A Contribution to the Solid State Forms of Bis(demethoxy)curcumin: Co-Crystal Screening and Characterization

Bis(demethoxy)curcumin (BDMC) is one of the main active components found in turmeric. Major drawbacks for its usage are its low aqueous solubility, and the challenging separation from other curcuminoids present in turmeric. Co-crystallization can be applied to alter the physicochemical properties of BDMC in a desired manner. A co-crystal screening of BDMC with four hydroxybenzenes was carried out using four different methods of co-crystal production: crystallization from solution by slow solvent evaporation (SSE), and rapid solvent removal (RSR), liquid-assisted grinding (LAG), and crystallization from the melt phase. Two co-crystal phases of BDMC were obtained with pyrogallol (PYR), and hydroxyquinol (HYQ). PYR-BDMC co-crystals can be obtained only from the melt, while HYQ-BDMC co-crystals could also be produced by LAG. Both co-crystals possess an equimolar composition and reveal an incongruent melting behavior. Infrared spectroscopy demonstrated the presence of BDMC in the diketo form in the PYR co-crystals, while it is in a more stable keto-enol form in the HYQ co-crystals. Solubility measurements in ethanol and an ethanol-water mixture revealed an increase of solubility in the latter, but a slightly negative effect on ethanol solubility. These results are useful for a prospective development of crystallization-based separation processes of chemical similar substances through co-crystallization.

Crystallisation studies of sodium acetate trihydrate – suppression of incongruent melting and sub-cooling to produce a reliable, high-performance phase-change material

Polymer additives reliably prevent incongruent melting of sodium acetate trihydrate when temperature-cycled over multiple thousands of melting and freezing cycles.

Detection of Intermediate Phases in Metal Alloys

In addition to property anomalies, a distinguishing feature of the intermediate phase is the qualitative change of the crystallization or recrystallization interval (Q∆LS) that occurs at congruent and incongruent melting phases, at eutectic or eutectoid points, at the ends of eutectic or eutectoid horizontals, and also at any nonmonotonicity of the liquidus, since the solidus or solidoid is a horizontal in eutectic or eutectoid systems. A technique has been developed that allows us to associate anomalies in the properties of industrial alloys with state diagrams based on the first established criterion - a qualitative change (length in temperature) of the crystallization (recrystallization) interval (Q∆LS), as well as with a difference in the structural heredity (genealogy) of the component atoms that make up dual system. A joint analysis of the anomalies in the properties of binary alloys with state diagrams (based on the established criterion (Q∆LS)) allows us to relate the latter to the presence of intermediate phases in Al − Si, Fe − C, Al − Cu systems. The intermediate phases AnBm-Q∆LS explaining the anomalies of properties are declared: ~Al7Si, Al41Cu9 − correspond to the eutectic point; Fe24C − eutectoid point; Al11Si, AlSi6 − the bend of the liquidus; Fe42C − bending liquidoid; Al49Cu, Al98.5Si1.5 − the end of the eutectic horizontal; Cu4Al, Cu7Al3 − to the ends of the eutectoid horizontal.

Phase equilibria in the SnBi2Te4MnBi2Te4 system and characterization of the Sn1-xMnxBi2Te4 solid solutions

The phase diagram of the SnBi2Te4-MnBi2Te4 system was established over the entire concentration range by means of differential thermal analysis and powder X-ray diffraction techniques. It was shown that the system is non-quasi-binary due to the incongruent melting character of SnBi2Te4 and MnBi2Te4 compounds, but it is stable below solidus. The formation of a continuous series of solid solutions with the tetradymite-like layered structure was observed. Due to ionic radius differences of Mn2+ and Sn2+, both unit cell parameters of solid solutions increase linearly with the increasing amount of Sn. Phase equilibria above the solidus curve cannot be completed until the SnTe-MnTe-Bi2Te3 system fully studied.