Chemical and Pharmaceutical Bulletin
Online ISSN : 1347-5223
Print ISSN : 0009-2363
ISSN-L : 0009-2363
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Glass-State Amorphous Salt Solids Formed by Freeze-Drying of Amines and Hydroxy Carboxylic Acids: Effect of Hydrogen-Bonding and Electrostatic Interactions
Saori KadoyaKen-ichi IzutsuEtsuo YonemochiKatsuhide TeradaChikako YomotaToru Kawanishi
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2008 Volume 56 Issue 6 Pages 821-826

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Abstract

We studied effect of molecular interactions on the physical properties of binary freeze-dried solids and frozen aqueous solutions using model chemicals containing various functional groups (amino, carboxyl, hydroxyl). Thermal analysis of frozen solutions containing alkyl diamines and hydroxy di- or tricarboxylic acids showed thermal transitions (Tg′: glass transition of maximally freeze-concentrated phase) at temperatures higher than those of the individual solutes. A binary frozen solution containing 80 mM 1,3-diamino-2-hydroxypropane (single-solute Tg′<−60 °C) and 120 mM citric acid (single-solute Tg′: −55.0 °C) made the transition at −30.8 °C. The molecular weight of the solutes had smaller effects on the transition temperatures of the frozen mixture component solutions. Lyophilization of some high Tg′ mixture frozen solutions (e.g., 1,3-diamino-2-hydroxypropane and citric acid) resulted in cake-structure amorphous solids with glass transition temperatures (Tg) higher than those of the individual components. Networking of intense hydrogen-bondings and electrostatic interactions between the heterogeneous molecules through the multiple functional groups was suggested to reduce the component mobility in the amorphous freeze-concentrated phase and the freeze-dried solids. Controlling the interactions should be a key to optimizing the physical properties of multi-component amorphous freeze-dried pharmaceutical formulations.

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© 2008 The Pharmaceutical Society of Japan
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