Investigations on the polymorphism and pseudopolymorphism of clobetasone butyrate

2011 ◽  
Vol 76 (5) ◽  
pp. 553-566
Author(s):  
Christian Näther ◽  
Inke Jeß
Keyword(s):  
Room Temperature ◽  
Polymorphic Form ◽  
Stable Form ◽  
Scanning Calorimetry ◽  
Amorphous Form ◽  
Space Group ◽  
Dsc Measurements ◽  
Independent Molecules ◽  
Solvent Molecules ◽  
Similar Conformation

Clobetasone butyrate was investigated for polymorphism and pseudopolymorphism. Solvent mediated conversion experiments reveal that the commercially available form I represent the thermodynamically most stable form at room temperature and DSC measurements shows that it should also be the most stable form until melting. Form I crystallizes in space groupP212121with three crystallographically independent molecules of similar conformation. From methanol an additional pseudo polymorphic form was discovered. In the crystal structure (space groupP212121) the solvent molecules are connected to the clobetasone butyrate molecules by O–H···O hydrogen bonding. Investigations of the solvate using thermogravimetry, differential thermoanalysis as well as differential scanning calorimetry proves, that on solvent removal an amorphous form is obtained that crystallizes into form I on further heating.

scholarly journals Occurrence of polymorphism in famotidine raw materials

2014 ◽  
Vol 70 (a1) ◽  
pp. C1563-C1563
Author(s):  
Marilene Ângelo ◽  
Jennifer Jacon ◽  
Olimpia Maria Santos ◽  
Edith Cristina Cazedey ◽  
Rudy Bonfilio ◽  
...  
Keyword(s):  
Raw Materials ◽  
Polymorphic Form ◽  
Raw Material ◽  
Stable Form ◽  
Reference Standard ◽  
H2 Receptor Antagonist ◽  
Scanning Calorimetry ◽  
Histamine H2 Receptor ◽  
Ulcer Disease ◽  
And Control

Polymorphs are compounds with the same chemical composition, however the molecules are arranged in at least two different ways in the solid state. Famotidine is a histamine H2-receptor antagonist inhibitor of gastric secretion and widely used in gastric and duodenal ulcer disease. Two polymorphs are described for famotidine, A and B. The polymorph A is the most thermodynamically stable form and polymorph B is the kinetically favored form being marketed because it presents greater pharmacological activity. The aim of this study was to evaluate the occurrence of famotidine polymorphs in five raw materials acquired from different suppliers. The reference standard (USP) was also analyzed. All samples were characterized by powder X-ray diffraction (PXRD), infrared spectrophotometry (IR-ATR) and differential scanning calorimetry (DSC). PXRD analysis enables us to identify form B in five raw material samples and in the reference standard (USP). However, one of the raw materials additionally shows the presence of polymorphic form A. The DSC and IR-ATR techniques were essential to identify the polymorphic forms of famotidine confirming the results obtained by PXRD. Since the presence of polymorphs can compromise the effectiveness and safety of medicines and there is no official methodology of analysis and control of polymorphism in famotidine raw materials, the polymorphic contamination found in this study are being further analyzed and their physicochemical properties are being evaluated.

The structures and phase transitions in 4-aminopyridinium tetraaquabis(sulfato)iron(III), (C5H7N2)[FeIII(H2O)4(SO4)2]

2019 ◽  
Vol 75 (6) ◽  
pp. 1144-1151
Author(s):  
Tamara J. Bednarchuk ◽  
Wolfgang Hornfeck ◽  
Vasyl Kinzhybalo ◽  
Zhengyang Zhou ◽  
Michal Dušek ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Single Crystal ◽  
Room Temperature ◽  
Variable Temperature ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Hybrid Compound ◽  
Space Group ◽  
X Ray

