrogen bond to a terminal carboxyl-ate oxygen atom.
PubMed: 33117566
DOI: 10.1107/S2056989020011895 -
Chemistry of Materials : a Publication... Feb 2022Layered cobalt oxide perovskites are important mixed ionic and electronic conductors. Here, we investigate LaBaCoO using neutron powder diffraction. This composition is...
Layered cobalt oxide perovskites are important mixed ionic and electronic conductors. Here, we investigate LaBaCoO using neutron powder diffraction. This composition is unique because it can be prepared in cubic, layered, and vacancy-ordered forms. Thermogravimetric analysis and diffraction reveal that layered and disordered samples have near-identical oxygen cycling capacities. Migration barriers for oxide ion conduction calculated using the bond valence site energy approach vary from ∼ 2.8 eV for the cubic perovskite to ∼ 1.5 eV for 2D transport in the layered system. Vacancy-ordered superstructures were observed at low temperatures, 350-400 °C for δ = 0.25 and δ = 0.5. The vacancy ordering at δ = 0.5 is different from the widely reported structure and involves oxygen sites in both CoO and LaO planes. Vacancy ordering leads to the emergence of additional migration pathways with low-energy barriers, for example, 1D channels with = 0.5 eV and 3D channels with = 2.2 eV. The emergence of these channels is caused by the strong orthorhombic distortion of the crystal structure. These results demonstrate that there is potential scope to manipulate ionic transport in vacancy-ordered LnBaCoO perovskites with reduced symmetry.
PubMed: 35431436
DOI: 10.1021/acs.chemmater.1c03726 -
Acta Crystallographica. Section E,... Oct 2020The crystal structures of magnesium hydrogen citrate dihydrate, Mg(HCHO)(HO), (I), and bis-(di-hydrogen citrato)magnesium, Mg(HCHO), (II), have been solved and refined...
The crystal structures of magnesium hydrogen citrate dihydrate, Mg(HCHO)(HO), (I), and bis-(di-hydrogen citrato)magnesium, Mg(HCHO), (II), have been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. In (I), the citrate anion occurs in the -conformation, and triply chelates to the Mg cation. In (II), the citrate anion is , and doubly chelates to the Mg cation. In both compounds the Mg cation coordination polyhedron is an octa-hedron. In (I), the MgO coordination polyhedra are isolated, while in (II), they share edges to form chains. Strong O-H⋯O hydrogen bonds are prominent in the two structures, as well as in the previously reported magnesium citrate deca-hydrate.
PubMed: 33117574
DOI: 10.1107/S2056989020011913 -
Acta Crystallographica. Section E,... May 2021The crystal structure of dilithium potassium citrate monohydrate, Li·2K·CHO ·HO or LiKCHO·HO, has been solved by direct methods and refined against laboratory X-ray...
The crystal structure of dilithium potassium citrate monohydrate, Li·2K·CHO ·HO or LiKCHO·HO, has been solved by direct methods and refined against laboratory X-ray powder diffraction data, and optimized using density functional techniques. The complete citrate trianion is generated by a crystallographic mirror plane, with two C and three O atoms lying on the reflecting plane, and chelates to three different K cations. The KO and LiO coordination polyhedra share edges and corners to form layers lying parallel to the plane. An intra-molecular O-H⋯O hydrogen bond occurs between the hydroxyl group and the central carboxyl-ate group of the citrate anion as well as a charge-assisted inter-molecular O-H⋯O link between the water mol-ecule and the terminal carboxyl-ate group. There is also a weak C-H⋯O hydrogen bond.
PubMed: 34026253
DOI: 10.1107/S2056989021003339 -
Journal of Young Pharmacists : JYP Dec 2013In the present study, simultaneous determination of degree of crystallinity content in abacavir (ABC), lamivudine (3TC) and neverapine (NVP) from there combination drug...
OBJECTIVE
In the present study, simultaneous determination of degree of crystallinity content in abacavir (ABC), lamivudine (3TC) and neverapine (NVP) from there combination drug product using X-ray powder diffraction (XRPD) technique is developed and validated.
METHODS
The X-ray procedure for the identification and determination of the degree of crystallinity in ABC, 3TC and NVP drug product is developed and validated. It is based on the X-ray diffraction from crystalline region of the drug product. The characteristic peaks of the three drugs were characterized using XRPD.
RESULTS
ABC, 3TC and NVP concentrations ranging from 70% to 130% in drug product were prepared and linearity in this concentration range is described. The % coefficient of variation (%CV) was found to be 0.9982 for ABC, 0.9978 for 3TC and 0.9984 for NVP. The mean recoveries were found to be 100.3% for ABC, 99.0% for 3TC and 100.8% for NVP. Regressions statistics and Analysis of variance (ANOVA) table results were evaluated and found to be satisfactory.
CONCLUSIONS
The method has been applied to unknown mixtures of drug formulations and stability samples. The proposed method can be useful in the quality control of combination drug products.
PubMed: 24563590
DOI: 10.1016/j.jyp.2013.10.003