Growth Habit Modification of Ice Crystals Using Antifreeze Glycoprotein (AFGP) Analogues

The research reported here considers the modification of ice crystal growth habit using analogues of antifreeze glycoproteins compounds that control the growth of ice crystals in the blood of Antarctic fishes A range of analogues of the smallest antifree e glycoprotein (AFGP8 Ala-Ala-Thr-Ala-Ala-Thr-Pro-Ala-Thr-Ala-Ala-Thr-Pro-Ala) were synthesized all of which have either N-acetyl-galactosamme or galactose moieties attached to their threonines instead of the native galactose-N acetyl-galactosamine disaccharide We also synthesized analogues in which the prolines wet e substituted with alanines in the protein sequence The analogues were systematically studied for their effects on ice crystal shape and their effects when combined with a range of salts chosen across the Hofmeister series A simple H-1 NMR freezing experiment was used to detect adsorption onto ice and indicate differences in water proton hydrogen bonding CD spectroscopy highlighted the role of the terminal galactoe, the proline residues, and the N-acetylamine group in modifying the solution conformation The results illustrate a delicate balance between the effects of hydrophobic and hydrophilic groups on the glycoprotein and the interactions between the glycoprotein, a developing ice crystal, and water We demonstrate three ways of modulating the ice crystal shape by changing the adsorbent concentration, by changing the adsorbent structure, or by altering the interaction of the glycoprotein with liquid water through the use of simple solution additives We show a continuum of behavior between no shape modification and no thermal hysteresis 10 a strong shape modification and a significant thermal hysteresis, and we relate the results to kinetic models for antifreeze activity