The organic–inorganic hybrid compound 4-aminopyridinium tetraaquabis(sulfato)iron(III), (C5H7N2)[FeIII(H2O)4(SO4)2] (4apFeS), was obtained by slow evaporation of the solvent at room temperature and characterized by single-crystal X-ray diffraction in the temperature range from 290 to 80 K. Differential scanning calorimetry revealed that the title compound undergoes a sequence of three reversible phase transitions, which has been verified by variable-temperature X-ray diffraction analysis during cooling–heating cycles over the temperature ranges 290–100–290 K. In the room-temperature phase (I), space group C2/c, oxygen atoms from the closest Fe-atom environment (octahedral) were disordered over two equivalent positions around a twofold axis. Two intermediate phases (II), (III) were solved and refined as incommensurately modulated structures, employing the superspace formalism applied to single-crystal X-ray diffraction data. Both structures can be described in the (3+1)-dimensional monoclinic X2/c(α,0,γ)0s superspace group (where X is ½, ½, 0, ½) with modulation wavevectors q = (0.2943, 0, 0.5640) and q = (0.3366, 0, 0.5544) for phases (II) and (III), respectively. The completely ordered low-temperature phase (IV) was refined with the twinning model in the triclinic P{\overline 1} space group, revealing the existence of two domains. The dynamics of the disordered anionic substructure in the 4apFeS crystal seems to play an essential role in the phase transition mechanisms. The discrete organic moieties were found to be fully ordered even at room temperature.

Hexagonal and cubic TiOF2

2010 ◽  
Vol 43 (4) ◽  
pp. 757-761 ◽  
Author(s):  
Samuel Shian ◽  
Kenneth H. Sandhage
Keyword(s):  
Room Temperature ◽  
Three Dimensional ◽  
Chemical Conversion ◽  
Rietveld Analysis ◽  
Hexagonal Structure ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Thermally Induced ◽  
Space Group ◽  
Structure Space

The chemical, electrochemical, optical and electro-optical properties of titanium oxyfluoride, TiOF2, have led to interest in this compound for a number of applications. Prior analyses have indicated that TiOF2possesses a simple cubic structure (space groupPm{\overline 3}m) at room temperature. Three-dimensional nanostructured assemblies of polycrystalline TiOF2have recently been synthesizedviachemical conversion of intricate SiO2structures by metathetic reaction with TiF4(g). Rietveld analysis has been used to evaluate the structure of the TiOF2product formed by such reaction at 623 K. Unlike prior reports, this TiOF2product possessed a hexagonal structure (space groupR{\overline 3}c) at room temperature. Upon heating through 333–338 K, the hexagonal TiOF2polymorph converted into cubic (Pm{\overline 3}m) TiOF2. Differential scanning calorimetry and X-ray diffraction analyses have been used to evaluate this thermally induced phase transformation.

scholarly journals X-ray structure analysis of symmetrically substituted 1,1′-diformylruthenocene

2018 ◽  
Vol 74 (9) ◽  
pp. 1186-1189
Author(s):  
Bertin Anzaldo ◽  
Pankaj Sharma ◽  
Francisco Lara Ochoa ◽  
Claudia P. Villamizar C. ◽  
René Gutiérrez Pérez
Keyword(s):  
Structure Analysis ◽  
Room Temperature ◽  
Dimensional Structure ◽  
Two Dimensional ◽  
Asymmetric Unit ◽  
Orthorhombic System ◽  
Space Group ◽  
X Ray ◽  
Π Interactions ◽  
Independent Molecules

1,1′-Diformylruthenocene, [Ru(C6H5O)2], crystallizes in the orthorhombic system in the P212121 space group at room temperature. There are two crystallographically independent molecules in the asymmetric unit. The cyclopentadienyl rings have eclipsed configuration. The molecules self-assemble in a two-dimensional structure by C—H...O and C—H...π interactions with cisoid relative orientations of the two formyl groups. The crystal studied was refined as an inversion twin.

Preparation and Characterization of Elastomers Based on Polydimethylsiloxane/Poly(methyl methacrylate) Blends

2012 ◽  
Vol 535-537 ◽  
pp. 1193-1196
Author(s):  
Nai Qiang Zhang ◽  
Jian Dong ◽  
Hong Yu Chen
Keyword(s):  
Methyl Methacrylate ◽  
Room Temperature ◽  
Radical Copolymerization ◽  
Cross Linking ◽  
Scanning Calorimetry ◽  
Silicone Elastomers ◽  
Poly Methyl Methacrylate ◽  
Dsc Measurements ◽  
Pmma Blends

