Stable-Form Screening: Overcoming Trace Impurities That Inhibit Solution-Mediated Phase Transformation to the Stable Polymorph of Sulfamerazine

2008 ◽  
Vol 97 (6) ◽  
pp. 2130-2144 ◽  
Author(s):  
Yuchuan Gong ◽  
Benjamin M. Collman ◽  
Shawn M. Mehrens ◽  
Enxian Lu ◽  
Jonathan M. Miller ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Stable Form ◽  
Trace Impurities ◽  
Stable Polymorph

In Situ Electron Microscopy observations of structural transformations in single crystal lanthanum aluminate

1995 ◽  
Vol 53 ◽  
pp. 238-239
Author(s):  
M. Grant Norton ◽  
James Bentley ◽  
Rand R. Biggers
Keyword(s):  
Phase Transformation ◽  
Elevated Temperatures ◽  
Film Deposition ◽  
Rhombohedral Structure ◽  
Stable Form ◽  
Lanthanum Aluminate ◽  
Nucleation Sites ◽  
In Situ Electron Microscopy ◽  
Rhombohedral Crystal Structure ◽  
Rhombohedral Crystal

Single crystals of lanthanum aluminate (LaAlO3) are of interest as substrates to support the growth of films of the superconducting oxide YBa2Cu3O7. In order to facilitate epitaxy the thin films will often be deposited onto heated (T ≥ 700°C) substrates. LaAlO3 has a cubic structure at elevated temperatures and undergoes a transformation on cooling to the rhombohedral crystal structure-the stable form at room temperature. The phase transformation from the cubic to the rhombohedral structure leads to the formation of twins. The twin boundary is predominantly the (100) plane of the pseudo-cubic cell. Several potential problems associated with the phase transformation in LaA1O3 and the concomitant formation of twins have been postulated. Firstly, defects related to the twin boundaries might act as preferred nucleation sites during film deposition. Secondly, on cooling through the transformation temperature, after film deposition, twinning of the substrate might introduce strains into the thin film deposited on the initially untwinned substrate.

scholarly journals A new method for the reproducible generation of polymorphs: two forms of sulindac with very different solubilities

2007 ◽  
Vol 40 (2) ◽  
pp. 379-381 ◽  
Author(s):  
Antonio Llinàs ◽  
Karl J. Box ◽  
Jonathan C. Burley ◽  
Robert C. Glen ◽  
Jonathan M. Goodman
Keyword(s):  
Physical Stability ◽  
Drug Efficacy ◽  
New Method ◽  
Drug Candidate ◽  
Limiting Factor ◽  
Stable Form ◽  
Anticancer Treatment ◽  
The Difference ◽  
Stable Forms ◽  
Stable Polymorph

Polymorphism of drugs has been the subject of intense interest in the pharmaceutical industry for over forty years. Although identical in chemical composition, polymorphs differ in bioavailability, solubility, dissolution rate, chemical and physical stability, melting point, colour, filterability, density, flow properties, and many other properties. The difference in solubility is particularly important for pharmaceuticals, as it can affect drug efficacy, bioavailability and safety. Despite significant investment in processes to find all the possible polymorphs of active pharmaceutical ingredients (APIs), new polymorphs can suddenly appear without warning. Polymorphs tend to convert spontaneously from less stable to more stable forms, and, therefore, it is best to discover and characterize the stable form as early as possible. Ideally the most stable polymorph will be found while the drug candidate is still in the discovery process, so that this is the form used for subsequent testing. The most stable polymorph will be the least soluble and solubility may be a limiting factor in the efficacy of the API. Despite the huge importance of polymorphism in the properties of materials, however, there is no method that can produce all the stable polymorphs of a compound, or even one that can provide confidence that the most stable polymorph has been obtained. Here we describe a new method, `potentiometric cycling for polymorph creation (PC)2', which is able to generate the most stable polymorph in aqueous solution. This new method has been applied to sulindac, a non-steroidal anti-inflammatory drug, which also shows promise in anticancer treatment, producing two polymorphs of this API, including a new more stable one. By adjusting the conditions, this method is able to produce either polymorph exclusively.

scholarly journals Comparison between the orthorhombic and tetragonal forms of the heptamer sequence d[GCG(xT)GCG]/d(CGCACGC)

2010 ◽  
Vol 66 (9) ◽  
pp. 1028-1031 ◽  
Author(s):  
Koen Robeyns ◽  
Piet Herdewijn ◽  
Luc Van Meervelt
Keyword(s):  
Dna Sequences ◽  
Crystal Packing ◽  
Building Blocks ◽  
Stable Form ◽  
Complementary Dna ◽  
Naturally Occurring ◽  
Artificial Dna ◽  
Tetragonal Form ◽  
Sugar Ring ◽  
Stable Polymorph

