Study on the Unfrozen Water Quantity of Maximally Freeze-Concentrated Solutions for Multicomponent Lyoprotectants

The concentration of maximally freeze-concentrated solutions [Formula: see text] and the corresponding glass transition temperature [Formula: see text] and ante-melting temperature [Formula: see text] of lyoprotectant solutions, are critical parameters for developing lyophilization process. Usually, the lyoprotectant solutions are multicomponent solutions composed of electrolytes, sugars, proteins, polymers, and other chemicals. In this article, the W_g^' values of several multicomponent solutions including trehalose/NaCl, bovine serum albumin/NaCl, and hydroxyethyl starch/NaCl with water were determined by differential scanning calorimetry. A linear relationship between the unfrozen water fraction W_un and the initial solute concentrations W_i was found: W_un = ∑(a_i·W_i), which suggested that in the multicomponent solutions each solute could hydrate a certain amount of water a_i (g water/g solute) that could not be frozen. The hypothesis was compared with more literature data. For the same solute in different solutions, variation in the fitted coefficient a_i is noticed and discussed. If a "universal" value a_i for each solute is adopted, both [Formula: see text] and [Formula: see text] for a multicomponent solution could be predicted if Couchman-Karasz equation is adopted for calculating glass transition temperature at the same time. The prediction discrepancies for [Formula: see text] with experimental data were less than 2°C. The finding is discussed about its molecular basis and applicability.