scholarly journals Parametric Rietveld refinement applied to dehydration of sodium naproxen

2014 ◽  
Vol 70 (a1) ◽  
pp. C503-C503
Author(s):  
Ioana Sovago ◽  
Andrew Bond ◽  
Jacco van de Streek ◽  
Diana Thomas
Keyword(s):  
Rietveld Refinement ◽  
Sigmoid Function ◽  
Chemical Transformations ◽  
Algebraic Equations ◽  
Continuous Transition ◽  
Cell Parameters ◽  
Sodium Naproxen ◽  
Dehydration Processes ◽  
Kinetics Of ◽  
Hydration And Dehydration

The identification of the hydration and dehydration transformations of drugs is vital to establish stable pharmaceutical components. Our aim is to monitor the kinetics of hydration and dehydration processes in pharmaceutical solids, and to relate these to the molecular-level crystal structures. One of the primary tools to achieve this is parametric Rietveld refinement. The dehydration of two dihydrate polymorphs of the non-steroidal anti-inflammatory drug (NSAID) sodium naproxen was monitored using synchrotron powder X-ray diffraction measurements at Beamline I711, MAX IV Laboratory, Lund University. Diffraction patterns were measured in the range 300-400 K at 1 K increments. Both polymorphs dehydrate to form identical monohydrate then anhydrous phases. Independent Rietveld refinements were initially performed for each unique phase in order to establish initial values for the parametric refinement. The refinements were performed using TOPAS-Academic [1]. The structures are molecular and both dihydrate polymorphs display pseudosymmetry, thereby requiring an extensive set of restraints. One of the key advantages of the parametric Rietveld refinement is the possibility to introduce algebraic equations that describe the evolution of various parameters [2]. The kinetics of the dehydration processes were monitored using a sigmoid function applied to the scale factors of the various phases (see Figure). The evolution of the unit-cell parameters and atomic displacement parameters were also treated parametrically, and the influence of using multiple coordinate sets (one model per temperature) or a single common coordinate set for each phase was examined. One dihydrate polymorph shows a smooth and continuous transition to the monohydrate, whereas the other polymorph shows an abrupt transition. These differences are linked to the existence of topotactic or non-topotactic chemical transformations between the dihydrate polymorphs and the monohydrate phase.

The Diffusion of Moisture in Paddy During Hydration and Dehydration Processes

2014 ◽  
Vol 32 (12) ◽  
pp. 1423-1434 ◽  
Author(s):  
Prakash Oli ◽  
Rachelle Ward ◽  
Benu Adhikari ◽  
Peter Torley
Keyword(s):  
Dehydration Processes ◽  
Hydration And Dehydration

Reaction Kinetics for the Hydrolysis of Titanium Isopropoxide Carboxylate Complexes

1992 ◽  
Vol 271 ◽  
Author(s):  
Charles D. Gagliardi ◽  
Dilum Dunuwila ◽  
Beatrice A. Van Vlierberge-Torgerson ◽  
Kris A. Berglund
Keyword(s):  
Carboxylic Acids ◽  
Ceramic Materials ◽  
Titanium Isopropoxide ◽  
General Interest ◽  
Chemical Transformations ◽  
Molecular Precursors ◽  
Novel Applications ◽  
Kinetics Of ◽  
Hydrolysis Of

ABSTRACTTitanium alkoxides modified by carboxylic acids have been widely studied as the molecular precursors to ceramic materials. These alkoxide complexes have also been very useful in the formation of stable, porous, optically clear films having many novel applications such as chemical sensors, catalytic supports, and ion-exchange media. To improve the processing of these materials, it is essential to better understand the kinetics of the chemical transformations which occur.The kinetics of the hydrolysis reaction are studied for selected carboxylic acids using Raman spectroscopy to probe the chemistry of the process. The study has a special emphasis on the titanium isopropoxide-valeric acid system due to the superior quality of these films over other carboxylates. Greater knowledge of the hydrolysis kinetics allows increased control over the quality of the film materials and should be of general interest to those working with modified metal alkoxides.

scholarly journals Desorption and re-adsorption of PAHS on aircraft soot surface

2020 ◽  
Vol 42 (4) ◽  
Author(s):  
Nguyen Mai Lan
Keyword(s):  
High Performance ◽  
Flow Reactor ◽  
Activation Energies ◽  
Binding Energies ◽  
Desorption Kinetics ◽  
Chemical Transformations ◽  
Polycyclic Aromatic ◽  
Kinetics Of Degradation ◽  
Kinetics Of ◽  
Pyrex Tube

