In crystalline molecular solids, in the absence of strong intermolecular interactions, entropy-driven processes play a key role in the formation of dynamically modulated transient phases. Specifically, in crystalline simvastatin, the observed fully reversible enantiotropic behavior is associated with multiple order-disorder transitions: upon cooling, the dynamically disordered high-temperature polymorphic Form I is transformed to the completely ordered low-temperature polymorphic Form III via the intermediate (transient) modulated phase II. This behavior is associated with a significant reduction in the kinetic energy of the rotating and flipping ester substituents, as well as a decrease in structural ordering into two distinct positions. In transient phase II, the conventional three-dimensional structure is modulated by periodic distortions caused by cooperative conformation exchange of the ester substituent between the two states, which is enabled by weakened hydrogen bonding. Based on solid-state NMR data analysis, the mechanism of the enantiotropic phase transition and the presence of the transient modulated phase are documented.

• Klíčová slova
• dynamics, enantiotropy, entropy, polymorphism, solid-state nuclear magnetic resonance (NMR), transient modulated phase,
• MeSH
• entropie * MeSH
• magnetická rezonanční spektroskopie metody   MeSH
• molekulární konformace * MeSH
• molekulární modely MeSH
• nízká teplota MeSH
• simvastatin chemie   MeSH
• vodíková vazba MeSH
• změna skupenství * MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• simvastatin MeSH