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  • Title: Molecular motions in sucrose-PVP and sucrose-sorbitol dispersions: I. Implications of global and local mobility on stability.
    Author: Bhattacharya S, Suryanarayanan R.
    Journal: Pharm Res; 2011 Sep; 28(9):2191-203. PubMed ID: 21499981.
    Abstract:
    PURPOSE: To characterize molecular mobility by dielectric spectroscopy and determine the effect of additives on α- and β-relaxation times in amorphous sucrose solid dispersions. METHODS: Sucrose was co-lyophilized with either PVP or sorbitol. The lyophiles were subjected to dielectric spectroscopy and differential scanning calorimetry. RESULTS: The additives did not have an appreciable effect on the calorimetric T(g). However, dielectric spectroscopy revealed pronounced effects on global mobility (α-relaxation), which correlated with the crystallization tendency of sucrose. The systems were characterized by two β-relaxations, and the relaxation times as well as their temperature dependence were influenced by the additive. Although sorbitol acted as a plasticizer of sucrose with respect to global mobility, it anti-plasticized sucrose in terms of local motions. PVP, on the other hand, acted as an anti-plasticizer with respect to both global and local mobility. The slower β-relaxation in amorphous sucrose was found to correlate with the α-relaxation and was identified as the Johari-Goldstein relaxation. CONCLUSIONS: Amorphous systems with identical calorimetric T(g) could have significantly different mobility and physical stability as revealed by dielectric spectroscopy. Additive effect on global mobility cannot be a predictor of the effects on local mobility. Additives could also be used to inhibit local mobility.
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