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<p>This study investigates the glass-forming ability (GFA), thermal stability, and molecular relaxation dynamics of amorphous forms of three model pharmaceuticals—acetohexamide, piroxicam, and 5-fluorouracil—using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and broadband dielectric spectroscopy (BDS). Crystalline samples were heated above their respective melting points (T<sub>m</sub>) and melt-quenched to induce vitrification. TGA confirmed thermal processing windows sufficient to prevent degradation during quenching. DSC measurements yielded glass transition temperatures (T<sub>g</sub>) of 323–331&#xa0;K for acetohexamide and 323&#xa0;K for piroxicam; however, a clear glass transition could not be resolved for 5-Fluorouracil due to its intense recrystallization tendency. Piroxicam exhibited superior GFA with no crystallization during cooling, whereas Acetohexamide and 5-Fluorouracil showed rapid recrystallization upon heating. BDS analysis, evaluated via permittivity and electric modulus formalisms, revealed primary α-relaxations associated with the glass transition alongside secondary γ-relaxations in piroxicam. In contrast, prominent ionic conductivity masked the structural α-process in acetohexamide and 5-fluorouracil, leaving only secondary relaxations detectable in acetohexamide. These findings demonstrate a clear correlation between molecular architecture (planarity, hydrogen-bonding capacity, and conformational flexibility) and amorphous state stability. The results highlight piroxicam’s intrinsic robustness for solubility enhancement, while underscoring the necessity of crystallization inhibitors for acetohexamide and 5-fluorouracil formulations. Ultimately, this integrated thermal and dielectric approach provides critical insights into glass transition dynamics, supporting predictive strategies for stable amorphous pharmaceutical development.</p>

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Structure-dependent glass-forming ability and relaxation dynamics in amorphous acetohexamide, piroxicam, and 5-fluorouracil: a thermal and dielectric investigation

  • 期刊论文

  • 发表日期：

    2026年7月3日

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  • K. Rasheed,
  • Aboothahir Afzal,
  • M. Shahin Thayyil,
  • K Jalaja,
  • M. P. Nighilnath,
  • Ahmed Saleh Yaseen,
  • M. Saifunnisa

摘要

This study investigates the glass-forming ability (GFA), thermal stability, and molecular relaxation dynamics of amorphous forms of three model pharmaceuticals—acetohexamide, piroxicam, and 5-fluorouracil—using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and broadband dielectric spectroscopy (BDS). Crystalline samples were heated above their respective melting points (Tm) and melt-quenched to induce vitrification. TGA confirmed thermal processing windows sufficient to prevent degradation during quenching. DSC measurements yielded glass transition temperatures (Tg) of 323–331 K for acetohexamide and 323 K for piroxicam; however, a clear glass transition could not be resolved for 5-Fluorouracil due to its intense recrystallization tendency. Piroxicam exhibited superior GFA with no crystallization during cooling, whereas Acetohexamide and 5-Fluorouracil showed rapid recrystallization upon heating. BDS analysis, evaluated via permittivity and electric modulus formalisms, revealed primary α-relaxations associated with the glass transition alongside secondary γ-relaxations in piroxicam. In contrast, prominent ionic conductivity masked the structural α-process in acetohexamide and 5-fluorouracil, leaving only secondary relaxations detectable in acetohexamide. These findings demonstrate a clear correlation between molecular architecture (planarity, hydrogen-bonding capacity, and conformational flexibility) and amorphous state stability. The results highlight piroxicam’s intrinsic robustness for solubility enhancement, while underscoring the necessity of crystallization inhibitors for acetohexamide and 5-fluorouracil formulations. Ultimately, this integrated thermal and dielectric approach provides critical insights into glass transition dynamics, supporting predictive strategies for stable amorphous pharmaceutical development.