Glass transition dynamics of anti-inflammatory ketoprofen studied by Raman scattering and terahertz time-domain spectroscopy

• Vibrational properties of pharmaceutical racemic ketoprofen were investigated.
• Low-frequency Raman scattering spectra clearly showed the boson peak.
• Remarkable change of Raman spectra was observed through a liquid–glass transition.
• The THz-TDS spectra of crystalline state were compared with Raman scattering spectra.

A liquid–glass transition and a crystalline state of pharmaceutical racemic ketoprofen were studied by Raman scattering and the broadband terahertz time-domain spectroscopy (THz-TDS) in the frequency range from 9 to 260 cm−1. The low-frequency Raman scattering spectra clearly shows the remarkable change related to a liquid–glass transition at about Tg = 267 K. After melt-quenching at liquid nitrogen temperature, a boson peak appears at about 16.5 cm−1 near and below Tg and the intensity of quasi-elastic scattering related to structural relaxation increases markedly on heating. The crystalline racemic ketoprofen of “conformer A” shows the noncoincidence effect of mode frequencies below 200 cm−1 between Raman scattering spectra and dielectric spectra observed by THz-TDS.

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