[Ice Crystal2]
Crystal growth mechanisms associated with the macromolecules adsorbed at a growing interface –Microgravity effect for self-oscillatory growth–

RESEARCH OVERVIEW

• Ice crystal morphologies growing in a supercooled antifreeze protein (AFP) solution are drastically modified from those growing in a supercooled pure water, and the self-oscillation of growth is also observed. Based on the results of ground experiments, a model is proposed to explain these phenomena. It is called the 2-step reversible adsorption inhibition model, and must be confirmed by careful experiments. The crystal morphology may be strongly be affected by convection, which cannot be prevented under gravity. This effect can be prevented, and the effects of AFP obtained for ice growth under ideal microgravity experimental conditions in the Kibo Module of ISS.
• Various images of ice crystals grown under supercooling temperatures are scheduled to be taken and data analyzed in hopes of clarifying the morphological changes and the time-sequence growth rates.
• This research project illustrates the principle of the growth model for ice in the AFP solution, and opens the way for new research fields related to the fundamentals of crystal growth mechanisms controlled by biological macromolecules.

SPACE APPLICATIONS

Antifreeze glycoproteins have been discovered in fish living in polar regions. Ice crystals grow in a dramatically different fashion in the presence of this protein, compared to ice crystals that form in pure super-cold water. Scientists have not been able to successfully demonstrate how these proteins work, because ice crystal formation is likely also affected by convection (induced by gravity). Studying the interaction between ice crystals and antifreeze glycoprotein in microgravity could help researchers describe how the protein adheres to water molecules to stop the formation of ice.

EARTH APPLICATIONS

Biological antifreeze is found in several species of polar fish, where it prevents the formation of ice crystals even in freezing water. Understanding how antifreeze glycoprotein works could lead to new research in the fundamental physics of crystal growth, and how biological molecules can affect crystal formation.

FURUKAWA Yoshinori [Hokkaido University]