Pit Formation on the Basal Plane of Ice in Antifreeze Protein Type III Solution for Different Growth Mechanisms of Ice

When a single crystal of ice that has the basal plane several tenths of mm² in area grows in a moderately active antifreeze protein (AFP) solution, numerous pits consisting of six pyramidal planes are formed on the basal plane. This pit formation suggests some interactions between the AFPs and the basal plane. In this study, we observed pit formation on the basal plane of ice growing in a 5 mg/mL fish AFP (type III) solution and examined three growth mechanisms (normal, spiral, and two-dimensional (2D) nucleation) of the basal plane by measuring the relationship between the growth rate and the degree of supercooling. We also measured the number density of pits in ice and found that the number density of pits for normal growth mode on molecularly rough surfaces was lower than that for spiral growth mode on relatively smooth surfaces, whereas pit formation was not observed during 2D nucleation growth mode. On the basis of these results, we proposed a model of pit formation during spiral growth mode. In this model, if only reversible adsorption of the AFP molecules on the smooth surfaces is considered to occur, then pit formation can be explained without assuming irreversible adsorption on the smooth surfaces

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

Anti-Ice Nucleating Activity of Surfactants against Silver Iodide in Water-in-Oil Emulsions

Various water-soluble substances are known as anti-ice nucleating agents (anti-INAs), which inhibit heterogeneous ice nucleation initiated by ice nucleating agents (INAs). Among them, several surfactants are reportedly effective as anti-INAs especially against silver iodide (AgI), which is a typical inorganic INA that induces heterogeneous ice nucleation at relatively high temperatures. In this study, the anti-ice nucleating activities of seven surfactants were examined in emulsified surfactant solutions containing AgI particles. Among previously reported anti-INAs (e.g., antifreeze proteins (AFPs), polyphenol compounds and synthetic polymers), a cationic surfactant used in this study, hexadecyltrimethylammonium bromide (C16TAB), showed the highest anti-ice nucleating activity against AgI. Based on the unique concentration-dependent dispersibility of AgI particles in C16TAB solution, the anti-ice nucleating activity of C16TAB must be caused by the adsorption of C16TAB molecules on AgI surfaces either as a monolayer or a bilayer depending on the C16TAB concentration

<i>O</i>‑Aryl-Glycoside Ice Recrystallization Inhibitors as Novel Cryoprotectants: A Structure–Function Study

Low-molecular-weight ice recrystallization inhibitors (IRIs) are ideal cryoprotectants that control the growth of ice and mitigate cell damage during freezing. Herein, we describe a detailed study correlating the ice recrystallization inhibition activity and the cryopreservation ability with the structure of <i>O</i>-aryl-glycosides. Many effective IRIs are efficient cryoadditives for the freezing of red blood cells (RBCs). One effective cryoadditive did not inhibit ice recrystallization but instead inhibited ice nucleation, demonstrating the significance of inhibiting both processes and illustrating the importance of this emerging class of cryoprotectants