Molecular Dynamic in Ethosuximide Glass Forming Pharmaceutical as Studied by Dielectric Relaxation Spectroscopy

Abstract

Polymorphism and molecular dynamics of ethosuximide with molecules of left- and right-handed chirality have been studied in detail using dielectric spectroscopy. Density functional theory calculations of molecular conformations and dimer formation were performed to aid the interpretation of measurements. Moving window correlation analysis of the imaginary part of dielectric permittivity spectra allowed us to complete the monotropic system of phases found by the differential scanning calorimetry method. Extra transition connected with freezing-in/activation of slow molecular motions was identified in partially ordered crystal CrI phase. In high-temperature orientationally disordered CrI_h and in low-temperature conformationally disordered CrI_l phases, 2 relaxation processes were detected at frequency range below 10⁵ Hz. In glass of CONDIS CrI_l, β-relaxation was identified.

Keywords: DFT; complex dynamics; dielectric spectroscopy; ethosuximide; moving window analysis; vitrification.