Cyclohexene nucleic acid (CeNA) building blocks can be introduced into natural DNA sequences without a large conformational influence because of the ability of the six-membered sugar ring to mimic both the C2′-endoand C3′-endoconformations of the naturally occurring ribofuranose sugar ring. The non-self-complementary DNA sequence d[GCG(xT)GCG]/d(CGCACGC) with one incorporated CeNA (xT) moiety crystallizes in two forms: orthorhombic and tetragonal. The tetragonal form, which diffracts to 3 Å resolution, is a kinetically stable polymorph of the orthorhombic form [Robeynset al.(2010),Artificial DNA,1, 1–7], which diffracts to 1.17 Å resolution and is the thermodynamically stable form of the CeNA-incorporated duplex. Here, the two structures are compared, with special emphasis on the differences in crystal packing and the irreversible conversion of the kinetic form into the high-resolution diffracting thermodynamic form.

scholarly journals Effect of Batchelor Flow on Polymorphic Crystallization in a Rotating Disk Crystallizer

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 701
Author(s):  
Zun-Hua Li ◽  
Jinsoo Kim ◽  
Woo-Sik Kim
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Induction Time ◽  
Rotation Speed ◽  
Fluid Motion ◽  
Rotating Disk ◽  
Stable Form ◽  
Ethanol Fraction

In this work, the influence of Batchelor flow on the polymorphic crystallization in a rotating disk (RD) crystallizer was investigated. By regulating crystallization parameters, i.e., the rotation speed, cooling rate, and ethanol fraction, we found that a higher fraction of L-histidine stable Form-A at the induction time and a faster rate of phase transformation could be obtained in the RD crystallizer as compared to previous results in a mixing tank crystallizer. Based on these results, we concluded that the polymorphic crystallization in the RD crystallizer was more effective due to Batchelor flow fluid motion.

Phase Transformation In Ti-6al-4v Alloys

1972 ◽  
Vol 30 ◽  
pp. 584-585
Author(s):  
Shiro Fujishiro
Keyword(s):  
Phase Transformation ◽  
Grain Boundary ◽  
Cryogenic Temperature ◽  
Β Phase ◽  
Heat Treated ◽  
Mixed Microstructure ◽  
Ductile Behavior

The Ti-6 wt.% Al-4 wt.% V commercial alloys have exhibited an improved formability at cryogenic temperature when the alloys were heat-treated prior to the tests. The author was interested in further investigating this unusual ductile behavior which may be associated with the strain-induced transformation or twinning of the a phase, enhanced at lower temperatures. The starting materials, supplied by RMI Co., Niles, Ohio were rolled mill products in the form of 40 mil sheets. The microstructure of the as-received materials contained mainly ellipsoidal α grains measuring between 1 and 5μ. The β phase formed an undefined grain boundary around the a grains. The specimens were homogenized at 1050°C for one hour, followed by aging at 500°C for two hours, and then quenched in water to produce the α/β mixed microstructure.

Microstructural and Microchemical Characterization of Nickel Sulfide Inclusions in Plate Glass

1991 ◽  
Vol 49 ◽  
pp. 962-963
Author(s):  
J. Cooper ◽  
O. Popoola ◽  
W. M. Kriven
Keyword(s):  
Thermal Expansion ◽  
Phase Transformation ◽  
Glass Matrix ◽  
Nickel Sulfide ◽  
Plate Glass ◽  
Thermal Expansion Mismatch ◽  
Volume Increase ◽  
Β Phase ◽  
Microchemical Characterization

Nickel sulfide inclusions have been implicated in the spontaneous fracture of large windows of tempered plate glass. Two alternative explanations for the fracture-initiating behaviour of these inclusions have been proposed: (1) the volume increase which accompanies the α to β phase transformation in stoichiometric NiS, and (2) the thermal expansion mismatch between the nickel sulfide phases and the glass matrix. The microstructure and microchemistry of the small inclusions (80 to 250 μm spheres), needed to determine the cause of fracture, have not been well characterized hitherto. The aim of this communication is to report a detailed TEM and EDS study of the inclusions.

