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.