Heterogeneity of the state and functionality of water molecules sorbed in an amorphous sugar matrix

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• 作者：Koreyoshi Imamura ; ^{kore@cc.okayama-u.ac.jp} ; Ryo Kagotani ; Mayo Nomura ; Kohshi Kinugawa ; Kazuhiro Nakanishi
• 关键词：Amorphous sugar ; Heterogeneity ; Water sorption ; Freeze-drying ; Compression ; Glass transition temperature
• 刊名：Carbohydrate Research
• 出版年：2012
• 期刊代码：15_00086215
• 类别：ch
• 出版时间：1 April, 2012
• 卷：351
• 期：Complete
• 页码：108-113
• 文件大小：624 K

摘要

An amorphous matrix, comprised of sugar molecules, is frequently used in the pharmaceutical industry. An amorphous sugar matrix exhibits high hygroscopicity, and it has been established that the sorbed water lowers the glass transition temperature T_g of the amorphous sugar matrix. It is naturally expected that the random allocation and configuration of sugar molecules would result in heterogeneity of states for sorbed water. However, most analyses of the behavior of water, when sorbed to an amorphous sugar matrix, have implicitly assumed that all of the sorbed water molecules are in a single state. In this study, the states of water molecules sorbed in an amorphous sugar matrix were analyzed by Fourier-transform IR spectroscopy and a Fourier self-deconvolution technique. When sorbed water molecules were classified into five states, according to the extent to which they are restricted, three of the states resulted in a lowering of T_g of an amorphous sugar matrix, while the other two were independent of the plasticization of the matrix. This finding provides an explanation for the paradoxical fact that compression at several hundreds of MPa significantly decreases the equilibrium water content at a given RH, while the T_g remains unchanged.