Production of stable amorphous form by means of spray drying

Spray drying is a very useful method for manufacturing of amorphous solid materials. This is mainly due to the possibility of fast solvent evaporation that leads to a rapid transformation of solution to a solid state. Besides evaporation kinetics, there are various process parameters that influence physical and chemical characteristics of such obtained material. The possibility of obtaining a stable amorphous structure of the active pharmaceutical ingredient in a spray dryer was examined. A solution of the hydrochloride crystalline structure of the active pharmaceutical ingredient in a mixture of water and acetonitrile was dried at different temperatures and flowrates of nitrogen used for atomization, as well as the flowrates of the solution. The influence of the process conditions on the properties of the product was analyzed. The final dried products were characterized and identified with a variety of analytical and physical methods. The results showed that a stable amorphous structure of the high purity active pharmaceutical ingredient is obtained, and that the optimal conditions of the process are defined. The amorphous structure is stable at temperatures below 200°C when it is transformed into a new crystal structure. Conditions of high relative air humidity lead to partial transformation.     

Liquid-liquid phase transition and glass transition in a monoatomic model system

We review our recent study on the polyamorphism of the liquid and glass states in a monatomic system, a two-scale spherical-symmetric Jagla model with both attractive and repulsive interactions. This potential with a parametrization for which crystallization can be avoided and both the glass transition and the liquid-liquid phase transition are clearly separated, displays water-like anomalies as well as polyamorphism in both liquid and glassy states, providing a unique opportunity to study the interplay between the liquid-liquid phase transition and the glass transition. Our study on a simple model may be useful in understanding recent studies of polyamorphism in metallic glasses.     

Structural Basis for Metastability in Amorphous Calcium Barium Carbonate (ACBC)

Metastable amorphous precursors are emerging as valuable intermediates for the synthesis of materials with compositions and structures far from equilibrium. Recently, it was found that amorphous calcium barium carbonate (ACBC) can be converted into highly barium‐substituted “balcite,” a metastable high temperature modification of calcite with exceptional hardness. A systematic analysis ACBC (Ca_1‐xBa_xCO₃·1.2H₂O) in the range from x = 0–0.5 is presented. Combining techniques that independently probe the local environment from the perspective of calcium, barium, and carbonate ions, with total X‐ray scattering and a new molecular dynamics/density functional theory simulations approach, provides a holistic picture of ACBC structure as a function of composition. With increasing barium content, ACBC becomes more ordered at short and medium range, and increasingly similar to crystalline balcite, without developing long‐range order. This is not accompanied by a change in the water content and does not carry a significant energy penalty, but is associated with differences in cation coordination resulting from changing carbonate anion orientation. Therefore, the local order imprinted in ACBC may increasingly lower the kinetic barrier to subsequent transformations as it becomes more pronounced. This pathway offers clues to the design of metastable materials by tuning coordination numbers in the amorphous solid state.     

Two successive amorphous‐to‐amorphous phase transformations in TiO2

Based on constant pressure ab initio simulations, we propose, for the first time, two successive amorphous‐to‐amorphous phase transformations for TiO₂. The first one is a gradual phase transformation from a low‐density amorphous phase to a high‐density amorphous phase, whereas the second one is a first‐order phase transformation from the high‐density amorphous phase to a very high‐density amorphous phase. The low‐density amorphous to high‐density amorphous phase change is irreversible, whereas the high‐density amorphous to very high‐density amorphous phase transformation is reversible. The high‐density amorphous and very high‐density amorphous phases consist of differently coordinated configurations. The sevenfold and ninefold‐coordinated arrangements formed in amorphous TiO₂ under pressure are similar to the main building motif of the baddeleyite and cotunnite polymorphs of TiO₂, respectively, while the eightfold‐coordinated configuration is different from the local structure of the cubic TiO₂ phase. The electronic structure calculations suggest that both dense amorphous phases present a semiconducting character with a band gap energy less than that of the original low‐density amorphous phase.