Crystallization kinetics and glass-forming ability of rapidly crystallizing drugs studied by Fast Scanning Calorimetry

Stability of Rapidly Crystallizing Sulfonamides Glasses by Fast Scanning Calorimetry: Crystallization Kinetics and Glass-Forming Ability

Production and evaluation of the kinetic stability of the amorphous forms of active pharmaceutical ingredients are among the current challenges of modern pharmaceutical science. In the present work, amorphous forms of several sulfonamides were produced for the first time using Fast Scanning calorimetry. The parameters, characterizing the glass-forming ability of the compounds, i.e. the critical cooling rate of the melt and the kinetic fragility, were determined. The cold crystallization kinetics was studied using both isothermal and non-isothermal approaches. The results of the present study will contribute to the development of approaches for producing amorphous forms of rapidly crystallizing active pharmaceutical ingredients.

Molecular aggregation by hydrogen bonding in cold-crystallization behavior of mixed nucleobases analyzed by temperature-controlled infrared spectroscopy

The cold-crystallization behaviors of dodecyl-substituted nucleobases (adenine, uracil, and thymine) were analyzed. The dodecyl derivative from uracil alone did not exhibit cold crystallization; however, a mixture of adenine and uracil derivatives at a molar ratio of 1 : 1 exhibited cold crystallization. These results are similar to the thermal behavior of dodecyl derivatives of adenine and thymine alone and in mixtures reported in a previous study. Temperature-controlled infrared spectroscopy was used to observe the molecular assembly states of the liquid, supercooled state, and cold-crystallized compounds. Hydrogen-bonded molecular pairs in the high-temperature liquid state, multiple hydrogen-bonded networks in the supercooled state, and reverse Hoogsteen-type complementary hydrogen bonds in cold-crystallized compounds were observed using infrared spectroscopy. The heterogeneity of the system, due to multiple types of hydrogen bonding, retarded the crystallization rate, resulting in supercooling and cold crystallization. Infrared spectroscopy, which can be used to measure the aggregation state of molecules, including the liquid and supercooled states, is an effective analytical method for clarifying the process of cold crystallization.

The Impact of Various Poly(vinylpyrrolidone) Polymers on the Crystallization Process of Metronidazole

In this paper, we propose one-step synthetic strategies for obtaining well-defined linear and star-shaped polyvinylpyrrolidone (linPVP and starPVP). The produced macromolecules and a commercial PVP K30 with linear topology were investigated as potential matrices for suppressing metronidazole (MTZ) crystallization. Interestingly, during the formation of binary mixtures (BMs) containing different polymers and MTZ, we found that linear PVPs exhibit maximum miscibility with the drug at a 50:50 weight ratio (w/w), while the star-shaped polymer mixes with MTZ even at a 30:70 w/w. To explain these observations, comprehensive studies of MTZ-PVP formulations with various contents of both components were performed using Fourier-transform infrared spectroscopy, differential scanning calorimetry, and X-ray diffraction. The obtained results clearly showed that the polymer's topology plays a significant role in the type of interactions occurring between the matrix and MTZ. Additionally, we established that for MTZ-PVP 50:50 and 75:25 w/w BMs, linear polymers have the most substantial impact on inhibiting the crystallization of API. The star-shaped macromolecule turned out to be the least effective in stabilizing amorphous MTZ at these polymer concentrations. Nevertheless, long-term structural investigations of the MTZ-starPVP 30:70 w/w system (which is not achievable for linear PVPs) demonstrated its complete amorphousness for over one month.

Kinetic Stability and Glass-Forming Ability of Thermally Labile Quinolone Antibiotics

The application of drugs in the amorphous state is one way to improve their bioavailability. As such, the determination of the optimal conditions for production and the assessment of the stability of the amorphous system are actively researched topics of present-day pharmaceutical science. In the present work, we have studied the kinetic stability and glass-forming ability of the thermally labile quinolone antibiotics using fast scanning calorimetry. The critical cooling rates for avoiding crystallization of the melts of oxolinic and pipemidic acids and sparfloxacin were determined to be 10 000, 40, and 80 K·s^-1, respectively. The studied antibiotics were found to be "strong" glass formers. Based on a combination of nonisothermal and isothermal kinetic approaches, the Nakamura model was suitable for describing the crystallization process of the amorphous forms of the quinolone antibiotics.

Predicting Glass-Forming Ability of Pharmaceutical Compounds by Using Machine Learning Technologies

Low aqueous solubility is a common and serious challenge for most drug substances not only in development but also in the market, and it may cause low absorption and bioavailability as a result. Amorphization is an intermolecular modification strategy to address the issue by breaking the crystal lattice and enhancing the energy state. However, due to the physicochemical properties of the amorphous state, drugs are thermodynamically unstable and tend to recrystallize over time. Glass-forming ability (GFA) is an experimental method to evaluate the forming and stability of glass formed by crystallization tendency. Machine learning (ML) is an emerging technique widely applied in pharmaceutical sciences. In this study, we successfully developed multiple ML models (i.e., random forest (RF), XGBoost, and support vector machine (SVM)) to predict GFA from 171 drug molecules. Two different molecular representation methods (i.e., 2D descriptor and Extended-connectivity fingerprints (ECFP)) were implemented to process the drug molecules. Among all ML algorithms, 2D-RF performed best with the highest accuracy, AUC, and F1 of 0.857, 0.850, and 0.828, respectively, in the testing set. In addition, we conducted a feature importance analysis, and the results mostly agreed with the literature, which demonstrated the interpretability of the model. Most importantly, our study showed great potential for developing amorphous drugs by in silico screening of stable glass formers.

