Abstract
The mechanisms by which the antifreeze protein (AFP) modifies the ice morphology are identified precisely as surface poisoning by the ice binding surface (IBS) of insect AFPs and as bridge-induced surface reconstruction by the IBS of fish AFPs and antifreeze glycoproteins. The primary surfaces of hexagonal ice have predetermined face indices. The "two-dimensional" insect type IBS has regularly spaced binding intervals in two directions. It causes surface poisoning by matching and reinforcing simultaneously intersecting strong bonding directions on the primary ice surfaces. The secondary ice surfaces have variable face indices. The "one-dimensional" and "irregular" IBS variants of fish AFPs and antifreeze glycoproteins are either linearly extended with regular ice binding intervals or have ice binding sites lacking spacing regularity. These variants can bridge transversely lattice periods or shorter oxygen-oxygen distances between parallel adjacent strong bonding directions that do not intersect. Thus, one-dimensional and irregular IBS variants induce supplementary bridges cross-wise on selected secondary surfaces by mimicking strong bonding directions that are not present in the ice structure. These proteins cause surfaces with variable face indices, which in the absence of the AFPs would not grow flat, to appear in the morphology. Whereas for the primary ice surfaces it is only the morphological importance that is determined by the experimental conditions, for the secondary ice surfaces it is the face indices themselves that become adjusted in the process of maximizing the AFP-substrate interaction through attainment of the best structural match. The growth morphology of the AFP-ice system is derived from various factors, including the face indices, surface molecular compositions, relative growth rates, and the mechanisms responsible for that morphology. The theoretical formulation agrees with experiments over a wide range and resolves these, to date, unexplained phenomena.
Highlights
Freezing is a process of ice crystallization from supercooled water
According to the periodic bond chain (PBC) theory, the growth environment can cause morphological modifications depending on the experimental situation
Surface Poisoning in the antifreeze protein (AFP)-Ice System—The natural morphology of ice when it grows out of water is an example of surface poisoning by water molecules
Summary
Freezing is a process of ice crystallization from supercooled water. Ice should first experience ice nucleation, followed by growth (1). The face indices, the surface molecular compositions, and the assessment of relative growth rates of the ice crystals as well as the AFP-induced morphological modification mechanisms are predicted, based on the AFP-ice system, by the periodic bond chain (PBC) theory developed by Hartman and Perdok
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