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ארועים עתידיים

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Biochemistry Seminar

תאריך: 
ה', 20/08/2020 12:00
מיקום: 
zoom

Michael Chasnitsky
PhD student at Prof. Ido Braslavsky's lab


Lecture title:
Investigation of the interface between ice and water with ice binding proteins using atomic force microscope, kinetic pinning model and directional freezing.
 
Zoom:
https://huji.zoom.us/j/99324345412?pwd=OVg3UlpYSTd6MFFGR1h3a2l4SzNyUT09


How ice grows in solution determines the outcome of many natural, industrial and medical processes such as survival of fish, insects and plants in cold environments, preservation of foods through freezing and cryosurgery to name a few. The interface between the crystal and liquid phases of water, namely water and ice, or any material in general is difficult to study due to the sensitivity of the interface to physical conditions, such as temperature and solute concentration. During crystal growth, the interactions of molecules and particles in the liquid with the growing interface determine the properties of the resulting crystal and are therefore important. One interesting case of such interaction is of antifreeze proteins (AFP) that inhibit and shape ice crystals growth in water by binding to specific crystal planes of ice.

In this work we developed a technique for imaging the surface of ice in the presence of antifreeze proteins in solution using atomic force microscopy (AFM).

We imaged ice crystals in water using AFM both in the presence of TmAFP and AFP III. Without antifreeze proteins, the ice was measured, but it was unstable and we could not obtain high quality images. We found that in the presence of TmAFP in solution, ice grows in parallel layers that are rough at the edges on the order of a few microns, with distances between the layers of less than a micron. The roughness (or waviness) of the surface of the layers is on the order of tens of nanometers. With AFP III in solution, we found ice to grow in conical shape trimmed at the edge. The cones are a few microns wide with substructures on the faces in a variety of submicron sizes.

We also investigate analytically the interaction of antifreeze proteins and ice by extending a model describing the mechanism of antifreeze proteins activity. The kinetic pinning model is a model that predicts the concentration of AFP that is needed to arrest ice crystal growth in supercooled aqueous solutions. We found this model to describe the activity of (moderate) AFP III well, but is inadequate for the (hyperactive) TmAFP.

Another line of research regarded the temperature profile in directional freezing apparatus. We investigated the dynamics of growing ice during directional freezing and melting in a translational gradient stage. We developed a model based on heat flux balance on both sides of the ice front that predicts the position of the ice front during the translation of the sample at constant speed and upon translation speed change.