Inactivation of ice nucleating activity of silver iodide by antifreeze proteins and synthetic polymers.

Antifreeze proteins (AFPs) and poly(vinyl alcohol) (PVA) are known as anti-ice nucleating agents (anti-INAs), which inhibit ice nucleation initiated by ice nucleating agents (INAs). Although the effectiveness of anti-INAs depends on the type of INA, most previous studies on anti-INAs used only a few types of biological INAs as targets to inactivate. In this study, the effects of fish AFPs (AFP I and AFP III) and PVA on the ice nucleating activity of silver iodide (AgI) were measured by using emulsified solutions. Results showed that AgI was inactivated not only by AFPs and PVA but also by two other polymers previously not considered as anti-INAs, namely, poly(vinylpyrrolidone) and poly(ethylene glycol). Even in the presence of AgI, a non-negligible fraction, typically more than 10%, of emulsified droplets of these anti-INA solutions at 1.0 mg mL(-1) was supercooled to about -37 °C, which corresponds to ice nucleation temperature measured in the absence of AgI.

Ice nucleation in emulsified aqueous solutions of antifreeze protein type III and poly(vinyl alcohol).

Antifreeze protein (AFP) III and poly(vinyl alcohol) (PVA) are known as anti-ice nucleating agents (anti-INAs), which inhibit heterogeneous ice nucleation. However, the effectiveness of these anti-INAs in inhibiting ice nucleation in water-in-oil (W/O) emulsions, in which homogeneous ice nucleation can be experimentally simulated, is unclear. In this study, the ice nucleation temperature in emulsified solutions of AFP III, PVA, and other nonanti-INA polymers was measured, and then the nucleation rate was analyzed based on classical nucleation theory. Results showed that ice nucleation was surface-initiated and, except for PVA solutions, probably caused heterogeneously by the emulsifier, SPAN 65, at the droplet surfaces. In this nucleation mode, AFP III had no significant effect on the ice nucleation rate. In contrast, PVA exhibited ice-nucleating activity only at the droplet surfaces, suggesting that the nucleation is due to the interaction between PVA and SPAN 65.