Metastable crystalline phase formation in deep eutectic systems revealed by simultaneous synchrotron XRD and DSC

Area of Science:

• Materials Science
• Physical Chemistry
• Crystallography

Background:

• Deep eutectic solvents (DES) are gaining attention for their unique properties.
• Understanding the phase behavior and stability of DES is crucial for their application.
• Co-crystalline structures within DES influence their overall thermodynamic behavior.

Purpose of the Study:

• To analyze the phase behavior of deep eutectic systems containing pharmaceuticals.
• To investigate the formation and stability of crystalline phases in binary mixtures with phenol.
• To explore the potential for separating metastable crystal structures from eutectic systems.

Main Methods:

• Concurrent synchrotron powder X-ray diffraction (PXRD) was employed.
• Differential scanning calorimetry (DSC) was utilized for thermal analysis.
• Analysis focused on binary mixtures of phenol with metacetamol, 2-ethoxybenzamide, and benzamide.

Main Results:

• New crystalline phases were identified in deep eutectic systems with pharmaceuticals.
• These new phases exhibited lower stabilities, melting before or with phenol crystals.
• The phenol:2-ethoxybenzamide system demonstrated the formation of multiple metastable phases.

Conclusions:

• Deep eutectic systems can be characterized by the formation and stability of metastable co-crystalline structures.
• The study deepens the understanding of the structure and thermodynamics of DES.
• Findings have relevance for analogous systems in materials science.