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Calorimetric Relaxation and the Glass-Liquid Temperature Range of Acetaminophen-Nifedipine Alloys

Calorimetric Relaxation and the Glass-Liquid Temperature Range of Acetaminophen-Nifedipine Alloys

Gyan P Johari, Ravi M Shanker

J Pharm Sci. 2008 Aug;97(8):3233-44.

PMID: 18064680

Abstract:

Glassy states of nine acetaminophen-nifedipine compositions have been made by slowly supercooling their melts, and calorimetric T(g) and the nonexponential, nonlinear relaxation parameters beta and x that are used in modeling the mobility of a pharmaceutical determined. The T(g)-endotherm's shape varies with the alloy's composition, T(g) increases approximately linearly with the mol% of nifedipine, beta and x increase, and the activation enthalpy Deltah* decreases. At T(g), the relaxation time tau(cal) of acetaminophen, nifedipine, and their alloys differs from 100 s to different extents. The distribution of relaxation times is lesser than that for polymers and other glasses. For a given composition, Deltah*, beta, x, and tau(cal) anomalously depend upon the heating rate, indicating that variation of beta with temperature would not yield better fits for modeling their stability. It is suggested that a pharmaceutical's relaxation is generally influenced by changes in intermolecular hydrogen bonds, chemical short-range order, vibrational frequency, isomerization, and impurity electrolyte dissociation, all of which contribute to the energy change with a distinctive kinetics.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
CS310314	Acetaminophen Impurity G			Price

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