Polycyclic Aromatic Hydrocarbons (PAHs) in aircraft soot are capable to distribute in the gas phase and particulate phase in chemical transformations in the atmosphere. The desorption of PAHs from the soot surface is a preliminary step in the study of the reactivity of particulate PAHs. The desorption kinetics of PAHs are measured from soot samples to determine desorption rate constants for different PAHs as a function of temperature and the binding energies between PAHs and soot. The kinetics of degradation of particulate PAHs were studied in the flow reactor. The soot samples previously deposited on a Pyrex tube are introduced into the reactor along its axis and the concentrations of PAHs adsorbed on soot are determined by the High-Performance Liquid Chromatography (HPLC) as a function of the desorption time. The results show a correlation between the size of PAHs and the thermodynamics of desorption: with the PAHs have the same number of carbon atoms, their energies of desorption are very similar and increase with this number. The activation energies EA and the number of carbon atoms in PAHs have a linear correlation. It is consistent with the additivity of the laws Van der Waals. The similarity between the activation energies of desorption of PAHs and the corresponding sublimation enthalpies is consistent with the similarity between the graphitic structure of soot and the structure of PAHs.

scholarly journals Geometrical parameterization of the crystal chemistry ofP63/mapatite. II. Precision, accuracy and numerical stability of the crystal-chemical Rietveld refinement

2006 ◽  
Vol 39 (3) ◽  
pp. 369-375 ◽  
Author(s):  
Patrick H. J. Mercier ◽  
Yvon Le Page ◽  
Pamela S. Whitfield ◽  
Lyndon D. Mitchell
Keyword(s):  
Least Squares ◽  
Rietveld Refinement ◽  
Numerical Stability ◽  
Structural Parameters ◽  
Structure Refinement ◽  
Standard Uncertainty ◽  
Crystal Chemical ◽  
Chemical Parameters ◽  
Cell Parameters ◽  
Order Of Magnitude

A script developed for crystal-chemical Rietveld refinement ofP63/mapatite withTOPASis implemented in parallel with standard structure refinement. Least-squares standard uncertainty (s.u.) values for directly extracted crystal-chemical parameters are nearly an order of magnitude lower than those obtained indirectly by analysis of atom coordinates derived by standard Rietveld refinement. This amazing finding originates partly in the reduction of the number of refinement parameters from 21 to 17 and partly in the fact that cell data now derive from crystal-chemical parameters instead ofvice versa. Great precision and accuracy otherwise funneled into unit-cell parameters is then more distributed among mostly crystal-chemical distance parameters. The least-squares s.u. values are supported by analysis of numerous refinements of the same experimental data with added artificial intensity noise. Structural parameters from single-crystal results agree better with those extracted by crystal-chemical refinement. On the basis of singular value decomposition analyses performed using the programSVDdiagnostic[Mercieret al.(2006).J. Appl. Cryst.39, 458–465], crystal-chemical and standard Rietveld refinements are shown to have similar numerical stability. Crystal-chemical parameters extracted by direct Rietveld refinement, therefore, are more precise than, more accurate than and numerically as reliable as those derived from analysis of regular crystallographic refinement of the same data.

Crystal structure and powder data of davidite-type La2Ti10.27Ga9.63O38

1999 ◽  
Vol 14 (1) ◽  
pp. 36-41 ◽  
Author(s):  
A. Meden ◽  
D. Kolar ◽  
S. Škapin
Keyword(s):  
Crystal Structure ◽  
Rietveld Refinement ◽  
Structure Type ◽  
Unit Cell ◽  
Unit Cell Parameters ◽  
Space Group ◽  
Cell Parameters

The structure type of La2Ti10.27Ga9.63O38 was revealed by a search-match using the PDF. A successful Rietveld refinement (Rp=8.9, Rwp=13.3, RB=4.20) confirmed the structure to be rhombohedral (space group R3¯, No. 148) with the refined unit cell parameters a=9.1878(1) Å, α=68.458(1)°, and V=646.374(1) Å3. The structure is compared to other compounds of the davidite type, and the observed and calculated powder data are given.

