Vapour pressure of aqueous antifreeze glycopeptide solutions

Measurements are reported of the vapour pressure of liquid, partially frozen and frozen aqueous solutions of antifreeze glycopeptides at temperatures ranging from -1 to 0 °C. Results indicate that at a given temperature, the activity of water in liquid or partially frozen (ca. 5% ice content) solutions is approximately the same as the activity of pure supercooled water. In a completely frozen solution, on the other hand, water activity is equal to that of pure ice. The data show that the antifreeze peptides only affect bulk properties of liquid as well as frozen solutions to a very limited extent, and thus provide direct evidence that the inhibiting effect of these molecules on ice formation is an entirely kinetic (non-equilibrium) phenomenon.