Calorimetric relaxation and the glass-liquid temperature range of acetaminophen-nifedipine alloys.
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.
Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L7, Canada. joharig@mcmaster.ca
Gyan P
GP
Johari
Ravi M
RM
Shanker
D000082:Acetaminophen / Q000737:chemistry*; D000497:Alloys / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D005898:Glass; D007700:Kinetics; D009543:Nifedipine / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
D000497:Alloys; D000082:Acetaminophen; D009543:Nifedipine