Scientific Results

Calorimetric relaxation in pharmaceutical molecular glasses and its utility in understanding their stability against crystallization

Year: 2008

Authors: Tombari E., Ferrari C., Johari G.P., Shanker R.M.

Autors Affiliation: Istituto per i Processi Chimico-Fisici, CNR, via G. Moruzzi 1, 56124 Pisa, Italy; Dept. of Materials Science and Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada; Groton Laboratories, Pfizer Inc., Groton, CT 06340, United States

Abstract: Glassy states of three pharmaceuticals, acetaminophen, griseofulvin. and nifedipine, and an acetaminophen-aspirin (1:1 mol) alloy were made by slow cooling of the melt and Studied by calorimetry. Measurements were performed by cooling and heating at significantly slow rates of 20 K/h, which were comparable to the rate used in adiabatic calorimetry. The results were modeled in terms of a nonexponential, nonlinear structural relaxation. The calorimetric relaxation of all four pharmaceutical samples were less nonexponential than those of polymeric or inorganic glasses, and this finding was attributed to additional contributions to energy change that Would arise from temperature and time dependent variation in the hydrogen bond population, the extent of isomerization, and/or the ionic equilibria that exist in these materials. Four calculated and relevant parameters for the pharmaceutical samples were, ln A = -1837 beta = 0.75, x = 0.4, and Delta h* = 457 kJ/mol for acetaminoplien, ln A = -170, beta = 0.75, x = 0.45, and Delta h* = 516 kJ/mol for griseofulvin, ln A = -189, beta = 0.69, x = 0.39, and Delta h* = 503 kJ/mnol for nifedipine, and ln A = -160, beta = 0.70, x 0.50, and Delta h* = 363 kJ/mol for the acetaminophen-aspirin alloy. The significance of these parameters and, in particular, their values are discussed in the context of the stability of the pharmaceuticals against crystallization and compared against the significance of the localized motions of the JG relaxation in the same context. Acetaminophen was found to be significantly more prone to crystallization on heating than the other two pharmaceuticals as well as the acetaminophen-aspirin alloy.

Journal/Review: JOURNAL OF PHYSICAL CHEMISTRY B

Volume: 112 (35)      Pages from: 10806  to: 10814

More Information: This research was supported in part by Pfizer Inc.
KeyWords: STRUCTURAL RELAXATION; DIELECTRIC-RELAXATION; SECONDARY RELAXATIONS; ENTHALPY RELAXATION; VISCOUS-LIQUIDS; HEAT-CAPACITY; FICTIVE TEMPERATURE; ULTRAVISCOUS MELT; ALPHA-GLASS; BETA-GLASS
DOI: 10.1021/jp801794a

Citations: 33
data from “WEB OF SCIENCE” (of Thomson Reuters) are update at: 2021-12-05
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