Detailed Analysis of the Ice Surface after Binding of an Insect Antifreeze Protein and Correlation with the Gibbs-Thomson Equation.

Antifreeze proteins (AFPs) are able to influence the ice crystal growth and the recrystallization process due to the Gibbs-Thomson effect. The binding of the AFP leads to the formation of a curved ice surface and it is generally assumed that there is a critical radius between the proteins on the ice surface that determines the maximal thermal hysteresis. Up to now, this critical radius has not yet been proven beyond doubt or only in poor agreement with the Gibbs-Thomson equation. Using molecular dynamics (MD) simulations, the resulting three-dimensional surface structure is analyzed and the location of the critical radius is identified. Our results demonstrate that the correct analysis of the geometry of the ice surface is extremely important and cannot be guessed upfront a simulation. In contrary to earlier expectations from the literature, we could show that the critical radius is not located directly between the adsorbed proteins. In addition, we showed that the minimum temperature at which the system does not freeze is in very good agreement with the value calculated with the Gibbs-Thomson equation at the critical radius, as long as dynamic system conditions are taken into account. This proves on the one hand that the Gibbs-Thomson effect is the basis of thermal hysteresis and that MD simulations are suitable for the prediction of the melting point depression.