Atomic force microscopy (AFM) of the topography of silicon surfaces exposed to ion beams

1992 ◽  
Vol 50 (2) ◽  
pp. 1132-1133
Author(s):  
Mark Denker ◽  
Jennifer Wall ◽  
Mark Ray ◽  
Richard Linton
Keyword(s):  
Secondary Ion Mass Spectrometry ◽  
Incidence Angle ◽  
Ion Beam ◽  
Depth Profiling ◽  
Depth Resolution ◽  
Ion Beams ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Trace Impurities ◽  
Energy Dose

Reactive ion beams such as O2+ and Cs+ are used in Secondary Ion Mass Spectrometry (SIMS) to analyze solids for trace impurities. Primary beam properties such as energy, dose, and incidence angle can be systematically varied to optimize depth resolution versus sensitivity tradeoffs for a given SIMS depth profiling application. However, it is generally observed that the sputtering process causes surface roughening, typically represented by nanometer-sized features such as cones, pits, pyramids, and ripples. A roughened surface will degrade the depth resolution of the SIMS data. The purpose of this study is to examine the relationship of the roughness of the surface to the primary ion beam energy, dose, and incidence angle. AFM offers the ability to quantitatively probe this surface roughness. For the initial investigations, the sample chosen was <100> silicon, and the ion beam was O2+.Work to date by other researchers typically employed Scanning Tunneling Microscopy (STM) to probe the surface topography.

Phase behavior of cationic and anionic surfactants at low concentrations

1992 ◽  
Vol 50 (1) ◽  
pp. 694-695
Author(s):  
E. Naranjo
Keyword(s):  
Phase Behavior ◽  
Structural Characterization ◽  
Dynamic Systems ◽  
Anionic Surfactants ◽  
Intermolecular Forces ◽  
Stable Form ◽  
Surfactant Mixtures ◽  
Low Concentrations ◽  
Cationic And Anionic Surfactants ◽  
General Method

Equilibrium vesicles, those which are the stable form of aggregation and form spontaneously on mixing surfactant with water, have never been demonstrated in single component bilayers and only rarely in lipid or surfactant mixtures. Designing a simple and general method for producing spontaneous and stable vesicles depends on a better understanding of the thermodynamics of aggregation, the interplay of intermolecular forces in surfactants, and an efficient way of doing structural characterization in dynamic systems.

AEM of reaction-bonded SiC

1992 ◽  
Vol 50 (1) ◽  
pp. 344-345
Author(s):  
K Das Chowdhury ◽  
R. W. Carpenter ◽  
W. Braue
Keyword(s):  
Mechanical Properties ◽  
Phase Transformation ◽  
High Temperature ◽  
Epitaxial Growth ◽  
Liquid Silicon ◽  
Structural Ceramic ◽  
Few Data

Research on reaction-bonded SiC (RBSiC) is aimed at developing a reliable structural ceramic with improved mechanical properties. The starting materials for RBSiC were Si,C and α-SiC powder. The formation of the complex microstructure of RBSiC involves (i) solution of carbon in liquid silicon, (ii) nucleation and epitaxial growth of secondary β-SiC on the original α-SiC grains followed by (iii) β>α-SiC phase transformation of newly formed SiC. Due to their coherent nature, epitaxial SiC/SiC interfaces are considered to be segregation-free and “strong” with respect to their effect on the mechanical properties of RBSiC. But the “weak” Si/SiC interface limits its use in high temperature situations. However, few data exist on the structure and chemistry of these interfaces. Microanalytical results obtained by parallel EELS and HREM imaging are reported here.

Phase transformation and layer evolution in molybdenum disilicide-silicon carbide nanolayered coatings

1994 ◽  
Vol 52 ◽  
pp. 538-539
Author(s):  
H. Kung ◽  
T. R. Jervis ◽  
J.-P. Hirvonen ◽  
M. Nastasi ◽  
T. E. Mitchell ◽  
...  
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Oxidation Resistance ◽  
Elevated Temperatures ◽  
Matrix Material ◽  
Molybdenum Disilicide ◽  
High Temperature Strength ◽  
Cross Sectional ◽  
Good Oxidation Resistance ◽  
Structural Applications

MoSi2 is a potential matrix material for high temperature structural composites due to its high melting temperature and good oxidation resistance at elevated temperatures. The two major drawbacksfor structural applications are inadequate high temperature strength and poor low temperature ductility. The search for appropriate composite additions has been the focus of extensive investigations in recent years. The addition of SiC in a nanolayered configuration was shown to exhibit superior oxidation resistance and significant hardness increase through annealing at 500°C. One potential application of MoSi2- SiC multilayers is for high temperature coatings, where structural stability ofthe layering is of major concern. In this study, we have systematically investigated both the evolution of phases and the stability of layers by varying the heat treating conditions.Alternating layers of MoSi2 and SiC were synthesized by DC-magnetron and rf-diode sputtering respectively. Cross-sectional transmission electron microscopy (XTEM) was used to examine three distinct reactions in the specimens when exposed to different annealing conditions: crystallization and phase transformation of MoSi2, crystallization of SiC, and spheroidization of the layer structures.

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