4 years ago

Molecular Mobility of an Amorphous Chiral Pharmaceutical Compound: Impact of Chirality and Chemical Purity

Molecular Mobility of an Amorphous Chiral Pharmaceutical Compound: Impact of Chirality and Chemical Purity
Samuel Petit, Laurent Delbreilh, Quentin Viel, Eric Dargent, Gérard Coquerel
A dielectric relaxation spectroscopy (DRS) study was performed to investigate the molecular mobility of amorphous chiral diprophylline (DPL). For this purpose, both racemic DPL and a single enantiomer of DPL were considered. After fast cooling from the melt at very low temperature (−140 °C), progressive heating below and above the glass transition (Tg ≈ 37 °C) induces two secondary relaxations (γ- and δ-) and primary relaxations (α-) for both enantiomeric compositions. After chemical purification of our samples by means of cooling recrystallization, no γ-process could be detected by DRS. Hence, it was highlighted that the molecular mobility in the glassy state is influenced by the presence of theophylline (TPH), the main impurity in DPL samples. We also proved that the dynamic behavior of a single enantiomer and the racemic mixture of the same purified compound are quasi-identical. This study demonstrates that the relative stability and the molecular mobility of chiral amorphous drugs are strongly sensitive to chemical purity.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcb.7b05667

DOI: 10.1021/acs.jpcb.7b05667

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