Abstract
The purpose of this study was to elucidate the effect of molecular interactions on the physical properties of frozen aqueous solutions and freeze-dried solids containing various carboxylic acids, amines, and alkali-metal-ions. Thermal analysis of frozen solutions containing the multivalent carboxylic acid and amines showed reduced tendency for the solute crystallization and bell-shaped profiles of the glass transition temperature of maximally freeze-concentrated amorphous solutes (T_g') depending on the number of functional groups on the solutes and their concentration ratios. Freeze-drying of the high T_g' frozen solute-mixture solutions (-40℃<T_g') resulted in cake structure amorphous solids that have the glass transition temperatures (T_g) much higher than the individual components. Network of electrostatic interactions and hydrogen-bonding between the amino and carboxyl groups, as well as anion network of strong "single hydrogen-bond" between the differently protonated carboxyl and carboxylate groups, should explain the high transition temperatures (T_g', T_g) of the frozen solutions and the freeze-dried solids.