Non-Isothermal Crystallization Kinetics of PBSu/Biochar Composites Studied by Isoconversional and Model Fitting Methods

Non-isothermal crystallization of Poly(butylene succinate) (PBSu)/biochar composites was studied at various constant cooling rates using differential scanning calorimetry. The analysis of the kinetics data revealed that the overall crystallization rate and activation energy of the PBSu polymer were significantly influenced by the addition of biochar. Specifically, the PBSu/5% biochar composite with a higher filler content was more effective as a nucleation agent in the polymer matrix, as indicated by the nucleation activity (ψ) value of 0.45. The activation energy of the PBSu/5% biochar composite was found to be higher than that of the other compositions, while the nucleation activity of the PBSu/biochar composites decreased as the biochar content increased. The Avrami equation, which is commonly used to describe the kinetics of crystallization, was found to be limited in accurately predicting the non-isothermal crystallization behavior of PBSu and PBSu/biochar composites. Although the Nakamura/Hoffman-Lauritzen model performed well overall, it may not have accurately predicted the crystallization rate at the end of the process due to the possibility of secondary crystallization. Finally, the combination of the Šesták-Berggren model with the Hoffman-Lauritzen theory was found to accurately predict the crystallization behavior of the PBSu/biochar composites, indicating a complex crystallization mechanism involving both nucleation and growth. The K_g parameter of neat PBSu was found to be 0.7099 K², while the melting temperature and glass transition temperature of neat PBSu were found to be 114.91 °C and 35 °C, respectively, very close to the measured values. The Avrami nucleation dimension n was found to 2.65 for PBSu/5% biochar composite indicating that the crystallization process is complex in the composites.

Cold crystallization and photo-induced thermal behavior of alkyl-derivatized diarylethene molecules

The thermal behavior of alkylated diarylethene molecules (2,3-bis(2,4,5-trimethyl-3-thienyl)-N-alkylmaleimides; DAE-Cn) was investigated. DAE-C1 and DAE-C2 exhibited cold crystallization, which is a heat-storage phenomenon. In addition, DAE-Cn showed photoisomerization; the open-ring isomer O-DAE-Cn was formed by visible light irradiation and transformed to the closed-ring isomer C-DAE-Cn by UV light irradiation. X-ray diffraction and optical microscopy analyses revealed that O-DAE-Cn exhibited cold crystallization and C-DAE-Cn showed poor crystallinity. UV irradiation (365 nm) inhibited cold crystallization, and visible light irradiation (525 nm) triggered cold crystallization, suggesting that heat storage by the cold crystallization of DAE-Cn can be photo-controlled.

The alkylated diarylethene molecules exhibited cold crystallization, and their thermal behavior can be photo-controlled.

Alkyl substituent-dependent systematic change in cold crystallization of azo molecules

The thermal behavior of alkyl-derivatized 1-(2,4-dimethylphenylazo)-4-naphthol and 1-(2,4-dimethylphenylazo)-2-naphthol (2,4-DM-4-Cn and 2,4-DM-2-Cn, respectively) was investigated. The change in the position of the alkyl substituent led to a variation in the thermal behavior, including the cold crystallization, which is a heat-storing phenomenon. In addition, a comprehensive study of the alkyl chain length revealed that 2,4-DM-4-Cn had better crystallinity and exhibited cold crystallization with short alkyl chains. The π–π, C–H⋯N, and C–H⋯π interactions stabilized the crystal structure of 2,4-DM-4-Cn. On the other hand, the polymorphism of 2,4-DM-2-Cn inhibited the formation of a uniform crystalline phase during cooling, which led to poor crystallinity. The only difference between the compounds, the position of the substituent, resulted in a clear variation in the cold crystallization and heat storage properties.

The change in alkyl substitution position and alkyl chain length of azo molecules led to the variation in cold crystallization behavior.

A Thermal Study on Peat Oxidation Behavior in the Presence of an Iron-Based Catalyst

Peat is a resource used for heat and energy, particularly in countries where peat is abundant and conventional fuels are not available. Some countries have made extensive use of peat resources to produce electricity and heat in addition to light hydrocarbons. By doing so, they were able to reduce the cost of importing fossil fuels. To the best of our knowledge, there is a lack of a detailed description of the peat oxidation process in the presence of other substances. Herein, the process of peat oxidation was studied in-depth by means of thermal analysis in the presence of iron tallate acting as a catalytic agent. Differential scanning calorimetry and thermogravimetric analysis demonstrated an oil-like oxidation behavior during the combustion of the used peat. The process of peat oxidation includes two main regions: low-temperature oxidation (LTO), which occurs during the oxidation of light hydrocarbons, followed by the so-called high-temperature oxidation (HTO), which includes the oxidation of the obtained coke-like product. Moreover, the application of non-isothermal kinetics experiments based on the isoconversional and model approach principle have confirmed the role of 2% iron tallate in peat mass by improving the oxidation rate at low- and high-temperature oxidation (HTO) regions. The results obtained from this study have proven that the added catalyst improves efficiency with regards to the energy activation in the process by leading to its significant decrease from 110.8 ± 7.8 kJ/mol to 81.8 ± 7.5 kJ/mol for LTO and from 157.8 ± 19.1 kJ/mol to 137.6 ± 9.3 kJ/mol for HTO. These findings clearly confirm the improvement in the rate of the process by shifting the LTO and HTO peaks to lower regions in the presence of the catalyst. These results further emphasize the possible impact which could be generated by the application of thermally enhanced oil recovery methods on peat development and exploitation.