A powder diffraction study of MIBaIn2(PO4)3 (MI=Na, K, Cs) with a langbeinite-type structure

2002 ◽  
Vol 17 (1) ◽  
pp. 1-6 ◽  
Author(s):  
D. Louër ◽  
V. Moise ◽  
M. Liégeois-Duyckaerts ◽  
A. Rulmont
Keyword(s):  
Diffraction Study ◽  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Type Structure ◽  
Monochromatic Radiation ◽  
Powder Diffraction Data ◽  
Asymmetric Unit ◽  
X Ray ◽  
Cell Parameters

Three phosphates, MIBaIn2(PO4)3 with MI=Na, K, Cs, isostructural to the langbeinite structure, have been studied from powder diffraction data collected with monochromatic radiation obtained from a conventional X-ray source. Precise powder data are reported, as well as cell parameters, i.e., a=10.026 08(9) Å, a=10.121 57(13) Å and a=10.226 94(9) Å for MI=Na, K and Cs, respectively. A Rietveld refinement has been carried out (space group P213), with final RF factors, 0.061, 0.041 and 0.027, and Rwp factors, 0.196, 0.142 and 0.129, for MI=Na, K and Cs, respectively. There are two octahedrally coordinated In3+ ions in the asymmetric unit and the final refinements suggest disorder on the two sites of the MI/Ba sublattice.

A time-resolved powder diffraction study of in-situ photodimerization kinetics of 9-methylanthracene using a CCD area detector and parametric Rietveld refinement

2012 ◽  
Vol 68 (4) ◽  
pp. 424-430 ◽  
Author(s):  
Ahmed F. Mabied ◽  
Melanie Müller ◽  
Robert E. Dinnebier ◽  
Shunsuke Nozawa ◽  
Manabu Hoshino ◽  
...  
Keyword(s):  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Quantitative Phase Analysis ◽  
Time Resolved ◽  
Anthracene Derivative ◽  
Area Detector ◽  
Dimensional Growth ◽  
Kinetics Of ◽  
Dimerization Process

The [4π + 4π] photodimerization process of the 9-substituted anthracene derivative crystalline 9-methylanthracene (9-MA) was investigated using time-resolved X-ray powder diffraction. The study was carried out in-situ using a CCD area detector. Sequential and parametric Rietveld refinement was applied for quantitative phase analysis. The results of traditional sequential Rietveld refinement showed that the evolution of the dimerization process can be described using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model. The parameters of the JMAK equation were obtained successfully by parametric Rietveld refinement and suggest that the reaction follows heterogeneous nucleation and one-dimensional growth with a decreasing nucleation rate.

Hydration and dehydration kinetics of xylazine hydrochloride

2009 ◽  
Vol 14 (4) ◽  
pp. 388-399 ◽  
Author(s):  
Agris Bērziņš ◽  
Andris Actiņš ◽  
Juris P.Kreišmanis
Keyword(s):  
Dehydration Kinetics ◽  
Kinetics Of ◽  
Hydration And Dehydration

Self-Modeling Mixture Analysis Applied to FT-Raman Spectral Data of Hydrogen Peroxide Activation by Nitriles

1997 ◽  
Vol 51 (3) ◽  
pp. 407-415 ◽  
Author(s):  
V. Vacque ◽  
N. Dupuy ◽  
B. Sombret ◽  
J. P. Huvenne ◽  
P. Legrand
Keyword(s):  
Spectral Data ◽  
Chemical Transformations ◽  
Mixture Analysis ◽  
Ft Raman Spectroscopy ◽  
Raman Spectral Data ◽  
Raman Spectral ◽  
Kinetics Of ◽  
Peroxide Activation ◽  
Ft Raman

In the analytical environment, spectral data resulting from analysis of samples often represent mixtures of several components. Extraction of information about pure components of these kinds of mixtures is a major problem, especially when reference spectra are not available or when unstable intermediates are formed. Self-modeling multivariate mixture analysis has been developed for this type of problem. In this paper two examples will be used to show the potential of this technique coupled with FT-Raman spectroscopy to elucidate reaction mechanisms and to follow in situ the kinetics of chemical transformations.

scholarly journals Synthesis and crystal structure of the quaternary semiconductor Cu2NiGeS4, a new stannite-type compound

2019 ◽  
Vol 65 (4 Jul-Aug) ◽  
pp. 355 ◽  
Author(s):  
G. E. Delgado ◽  
And V. Sagredo
Keyword(s):  
Crystal Structure ◽  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Powder Diffraction Data ◽  
Unit Cell Parameters ◽  
Quaternary Compound ◽  
Synthesis And Crystal Structure ◽  
X Ray ◽  
Cell Parameters

The crystal structure of the quaternary compound Cu2NiGeS4, belonging to the system I2-II-IV-VI4, was characterized by Rietveld refinement using X-ray powder diffraction data. This material crystallize with a stannite structure in the tetragonal space group I2m (Nº 121), Z = 2, unit cell parameters a = 5.3384(1) Å, c = 10.5732(3) Å, V = 301.32(3) Å3, acknowledged as a normal valence adamantane-structure.

Sign in / Sign up

Export Citation Format

Share Document