Application of DSC-XRD Coupled Techniques for the Evaluation of Phase Transition in Oils and Fats and Related Polymorphic Forms

Single-crystal diffuse X-ray scattering from paracetamol polymorphs is successfully calculated with Monte Carlo (MC) models that are used to simulate the crystals. In order to obtain the correct model appropriate force constants are required that describe the interatomic potentials used in the MC algorithm. Coefficients for an empirical `Buckingham'-type formula are used to determine these force constants. These coefficients are subsequently refined using the least-squares method and are found to converge on similar values for both polymorphic forms. An investigation of the correlation space generated from each model provides what would be expected given that strong displacive correlations exist between the molecules comprising the densely hydrogen-bonded layers. More disordered motions between these layers are present in the model for form (II) as opposed to form (I). An investigation into the peculiarities of librational disorder was also conducted, however, correlation values turn out to be so small that any structural information concerning librational correlation is inconclusive. The purpose of this experiment was to identify if the diffuse scattering features could provide further insight into understanding the physical reasoning behind the metastability of form (II). The form (II) → (I) phase transition is also not currently well understood and usually phase transitional information can be obtained from pronounced diffuse scattering features. Since the diffuse scattering is modelled adequately using harmonic potentials it is our conjecture that the `diffuse' is essentially thermal in origin and does not afford any extra information about the form (II) → (I) phase transition.

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Thermodynamic Relationship and Phase Transition Study Involving Two Polymorphs of Sulfamethoxazole: Form I vs. Form II

New Journal of Chemistry ◽

10.1039/d1nj03597e ◽

2021 ◽

Author(s):

Carlos Henrique de Moura Oliveira ◽

Jennifer Tavares Jacon Freitas ◽

Iara M. L. Rosa ◽

Antonio Carlos Doriguetto

Keyword(s):

Phase Transition ◽

Broad Spectrum ◽

Broad Spectrum Antibiotic ◽

Thermodynamic Relationship ◽

Polymorphic Forms ◽

Transition Study

Sulfamethoxazole (SMZ) is a synthetic, broad-spectrum antibiotic presenting five known polymorphic forms. Herein, the SMZ polymorph I (SMZI), which is the preconised form for SMZ pharmaceutical oral solid formulations, and...

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On the polymorphism of benzocaine; a low-temperature structural phase transition for form (II)

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768109018898 ◽

2009 ◽

Vol 65 (4) ◽

pp. 509-515 ◽

Cited By ~ 21

Author(s):

Eric J. Chan ◽

A. David Rae ◽

T. Richard Welberry

Keyword(s):

Phase Transition ◽

Low Temperature ◽

Structural Phase Transition ◽

Room Temperature ◽

Structural Phase ◽

Space Group ◽

Polymorphic Forms ◽

Similar Phase

A low-temperature structural phase transition has been observed for form (II) of benzocaine (BZC). Lowering the temperature doubles the b-axis repeat and changes the space group from P212121 to P1121 with γ now 99.37 °. The structure is twinned, the twin rule corresponding to a 21 screw rotation parallel to a. The phase transition is associated with a sequential displacement parallel to a of zigzag bi-layers of ribbons perpendicular to b*. No similar phase transition was observed for form (I) and this was attributed to the different packing symmetries of the two room-temperature polymorphic forms.

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Microstructure of laser-irradiated, conducting Kapton polyimide

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100138889 ◽

1995 ◽

Vol 53 ◽

pp. 502-503

Author(s):

D. L. Callahan ◽

Z. Ball ◽

H. M. Phillips ◽

R. Sauerbrey

Keyword(s):

Electron Microscopy ◽

Phase Transition ◽

Transmission Electron Microscopy ◽

Cross Section ◽

Film Surface ◽

Cross Sectional ◽

General Utility ◽

Transmission Electron ◽

Considerable Debate ◽

Potential Applications

Ultraviolet laser-irradiation can be used to induce an insulator-to-conductor phase transition on the surface of Kapton polyimide. Such structures have potential applications as resistors or conductors for VLSI applications as well as general utility electrodes. Although the percolative nature of the phase transformation has been well-established, there has been little definitive work on the mechanism or extent of transformation. In particular, there has been considerable debate about whether or not the transition is primarily photothermal in nature, as we propose, or photochemical. In this study, cross-sectional optical microscopy and transmission electron microscopy are utilized to characterize the nature of microstructural changes associated with the laser-induced pyrolysis of polyimide.Laser-modified polyimide samples initially 12 μm thick were prepared in cross-section by standard ultramicrotomy. Resulting contraction in parallel to the film surface has led to distortions in apparent magnification. The scale bars shown are calibrated for the direction normal to the film surface only.