Polydimethylsiloxane/poly (methyl methacrylate) (PDMS/PMMA) blends were prepared by radical copolymerization of methyl methacrylate (MMA) and divinylbenzene (DVB) in the presence of PDMS. Elastomers based on PDMS/PMMA blends were formed by cross-linking PDMS with methyltriethoxysilane (MTES). Mechanical property measurements show that the elastomers thus formed exhibit superior tensile strength with respect to general room temperature vulcanized silicone elastomers containing silica. Moreover, investigations were carried out on the elastomers by extraction, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) measurements. SEM shows that the elastomer has a microphase-separated structure consisting of dispersed PMMA domains within a continuous PDMS matrix. DSC result shows that the elastomers display two glass transition temperatures and confirm the incompatible nature of PDMS and PMMA.

scholarly journals Lithium tetrachloridoaluminate, LiAlCl4: a new polymorph (oP12,Pmn21) with Li+in tetrahedral interstices

2017 ◽  
Vol 73 (10) ◽  
pp. 1426-1429 ◽  
Author(s):  
Stephan W. Prömper ◽  
Walter Frank
Keyword(s):  
Room Temperature ◽  
Aluminium Chloride ◽  
Lithium Cation ◽  
Scanning Calorimetry ◽  
Lithium Ions ◽  
Monoclinic Modification ◽  
Cation Site ◽  
Monoclinic Form ◽  
Dsc Measurements ◽  
Orthorhombic Modification

Dissolving lithium chloride and aluminium chloride in boilingpara- ormeta-xylene and keeping the colourless solution at room temperature led to crystal growth of a new modification of lithium tetrachloridoaluminate, LiAlCl4, which represents a second modification (oP12,Pmn21) of the ternary salt besides the long known monoclinic form [LiAlCl4(mP24,P21/c); Mairesseet al.(1977).Cryst. Struct. Commun.6, 15–18]. The crystal structures of both modifications can be described as slightly distorted hexagonal closest packings of chloride anions. While the lithium cations in LiAlCl4(mP24) are in octahedral coordination and the aluminium and lithium ions in the solid of orthorhombic LiAlCl4occupy tetrahedral interstices with site symmetriesmand 1, respectively, the lithium cation site being half-occupied (defect wurtz-stannite-type structure). From differential scanning calorimetry (DSC) measurements, no evidence for a phase transition of the orthorhombic modification is found until the material melts at 148 °C (Tpeak= 152 °C). The melting point is nearly identical to the literature data for LiAlCl4(mP24) [146 °C; Weppner & Huggins (1976).J. Electrochem. Soc.124, 35–38]. From the melts of both polymorphs, the monoclinic modification recrystallizes.

Thermodynamic Interactions in Blends of Polydienes

1999 ◽  
Vol 72 (4) ◽  
pp. 580-586 ◽  
Author(s):  
Ramanan Krishnamoorti
Keyword(s):  
Small Angle Neutron Scattering ◽  
Room Temperature ◽  
Single Phase ◽  
Solution Temperature ◽  
Scanning Calorimetry ◽  
Binary Blends ◽  
Critical Solution Temperature ◽  
Dsc Measurements ◽  
Lcst Behavior ◽  
Mixed Microstructure

Abstract Thermodynamic interactions and phase behavior in binary blends of model mixed microstructure polybutadienes with model 1,4-polyisoprene were studied using small angle neutron scattering and differential scanning calorimetry (DSC). The microstructure of the polybutadiene ranged from 8% 1,2 (92% 1,4) to 90% 1,2 (10% 1,4) units, while the polyisoprene contained 93% 1,4 and 7% 3,4 units. The blends of protonated polybutadienes (HPB) with deuterated 1,4 polyisoprene (DPI) exhibited lower critical solution temperature (LCST) behavior when the polybutadiene contained 38 mol % or more of 1,2 units. Below this 1,2 content of the polybutadiene, all HPB/DPI blends were found to be phase separated at all temperatures above 25 °C. The DSC measurements revealed that other than a blend containing 8% 1,2-polybutadiene and (protonated) 1,4 polyisoprene, all other blends were single phase at room temperature. These results are understood in the context of previous work performed by Han and coworkers on deuterated polybutadiene-protonated polyisoprene blends.

