Drug-Polymer Solubility Determination: A New Thermodynamic Model Free from Lattice Theory Assumptions.

PURPOSE: Traditional methods for estimating drug-polymer solubility either require fast dissolution in the polymeric matrix, rapid re-crystallization kinetics from supersaturated states or derive from regular solution theories. In this work, we present a new method for determining drug solubility, purely based on thermodynamic considerations, that uses only experimental data from DSC for calculations. METHODS: The new thermodynamic model presented combines DSC analysis and application of Hess's law to determine free energies of conversion of binary mixtures to amorphous solid dispersions, free energies of mixing as well as solubility as a function of temperature. The model drug indomethacin and polymers HPMCAS LF, PVP K29/32 and Eudragit EPO were used in these studies. RESULTS: Free energies were calculated as a function of temperature, for different drug-polymer compositions and the results show that HPMCAS LF solid dispersion with high drug content are less thermodynamically favorable compared to other polymer systems. Solubility of indomethacin in HPMCAS LF, PVP K29/32 and Eudragit EPO was 24, 55 and 56% w/w, respectively, at 25°C. CONCLUSIONS: The thermodynamic model presented has great advantages over traditional methods. It does not require estimation of any interaction parameters, it is almost assumption-free and uses only thermal data for calculations.

Investigations of the Density and Solubility of Ammonium Perrhenate and Potassium Perrhenate Aqueous Solutions.

Rhenium is largely used as an additive to nickel- and cobalt-based superalloys. Their resistance to temperature and corrosion makes them suitable for the production of turbines in civil and military aviation, safety valves in drilling platforms, and tools working at temperatures exceeding 1000 °C. The purity of commercial rhenium salts is highly important. Potassium, which is a particularly undesirable element, can be removed by recrystallization. Therefore, it is crucial to possess detailed knowledge concerning process parameters including the dissolved solid concentration and the resulting saturation temperature. This can be achieved using simple densimetric methods. Due to the fact that data concerning the physicochemical properties of ammonium perrhenate (APR) NH4ReO4 and potassium perrhenate (PPR) KReO4 are imprecise or unavailable in the scientific literature, the goal of this study is to present experimental data including the solubility and density of water solutions of both salts. In the experiments, a densimeter with a vibrating cell was used to precisely determine the densities. Although the investigated solutions did not fit into the earlier proposed mathematical model, some crucial conclusions could still be made based on the results.

Solubility products of sparingly soluble barium perborates in aqueous solution that contains B(OH)3 and H2O2 at 25°C.

Chemical oxo-precipitation (COP) has become a promising method for treating boron wastewater at room temperature; it uses hydrogen peroxide to convert boric acid to perborate species, which are precipitated using alkaline earth metals. In this work, solubility models of barium perborates were established to predict residual boron levels from COP. The solubility product constants (pKsp) of two major barium perborates - amorphous Ba(B(OH)3OOH)2 (A-BaPB) and crystalline BaB(OH)2(OO)2B(OH)2 (C-BaPB) - were experimentally estimated (8.335±0.109 and 9.190±0.057, respectively) to define the solubility curves of BaPBs at given pH, ionic strength and concentrations of barium and peroxide species. The characterization of precipitates that were formed by COP confirmed that the boron levels in aqueous solution were governed by the phase transformation of A-BaPB to C-BaPB. The predictive solubility models of barium perborates can perfectly predict the residual concentration of boron after COP treatment and can be used to optimize the process for reducing boron concentrations in wastewater.

Effective recovery of poly-ß-hydroxybutyrate (PHB) biopolymer from Cupriavidus necator using a novel and environmentally friendly solvent system.

This work demonstrates a significant advance in bioprocessing for a high-melting lipid polymer. A novel and environmental friendly solvent mixture, acetone/ethanol/propylene carbonate (A/E/P, 1:1:1 v/v/v) was identified for extracting poly-hydroxybutyrate (PHB), a high-value biopolymer, from Cupriavidus necator. A set of solubility curves of PHB in various solvents was established. PHB recovery of 85% and purity of 92% were obtained from defatted dry biomass (DDB) using A/E/P. This solvent mixture is compatible with water, and from non-defatted wet biomass, PHB recovery of 83% and purity of 90% were achieved. Water and hexane were evaluated as anti-solvents to assist PHB precipitation, and hexane improved recovery of PHB from biomass to 92% and the purity to 93%. A scale-up extraction and separation reactor was designed, built and successfully tested. Properties of PHB recovered were not significantly affected by the extraction solvent and conditions, as shown by average molecular weight (1.4 × 10(6) ) and melting point (175.2°C) not being different from PHB extracted using chloroform. Therefore, this biorenewable solvent system was effective and versatile for extracting PHB biopolymers. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:678-685, 2016.