Aspirin Research Today is a free monthly online journal that collates and summarizes the latest research about Aspirin, including details on acetylsalicylic acid, baby aspirin, side effects, overdose, allergy.

Dielectric relaxation and crystallization of ultraviscous melt and glassy states of aspirin, ibuprofen, progesterone, and quinidine.

Johari GP, Kim S, Shanker RM

Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4L7. joharig@mcmaster.ca

Molecular relaxation in ultraviscous melt and glassy states of aspirin, ibuprofen, progesterone, and quinidine has been studied by dielectric spectroscopy. The asymmetric relaxation spectra is characterized by the Kohlrausch distribution parameter of 0.46 +/- 0.02 for aspirin to 0.67 +/- 0.02 for progesterone. The dielectric relaxation time varies with the temperature, T, according to the Vogel-Fulcher-Tammann Equation, log(10)(tau(0)) = A(VFT) + [B(VFT)/(T - T(0))], where A(VFT), B(VFT), and T(0) are empirical constants. The extrapolated tau(0) at calorimetric glass-softening temperature is close to the value expected. The equilibrium permittivity, epsilon(0), is lowest for ibuprofen which indicates an antiparallel orientation of dipoles in its liquid's hydrogen-bonded structure. A decrease in epsilon(0) with time shows that ultraviscous aspirin, progesterone, and quinidine begin to cold-crystallize at a relatively lower temperature than ibuprofen. epsilon(0) of the cold-crystallized phases are, 4.7 for aspirin at 290 K, 2.55 for ibuprofen at 287 K, 2.6 for progesterone at 320 K, and 3.2 for quinidine at 375 K. It is argued that hydrogen-bonding, the Kohlrausch parameter, extent of localized motions and the long-range diffusion times all determine the physical and chemical stability of an amorphous pharmaceutical during storage.

Published 30 April 2007 in J Pharm Sci, 96(5): 1159-75.
Full-text of this article is available online (may require subscription).

© 2004-2008 Aspirin Research Today. All Rights Reserved.