Amorphous pharmaceutical solids: preparation, characterization and stabilization.

The dependence of iron oxide nanoparticle formation on the structure and thermal properties of Fe oleate complexes has been studied using FTIR, elemental analysis, X-ray photoelectron spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM. The combination of FTIR, elemental analysis, and DSC allowed us to reveal differences between Fe oleate structures for as-synthesized and postsynthesis treated (drying and extraction with polar solvents) compounds. As-synthesized Fe oleate was found to contain a significant fraction of oleic acid, which works as a modifier altering the decomposition process and as an extra stabilizer during iron oxide nanoparticle formation. The thermal treatment of as-synthesized Fe oleate at 70 °C leads to removal of the crystal hydrate water and dissociation of oleic acid dimers, leading to a more thermally stable iron oleate complex whose final decomposition occurs at about 380 °C. Extraction of...

Influence of Iron Oleate Complex Structure on Iron Oxide Nanoparticle Formation

Supercooled liquids and glasses are important for current and developing technologies. Here we provide perspective on recent progress in this field. The interpretation of supercooled liquid and glass properties in terms of the potential energy landscape is discussed. We explore the connections between amorphous structure, high frequency motions, molecular motion, structural relaxation, stability against crystallization, and material properties. Recent developments that may lead to new materials or new applications of existing materials are described.

Perspective: Supercooled liquids and glasses

Superionic conductors are compounds that exhibit exceptionally high values of ionic conductivity within the solid state. Indeed, their conductivities often reach values of the order of 1 Ω−1 cm−1, which are comparable to those observed in the molten state. Following Faraday's first observation of high ionic conductivity within the solids β-PbF2 and Ag2S in 1836, a fundamental understanding of the nature of the superionic state has provided one of the major challenges in the field of condensed matter science. However, experimental and theoretical approaches to their study are often made difficult by the extensive dynamic structural disorder which characterizes superionic conduction and the inapplicability of many of the commonly used approximations in solid state physics. Nevertheless, a clearer picture of the nature of the superionic state at the ionic level has emerged within the past few decades. Many different techniques have contributed to these advances, but the most significant insights have been provided by neutron scattering experiments and molecular dynamics simulations. This review will summarize the state of current knowledge concerning the crystal structures and conduction processes of superionic conductors, beginning with a comparison of the behaviour of two of the most widely studied binary compounds, AgI and β-PbF2. Each can be considered a parent of two larger families of highly conducting compounds which are related by either chemical or structural means. These include perovskite-structured oxides and Li+ containing spinel-structured compounds, which have important commercial applications in fuel cells and lightweight batteries, respectively. In parallel with these discussions, the relative importance of factors such as bonding character and the properties of the mobile and immobile ions (charge, size, polarizability, etc) in promoting the extensive lattice disorder which characterizes superionic behaviour will be assessed and the possibilities for predicting a priori which compounds will display high ionic conductivity discussed.

/pdf/superionics-crystal-structures-and-conduction-processes-1q9bpg4zfv.pdf

Superionics: crystal structures and conduction processes

Objectives With poorly soluble drug candidates emerging in the drug discovery pipeline, the importance of the solid dispersion formulation approach is increasing. This strategy includes complete removal of drug crystallinity, and molecular dispersion of the poorly soluble compound in a hydrophilic polymeric carrier. The potential of this technique to increase oral absorption and hence bioavailability is enormous. Nevertheless, some issues have to be considered regarding thermodynamic instability, as well in supersaturated solutions that are formed upon dissolution as in the solid state. Key findings After a brief discussion on the historical background of solid dispersions and their current role in formulation, an overview will be given on the physical chemistry and stability of glass solutions as they form supersaturated solutions, and during their shelf life. Conclusions Thorough understanding of these aspects will elicit conscious evaluation of carrier properties and eventually facilitate rational excipient selection. Thus, full exploitation of the solid dispersion strategy may provide an appropriate answer to drug attrition due to low aqueous solubility in later stages of development.

https://www.onlinelibrary.wiley.com/doi/epdf/10.1211/jpp.61.12.0001

Review: physical chemistry of solid dispersions

A homogeneous-nucleation-based crystallization was found in o-terphenyl in the glass-transition temperature region with an adiabatic calorimeter, and the crystallization process was investigated by direct microscopic observation. The crystallization showed its maximum rate at 248 and ceased at 250 K, while the ordinary crystal-growth process was observed to proceed only above 255 K. The two crystals formed at 248 and 297 K showed the same x-ray-diffraction patterns, indicating that they were in the same crystalline phase. The nucleation-based crystallization was observed in the temperature range of 225 to 250 K as advance of the crystal front into the liquid phase under the microscope, and the crystalline phase exhibited the appearance of the aggregation of fine crystallites which was consistent with the presence of residual entropy and the premelting property. From these results, the crystallization process was interpreted to proceed through the coalescence of crystal embryos into the crystalline phase on the liquid-crystal interface. It was concluded that the decrease in the effective interfacial energy of the embryo due to the coalescence produced an enhancement of the crystal nucleation, and that the enhancement mechanism must have played an essential role for the macroscopically observable crystallization below 250 K.

Determination of potentially homogeneous-nucleation-based crystallization in o-terphenyl and an interpretation of the nucleation-enhancement mechanism.

Microscopic observation of a peculiar crystallization in the glass transition region and β-process as potentially controlling the growth rate in triphenylethylene

Triphenyl phosphite was studied by powder X-ray diffractometry, adiabatic calorimetry, and dielectric relaxation measurements. The highly correlated liquid, denoted by LC, phase corresponding with ...

Presence of Two Freezing-In Processes Concerning α-Glass Transition in the New Liquid Phase of Triphenyl Phosphite and Its Consistency with “Cluster Structure” and “Intracluster Rearrangement for α Process” Models

A mixed-valence trinuclear iron cyanoacetate complex, [Fe3O(O2CCH2CN)6(H2O)3] (1), was prepared, and the nature of the electron-detrapping phase transition was studied by a multitemperature single-crystal X-ray structure determination (296, 135, and 100 K) and calorimetry by comparison with an isostructural mixed-metal complex, [CoFe2O(O2CCH2CN)6(H2O)3] (2). The mixed-valence states at various temperatures were also determined by 57Fe Mossbauer spectroscopy. The Mossbauer spectrum of 1 showed a valence-detrapped state at room temperature. With decreasing temperature the spectrum was abruptly transformed into a valence-trapped state around 129 K, well corresponding to the heat-capacity anomaly due to the phase transition (Ttrs = 128.2 K) observed in the calorimetry. The single-crystal X-ray structure determination revealed that 1 has an equilateral structure at 296 and 135 K, and that the structure changes into an isosceles one at 100 K due to the electron trapping. The crystal system of 1 at 296 K is rhom...

Minoru Hanaya

Papers

Determination of potentially homogeneous-nucleation-based crystallization in o-terphenyl and an interpretation of the nucleation-enhancement mechanism.

Microscopic observation of a peculiar crystallization in the glass transition region and β-process as potentially controlling the growth rate in triphenylethylene

Presence of Two Freezing-In Processes Concerning α-Glass Transition in the New Liquid Phase of Triphenyl Phosphite and Its Consistency with “Cluster Structure” and “Intracluster Rearrangement for α Process” Models

The Valence-Detrapping Phase Transition in a Crystal of the Mixed-Valence Trinuclear Iron Cyanoacetate Complex [Fe3O(O2CCH2CN)6(H2O)3]

Optimization of two-dimensional multiple-quantum mas nmr experiments for i= 3/2 nuclei on a moderate-field spectrometer