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The structure of membranes and membrane proteins embedded in amorphous ice

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122563 ◽

1992 ◽

Vol 50 (1) ◽

pp. 432-433

Author(s):

Uwe Lücken ◽

Joachim Jäger

Keyword(s):

Phase Transition ◽

Transition Temperature ◽

Membrane Proteins ◽

Phase Transition Temperature ◽

Lipid Vesicles ◽

Freezing Stress ◽

Amorphous Ice ◽

Different Temperatures ◽

Band Pass ◽

Lipid Polymorphism

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.

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Polymorphic phase transition of a membrane protein - analysis of continuous diffuse electron diffraction intensity

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100142451 ◽

1986 ◽

Vol 44 ◽

pp. 166-167

Author(s):

Douglas L. Dorset ◽

Andrew K. Massalski

Keyword(s):

Molecular Sieve ◽

Three Dimensional ◽

Pore Geometry ◽

Two Dimensional ◽

Diffraction Intensity ◽

Polymorphic Phase Transition ◽

E Coli ◽

Crystallographic Study ◽

Hexagonal Form ◽

Polymorphic Forms

Matrix porin, the ompF gene product of E. coli, has been the object of a electron crystallographic study of its pore geometry in an attempt to understand its function as a membrane molecular sieve. Three polymorphic forms have been found for two-dimensional crystals reconstituted in phospholipid, two hexagonal forms with different lipid content and an orthorhombic form coexisting with and similar to the hexagonal form found after lipid loss. In projection these have been shown to retain the same three-fold pore triplet geometry and analyses of three-dimensional data reveal that the small hexagonal and orthorhombic polymorphs have similar structure as well as unit cell spacings.

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Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100173996 ◽

1990 ◽

Vol 48 (4) ◽

pp. 172-173

Author(s):

Naoki Yamamoto ◽

Makoto Kikuchi ◽

Tooru Atake ◽

Akihiro Hamano ◽

Yasutoshi Saito

Keyword(s):

Phase Transition ◽

Electron Microscope Study ◽

Room Temperature ◽

Hexagonal Lattice ◽

Ferroelectric Materials ◽

Temperature Phase ◽

X Ray Diffraction ◽

X Ray ◽

Periodic Arrays ◽

Modulation Wave Vector

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

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Dynamic low-dose electron diffraction and imaging of phase transitions in polymers

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100150289 ◽

1993 ◽

Vol 51 ◽

pp. 890-891

Author(s):

David C. Martin ◽

Jun Liao

Keyword(s):

Crystal Structure ◽

Phase Transition ◽

Electron Diffraction ◽

Low Dose ◽

Dark Field ◽

Continuous Change ◽

Selected Area Electron Diffraction ◽

Resolution Electron ◽

Chain Axis ◽

High Resolution Electron Micrographs

By careful control of the electron beam it is possible to simultaneously induce and observe the phase transformation from monomer to polymer in certain solid-state polymcrizable diacetylenes. The continuous change in the crystal structure from DCHD diacetylene monomer (a=1.76 nm, b=1.36 nm, c=0.455 nm, γ=94 degrees, P2l/c) to polymer (a=1.74 nm, b=1.29 nm, c=0.49 nm, γ=108 degrees, P2l/c) occurs at a characteristic dose (10−4C/cm2) which is five orders of magnitude smaller than the critical end point dose (20 C/cm2). Previously we discussed the progress of this phase transition primarily as observed down the [001] zone (the chain axis direction). Here we report on the associated changes of the dark field (DF) images and selected area electron diffraction (SAED) patterns of the crystals as observed from the side (i.e., in the [hk0] zones).High resolution electron micrographs (HREM), DF images, and SAED patterns were obtained on a JEOL 4000 EX HREM operating at 400 kV.

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