Phase behaviour and crystal structures of 2′,3′-difluorinated p-terphenyl derivatives

2021 ◽  
Vol 77 (7) ◽  
Author(s):  
Sakuntala Gupta ◽  
Partha Pratim Das ◽  
Przemysław Kula ◽  
Emmanuele Parisi ◽  
Roberto Centore
Keyword(s):  
Crystal Structures ◽  
Crystal Packing ◽  
Phase Behaviour ◽  
Dsc Analysis ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Space Group ◽  
X Ray ◽  
Independent Molecules ◽  
Derivatives Of

The crystal structures of difluorine derivatives of p-terphenyls (nTm) have been determined by single-crystal X-ray diffraction. For the unsymmetrical substituted compounds 2′,3′-difluoro-4-methyl-p-terphenyl (1T0, C19H14F2) and 4-ethyl-2′,3′-difluoro-4′′-methyl-p-terphenyl (1T2, C21H18F2), the crystal structure is disordered, with molecules statistically entering the crystal in up and down orientations, with full superposition of all the atoms, except for those of the terminal groups (H/methyl for 1T0 and methyl/ethyl for 1T2). For triclinic 2′,3′-difluoro-4,4′′-dimethyl-p-terphenyl (1T1, C20H16F2), with the space group P\overline{1}, the two crystallographically independent molecules have the same conformation, which is different from monoclinic 1T0 (space group C2) and 1T2 (space group C2/c). A common feature of the conformation of the three compounds is the noncoplanar twisted arrangement of the three rings of the p-terphenyl moiety. Two-dimensional (2D) Hirshfeld fingerprint plots are consistent with H...H and C...H contacts in the crystal packing. For the three compounds, the phase behaviour has been investigated by POM (Petra/Osiris/Molinspiration) and differential scanning calorimetry (DSC) analysis. 1T2 is mesogenic, with enantiotropic nematic behaviour.

scholarly journals Crystal Structure and 35Cl NQR of ( — ) β-(trichloromethyl)- β-propiolactone. Comparison with (±) β-(trichloromethyl)-β-propiolactone

1993 ◽  
Vol 48 (3) ◽  
pp. 491-496 ◽  
Author(s):  
Shi-qi Dou ◽  
Reha Basaran ◽  
Helmut Paulus ◽  
Alarich Weiss
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Unit Cell ◽  
Intramolecular Interactions ◽  
Space Group ◽  
Solid States ◽  
35Cl Nqr ◽  
Independent Molecules ◽  
Group D ◽  
Limits Of Error

Abstract The crystal structure of(-)β-(trichloromethyl)-β-propiolactone at room temperature is reported, as is the 35Cl NQR spectrum in the range 77 ≦ T/K ≦ 323.5. The compound crystallizes with the space group D24-212121, Z = 8, a = 2416.0 (10) pm, b = 975.6 (4) pm, c = 595.0 (2) pm. The intramolecular distances and angles of the two crystallographically independent (-) molecules in the unit cell are equal within the limits of error. The spread of the 35Cl NQR spectrum is within 600 kHz, not changing in the temperature range covered. The crystal structure and 35Cl NQR spectrum are discussed.The results found for the (-) compound are compared with the corresponding ones reported for the (±) compound [1], and the influence of the different intramolecular interactions in the two solid states of the chemically identical compounds on the NQR spectrum is discussed.

scholarly journals Solubility and Crystallization of Piroxicam from Different Solvents in Evaporative and Cooling Crystallization

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1552
Author(s):  
Iben Ostergaard ◽  
Haiyan Qu
Keyword(s):  
Room Temperature ◽  
Evaporation Rate ◽  
Solute Concentration ◽  
Polymorphic Form ◽  
Stable Form ◽  
Stochastic Nature ◽  
Cooling Crystallization ◽  
Evaporative Crystallization ◽  
Polymorphic System ◽  
Simple Link

In this work, the solubility of a non-steroidal anti-inflammatory drug (NSAID), piroxicam, is investigated. The polymorphic form II, which is the most stable form at room temperature, was investigated in seven different solvents with various polarities. It has been found that the solubility of piroxicam in the solvents is in the following order: chloroform > dichloromethane > acetone > ethyl acetate > acetonitrile > acetic acid > methanol > hexane. Crystallization of piroxicam from different solvents has been performed with evaporative crystallization and cooling crystallization; the effects of solvent evaporation rate and solute concentration have also been studied. Both form I and form II could be produced in cooling and evaporative crystallization, and no simple link can be identified between the operating parameters and the polymorphic outcome. Results obtained in the present work showed the stochastic nature of the nucleation of different polymorphs as well as the complexity of the crystallization of a polymorphic system.

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